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The New South Wales Arbovirus Surveillance & Mosquito Monitoring Program, 2018-2019 Annual Report

September 2019

Authors:

Stephen L. Doggett

Westmead Hospital

Cameron Webb

The University of Sydney

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The annual report of the NSW Arbovirus Surveillance Program

Mosquito trapping locations and Sentinel Chicken sites, 2018-2019.

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Barmah Forest virus and Ross River virus infections in NSW residents: notifications by month of onset for the 2018-2019 financial year, compared to the 5-year monthly means for the period from July 2013 to June 2018.

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Barmah Forest virus infections in NSW residents: annual notifications by year of disease onset and geographical region for the past 10 years (2009-2010 to 2018-2019).

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Ross River virus infections in NSW residents: annual notifications by year of disease onset and geographical region for the past 10 years (from 2009-2010 to 2018-2019).

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Barmah Forest virus infections in NSW residents.

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S. DOGGETT, J. HANIOTIS,

J. CLANCY, C. WEBB & C. TOI

Mosquito & Arbovirus Surveillance Laboratory,

Medical Entomology Department, CIDMLS,

ICPMR, Pathology West,

Westmead Hospital, Westmead, NSW 2145.

L. HUESTON, L. McINTYRE,

J. GOODWIN, & D.E. DWYER

Arbovirus Laboratory, Clinical Virology, CIDMLS,

ICPMR, Pathology West,

Westmead Hospital, Westmead, NSW 2145.

S. TOBIN & V. SHEPPARD

Communicable Disease Branch, Health Protection

NSW Health, North Sydney, NSW 2059.

THE NEW SOUTH WALES

ARBOVIRUS SURVEILLANCE &

MOSQUITO MONITORING PROGRAM

2018-2019

Annual Report

Culex annulirostris

NSW Arbovirus Surveillance Program, 2018-2019

• For the 2018-2019 season, the NSW Arbovirus Surveillance Program: (i)

monitored mosquito populations and undertook surveillance of arbovirus activity

through virus isolation in the NSW inland, coastal regions and Sydney area, (ii)

monitored flavivirus transmission through the testing of sentinel chickens across

inland NSW. Surveillance operated over mid-October to mid-May.

• The climatic conditions leading up to 2018-2019 was a spell of extremely dry

weather over July to September 2018. While precipitation levels were average for

the last three months of 2018, conditions became extremely dry for the first six

months of 2019. Neither the Forbes nor the Nicholls hypotheses were suggestive

of a potential MVEV epidemic for the 2018-2019 season.

• For the inland, 7,998 mosquitoes were trapped and this was one of the lowest

collections for the history of the program, and around one quarter of the previous

season collection of 33,257. There was one EHV detection from Griffith. There

were no seroconversions in the sentinel chickens from any location.

• Human notifications from the inland of RRV and BFV totalled 181 (177RRV &

4BFV), which was slightly less than that of the previous season and around half

the previous nine season average of 343 (311RRV & 32BFV). The statistical local

areas that produced the highest notifications for RRV from the inland was Griffith

(12), while the Far West (179/100,000) had the highest notification rate. There

were no human cases of infection with MVEV of KUNV.

• As of August 2019, the Forbes hypothesis is not suggestive of a possible MVEV

epidemic for 2019-2020 and such an outbreak seems unlikely with the ongoing

drought. The El Niño-Southern Oscillation is currently neutral, suggesting normal

rainfall patterns for the remainder of the year.

• For the coast, 48,214 mosquitoes were trapped, which was close to the total of

the previous season. There were seven isolates from the coast, including 3RRV

from Ballina, 1RRV & 1STRV from Ourimbah, 1BFV from Port Macquarie, and

1BFV from Tweed Heads.

• Human notifications from the coast totalled 412 cases, including 347RRV and

65BFV, and this was below the previous nine season average of 627 (438RRV &

189BFV).

• Sydney experienced a dramatic increase in mosquito numbers upon the previous

season with almost 180,000 trapped compared to the previous season of 31,000.

Over 50,000 mosquitoes were collected at Picnic Point alone, and over 45,000

from the new site at Duck River, along the Parramatta River. There were 20

arboviral isolates, including: 1EHV from Blacktown; 2RRV, 8EHV, 1KOKV &

1STRV from the Georges River sites; 1EHV from the Hills District, 4STRV from

Parramatta; and 1RRV & 1STRV from Sydney Olympic Park. Human notifications

were slightly below average with a total of 62 (61RRV & 1BFV).

• Detections of exotic mosquitoes at Sydney Airport continue. This included

multiple detections of Aedes aegypti trapped at the Sydney International Airport

and an approved arrangement facility (that handles freight), and a single detection

of an Aedes albopictus the Sydney International Airport. Responses included

regular teleconferences initiated by the NSW Ministry of Health, enhanced

surveillance at the airport, vector surveys, insecticidal applications, and ongoing

larval treatments.

NSW Arbovirus Surveillance Program, 2018-2019

W _____________________________________________ 1

N ____________________________________________________ 3

S _________________________________________________________ 3

S ___________________________________________ 5

A ___________________________________________________ 5

MVEV Predictive Models _________________________________________________________ 6

G ____________________________________________ 8

Methods ______________________________________________________________________ 8

Results _______________________________________________________________________ 9

Inland _______________________________________________________________ 9

Coastal ______________________________________________________________ 9

Metropolitan Sydney ___________________________________________________ 9

S _________________________ 9

Methods ______________________________________________________________________ 9

Results ______________________________________________________________________ 10

M _____________________________________ 11

Location of flocks ______________________________________________________________ 11

Methods _____________________________________________________________________ 11

Results ______________________________________________________________________ 12

Y-

-A

S ______ 12

N _____________________________________________________ 18

E _____________________________________ 19

T _ 22

N-

-B

Y-

-L

Y______________________ 25

Inland Locations _______________________________________________________________ 25

Coastal Locations _____________________________________________________________ 24

Sydney Locations ______________________________________________________________ 25

. T

S ______________________________________ 26

S __________________________________________ 27

S _______________________________________ 29

S ____________________________ 30

S _____________________________________________ 31

S ____________________________________________________ 35

NSW Arbovirus Surveillance Program, 2018-2019

-2

The aim of the Program is to provide an early warning of the presence of Murray

Valley encephalitis virus (MVEV) and Kunjin (KUNV) virus in the state, in an effort to

reduce the potential for human disease. In addition, the Program compiles and

analyses mosquito and alphavirus, especially Ross River (RRV) and Barmah Forest

(BFV), data collected over a number of successive years. This will provide a solid

base to determine the underlying causes of the seasonal fluctuations in arbovirus

activity and the relative abundance of the mosquito vector species, with the potential

to affect the well-being of human communities. This information can then be used as

a basis for modifying existing local and regional vector control programs, and

creation of new ones.

Background

Arbovirus activity within NSW has been defined by the geography of the state, and

three broad virogeographical zones are evident: the inland, the tablelands and the

coastal strip (Doggett 2004, Doggett and Russell 2005). Within these zones, there

are different environmental influences (e.g. irrigation provides a major source of

water for mosquito breeding inland, while tidally influenced saltmarshes along the

coast are highly productive), different mosquito vectors, different viral reservoir hosts

and different mosquito borne viruses (e.g. MVEV and KUNV occur only in the inland,

while BFV is active mainly on the coast, and RRV is active in both inland and coastal

areas). As a consequence, arboviral disease epidemiology often can be vastly

different between regions and thus the surveillance program is tailored around these

variables.

Arbovirus surveillance can be divided into two categories: those methods that

attempt to predict activity and those that demonstrate viral transmission. Predictive

methods include the monitoring of weather patterns, the long-term recording of

mosquito abundance, and the isolation of virus from vectors. Monitoring of rainfall

patterns, be it short term with rainfall or longer term with the Southern Oscillation, is

critical as rainfall is one of the major environmental factors that influences mosquito

abundance; in general, with more rain come higher mosquito numbers. The long-

term recording of mosquito abundance can establish baseline mosquito levels for a

location (i.e. determine what are ‘normal’ populations), and this allows the rapid

recognition of unusual mosquito activity. The isolation of virus from mosquito vectors

can provide the first indication of which arboviruses are circulating in an area. This

may lead to the early recognition of potential outbreaks and be a sign of the disease

risks for the community. Virus isolation can also identify new viral incursions, lead to

the recognition of new virus genotypes and identify new vectors. Information from

vector monitoring can also reinforce and strengthen health warnings of potential

arbovirus activity.

NSW Arbovirus Surveillance Program, 2018-2019

Methods that demonstrate arboviral transmission include the monitoring of suitable

sentinel animals (such as chickens) for the presence of antibodies to particular

viruses (e.g. MVEV and KUNV within NSW), and the recording of human disease

notifications. Sentinel animals can be placed into potential ‘hotspots’ of virus activity

and, as they are continuously exposed to mosquito bites, can indicate activity in a

region before human cases are reported. Seroconversions in sentinel flocks provide

evidence that the level of virus in mosquito populations is high enough for

transmission to occur.

The monitoring of human cases of arboviral infection usually has little direct value for

surveillance, as by the time the virus activity is detected in the human population,

often not much can be done to control the viral transmission. Via the other

methodologies, the aim of the surveillance program is to recognise both potential and

actual virus activity before it impacts greatly on the human population, so that

appropriate preventive measures can be implemented. The recording of human

infections does, however, provide important epidemiological data and can indicate

locations where surveillance should occur.

These methods of surveillance are listed in order; generally, with more rainfall comes

more mosquito production; the higher the mosquito production, the greater the

probability of enzootic virus activity in the mosquito/host population; the higher the

proportion of virus infected hosts and mosquitoes, the greater the probability of

transmission and thus the higher the risk to the human population. The NSW

Arbovirus Surveillance and Mosquito Monitoring Program undertakes the first four

methods of arbovirus surveillance and the results for the 2018-2019 season follow.

Fig 1. Mosquito trapping locations and Sentinel Chicken sites, 2018-2019.

NSW Arbovirus Surveillance Program, 2018-2019

For 2018-2019, mosquito-trapping sites were operated at 7 inland, 9 coastal and 8

Sydney locations. Chicken sentinel flocks were located at 9 locations (Fig 1).

Mosquito abundance is dictated principally by rainfall patterns and irrigation practices

in inland regions, while in coastal regions tidal inundation along with rainfall is

important. Temperature and/or day-length are often critical in determining the

initiation and duration of mosquito activity for species in temperate zones. Hence, the

monitoring of environmental parameters, especially rainfall, is a crucial component of

the Program.

Figures 2-5. Australian Rainfall deciles for the three month periods, Jul-Sep 2018,

Oct-Dec 2018, Jan-Mar 2019 & Apr-Jun 2019. The stronger the red, the drier the

conditions. Conversely, the stronger the blue, the wetter the conditions. Modifed from the

Australian Bureau of Meterology, 2019.

NSW Arbovirus Surveillance Program, 2018-2019

The first quarter of 2018 (January to March, not shown) produced below average

rainfall patterns for almost the entire state. The second quarter (also not shown) was

even drier with very much below average precipitation for many parts of NSW. This

dry spell continued with very much below average for almost all the state and some

central regions experiencing record low precipitation (Figure 2). The final quarter of

the year (Figure 3) had close to average rainfall patterns. However, conditions soon

became dry again with well below average rainfall for many parts of NSW during the

first six months of 2019 (Figures 4 & 5).

Maximum temperatures for the last half of 2018 were slightly (1-2o) above average

for both inland and coastal regions. The first three months of 2019 continued to be

above average with maximum temperatures of 2-3 degrees above normal for

northern regions of the inland, and 1-2 degrees above for the coast. By the second

quarter of 2018, temperatures were again 1-2 degrees higher than the norm across

the state.

MVEV Predictive Models

Two main models have been developed for the prediction of MVEV epidemic activity

in south-eastern Australia: the Forbes’ (1978) and Nicholls’ (1986) hypotheses.

Forbes associated rainfall patterns with the 1974 and previous MVEV epidemics, and

discussed rainfall in terms of 'decile' values. A decile is a ranking based on historical

values. The lowest 10% of all rainfall values constitute decile 1, the next 10% make

up decile 2, and so on to the highest 10% of rainfall constituting decile 10. The higher

the decile, the greater the rainfall.

The Forbes’ hypothesis refers to rainfall levels in the catchment basins of the main

river systems of eastern Australia. These include:

• The Darling River system,

• The Lachlan, Murrumbidgee & Murray River systems,

• The Northern Rivers (that lead to the Gulf of Carpentaria), and

• The North Lake Eyre system.

The hypothesis states that if rainfall levels in these four catchment basins are equal

to or greater than decile 7 for either the last quarter of the previous year (e.g.

October-December 2017) or the first quarter of the current year (January-March

2018) and the last quarter of the current year (October-December 2018), then a

MVEV outbreak is probable. By comparing the relevant quarterly rainfall amounts

with historical decile 7 years, it is possible to obtain a ratio; a figure of 1 or greater

indicates that rainfall was above the historical decile 7 average (Table 1). Rainfall

was below decile 7 in all but one of the catchment basins for the last quarter of 2017,

was above decile 7 in only one catchment basin in the first quarter of 2018, and

below decile 7 in all of the catchment basins for the last quarter of 2018, thus the

Forbes’ hypothesis was not fulfilled for 2018-2019 (Table 1). Additionally, decile 7 or

above rainfall did not occur in any of the catchment basins during the first quarter of

2019. Therefore according to Forbes’, there should be a lower risk of an MVEV

epidemic for the upcoming 2019-2020 season.

NSW Arbovirus Surveillance Program, 2018-2019

Table 1. Rainfall indices for the main catchment basins of eastern Australia as per

Forbes’ hypothesis, relevant to the 2017-2018 and 2018-2019 seasons.

-D

-M

-D

-M

Darling River

0.93

0.52

0.71

0.68

Lachlan/Murrumbidgee/

Murray Rivers

1.15 0.70 0.87 0.96

Northern Rivers

0.81

1.07

0.70

0.78

North Lake Eyre

system

0.75 0.69 0.56 0.82

The Nicholls’ hypothesis

uses the Southern

Oscillation (SO) as a tool to

indicate a possible MVEV

epidemic. Typically

atmospheric pressures

across the Pacific Ocean

tend to be low on one side

of the ocean and high on

the other. This pattern then

oscillates from year to year.

Nicholls noted a correlation

between past outbreaks of

MVEV and the SO (as

measured by atmospheric

pressures at Darwin) for the

autumn, winter, and spring

period prior to a disease

outbreak. For the autumn,

winter, and spring periods

of 2018, the SO values

were respectively:

1009.27mm, 1011.80mm

and 1010.90mm (indicated

on Figure 6 by the yellow

arrows and Table 2). The

graph on the right has been

updated from the originally

published figure to include

those MVEV active years

between 2000 and 2012

(added to the MVEV tallied

black columns), and

includes the values for the

years 2000-2001, 2007-

2008, 2010-2011 and 2011-

2012. The SO values

leading up to the 2003-2004

Figure 6.

The SO by seasons prior to MVEV active years,

according to Nicholls (1986), updated up to Spring 2018. The black

bars represent the pre-

MVEV active seasons. The yellow arrows

indicate the respective SO values relevant to the 2018-2019

season.

NSW Arbovirus Surveillance Program, 2018-2019

season were not included as there was only one detection of MVEV, which may have

resulted from over-wintering mosquitoes.

As of August 2019, the autumn Nicholls’ value is 1010.27mm and the winter value is

1012.08mm. Only the winter value is within the range of values for past MVEV

outbreak years, however the ongoing dry conditions suggests that an MVEV

outbreak would be unlikely for 2018-2019.

Currently (as of August, 2019), the El Niño–Southern Oscillation (ENSO) is neutral,

suggesting average rainfall for the remainder of the year.

Table 2. The seasonal atmospheric pressures (in mm) according to Nicholls’

hypothesis, relevant to the 2018-2019 season.

2018 Value

1009.27

1011.8

1010.90

Past MVEV seasons

<1009.74

<1012.99

<1009.99

It is important to note that the Forbes’ hypothesis was calculated on environmental

conditions experienced during major MVEV epidemic seasons and the models do not

propose to predict low to moderate level activity. Thus, negative MVEV models do

not necessarily indicate an absence of MVEV activity. Also, these climatic based

models do not take into account unusual environmental conditions such those

experienced during the summer of 2008, whereby a low pressure cell that began in

northern Australia moved through to the south and possibly facilitated the movement

of MVEV into NSW (Finlaison et al., 2008). A similar phenomenon may have

occurred during the 2010-11 season, whereby a low pressure cell that formed from

Tropical Cyclone Yasi and moved into Victoria bringing intense rainfall, coincided

with major MVEV and KUNV activity (Doggett et al. 2011). Nor do these models take

into account virus existing in cryptic foci in south-eastern Australia.

Methods

Mosquitoes were collected overnight in dry-ice baited Encephalitis Virus Surveillance

(EVS) type traps. They were then sent live in cool, humid Eskies via overnight

couriers to the Department of Medical Entomology, Institute of Clinical Pathology and

Medical Research (ICPMR), NSW Health Pathology, Westmead, for identification and

processing for arbovirus isolation. The mosquitoes were identified via taxonomic keys

and illustrations according to Russell (1993, 1996), Dobrotworsky (1965) and Lee et

al. (1980 – 1989). A brief description of the main mosquito species for NSW appears

in Appendix 2.

Mosquito abundances are best described in relative terms, and in keeping with the

terminology from previous reports, mosquito numbers are depicted as:

• 'low' (<50 per trap),

• 'moderate' (50-100 per trap),

• 'high' (101-1,000 per trap),

NSW Arbovirus Surveillance Program, 2018-2019

• 'very high' (>1,000 per trap), and

• ‘extreme’ (>10,000 per trap).

All mosquito and arboviral monitoring results (with comments on the collections) were

compiled into a weekly report, which was disseminated to stakeholders and included

on the NSW Health web site.

Results

Overall, 187,397 mosquitoes representing 53 species were collected in NSW during

2018-2019, with the total being just over fifty percent higher than the previous season

(with a total of 113,132 mosquitoes), but considerably lower than the number trapped

in 2016-2017 (299,239). Culex annulirostris was the most abundant and most

important of the inland mosquito species during the summer months, whereas Aedes

vigilax, Culex sitiens, Aedes notoscriptus, Culex annulirostris, Coquillettidia linealis,

Aedes procax, and Verrallina funerea were the most numerous species on the coast.

A full summary of the results on a location-by-location basis is included in Appendix

1. A brief description of the most important vectors is provided in Appendix 2.

Inland

The total of 7,998 mosquitoes comprising 19 species was one of the lowest

collections on record from the inland and around one quarter that of the previous

season collection of 33,527. Culex annulirostris was the dominant species trapped at

most sites and comprised 67.6% of the total inland collections. Anopheles annulipes

(14.6%) was the next most common species followed by Culex quinquefasciatus

(11.2%).

Coastal

In total, 48,214 mosquitoes comprising 43 species were collected from coastal NSW

and close in number to the previous season’s collection (48,660). The most common

species collected were Culex sitiens (24.8%), Aedes vigilax (19.8%), Verrallina

funerea (14.6%), Aedes notoscriptus (12.0%), Aedes multiplex (9.1%), Culex

annulirostris (4.9%), and Aedes procax (2.4%).

Metropolitan Sydney

A total of 179,395 mosquitoes, comprising 36 species, was collected from

metropolitan Sydney and this was almost six times the previous season’s total

collection of 30,945. Aedes vigilax (83.2% of the total Sydney mosquitoes trapped)

was the most common species, followed by Culex annulirostris (4.0%), Aedes

notoscriptus (3.8%), Anopheles annulipes (2.3%), Coquillettidia linealis (2.2%), and

Culex quinquefasciatus (1.4%).

Methods

Viral detection involves modern molecular techniques for identifying viral nucleic acid.

For viral nucleic acid detection through molecular analysis from the mosquito grinds,

the homogenates were screened for alpha (BFV, RRV, and SINV), and flaviviruses

NSW Arbovirus Surveillance Program, 2018-2019

(MVEV, KUNV, EHV KOKV, and STRV) using a series of multiplexed fluorogenic

Taqman real-time RT-PCR assays, with modifications (Pyke AT, et al. 2004, van den

Hurk AF, et al. 2014). Viral RNA was extracted using the EZ1® Virus Mini Kit

(Qiagen), and amplified on the Corbett™ Rotor-Gene 6000. In the case of identifying

flavivirus ‘unknowns’, a general screen using a pan-flavivirus PCR was performed

(Moureau G, et al. 2007). For other unidentified virus from cell culture, a Pan-TBMV

(Trubanaman, Buffalo Creek and Murrumbidgee virus), Pan SGV (Salt Ash and Gan

Gan virus), and PCRs specific for Umatilla virus (UMAV), Wongorr virus (WGRV),

Liao Ning virus (LNV), Wallal virus (WALV), Warrego virus (WARV), Beaumont virus

(BEAUV), Whataroa (WHAV), and North Creek virus (NORCV) were used. Positive

amplification of any one of these viruses was confirmed by Sanger Sequencing at the

Australian Genome Research Facility (AGRF). The test sequence was compared by

alignment against a database via the National Centre for Biotechnology information

(NCBI) using the Basic Local Alignment Search Tool (BLAST).

In numerous locations across the state as part of an ongoing evaluation in

surveillance technologies, honey-soaked FTA® cards (Flinders Technology

Associates filter paper) were placed in the EVS traps (see discussion in greater detail

below). The processing and screening for arboviruses from FTA cards were done

using the protocol by Hall-Mendelin et al. 2010. Similarly, Taqman real-time RT-PCR

detection procedures were used for virus detection from FTA card eluates described

above for virus detection in mosquitoes.

Arboviral detection methodologies from the trapped mosquitoes continue to be

validated within the surveillance program. As the FTA cards produced few arboviral

detections, an alternative method was employed late in the season. Instead of

grinding mosquitoes in pools of 25 for cell culture, as undertaken in previous years,

whole mosquito collections from the one trap were pooled and tested. The basic

procedure was:

• Mosquitoes (up to 500) placed into one 50ml urine pot,

• 20 x 5mm glass beads added,

• 3-5mls sterile PBS added,

• Ground for 20mins in MOSAVEX,

• PCR as above.

A short description of the various viruses and their clinical significance is detailed in

Appendix 3. Positive virus results were sent to the Communicable Diseases Branch

and the Environmental Health Branch of NSW Health and to the relevant Public

Health Unit.

Results

From the mosquitoes processed, there were 28 detections, including 2BFV, 7RRV,

1KOKV, 11EHV and 7STRV (Table 3). From the inland, 1EHV was made from

Griffith. From the coast, Georges River produced 12 isolates (2RRV, 1KOKV, 8EHV

& 1STRV), while another six isolates (1 RRV & 5 STRV) were made from the sites

along the Parramatta River.

NSW Arbovirus Surveillance Program, 2018-2019

Table 3. Arboviral isolates from NSW, 2018-2019.

FTA Card = Sugar based surveillance. Whole trap grind = all the mosquitoes are ground (or a

subsample of the larger collections) and tested for arboviral nucleic acid.

Location of flocks

The 2018-2019 season began on 3rd November 2018 with the first bleed and ended

on 30th April 2019 with the last. A total of nine flocks each containing up to 15 Isa

Brown pullets was deployed, with one flock each at Deniliquin, Dubbo, Forbes,

Griffith, Hay, Leeton, Macquarie Marshes, Menindee, and Moree (Figure 1).

Methods

The NSW Chicken Sentinel Program was approved by the Western Sydney Local

Health Network Animal Ethics committee. This approval requires that the chicken

handlers undergo training to ensure the chickens are cared for appropriately and that

LOCATION – Site Date

Trapped Detection Method Virus

BALLINA – North Creek Road

23/Apr/2019

Whole trap grind

Ross River

BALLINA – Pacific Pines

23/Apr/2019

Whole trap grind/FTA Card

Ross River

BALLINA – Pacific Pines

17/Apr/2019

Whole trap grind

Ross River

TWEED – Piggabeen Road

2/Apr/2019

Whole trap grind

Barmah Forest

PORT MACQUARIE – Stevens Street

2/Apr/2019

Whole trap grind

Barmah Forest

GEORGES RIVER – Alfords Point

14/Mar/2019

Whole trap grind

Stratford

CENTRAL COAST – Ourimbah

13/Mar/2019

Whole trap grind

Ross River

PARRAMATTA – Duck River

12/Mar/2019

Whole trap grind

Stratford

PARRAMATTA – Duck River

25/Feb/2019

Whole trap grind

Stratford

GEORGES RIVER – Alfords Point

20/Feb/2019

Whole trap grind

Ross River

SOPA – Haslams Creek

18/Feb/2019

Whole trap grind

Ross River

PARRAMATTA – Duck River

18/Feb/2019

Whole trap grind

Stratford

GEORGES RIVER – Deepwater

12/Feb/2019

Whole trap grind

Ross River

GEORGES RIVER – Deepwater

12/Feb/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

12/Feb/2019

Whole trap grind

Edge Hill

SOPA – Newington

12/Feb/2019

Whole trap grind

Stratford

GEORGES RIVER – Alfords Point

6/Feb/2019

Whole trap grind

Edge Hill

CENTRAL COAST – Ourimbah

4/Feb/2019

Whole trap grind

Stratford

GRIFFITH – Lake Wyangan

29/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Alfords Point

24/Jan/2019

Whole trap grind

Edge Hill

PARRAMATTA – Duck River

23/Jan/2019

Whole trap grind

Stratford

HILLS – Glenorie

23/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

23/Jan/2019

Whole trap grind

Edge Hill

BLACKTOWN – Ropes Crossing

22/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

16/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Alfords Point

10/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

9/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

9/Jan/2019

FTA card

Kokobera

NSW Arbovirus Surveillance Program, 2018-2019

blood sampling is conducted in a manner that minimises trauma to the chickens. The

chickens are cared for and bled by local council staff and members of the public.

Laboratory staff are responsible for training the chicken handlers. A veterinarian

(usually the Director of Animal Care at Westmead) must inspect all new flock

locations prior to deployment to ensure animal housing is adequate. Existing flocks

are inspected approximately every two years. The health of each flock is reported

weekly, and is independently monitored by the Animal Ethics Committee via the

Director of Animal Care.

Full details of the bleeding method and laboratory testing regimen were detailed in

the 2003-2004 NSW Arbovirus Surveillance Program Annual Report (Doggett et al.

2004).

Results are disseminated via email to the relevant government groups as determined

by NSW Health and are placed on the NSW Arbovirus Surveillance website.

Confirmed positives are notified by telephone to NSW Health and Communicable

Diseases Network, Australia.

Results

The season began with 135 pullets. A total of 2,545 samples was received from the

ten flocks in NSW over the six-month period in 2018-2019. This represented 5,090

ELISA tests (excluding controls and quality assurance samples), with each specimen

being tested for MVEV and KUNV antibodies. There no seroconversions in the

sentinel chickens.

Y-

-A

All arboviral infections detected in humans are notifiable under the NSW Public

Health Act 2010. When a person tests positive for an arboviral infection pathology

laboratories notify public health authorities who assess the notification against

agreed surveillance case definitions and take appropriate actions using NSW Health

disease control guidelines.

Annual reports (by calendar year) of notifiable vector-borne diseases (VBD),

including locally acquired arbovirus infections, are available on the NSW Health VBD

reports website.

The two most common locally-acquired arbovirus infections notified in NSW are

infections with Ross River virus (RRV) and Barmah Forest virus (BFV).

In the 2018-2019 financial year there were 585 notifications of RRV infection in NSW

residents (Table 4), a small (2%) decrease compared to the previous year (599

notifications). There were 70 notifications of BFV infection (Table 4), which is 35%

lower than the previous year (93 notifications). There were no notifications of other

locally-acquired arbovirus infections in NSW during 2018-2019.

Monthly BFV notifications were low throughout the year, with a peak of 10

notifications in April 2019 (Figure 7).

NSW Arbovirus Surveillance Program, 2018-2019

RRV notifications were generally lower than the five-year mean throughout the year

(Figure 7). Notifications were highest in the autumn months of 2019, peaking in

March and April 2019 with 82 notifications each. This followed the typical seasonal

pattern of RRV activity.

Figure 7. Barmah Forest virus and Ross River virus infections in NSW residents:

notifications by month of onset for the 2018-2019 financial year, compared to the

5-year monthly means for the period from July 2013 to June 2018.

BFV and RRV notifications by place of residence of the case are presented by NSW

local health district (LHD), by geographic region (Coastal, Inland, and Sydney

metropolitan) and by Australian Bureau of Statistics (ABS) statistical area level 2

(SA2). See Appendix 5 for definitions of the Coastal, Inland, and Sydney metropolitan

regions. Due to incomplete address information, a handful of cases (approximately

one per year) could not be allocated to a region. Population rates based on the

Australian Bureau of Statistics estimated resident populations. Population projections

for LHDs in 2018-19 based on data from the NSW Department of Planning and

Environment. The place of residence of a case may not, however, be where the

infection was acquired.

Notifications of BFV and RRV infection by LHD are shown in Table 4. The highest

number of notifications for BFV infection were in the Northern NSW, Mid North Coast

and Hunter New England LHDs, with few notifications in other LHDs. The highest

population notification rates were in the Northern NSW and Mid North Coast LHDs.

RRV notifications were highest in the Hunter New England, Western NSW and

Northern NSW LHDs, while RRV population notification rates were highest in the Far

West and Western NSW LHDs.

NSW Arbovirus Surveillance Program, 2018-2019

Table 4. Barmah Forest virus and Ross River virus infections in NSW residents:

notifications and population rates (notifications per 100,000 population) by local

health district for the 2018-2019 financial year.

Central Coast

0.00

10.46

Far West

0.00

46.69

Hunter New England

1.29

168

18.02

Illawarra Shoalhaven

0.48

4.36

Mid North Coast

6.33

23.98

Murrumbidgee

0.00

17.93

Nepean Blue

Mountains

0 0.00 4 1.05

Northern NSW

11.53

22.74

Northern Sydney

0.11

2.78

South Eastern Sydney

0.00

0.85

South Western Sydney

0.00

0.60

Southern NSW

1.42

14.21

Sydney

0.00

0.89

Western NSW

1.06

28.70

Western Sydney

0.00

1.30

Total

70 0.88 585 7.35

*Notifications per 100,000 estimated resident population, based on ABS population

estimates. Population projections by the Centre for Epidemiology and Evidence, NSW

Ministry of Health, based on data from the NSW Department of Planning and Environment.

Notifications of BFV and RRV infection by geographic region (Coastal, Inland, and

Sydney metropolitan) of residence are shown in Figures 8 and 9, respectively, by

financial year of disease onset from 2009-2010 to 2018-2019.

The Coastal region again accounted for the vast majority of BFV notifications (n=65,

92.9%) followed by the Inland region (n=4, 5.7%) with only 1 notification reported in a

resident of the Sydney region (Figure 8).

Notification maps of BFV and RRV infection by ABS statistical area level 2 (SA2) of

residence for the 2018-2019 financial year are shown in Figures 10 and 11, together

with maps of population notification rates.

The SA2 areas with the highest total number of BFV notifications were Maclean-

Yamba-Iluka (n=8) and Brunswick Head – Ocean Shores (n=6) (Figure 10(a)). The

two SA2 areas with the highest notification rates per 100,000 population were also

Brunswick Head – Ocean Shores (70) and Maclean-Yamba-Iluka (49) (Figure 10(b)).

The SA2 areas with the highest total number of RRV notifications were Griffith (n=12)

and Old Bar – Manning Point – Red Head (n=11) (Figure 11(a)). The SA2 areas with

the highest notification rates per 100,000 population were Far West (179) and

Forster-Tuncurry Region (151) (Figure 11(b)).

NSW Arbovirus Surveillance Program, 2018-2019

Figure 8: Barmah Forest virus infections in NSW residents: annual notifications by

year of disease onset and geographical region for the past 10 years (2009-2010 to

2018-2019).

Figure 9: Ross River virus infections in NSW residents: annual notifications by year

of disease onset and geographical region for the past 10 years (from 2009-2010 to

2018-2019).

NSW Arbovirus Surveillance Program, 2018-2019

Figure 10: Barmah Forest virus infections in NSW residents.

(a) Notifications by statistical area level 2 (SA2), for 2018-2019.

(b) Population notification rates* by statistical area level 2 (SA2), for 2018-2019.

* Notifications per 100,000 estimated resident population based on ABS census data.

NSW Arbovirus Surveillance Program, 2018-2019

Figure 11: Ross River virus infections in NSW residents.

(a) Notifications by statistical area level 2 (SA2), for 2018-2019.

(b) Population notification rates* by statistical area level 2 (SA2), for 2018-2019.

*Notifications per 100,000 estimated resident population based on ABS census data.

For further information on surveillance for human infections with vector-borne

diseases, including exotic arbovirus infections, see the following:

• NSW Health Vector-borne diseases reports

• NSW Health Notifiable diseases data (and select the relevant disease).

NSW Arbovirus Surveillance Program, 2018-2019

The 2018-2019 season, as per last year, was dominated by a protracted period of

continually hot and dry weather patterns. The entire year of 2018 produced rainfall

that was below average for the entire state, and most of NSW even had very much

below average precipitations. In spite of the last three months of 2018 having

average rainfall, the ongoing dry conditions and parched soils meant that any free

standing water was quickly absorbed. Furthermore, the state experienced

temperatures of up to 2.5oC above average for the entire 2018 and 1-2oC above

average for the first six months of 2019.

As a consequence, mosquito numbers were at a record low from the inland, with only

7,998 collected from the entire season from all set traps. In a more typical year, this

number is often collected on the one night, from one trap. The one arboviral isolate,

no seroconversions in the sentinel flocks, and few human notifications, were in

accordance with the low mosquito numbers. For the inland, in total there were 181

notifications, which included 177RRV & 4BFV, and this was almost half the previous

nine season average of 343 (311RRV & 32BFV). The statistical local areas that

produced the highest notifications for RRV from the inland was Griffith (12), while the

Far West (179/100,000) had the highest notification rate.

With the hot and dry weather patterns continuing into August 2019, the SOI being

neutral, and that current models are in the negative, an MVEV outbreak would seem

unlikely for 2019-2020. However, not dissimilar conditions have existed in the past

when MVEV activity has occurred following the southerly movement of low pressure

cells formed from tropical cyclones. The hypothesis is that the low pressure cell

pushed infected vectors south. Thus the residual weather patterns from tropical

cyclones are now closely monitored by the Department of Medical Entomology. The

forecast ahead is for temperatures that are higher than the norm and this may push

forward the mosquito season, with activity occurring earlier than normal. If this does

happen, then the start of the surveillance season may need to be brought forward.

While the coast experienced similar dry conditions, other environmental factors

influence mosquito numbers, notably tides. In fact dry conditions can result in larger

collections of the saltmarsh mosquito, Aedes vigilax. However for this season,

mosquito collections from the coastal region were not extraordinary, the 48,214

trapped was similar to last year’s total (48,660). Arboviral notifications were also very

similar to last year; for 2018-2019 there were 412 cases, including 347RRV and

65BFV, compared to 2017-2018 when there was a total of 428 notifications, including

343 RRV and 85BFV. Both of these years were around 30% lower than average (627

cases, including 438RRV & 189BFV).

One key difference this season for the coastal sites was the higher number of

arboviral detections from the trapped mosquitoes (seven this year compared with

three in 2017-2018). However, this is probably due to the enhancements made this

season to improve the sensitivity of the arboviral detection procedures.

While mosquito activity for both the inland and coast were unremarkable, in strong

contrast the sites around Sydney, notably those along the Georges and Parramatta

River were extremely productive. In fact this season produced the highest collections

NSW Arbovirus Surveillance Program, 2018-2019

to date from the Sydney region. From the Georges River, the site of Picnic Point

alone trapped over 50,000 mosquitoes and five arboviral isolates were yielded (4EHV

& 1KOKV, Table 6). Aedes vigilax comprised more than 90% of the sample,

suggesting that the dry conditions coupled with the high tides contributed to this

seasons dramatic increase (if the mudflats are continually dry, the mosquito eggs can

maturate producing larger hatches in subsequent tidal flushings). From the other

trapping locations along the Georges River, there were another seven arboviral

isolates, including from Alfords Point, 1RRV, 3EHV & 1STR, and from Deepwater,

1RRV & 1EHV.

In spite of the high mosquito numbers and multiple arboviral detections, human

notifications were below average with a total of 62 reports (61RRV and 1BFV). In

comparison, the average from the previous nine seasons was 81 notifications,

including 73RRV and 8BFV. In the past there have been large numbers of arboviral

isolates from the Georges River without a concomintant increase in arboviral

notifications. In fact notifications from Sydney tend to only increase when there is a

large amount of activity elsewhere along the coast.

The Picnic Point trapping site is located along Henry Lawson Drive, east of Yeramba

Lagoon. The Department of Medical Entomology has undertaken sampling from this

water body and it is not the source for the large mosquito populations. Rather, the

mosquitoes appear to be coming from the south side of the Georges River where

there are two moderately sized mudflats, as can be observed on Google Maps.

Fortunately there is little housing directly around these areas. Access to the site to

survey the habitat is difficult, as are most of the mosquito breeding sites along the

Georges River, due to the topography, lack of vehiclar access, and privately owned

lands. However, plans are underway to better document the breeding sites along the

river this coming season.

The other Sydney location that produced an extraordinary high number of

mosquitoes this season, was the new trapping site at Duck River, which is a tributary

of the Parramatta River, and west of Sydney Olympic Park. Duck River trapped over

45,000 mosquitoes, the majority being Aedes vigilax, plus there were four isolates.

Duck River runs through industrial estates; a petroleum plant is situated to the west

and factories towards the east. The river is bordered by a narrow strip of vegetation

along each bank (Figure 12), with some small areas of mudflats. Like the Georges

River, access for mosquito sampling is very difficult due to the topography and that

the river is fenced off for most of its margin. However, preliminary surveys

undertaken with Unmanned Aerial Vehicles (UAVs or ‘drones’) by Medical

Entomology has revealed that the size of the potential mosquito habitat is quite small,

probably under 300 square metres. Yet this location is extremely productive and

many factor workers in the area complained of the mosquito nuisance problem when

staff were setting the traps.

As a comparison, the three nearby trapping sites of Sydney Olympic Park (SOP)

trapped a total of 18,331 mosquitoes for the entire season (Figure 13). Active

mosquito management through aerial application of larvicides is undertaken on a

routine basis at SOP, successfully reducing the mosquito nuisance problem. Even a

small scale management program with the use of UAVs at Duck River should be

highly effective a reducing mosquito numbers. Further mapping of the mosquito

NSW Arbovirus Surveillance Program, 2018-2019

breeding habitats will be undertaken this season.

Figure 12. Drone footage showing the nature of Duck River, with large industrial

estates to the east and a petroleum plant to t

he west. Habitat for mosquito

breeding is limited to small areas of mudflats.

Figure 13. Mosquito collections at Duck River (brown line) and SOP (blue line).

The asterisks represent viral detections at Duck River.

NSW Arbovirus Surveillance Program, 2018-2019

Figure 14. Weekly Ross River virus notifications in NSW residents, Jul 2018 to June 2019.

(Source: NSW Heath Communicable Diseases Weekly Report,

www.health.nsw.gov.au/Infectious/reports/Pages/CDWR.aspx).

Figure 14 represents reports of RRV by notification date, which is directly from the

NSW Health Communicable Diseases Weekly Report, and is the data that is included

in the weekly report of the NSW Arbovirus Surveillance Program. In comparison,

Figure 7 shows notifications by date of onset.

In the case of the RRV reports by notification date (Figure 14), just under 40% of the

reports during the fiscal year of 2018-19 occurred over the months of July to

December 2018, and approximately 35% of the RRV positives by date of onset

(Figure 7) originated from the same period. All of these reported cases occurred

during the cooler months before mosquito numbers notably increased. This highlights

the ongoing issues with the reliability of notification data as an indication of recent

infection as patients reported during the cooler months were clearly not infected with

the virus at that time of the year as mosquito numbers were low and there was little

evidence of arbovirus activity. However, it should be noted that date of onset is the

better indication of the two notification types in terms of an indication of possible viral

acquisition date.

The data points to the key limitation of testing for RRV (and BFV) infection as it relies

solely upon serological tests that detect the person’s antibody response to an

infection rather than the virus itself. Furthermore, most cases that are notified are

suggestive (single specimen with both IgM and IgG RRV antibodies) and not

definitive (where specimens are taken during the acute and convalescent stage and

a four-fold rise in antibodies are recorded). As IgM antibody levels can remain

elevated for months to even years (and IgG for years to decades), it is likely that

NSW Arbovirus Surveillance Program, 2018-2019

most of the RRV notifications reported in these cooler months actually represent

infections that were acquired during the previous season when RRV activity was

high. The possibility of cross-reacting antibodies cannot be discounted with a single

positive result. Issues with the serological tests must also be considered, as

happened with the commercial BFV kit over 2012-2013 whereby almost 90% of those

that tested positive were subsequently found to be false (Doggett, 2014; Knope et al.,

2016; Kurucz et al., 2016). The limitations in the notification data also indicates why

RRV models are unlikely to ever accurately predict activity and future outbreaks

(Doggett, 2018).

Arboviral detection methodologies from the trapped mosquitoes continued to be

investigated within the surveillance program, in order to produce the most sensitive

assay system with results available in the shortest possible time. In recent years, the

use of FTA cards have been evaluated, which enabled results to be quickly available.

The power of this technique is that arboviral detections from mosquitoes are typically

available in under 24hours of receipt of the sample into the laboratory. However,

analysis from the last two seasons have shown that FTA cards were not the most

sensitive system available. Instead, Medical Entomology has been testing a novel

approach, grinding all the mosquitoes from the same catch in the one vial, and

testing the supernatant via PCR as per described methods.

Last season, this updated methodology was found to be considerably more sensitive

than FTA cards. For example, while there were 8 arboviral detections with the whole

trap grind (WTG) protocol, the FTA cards yielded only two positive results. This

season produced an even more compelling result for the whole trap grinds; of the 28

detections only two were picked up by the FTA cards.

Furthermore, not only are WTGs more sensitive, the system offers a number of

advantages over FTA cards: no FTA card preparation by field operatives; no FTA

card elution; and no FTA cards. Thus WTGs are cheaper, quicker, as well as being

more sensitive.

For the 2019-2020 season, FTA cards will no longer be deployed in the mosquito

traps.

Background. Over the decade there has been an increasing number of detections of

exotic mosquitoes at major Australian ports. The main species have been the

Dengue/Yellow Fever mosquito, Aedes aegypti, and the Asian Tiger Mosquito, Aedes

albopictus. Both of these pose a serious biosecurity risk to Australia being major

vectors of serious arboviral diseases including Dengue, Yellow Fever, Zika, and

Chikungunya viruses.

Aedes aegypti, being a tropical species, mainly poses a threat to the more northern

NSW Arbovirus Surveillance Program, 2018-2019

regions of the nation, whereas Aedes albopictus is more cold tolerant. This species

has the potential to become established along the eastern coast of Australia

including the major population centre of Sydney. As such, Aedes albopictus has the

potential to cost the national economy hundreds of millions of dollars, through the

transmission of diseases and vector control costs. Thus, it is imperative that these

mosquitoes are kept out of regions of the country where they presently do not exist.

Furthermore, the mosquitoes that have been collected have undergone genetic

analysis for the presence of insecticide resistant genes and most of the mosquitoes

have these. In Australia, there is no evidence for insecticide resistance in our local

mosquitoes, including invading species such as Ae. aegypti. The presence of

resistant insects will make the mosquito much more difficult to control and limit

management options.

Sydney has seen numerous detections of exotic mosquitoes in recent years, the

majority being Ae. aegypti, although specimens of Ae. albopictus and Culex gelidus

have also been trapped. Most detections have occurred within the baggage handling

area of Sydney International Airport. However, some detections have occurred at

various freight handling facilities, both at Sydney Airport and in a facility close to the

airport.

Table 5 details the detections for the period July 2018 to August 2019. The finding of

Aedes quasirubrithorax was of initial concern, for it is very similar in appearance to

the highly invasive species, Aedes japonicus, which has been detected on a number

of occasions in Brisbane port facilities. Aedes quasirubrithorax is a native mosquito

species but previously unknown from the south coast of NSW.

Table 5. Detection of Exotic Mosquitoes in NSW, July 2018 – August 2019.

*see text for discussion.

In response to the Aedes aegypti detections a number of actions have been

implemented. NSW Health established regular teleconferences, the Department of

Agriculture and Water Resources (DAWR) undertook enhanced surveillance (both

increasing the number of traps used and the frequency of trap inspections),

Date Mosquito Species & Sex Location

3 Aug 2019

Aedes aegypti ♀

Sydney International Airport

31 Jul 2019

Aedes aegypti ♀

Sydney International Airport

14 May 2019

Aedes albopictus ♂

Sydney International Airport

2 May 2019

Aedes aegypti ♀

Approved Arrangement Facility, Sydney

23 Apr 2019

Aedes aegypti ♂

Sydney International Airport

6 Feb 2019

Aedes aegypti ♀

Approved Arrangement Facility, Sydney Airport

16 Jan 2019

Aedes aegypti ♂

Approved Arrangement Facility, Sydney Airport

2 Jan 2019

Aedes aegypti ♀

Approved Arrangement Facility, Sydney

7 Dec 2018

Aedes aegypti ♀

Approved Arrangement Facility, Sydney

23 Nov 2018

Aedes aegypti ♀

Approved Arrangement Facility, Sydney

9 Oct 2018

Aedes quasirubrithorax ♀*

Eden Sea Port

NSW Arbovirus Surveillance Program, 2018-2019

insecticidal treatment of the detection areas were undertaken, and vector surveys

were conducted both within and around the sites with previously unrecorded

detections, which included staff from the Department of Medical Entomology at

Westmead Hospital.

The reason for the recent increase in detections is not presently fully clear. In spite of

this, there has been a co-ordinated effort across multiple agencies to ensure the

exotic mosquitoes do not become established in NSW. Recently a new invasive

mosquito species was detected in Europe, Aedes flavopictus (Ibáñez-Justicia et al.

2019), which is closely related to Aedes albopictus and shown to be an efficient

vector of dengue virus. This is another species that will be closely monitored for.

NSW Arbovirus Surveillance Program, 2018-2019

N-

-B

Y-

-L

Inland Locations

Albury: mosquito numbers were ‘low’ for the entire season. There were no arboviral

detections from the trapped mosquitoes. Sentinel chicken flocks did not operate at

Albury.

Bourke: mosquito collections were ‘low’ for the entire season. There were no

arboviral isolates and sentinel chickens did not operate at this location.

Deniliquin: no mosquito collections were undertaken at this location. There were no

seroconversions to MVEV or KUNV in the sentinel chickens.

Forbes: other than the one ‘high’ yield in mid-December, mosquito numbers were

‘low’ for most of the season. There were no arboviral isolations nor any

seroconversions to MVEV or KUNV in the sentinel chickens.

Griffith: during January to early February, mosquito numbers were ‘high’, but never

reached ‘very high’ as per most years. Outside this period, numbers were ‘low’ to

‘medium’. There was one arboviral isolate this season from Griffith, an EHV isolated

from a collection made at Lake Wyangan trapped on 29/Jan/2019. There were no

seroconversions to MVEV or KUNV in the sentinel chickens.

Hay: no mosquito collections were undertaken this season, and there were no

seroconversions to MVEV or KUNV in the sentinel chickens.

Leeton: mosquito numbers were ‘low’ to ‘medium’ throughout the entire season.

There were no arboviral isolates from the mosquitoes nor any seroconversions in the

sentinel chickens.

Macquarie Marshes: five mosquito collections were made this season and numbers

were mostly ‘low’, with one ‘high’ collection in mid-December. There were no

arboviral detections or any seroconversions to MVEV or KUNV in the sentinel

chickens.

Menindee: no mosquito collections were undertaken this season, and there were no

seroconversions to MVEV or KUNV in the sentinel chickens.

Moree: no mosquito collections were undertaken this season, and there were no

seroconversions to MVEV or KUNV in the sentinel chickens.

Wagga Wagga: mosquito numbers were ‘low’ for the entire the season and there

were no arboviral detections. Sentinel chickens did not operate at Wagga Wagga.

NSW Arbovirus Surveillance Program, 2018-2019

Coastal Locations

Ballina: mosquito numbers were ‘high’ throughout the season with three ‘very high’

traps late in the season, in mid-March and April. For the most part, these elevated

numbers coincided with larger collections of Aedes vigilax. However for most of the

season, collection of Aedes vigilax were ‘low’ and only became ‘high’ in mid-March.

In spite of the lower numbers of this species, collections were dominated by salt

water breeding mosquitoes including Culex sitiens and Verrallina funerea, neither of

which are notable vectors. There were three RRV isolates detected, including one

from North Creek Rd from mosquitoes trapped on 23/Apr/2019, and two detections

from Pacific Pines, one each on 17/Apr/2019 and 23/Apr/2019.

Coffs Harbour: trapping was undertaken at Moller Drive and Christmas Bells Road.

Collections tended to be ‘low’ to ‘medium’, with the one ‘high’ yield late in early

January. Numbers of Aedes vigilax remained ‘low’ for the entire season. No arboviral

isolates were detected.

Gosford: as per usual, the Empire Bay site dominated the mosquito collections on

the Central Coast, where numbers were ‘high’ for most of the season. However,

Aedes vigilax collections were mostly ‘low’, with only the two ‘high’ yields. Aedes

notoscriptus was the most common species, comprising more than 50% of the overall

collections. No arboviral isolates were detected.

Lake Macquarie: collections were undertaken from three sites: Belmont Lagoon,

Teralba, and Dora Creek. Mosquito numbers were ‘low’ for most of the season until

late March with two ‘high’ collections. Aedes vigilax were ‘low’ for the majority of the

season. No arboviral isolates were detected.

Nambucca: four traps were set towards the end of the season and mosquito

numbers were mostly ‘low’ to ‘medium’. No arboviral isolates were detected.

Port Macquarie: trapping was again undertaken at three sites; Wall Reserve,

Fernbank Creek Road, and Steven Street. Mosquito collections were ‘low’ throughout

most of the season with some ‘medium’ catches in March and April. Aedes vigilax

collections remained ‘low’ throughout the entire season. There was one BFV

detected at Stevens St from mosquitoes trapped on 2/Apr/2019.

Tweed Heads: trapping continued at the three sites of Koala Beach, Beltana Drive,

and Piggabeen Road. Beltana Drive again yielded the largest collections for the

season. Overall numbers were mostly ‘medium’, with a series of ‘high’ numbers over

February and March. Aedes vigilax collections peaked during the same period but

were mostly ‘medium’ in number. Culex sitiens close to half of the overall collections.

There was one BFV detected at Piggabeen Rd from mosquitoes trapped on

2/Apr/2019.

Wyong: trapping was undertaken at three sites: Ourimbah, Halekulani, and North

Avoca. Mosquito numbers were ‘low’ for the entire season, except for some ‘medium’

collections early in the season. There were two arboviral isolates detected from

Ourimbah. This included one STRV from 4/Feb/2019 and one RRV from

13/Mar/2019

NSW Arbovirus Surveillance Program, 2018-2019

Sydney Locations

Bankstown: collections this season were undertaken at Deepwater and Picnic Point.

These sites are known for intense local Aedes vigilax production, which again

dominated the catches this year comprising over 93% of the collections. Picnic Point

was especially productive, trapping over 50,000 mosquitoes from this trap alone.

Mosquito numbers were consistently ‘high’ to ‘very high’ for the entire period from

early December to mid-April. There were seven arboviral isolates and these are listed

in the table below.

Table 6. Arboviral isolates from the Georges River sites, 2018-2019.

FTA Card = Sugar based surveillance. Whole trap grind = all the mosquitoes are ground (or a

subsample of the larger collections) and tested for arboviral nucleic acid.

Blacktown: mosquito trapping was undertaken at Nurrangingy Reserve and Ropes

Crossing. Numbers were ‘low’ for most of the season with the very occasional

‘medium’ collection. There was one EHV yielded from mosquitoes trapped on

22/Jan/2019 from Ropes Crossing.

Georges River: trapping continued to be undertaken at Alfords Point and Illawong,

with the former site producing the vast majority of the catch. Collections were ‘high’ or

greater for the majority of the season, with numbers peaking during

December/January. Aedes vigilax comprised more than 90% of the collections. There

were five arboviral detections this season, which are detailed in Table 6 above.

Hawkesbury: trapping was undertaken at four main sites, including at Wheeny

Creek, McGraths Hill, Yarramundi, and Richmond. Mosquito numbers tended to be

‘low’ throughout most of the season with some ‘medium’ collections in late March. No

arboviral isolates were detected.

Hills Shire: mosquito trapping was undertaken at Rouse Hill, Glenorie, and

Baulkham Hills. Numbers were ‘low’ for most of the season. There was one EHV

yielded from mosquitoes trapped on 23/Jan/2019 from Glenorie.

LOCATION – Site Date

Trapped Detection Method Virus

GEORGES RIVER – Alfords Point

14/Mar/2019

Whole trap grind

Stratford

GEORGES RIVER – Alfords Point

20/Feb/2019

Whole trap grind

Ross River

GEORGES RIVER – Deepwater

12/Feb/2019

Whole trap grind

Ross River

GEORGES RIVER – Deepwater

12/Feb/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

12/Feb/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Alfords Point

6/Feb/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Alfords Point

24/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

23/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

16/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Alfords Point

10/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

9/Jan/2019

Whole trap grind

Edge Hill

GEORGES RIVER – Picnic Point

9/Jan/2019

FTA card

Kokobera

NSW Arbovirus Surveillance Program, 2018-2019

Parramatta: collections were undertaken at the three sites of George Kendall

Reserve, Eric Primrose Reserve and Duck River. The latter site yielded the largest

collections, trapping over 45,000 mosquitoes during the season. Here, Aedes vigilax

comprised over 90% of the collections. For the season, overall numbers were

consistently ‘high’ and ‘very high’ during late March and early April. There were four

STRV isolated from mosquito collections at Duck River, one each for 23/Jan/2019,

18/Feb/2019, 25/Feb/2019 and 12/Mar/2019.

Penrith: trapping was undertaken at the sites of Emu Plains, Muru Mittiger,

Glenmore Park, and Werrington. Mosquito numbers were ‘low’ from most of the

season, with a series of ‘high’ collections during December and January. No arboviral

isolates were detected.

Sydney Olympic Park (SOP): mosquito monitoring at this location included the long-

term locations of Narawang and Haslams Creek, as well as Newington. Mosquito

numbers were consistently ‘high; for almost the entire season, with Aedes vigilax

being the predominant species. There were two arboviral detections this season, one

STRV from Newington (12/Feb/2019) and one RRV from Haslams Creek

(18/Feb/2019).

NSW Arbovirus Surveillance Program, 2018-2019

. T

The following briefly details the main mosquito species collected in NSW.

The Common Domestic Mosquito,

Aedes notoscriptus.

A common species that breed in a variety of natural and

artificial containers around the home. It is the main

vector of dog heartworm and laboratory studies shows it

be an excellent transmitter of both RRV and BFV.

The Bushland Mosquito,

Aedes procax.

Common throughout coastal NSW and breed

s in

bushland freshwater groundwater. Numerous isolates of

BFV have been recovered from this species and it is

probably involved in the transmission of the virus.

The Northern Saltmarsh Mosquito,

Aedes vigilax.

An important species along coastal NSW. This species

breeds on the mud flats behind saltmarshes and can be

extremely abundant and a series nuisance biter. It is a

major vector for RRV and BFV along the coast.

The Common Australian Anopheline,

Anopheles annulipes.

A mosquito from throughout NSW, but is most common

in the irrigated region of the Murrumbidgee where it can

be collected in the 1,000’s. Despite its abundance, it is

not thought to be a serious disease vector.

The Common Marsh Mosquito,

Coquillettidia linealis.

Found throughout N

SW but especially in areas with

freshwater marshes such as the Port Stephens area.

Both BFV & RRV have been isolated from this species

and is probably involved in some transmission.

The Common Banded Mosquito,

Culex annulirostris.

The species is common in the NSW inland regions that

have intense irrigation. This species is highly efficient at

transmitting most viruses and is responsible for the

spreading of most of the arboviruses to humans inland.

It is also involved in coastal RRV transmission.

NSW Arbovirus Surveillance Program, 2018-2019

Alphaviruses

Barmah Forest virus (BFV): disease from this virus is clinically similar to that of

RRV disease, although BFV disease tends to be associated with a more florid rash

and a shorter duration of clinical severity. Serological over diagnosis of this condition

through the non-specificity of the commercial kit was a major issue, and the kit was

withdrawn from the market. This has resulted in a dramatic reduction in BFV

notifications and the disease may now be under reported. Despite being first isolated

from an inland region, cases of BFV disease tend to occur mostly in coastal regions

in NSW. The main vector in NSW is Aedes vigilax although other species are

involved, notably Aedes procax. In 2010-2011 for the inland, there was a small

epidemic of BFV, but this was the largest outbreak to date for the region.

Ross River virus (RRV): this virus causes RRV disease and is the most common

cause of human arboviral disease in Australia. In NSW, approximately 700 cases per

season are reported. A wide variety of symptoms may occur from rashes with mild

fever, to arthritis that can last from months to years. The virus occurs in both inland

and coastal rural regions. The main vectors are Culex annulirostris (inland) and

Aedes vigilax (coast), although other mosquitoes are undoubtedly involved in the

transmission of the virus as isolates have been made from many species.

Sindbis virus (SINV): this is an extremely widespread virus throughout the world and

occurs in all mainland states of Australia. In contrast with Africa and Europe where

outbreaks have been reported, disease from SINV is relatively uncommon in

Australia; only 24 infections were notified in NSW from Jul/1995-Jun/2003 (Doggett

2004), with few cases reported since then. Symptoms of disease include fever and

rash. Birds are the main host, although other animals can be infected, including

macropods, cattle, dogs and humans. The virus has been isolated from many

mosquito species, but most notably Culex annulirostris in south-eastern Australia. It

is also not routinely tested for any longer and it is possible that this would cross react

with RRV in the commercial tests.

Flaviruses*

Alfuy virus (ALFV): no clinical disease has been associated with this virus and it has

not been isolated from south-eastern Australia.

Edge Hill virus (EHV): a single case of presumptive infection with EHV has been

described, with symptoms including myalgia, arthralgia, and muscle fatigue. Aedes

vigilax has yielded most of the EHV isolates in southeast Australia, although it has

been recovered from several other mosquito species. The virus is quite common,

with isolates from most years. The vertebrate hosts may be wallabies and

bandicoots, but studies are limited.

Kokobera virus (KOKV): only three cases of illness associated with KOKV infection

have been reported and all were from southeast Australia. Symptoms included mild

NSW Arbovirus Surveillance Program, 2018-2019

fever, aches and pains in the joints, and severe headaches, and lethargy. Symptoms

were still being reported by the patients five months after onset. This virus historically

was only known from inland regions of NSW until it was detected in a mosquito

trapped from the coastal region in 2009-2010. Culex annulirostris appears to be the

principal vector.

Kunjin virus (KUNV): disease from this virus is uncommon, with only two cases

being notified from 1995-2003 (Doggett 2004), and one case in 2011 (Doggett et al.

2012). Historically, activity has been confined to the inland region of NSW where it is

detected every few years. However, in the summer of 2010-2011, the virus was

detected on the coast, which resulted in an outbreak amongst horses with a number

of animal deaths resulting. Culex annulirostris appears to be the main vector.

Murray Valley Encephalitis (MVEV): major activity of this virus is rare in south-

eastern Australia and the last epidemic occurred in 1974. However, since the year

2000 there has been six seasons when MVEV activity has been detected within the

state: 2000-2001, 2003-2004, 2007-2008, 2010-2011, 2011-2012, and most recently,

2013-2014. There have been four human cases reported over 2008-2012. The virus

occurs only in inland regions of the state and symptoms are variable, from mild to

severe with permanent impaired neurological functions, to sometimes fatal. Culex

annulirostris is the main vector.

Stratford virus (STRV): there have been very few documented symptomatic

patients, only three described to date and symptoms included fever, arthritis, and

lethargy. The virus has mostly been isolated from coastal NSW, particularly from the

saltmarsh mosquito, Aedes vigilax, although recent isolates from the Sydney

metropolitan area have been from Aedes notoscriptus and Aedes procax. This is a

common virus, being isolated most years.

*Note that not all the flaviviruses above (excluding MVEV and KUNV) are tested

for, and so it is not possible to determine the disease burden associated with

these arboviruses. In light of some of these viruses being extremely common,

it may be that disease is unrecognised (as symptoms are non-specific) and

without supportive testing, is likely to remain undetected.

NSW Arbovirus Surveillance Program, 2018-2019

AHS Area Health Service

BFV Barmah Forest virus

BOM Bureau of Meteorology

CC Central Coast Public Health Unit

CS Central Sydney Public Health Unit

EHV Edge Hill virus

FW Far West Public Health Unit

GM Greater Murray Public Health Unit

HUN Hunter Public Health Unit

IgG Immunoglobin G (a type of antibody)

IgM Immunoglobin M (a type of antibody)

ILL Illawarra Public Health Unit

ICPMR Institute for Clinical Microbiology and Medical Research

MAC Macquarie Public Health Unit

MNC Mid North Coast Public Health Unit

MVEV Murray Valley Encephalitis virus

MW Mid West Public Health Unit

NE New England Public Health Unit

NR Northern Rivers Public Health Unit

NS Northern Sydney Public Health Unit

KOKV Kokobera virus

KUNV Kunjin virus

PHU Public Health Unit

RRV Ross River virus

SA Southern Area Public Health Unit

SA2 Statistical area level 2

SES South Eastern Sydney Public Health Unit

SINV Sindbis virus

SLA Statistical Local Area

SO Southern Oscillation

STRV Stratford virus

SWS Public Health Unit

TC Tropical Cyclone

WEN Public Health Unit

WS Western Sydney Public Health Unit

VADCP Victorian Arbovirus Disease Control Program

Virus? Virus unknown (not BFV, RRV, SINV, EHV, KOKV, KUNV, MVEV, STRV)

NSW Arbovirus Surveillance Program, 2018-2019

–

(

)

NSW Arbovirus Surveillance Program, 2018-2019

This project is funded and supported by the Environmental Health Branch of the

NSW Ministry of Health. The following are acknowledged for their efforts in the

Arbovirus Program:

Kishen Lachireddy, Anna Bethmont, Neil Hime, Aditya Vyas & Richard Broome

(Environmental Health Branch, NSW Health); Tracey Oakman, James Allwood,

Tony Burns, Ian Hardinge & Kev Prior (Murrumbidgee & Southern LHDs); David

Ferrall, Gerard van Yzendoorn & Jason Harwood (Far West & Western LHDs); Dr

David Durrheim, Philippe Porigneaux, Glenn Pearce (Hunter New England LHD);

Paul Corben, Kerryn Lawrence, David Basso, Greg McAvoy, Matthew Rand, Greg

Bell, Tony Kohlenberg & Geoff Sullivan (Mid North Coast & Northern NSW LHDs),

Dr Peter Lewis, Sam Curtis, Adam McEwen, Wayne McCallum & Kerry Spratt

(Northern Sydney & Central Coast LHDs); Prof. Mark Ferson, Toni Cains & Brian

Huang (South Eastern Sydney LHD); Helen Noonan, Haylee Sneesby & Annie

Truong (Western Sydney & Nepean Blue Mountains LHD); Peter Cavagnino, John

Birkett, Angela Daly & Mike Cassidy (South Western Sydney & Sydney LHDs);

Philip Palenkas & Lauriston Muirhead (Albury City Council, Albury); Kristy Bell &

Tom McAully (Ballina Shire Council, Ballina); Jackie Davis (Nursery on Mertin,

Bourke); Krystle Knowles, Erin Downes, Calee Bancroft & James Moss (Coffs

Harbour City Council, Coffs Harbour); Mathew Teale (Forbes Council), Laura

Turner & Fiona De Wit (Griffith Shire Council, Griffith); Anthony Gleeson

(Hawkesbury City Council, Windsor); Bill Larkin (Kempsey), Derek Poulton &

Keith Lainson (Lake Macquarie City Council); Peter Skarlis & Craig McVittie

(Leeton Shire Council, Leeton); Linda McLellan (Macquarie Marshes), Emma

Shaw & Daniel Walsh (Nambucca), David Durie, Stevie McCormack & Belinda

Comer (Penrith City Council, Penrith); Brian Falkner (Tweed Shire Council,

Murwillumbah).

The chicken handlers included: Maggie McCalman (Deniliquin), Denyell Woodhouse

(Dubbo), Mathew Teale (Forbes), Renae Foggiato & Fiona de Wit (Griffith), Kevin

Rosser (Hay), David Lang (Leeton), Linda McLellan (Macquarie Marshes), Barbara

Turner (Menindee), Lester Rodgers (Moree). The laboratory staff within CIDMLS are

acknowledged, particularly Heang Lim, Laurence McIntyre & James Goodwin.

The section on ‘Notifications of Locally-Acquired Arbovirus Infections’ was produced

by the Communicable Diseases Branch, Health Protection NSW, NSW Ministry of

Health.

The input of Dr Ross Matthews, Director of Animal Care, Westmead Hospital in the

continuation of the chicken surveillance program is greatly appreciated. The Sydney

Olympic Park Authority funds the Department to undertake mosquito surveillance in

the Homebush area.

The cooperation of the Department of Agriculture and Water Resources (especially

Laura Marsh) and the Sydney Airport Corporation were integral in the surveillance of

mosquitoes at ports and approved arrangement facilities (freight). Our apologies to

anyone inadvertently omitted.

NSW Arbovirus Surveillance Program, 2018-2019

Bureau of Meteorology, Australia. (2019). Rainfall Maps. http://www.bom.gov.au/cgi-

bin/climate/rainmaps.cgi, accessed 15/Aug/2019.

Dobrotworsky N.V. (1965). The Mosquitoes of Victoria. Melbourne University Press,

Carlton.

Doggett S. (2004). Population health aspects of mosquito-borne disease in New South

Wales. NSW Public Health Bulletin, 15: 193-199.

Doggett S.L. (2014). The Forum: It’s Barmah…or is it? Mosquito Bites, 8(2): 40-42.

Doggett S.L. (2018). Your number’s up! Mosquito Bites, 13(1): 24-27.

Doggett S., Clancy J., Haniotis J., Russell R.C., Hueston L., Marchetti M. and Dwyer D.

(2001). The New South Wales Arbovirus Surveillance & Mosquito Monitoring Program.

2000 –2001 Annual Report. Department of Medical Entomology, Westmead. 27pp.

Doggett S., Clancy J., Haniotis J., Russell R.C., Hueston L., Marchetti M. and Dwyer D.

(2004). The New South Wales Arbovirus Surveillance & Mosquito Monitoring Program.

2003 – 2004 Annual Report. Department of Medical Entomology, Westmead. 23pp.

Doggett S., Clancy J., Haniotis J., Russell R.C., Hueston L., and Dwyer D. (2011). The New

South Wales Arbovirus Surveillance & Mosquito Monitoring Program. 2010 – 2011

Annual Report. Department of Medical Entomology, Westmead. 37pp.

Doggett S.L. and Russell R.C. (2005). The epidemiology of Ross River and Barmah

Forest viruses in New South Wales. Arbovirus Research in Australia, 9: 86-100.

Doggett S.L., Russell R.C., Clancy J., Haniotis J. and Cloonan M.J. (1999). Barmah Forest

virus epidemic on the south coast of New South Wales, Australia, 1994-1995: Viruses,

Vectors, Human Cases, and Environmental Factors. Journal of Medical Entomology, 36:

861-868.

Doggett S.L., Webb C., Clancy J. and Haniotis J. (2017). Mosquito survey of the QANTAS

freight terminal, Sydney International Airport, 2017. Report for the NSW Ministry of

Health.

Finlaison D.S., Read A. J. and Kirkland P.D. (2008). An epizootic of bovine ephemeral

fever in New South Wales in 2008 associated with long-distance dispersal of vectors.

Australian Veterinary Journal, 88(8): 301-306.

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1914 and predisposing rainfall patterns. Australasian Medical Publishing Co., Glebe.

20pp.

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Service, Canberra.

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Australia, 2012-23: annual report of the National Arbovirus and Malaria Advisory

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Kurucz N., Markey P., Draper A. et al. (2016). Investigation into High Barmah Forest

Virus Disease Case Numbers Reported in the Northern Territory, Australia in 2012-

2013. Vector-Borne and Zoonotic Diseases, 16(2): 110-116.

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identification of flaviviruses. Vector Borne Zoonotic Diseases, 7(4):467-477.

Nicholls N. (1986). A method for predicting Murray Valley encephalitis in southeast

Australia using the Southern Oscillation. Australian Journal of Experimental Biology and

Medical Science, 64: 587-94

Pyke, A. T., I. L. Smith, A. F. van den Hurk, J. A. Northill, T. F. Chuan, A. J. Westacott, and

G. A. Smith. 2004. Detection of Australasian Flavivirus encephalitic viruses using rapid

fluorogenic TaqMan RT-PCR assays. Journal of Virological Methods, 117: 161-167.

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Arboviral diseases and malaria in Australia, 2014–15: Annual report of the National Arbovirus and Malaria Advisory Committee

Article

Full-text available

Apr 2019

This report describes the epidemiology of mosquito-borne diseases of public health importance in Australia during the 2014–15 season (1 July 2014 to 30 June 2015) and includes data from human notifications, sentinel chicken, vector and virus surveillance programs. The National Notifiable Diseases Surveillance System received notifications for 12,849 cases of disease transmitted by mosquitoes during the 2014–15 season. The Australasian alphaviruses Barmah Forest virus and Ross River virus accounted for 83% (n=10,723) of notifications. However, over-diagnosis and possible false positive diagnostic test results for these two infections mean that the true burden of infection is likely overestimated, and as a consequence, revised case definitions were implemented from 1 January 2016. There were 151 notifications of imported chikungunya virus infection. There were 74 notifications of dengue virus infection acquired in Australia and 1,592 cases acquired overseas, with an additional 34 cases for which the place of acquisition was unknown. Imported cases of dengue were most frequently acquired in Indonesia (66%). There were 7 notifications of Zika virus infection. No cases of locally-acquired malaria were notified during the 2014–15 season, though there were 259 notifications of overseas-acquired malaria and one notification for which no information on the place of acquisition was supplied. Imported cases of malaria were most frequently acquired in southern and eastern Africa (23%) and Pacific Island countries (20%). In 2014–15, arbovirus and mosquito surveillance programs were conducted in most of the states and territories. Surveillance for exotic mosquitoes at international ports of entry continues to be a vital part of preventing the establishment of vectors of mosquito-borne diseases such as dengue to new areas of Australia. In 2014-15, there was a sharp increase in the number of exotic mosquitoes detected at the Australian border, with 36 separate exotic mosquito detections made, representing a 280% increase from the 2013-14 period where there were 13 exotic mosquito detections. Commun Dis Intell 2016;40(3):e401–436.

Your number's up!

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Aug 2018

Stephen L. Doggett

Modelling to predict arboviral activity and outbreaks is extremely challenging. Typically models are developed from a limited data set, which means their predictive power is poor. It is highly unlikely that a useful predictive model will ever be produced.

The epidemiology of Ross River & Barmah Forest viruses in NSW, 1995 – 2004

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Full-text available

Jan 2005

Applications of a Sugar-Based Surveillance System to Track Arboviruses in Wild Mosquito Populations

Article

Full-text available

Dec 2013
VECTOR-BORNE ZOONOT

Abstract Effective arbovirus surveillance is essential to ensure the implementation of control strategies, such as mosquito suppression, vaccination, or dissemination of public warnings. Traditional strategies employed for arbovirus surveillance, such as detection of virus or virus-specific antibodies in sentinel animals, or detection of virus in hematophagous arthropods, have limitations as an early-warning system. A system was recently developed that involves collecting mosquitoes in CO2-baited traps, where the insects expectorate virus on sugar-baited nucleic acid preservation cards. The cards are then submitted for virus detection using molecular assays. We report the application of this system for detecting flaviviruses and alphaviruses in wild mosquito populations in northern Australia. This study was the first to employ nonpowered passive box traps (PBTs) that were designed to house cards baited with honey as the sugar source. Overall, 20/144 (13.9%) of PBTs from different weeks contained at least one virus-positive card. West Nile virus Kunjin subtype (WNVKUN), Ross River virus (RRV), and Barmah Forest virus (BFV) were detected, being identified in 13/20, 5/20, and 2/20 of positive PBTs, respectively. Importantly, sentinel chickens deployed to detect flavivirus activity did not seroconvert at two Northern Territory sites where four PBTs yielded WNVKUN. Sufficient WNVKUN and RRV RNA was expectorated onto some of the honey-soaked cards to provide a template for gene sequencing, enhancing the utility of the sugar-bait surveillance system for investigating the ecology, emergence, and movement of arboviruses.

Barmah Forest Virus Epidemic on the South Coast of New South Wales, Australia, 1994-1995: Viruses, Vectors, Human Cases, and Environmental Factors

Article

Full-text available

Dec 1999

In 1995, the largest recorded outbreak of human disease resulting from infection with the mosquito transmitted alphavirus Barmah Forest (BF) virus occurred along the south coast of New South Wales, Australia. The virus was first isolated in early January from mosquitoes collected at Batemans Bay and predisposed the recognition of 135 human clinical cases. The cases of BF virus were identified initially from Batemans Bay during late January, and the majority (30%) of all cases came from this town. After 5 wk, all major centers on the south coast had clinical patients. Aedes vigilax (Skuse) were especially abundant at Batemans Bay, with levels up to 8 times greater than normal. This species yielded 111 isolates and appeared to be the major vector of BF virus. Attempts to examine if BF virus was maintained in the field by vertical transmission within Ae. vigilax populations were unsuccessful; no evidence of vertical transmission with BF virus, nor any other arbovirus, was found in > 17,000 adults emerging from field-collected larvae from the region following peak virus activity. In addition to BF virus, other viruses were recovered from field-collected adult mosquitoes, including Ross River (10 isolates), Edge Hill (21), and Stratford (10). Ae. vigilax again yielded the majority of these viral isolates. The BF virus outbreak appeared to be associated with several factors. A lack of recent BF virus activity in the region provided a highly susceptible human population, and unusual weather conditions of above average rainfall coupled with high tides resulted in extraordinarily large populations of Ae. vigilax.

Detection of Australian Flavivirus encephalitis viruses using rapid fluorogenic TaqMan RT-PCR assays

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Jun 2004
J VIROL METHODS

The development of single, sensitive, fluorogenic reverse transcriptase-polymerase chain reaction (TaqMan) assays were required for the rapid and specific detection of three encephalitic viruses found in the Australasian region, namely; Japanese encephalitis virus (JEV), Murray Valley encephalitis virus (MVEV), and Kunjin virus (KUNV). Primers and a fluorogenic probe were individually designed to be complementary to a nucleotide region encompassing the 3' terminus of the nonstructural (NS) 5 gene and a portion of the 3' untranslated region (NS5-3'UTR) of each of the viral genomes respectively. Synthetically produced primer and probe controls were developed to minimize the likelihood of contamination and generation of false positives. Viral RNA from singly infected mosquitoes could be detected in pools of 1000 mosquitoes and positive mosquito pools collected from the field have been identified using each assay, indicating a high level of sensitivity and suitability for use in mosquito surveillance programs. In addition, the JEV TaqMan assay has been used to detect successfully viral RNA in sentinel pig serum samples. These assays potentially offer superior and timely detection of encephalitic viruses from surveillance samples, which is essential for the rapid implementation of vector control measures and continued monitoring of virus activity in the Australasian region.

Population health aspects of mosquito-borne disease in New South Wales

Article

Full-text available

Nov 2004

Stephen L. Doggett

Human pathogens transmitted by mosquitoes pose a significant threat to population health in New South Wales. Within the State, there is annual activity of Ross River virus and Barmah Forest virus, occasional activity from Kunjin virus and Sindbis virus, and rare epidemics of Murray Valley encephalitis virus. For the traveller, dengue and malaria are constant threats. The focus of this article will be the mosquito-borne viruses (the ‘arboviruses’), including the factors that influence their activity in New South Wales, how they affect the community, and the future threats they pose to population health in the State.

Investigation into High Barmah Forest Virus Disease Case Numbers Reported in the Northern Territory, Australia in 2012-2013

Article

Jan 2016
VECTOR-BORNE ZOONOT

Between October 2012 and October 2013, unprecedented high numbers of Barmah Forest virus (BFV) disease cases were reported in the Northern Territory (NT). An investigation was launched by the NT Department of Health in cooperation with the Department of Primary Industry and Fisheries and the Department of Land Resource Management to investigate possible causes for this phenomenon. The investigation included virus isolations from mosquitoes collected in Darwin urban areas, BFV antibody testing in peri-urban small mammals and a human BFV disease case series investigation of recent cases. No BFV was isolated from the 4641 mosquitoes tested, none of the mammals tested positive for BFV antibodies, and the high BFV disease case numbers did not correlate with the relatively low mosquito vector numbers trapped in 2012-2013. It was estimated that up to 89% of the 79 human cases investigated did not have an acute arboviral illness and therefore had tested falsely positive. An Alere PanBio BFV immunoglobulin M enzyme-linked immunosorbent assay test kit is generally used to test for BFV, with the BFV disease case definition based on immunoglobulin M positives only. Other jurisdictions in Australia also reported high numbers of BFV disease cases, with the majority of the cases suspected to be false positives. Therefore, current testing methods need to be revised to reflect the true numbers of BFV disease cases occurring in Australia and to provide correct diagnoses for patients.

An epizootic of bovine ephemeral fever in New South Wales in 2008 associated with long-distance dispersal of vectors

Article

Aug 2010
AUST VET J

To report the rapid transmission of bovine ephemeral fever (BEF) virus from north-western New South Wales south to the Victorian border in January 2008 and to present data that suggests an uncommon meteorological event caused this rapid southward dispersal of vectors. The locations of reported clinical cases, data from sentinel herds and results from a survey of cattle in the southern affected area were examined to delineate the distribution of virus transmission. Synoptic weather charts for January 2008 were examined for meteorological conditions that may have favoured movement of vectors in a southerly direction. Cases of BEF and exposure to BEF virus in NSW were confirmed west of the Great Dividing Range, extending from the Queensland border to Finley, on the far North Coast and around the Hunter Valley. A low-pressure system moved south across the state on 18-19 January 2008, preceding the first cases of BEF in the south of NSW by 1-2 days. Heavy rainfall in December 2007 provided a suitable environment for vector breeding, resulting in the initiation of and support for continuing BEF virus transmission in north-western NSW. The movement of a low-pressure system south across central western NSW in mid-January 2008 after the commencement of BEF virus transmission in the north-west of the state provided a vehicle for rapid southward movement of infected vectors.

A method for predicting Murray Valley Encephalitis in southeast Australia using the Southern Oscillation

Article

Jan 1987
Aust J Exp Biol Med Sci

Neville Nicholls

Clinical cases of Murray Valley Encephalitis in southeast Australia have tended to occur in summer and autumn following extended periods of above average rainfall over most of eastern and northern Australia. The Southern Oscillation, an important mode of climatic fluctuations over the Indian and Pacific Oceans, is closely related to eastern and northern Australian rainfall. The Southern Oscillation has been used previously to develop methods for predicting rainfall fluctuations over Australia and their biological and economic impacts. The relationship, therefore, between the Southern Oscillation and Murray Valley Encephalitis in southeast Australia was examined. Darwin atmospheric pressure, an index of the Southern Oscillation, was found to be well below average during the autumn, winter and spring preceding the occurrence of Murray Valley Encephalitis. It is suggested that this relationship can be used to provide a simple, objective early warning system.

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