BookPDF Available

Risk of introduction of Rift Valley fever into the Southern Mediterranean area through movement of infected animals

Book

Risk of introduction of Rift Valley fever into the Southern Mediterranean area through movement of infected animals

Abstract and Figures

The Animal Health and Animal Welfare (AHAW) scientific network was created in 2009 with the aim to facilitate scientific cooperation in the field of the EFSA‘s miss ion by coordinating activities, exchanging information, developing and implementing joint projects, exchanging expertise and best practices. During the AHAW scientific network meetings, in November 2012, and January 2013, an expert knowledge elicitation (EKE) workshop was conducted to assess the risk of introduction of Rift Valley fever virus (RVFV) through the movement of RVFV-infected (previraemic and viraemic) animals into designated countries of North Africa and the Near East, also referred to in this report as the Region Concerned (RC). The conclusion of the assessment was that in 2013 (a year in which there appears to be a strong possibility of an outbreak occurring in both the east and west sources), the number of RVFV infected animals moved into the RC is likely to be a few hundreds of ruminants, but this number has substantial uncertainty. The number of infected ruminants to be introduced into the RC from the east source (East Africa and the Arabian Peninsula) would be higher compared to the west source (West and Central Africa). This is mainly due to the higher number of animals expected to be moved from the East Source into the RC, and the shorter duration of the journey, resulting in a higher probability of remaining infected when entering the RC. The EKE workshops provided an overview of the current knowledge of the parameters needed to carry out a quantitative risk assessment for introduction of RVFV into the RC and gave the opportunity to identify gaps of knowledge.
Content may be subject to copyright.
Supporting Publications 2013:EN-416
Suggested citation: European Food Safety Authority; Technical meeting of the EFSA Scientific Network on EFSA Scientific
Network for risk assessment in Animal Health and Welfare - Risk of introduction of Rift Valley fever into the Southern
Mediterranean area through undocumented movement of infected animals, 2013:EN-416. [24 pp.]. Available online:
www.efsa.europa.eu/publications
© European Food Safety Authority, 2013
TECHNICAL REPORT
Technical meeting of the EFSA Scientific Network for risk assessment in
Animal Health and Welfare1
Risk of introduction of Rift Valley fever into the Southern Mediterranean
area through movement of infected animals
Parma, 23 April 2013
European Food Safety Authority2,3
European Food Safety Authority (EFSA), Parma, Italy
SUMMARY
The Animal Health and Animal Welfare (AHAW) scientific network was created in 2009 with the aim
to facilitate scientific cooperation in the field of the EFSA‘s mission by coordinating activities,
exchanging information, developing and implementing joint projects, exchanging expertise and best
practices. During the AHAW scientific network meetings, in November 2012, and January 2013, an
expert knowledge elicitation (EKE) workshop was conducted to assess the risk of introduction of Rift
Valley fever virus (RVFV) through the movement of RVFV-infected (previraemic and viraemic)
animals into designated countries of North Africa and the Near East, also referred to in this report as
the Region Concerned (RC). The conclusion of the assessment was that in 2013 (a year in which there
appears to be a strong possibility of an outbreak occurring in both the east and west sources), the
number of RVFV infected animals moved into the RC is likely to be a few hundreds of ruminants, but
this number has substantial uncertainty. The number of infected ruminants to be introduced into the
RC from the east source (East Africa and the Arabian Peninsula) would be higher compared to the
west source (West and Central Africa). This is mainly due to the higher number of animals expected to
be moved from the East Source into the RC, and the shorter duration of the journey, resulting in a
higher probability of remaining infected when entering the RC. The EKE workshops provided an
overview of the current knowledge of the parameters needed to carry out a quantitative risk
assessment for introduction of RVFV into the RC and gave the opportunity to identify gaps of
knowledge.
1 On request from EFSA, Question No EFSA-Q2013-00285, approved on 19 April 2013.
2 Correspondence: AHAW@efsa.europa.eu
3 Acknowledgement: EFSA wishes to thank the participants of the meeting: Adel I. Al-Afaleq, Ahmed Bezeid El Mamy,
Ana Alba, Bernard Bett, Anca Hanea, Andrea Capobianco Dondona, Anthony O'Hagan, Antonio Petrini, Gregorio Torrres,
Imad Mukarker, Jorge Fernandez, Lilian Puech, Mervat Fathy Mohamed Ali Emaru, M odou Moustapha Lo, Nadav Galon,
Ouafaa Fassi Fihri, Eyal Klement, Rania Queslati, Renaud Lancelot, Soheir Hassan Abd El Kader, Taoufik Bouzid, Vincent
Brioudes, for the preparatory work on this scientific output and the members of the Working Group of the AHAW Panel on
Rift Valley fever: Baldet Thierry, Bøtner Anette, Chevalier Veronique, Fassi Fihri Ouafaa, Fisher Egil, Klement Eyal, Plee
Ludovic, Stegeman Jan Arend, Thulke Hans-Hermann for the preparatory work on the Technical meeting on RVF of the
EFSA Scientific Network and EFSA staff: Sofie Dhollander, Andrea Gervelmeyer and Olaf Mombach for the support
provided to this output.
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 2
© European Food Safety Authority, 2013
KEY WORDS
Rift Valley fever, risk assessment, introduction, animal movement and expert knowledge elicitation
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 3
TABLE OF CONTENTS
Summary........................................................................................................................................1
Table of contents ............................................................................................................................3
Background as provided by EFSA....................................................................................................4
AHAW-Network mandate and mission.............................................................................................4
Objectives of the workshop .............................................................................................................4
Participants of the workshop ............................................................................................................4
Methodology ..................................................................................................................................4
1. Expert Knowledge Elicitation ..................................................................................................4
2. The model ..............................................................................................................................5
Results ...........................................................................................................................................6
Conclusions..................................................................................................................................17
Discussion ....................................................................................................................................17
Appendices...................................................................................................................................19
A. EFSA Mandate on Rift Valley fever .......................................................................................19
B. Data collected on the different parameters of the model ...........................................................20
References....................................................................................................................................23
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 4
BACKGROUND AS PROVID ED B Y EFSA
AHAW-NETWORK MANDATE AND MISSION
The Animal Health and Animal Welfare (AHAW) scientific network was created in 2009 with the aim
to facilitate scientific cooperation in the field of EFSA‘s mission, by coordinating activities,
exchanging information, developing and implementing joint projects, exchanging expertise and best
practices. On 5 March 2012, EFSA received a request4 from the European Commission (EC), to
provide scientific advice on Rift Valley fever (RVF). One of the terms of reference of that mandate
was to assess the risk of introduction of RVFV into the neighbouring Mediterranean countries of the
EU. Due to scarcity of quantitative information, EFSA‘s working group on RVF and the AHAW Panel
proposed to address this assessment with a quantitative approach, and elicit knowledge on those
parameters where no exact qualitative figures are known. Therefore, two expert knowledge elicitation
(EKE) workshops were organised, on 14-15 November 2012 in Montpellier and on 29-30 January
2013 in Parma, under the network framework, to exchange expertise and gather expert opinion on the
parameters needed for the risk assessment.
OBJECTIVES OF THE WORKSHOP
The purpose of the workshops was to assess the risk of introduction of RVFV into designated
countries of North Africa and the Near East through the undocumented movement of live animals. For
the purposes of the elicitation workshop and this report, relevant countries are termed the ‗Region
Concerned‘ (RC) and comprise: Morocco, Algeria, Tunisia, Libya, Jordan, Israel, The Palestinian
Territories, Lebanon, Syria. Although Egypt and Mauritania are also part of the RC, as defined by the
question of the EC4, they were not considered in the EKE because RVF outbreaks were reported in the
past in both countries.
PARTICIPANTS OF THE WORKSHOP
Soheir Hassan Abd El Kader (Egypt), Nadav Galon (Israel), Taoufik Bouzid (Morocco), Ahmed
Bezeid El Mamy (Mauritania), Mervat Fathy Mohamed Ali Emaru (Egypt), Ouafaa Fassi Fihri
(Morocco), Eyal Klement (Israel), Modou Moustapha Lo (Senegal), Imad Mukarker (Pal. Territories),
Jorge Fernandez (Spain), Andrea Capobianco Dondona (Italy), Renaud Lancelot (France), Gregorio
Torrres (Spain), Vincent Brioudes (OIE, Tunis), Ana Alba (Spain), Bernard Bett (Kenya), Adel I. Al-
Afaleq (Saudi Arabia), Antonio Petrini (OIE, Tunis), Queslati Rania (FAO, Tunis), Lilian Puech
(FAO, Tunis), Anthony O'Hagan (Facilitator-UK), Anca Hanea (Facilitator-The Netherlands), Sofie
Dhollander (EFSA-AHAW Unit), Andrea Gervelmeyer (EFSA-AHAW Unit), Olaf Mosbach-Schulz
(EFSA-SAS Unit) and Jan-Arend Stegeman (EFSA-AHAW Panel).
METHODOLO GY
1. EXPERT KNOWLEDGE ELICITATION
The parameters for the model were estimated through Expert Knowledge Elicitation (EKE). More
details about EKE processes are described by the Australian Centre of Excellence for Risk Analysis
(Acera, 2006; 2010). This elicitation process followed the Sheffield method. Materials and guidance
for using the Sheffield method are contained in the SHELF package, available freely online at
http://tonyohagan.co.uk/shelf.
The experts received a briefing document before the workshop. The briefing document explained the
purpose of the elicitation workshop and gave a brief explanation of the tasks that experts would be
asked to perform. In the workshop, the facilitator gave a presentation in which the task of judging
probabilities was explained in more detail. The experts then carried out a practice elicitation, followed
by further training on the nature of the aggregated distribution that is the result of an elicitation. The
experts were then given an outline of the EFSA risk model and the parameters that they would be
asked to elicit.
4 Question No EFSA-Q-2012-00496
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 5
2. THE MODEL
In any modelling exercise, there is a trade-off between realism and feasibility. There is naturally a
wish to make the model as detailed and realistic as possible, but more realism always means more
complexity. A more complex model has more uncertain quantities (and more complex science-based
models typically introduce more equations that might be wrong). In order to provide sensible values
for all those parameters, there is a need for more detailed data. Given the practical difficulties of
eliciting probability distributions, and the fact that this cannot be done without some degree of
imprecision, more complexity may in practice not produce a better model. The proposed model was
considered the best compromise between realism and feasibility by the RVF working group and the
AHAW Panel.
The regions in which RVF has occurred in the past were divided into three source regions:
the ‗east source‘: Ethiopia, Djibouti, South and North Sudan, Egypt, Somalia, Qatar, Saudi
Arabia, Yemen, Kenya, Tanzania, Eritrea and Somalia
the ‗west source‘: Senegal, The Gambia, Guinea Conakry, Cameroon, Sierra Leone,
Mauritania, Mali, Niger and Chad
the ‗southern source‘: Mozambique, Madagascar, South Africa, Namibia, Zimbabwe,
Botswana, Malawi, Swaziland and Zambia.
Trade flows of susceptible animals towards the RC were considered to be important only from the east
and west source of RVF. Trade flows between the southern source and the RC were considered very
unlikely. According to reports from the Veterinary Services from the RC (no replies were received
from Syria, Libya and Lebanon) there is currently no official trade between the RVFV infected
countries and the RC. Consequently, the assessment is based on quantities of undocumented
movement of animals elicited from expert opinion. The number of infected animals entering the RC
was modelled as:
the volumes of animals transported from the east and west sources to the RC in 2013 (vE and vW,
respectively),
the prevalence of RVFV in animals for export in the east and west sources (pE and pW,
respectively),
the proportions of infected animals that, despite export controls, left the east and west sources (dE
and dW, respectively),
the proportions of infected animals remaining infected after transport from the east and west
sources to the RC (tE and tW, respectively),
the proportion of infected animals that entered despite import controls at the RC (e).
Further, it is important to mention that some source countries (Qatar, Saudi Arabia…) play the role of
mediators between the Source countries and RC countries because they import animals from source
countries and export them to the RC. For example, Qatar import camels from source countries and sell
them to Jordan. In 2012, 200 camels were imported from Qatar to Jordan (Imad Mukarker, personal
communication).
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 6
vE and vWthe volumes of animals transported from the east and west sources to the RC in 2013
pE and pWthe prevalences of RVFV in animals for export in the east and west sources
dE and dWthe proportions of infected animals allowed to depart from the east and west sources
tE and tWthe proportions of infected animals remaining infected after transport from the east and west sources to the
RC
ethe proportion of infected animals that are allowed entry on arrival at the RC
Red ruminants = infected with RVFV; white ruminants = not infected with RVFV.
M is the number of infected animals entering the RC and, NE and NW are the number of infected animals entering through
the eastern and western pathway respectively.
Figure 1: The model for assessing the risk for introduction of RVFV through the movement of
animals (fictitious example)
The total number of infected animals entering the RC (N) is the sum of the products of the number of
infected animals entering through the eastern (NE) and western (NW) pathway if outbreaks occur in
these sources and the probability of outbreaks in the east (OE) and west source (OW) respectively in
2013:
N = OE x NE + OW x NW
RES ULTS
The experts judged that the most likely probability for an outbreak in the east source is 0.75, and in the
west source this even could be as high as 1.00. Thus:
N = OE x NE + NW,
where OE is equal to 1 with probability 0.75 and is equal to 0 with probability 0.25, representing the
probability of an outbreak in the east source, NE is the number of infected animals introduced from the
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 7
east source on condition that there is an outbreak in the east source in 2013, and NW is the number of
infected animals introduced from the west source (where it is assumed that there will be an outbreak in
2013).
The distribution of N was constructed by sampling one million values from the elicited distributions
for the various parameters and combining them with the model to produce one million sampled values
of N. The distribution is very skew. The bulk of the probability lies below N = 1000, but there is a
long tail giving some probability that it will be as much as 6000 or more. These properties can be seen
in the sketch of the distribution on page 3, Figure 2. The distribution is so skew that it is hard in Figure
2 to see what is happening at the left hand side, so Figure 3 shows just the part of the distribution for N
less than or equal to 300.
The distribution actually peaks around N = 20, but is very flat, signifying the large amount of
uncertainty.
The distributions for NE and NW are shown in Figures 4 to 6, in the same way. Notice that if there is no
outbreak in the east source, then the total will be like the distribution of NW alone. These curves really
show lognormal approximations to the million simulations. The simulated distributions are very close
to the curves shown.
A list of the most important reasons of the experts for the elicitation of the different parameters that
were given during the EKE process, as well as details on all the individual probability distributions of
the parameters can be found in Table 1.
0 1000 2000 3000 4000 5000
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
n
Figure 1: Probability distribution for the number of infected animals being moved undocumented from the East
and west source into the RC in a year with an outbreak in the east and west source.
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 8
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
0.000
0.001
0.002
0.003
n
Figure 2: Left part of the probability distribution for the number of infected animals being moved
undocumented from the east and west source into the RC in a year with an outbreak in the east and west source
0 1000 2000 3000 4000 5000 6000 7000 8000
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
nE
Figure 3: Probability distribution for the number of infected animals being moved undocumented from the east
source into the RC in a year with an outbreak in the east source
P
P
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 9
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
nE
Figure 4: Left part of the probability distribution for the number of infected animals being moved
undocumented from the east source into the RC in a year with an outbreak in the east source
0 100 200 300 400 500 600 700 800 900 1000
0.000
0.002
0.004
0.006
0.008
0.010
nW
Figure 5: Probability distribution for the number of infected animals being moved undocumented from the west
source into the RC in a year with an outbreak in the west source
P
P
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 10
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
0.000
0.002
0.004
0.006
0.008
0.010
nW
Figure 6: Left part of the probability distribution for the number of infected animals being moved
undocumented from the west source into the RC in a year with an outbreak in the west source
P
Supporting Publications 2013:EN-416
Suggested citation: European Food Safety Authority; Technical meeting of the EFSA Scientific Network on EFSA Scientific
Network for risk assessment in Animal Health and Welfare - Risk of introduction of Rift Valley fever into the Southern
Mediterranean area through undocumented movement of infected animals, 2013:EN-416. [24 pp.]. Available online:
www.efsa.europa.eu/publications
© European Food Safety Authority, 2013
CONCLUS IONS
1. The conclusion is that in 2013 (a year in which there appears to be a strong possibility of an
outbreak occurring in both the east and west sources) the number of RVFV infected animals
introduced to the RC is likely to be a few hundred, with substantial uncertainty, so it could be very
small or it could be a few thousands.
2. The number of infected animals to be introduced into the RC from the east source would be higher
compared to the west source. This is mainly due to the higher number of animals expected to be
moved from the east source into the RC, and the shorter duration of the journey of the animals,
resulting in a higher probability of remaining infected when entering the RC.
DISCUSS ION
The group of experts consisted mainly of epidemiologists and virologists, who had built up large
expertise with research activities related to RVF, prevention and control of RVFV or networking
activities in the RC or the source areas. The experts expressed their concerns about the difficulty to
make judgements on the probabilities of certain parameters. Especially, the number of animals moved
into the RC were considered hard to quantify. Including animal traders into the group of experts would
have broadened up this capability, although it would have been cumbersome to invite traders involved
with undocumented transport of animals to the workshop. Official reports of the Veterinary Services
of the RC reported that there is currently no official import of ruminants into the RC from potentially
infected areas.
Nonetheless, the participants showed to be very well acquainted with the epidemiology of RVF in
their area, and knew well the current practices related to trade of animals and traditional farming in
their region. The EKE methodology was perceived as a good methodology to elicit the probabilities of
parameters needed for the import risk assessment. The methodology is transparent in all its steps. It
shows the uncertainties around values of parameters, and it gives outcomes that are more meaningful
than qualitative scores of likelihoods, which may have different meanings for different people. In
addition, probability distributions for the numbers of infected animals entering the RC were derived by
doing a million simulations of the model using randomly drawn values from the elicited parameter
distributions. Working with distributions should avoid focusing on precise numerical values of
individual estimated parameters and visualise more the importance of uncertainty (the range of the
distribution) related to the parameters.
The conclusion of the experts‘ analysis of the risk for introduction of RVFV into the RC through
movement of infected animals, is that it is likely that infected animals will be imported outbreak years.
Trade flows from RVF endemic areas towards countries adjacent to the RC (i.e. towards Mauritania,
Egypt, Yemen and Saudi Arabia) have already led to introduction of RVFV into these countries in the
past and parallel, undocumented trade flows of ruminants towards the RC can be assumed.
Examples of the spread of other animal diseases in the Middle east and North Africa region, indeed,
illustrate that such animal movements do occur. For example, the spread of FMD viruses in the region
and its impact on FMD-status on some countries of the RC may be considered as an indicator of
animal movements in the region and its risk to introduce infection. Furthermore, serological positive
camels in the south of Morocco indicated the permeability of Saharan desert barrier to RVFV (El-
Harrak, et al., 2011).
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 18
This assessment did only focus on the risk of introduction of RVFV into RC by movement of infected
animals. The other routes for entry of the virus, or the risk for exposure of the introduced RVFV to
susceptible livestock in the RC, possibly leading to outbreaks and eventually endemicity are assessed
in the Scientific Opinion on Rift Valley fever of EFSA‘s Panel on Animal Health and Welfare,
available online at: http://www.efsa.europa.eu/en/efsajournal/doc/3180.pdf.
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 19
APPENDICES
A. EFSA Mandate on Rift Valley fever
Background of EFSA’s RVF mandate
Rift Valley fever (RVF) is caused by the RVF virus, a member of the genus Phlebovirus (family
Bunyaviridae). It is a highly contagious infection of ruminants, with the potential for very serious and
rapid spread, irrespective of national borders. It is also a major zoonotic disease, with severe
consequences on affected people, potentially leading to death. It is transmitted through the bites of
various species of mosquitoes (typically the Aedes or Culex genera) and possibly midges (Culicoides),
and through contacts with infective tissues such as blood. It has a strong seasonal pattern, with long
silent periods followed by explosive flare-ups when climatic (rain) conditions are favourable to the
vectors. RVF has serious socio-economic impact on people's livelihoods, on trade of animals and
animal products, on food security in countries where ruminants are the basic source of proteins, and on
human health.
The current distribution of the infection is mainly Eastern Africa and Western Africa, but the disease
often spreads to the north down the Nile Valley, to the east across the Red Sea (where it created a
major animal and human health problem in Yemen and Saudi Arabia in 2000-2001), to the South to
Madagascar and Southern Africa. Due to the multiplicity of possible vectors, wherever cattle and
small ruminants are raised and climatic conditions are favourable, RVF may emerge. In areas where
competent vectors exist, transmission via these vectors can be important for virus persistence over a
long time and overwintering mechanisms may exist. Therefore most countries free of the infection
take strict measures to prevent entry.
Outbreaks of Rift Valley fever (RVF) have been reported in the last decade in the Nile valley (up to
Egypt), in the east and south of Africa (from Kenya to South Africa) and the Western African region
(up to Mauritania). The epidemiology of the disease in Africa, especially sub-Saharan and Sahel
region needs to be regularly updated since the evolution of the infection and waves of outbreaks
follows a highly complicated pattern. Although officially no new cases have been reported during the
last months in Northern Africa, there is still a probability that the disease spreads through uncontrolled
movements of animals in the region and there is still information indicating that the disease is
circulating throughout the region of eastern Africa. From the information available it can thus be
assumed that the disease poses a permanent threat to the EU neighbouring region of the Mediterranean
(North Africa and Near East), posing a possible risk to the EU.
Concerning the complex epidemiology of RVF, important gaps of information remain about what is
the real role of wild animals and vectors regarding the maintenance of RVF virus and their possible
transmission to domestic ruminants. The presence of RVF in the Southern Mediterranean area would
represent a challenge for animal health risk managers. It is therefore necessary to determine the extent
of the problem in order to better manage this risk. In addition, risk managers have to manage areas of
uncertainty, such as the role played by vectors or the risk of the disease becoming endemic in this area.
Terms of reference as provided by the European Commission
1. Provide an update on the global occurrence of Rift Valley fever and possible changes in the
distribution during the last 10 years.
2. Provide maps of the region of concern and other countries of the Mediterranean Basin (including
EU Member States), displaying the geographical distribution of potential invertebrate hosts, taking
into account their vector competence and seasonal variation in abundance.
3. Assess the risk of introduction of RVF into the region of concern especially through the movements
of live animals and vectors.
4. Assess the risk of RVF becoming endemic, with clinical outbreaks or not, in animal and vector
populations in the region of concern.
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 20
B. Data collected on the different parameters of the model
Animal trade
The numbers of ruminants officially imported in 2012 from the east- or west source as reported
directly by the Veterinary Services of the RC were equal to zero (no replies were received from Syria,
Libya and Lebanon, however). Also questionnaires, which were distributed by the Mediterranean
Animal Health Network (REMESA Réseau méditerranéen de santé animale) to the Maghreb
countries in 2012 on the same subject, did not report any import of live ruminants from either the east
or west source into the RC.
Also by consulting international trade databases, very few ruminants were found to be imported into
the RC. In the UN Comtrade database, import of 19,728 ruminants from the East Source, and 53
ruminants from the west source was reported. To FAO STAT, import of 24, 269 ruminants from the
East Source, and 12,410 ruminants from the west source was reported. No import of ruminants from
the East Source or west source into the RC was reported to COMEXT in 2011. It has to be mentioned,
however, that these databases are completed on a voluntary basis by the national authorities, and may
therefore be incomplete (Table 1).
A consultation process with stakeholders (private and public) from northern African countries
organised by the Pan-African Forum for Livestock Trading Countries (African Union-International
Bureau for Animal Resources/PAFLEC), elicitated knowledge on both formal and informal flows of
ruminants. These added up to 167,000 ruminants from the west source to the RC (Figure 20 in
Appendix C).
On the contrary, larger volumes of ruminants are traded between the countries of the RC. Given an
example, UN Comtrade reports a total of 571,538 heads of ruminants traded between the countries of
the RC in 2010. Furthermore, countries adjacent to the RC, such as Egypt, Saudi Arabia or Yemen
import large numbers of ruminants from the east Source. According to the Food Security and Nutrition
Analysis Unit of the FAO in Somalia, large numbers of live ruminants are imported from the Horn of
Africa into Egypt or Saudi Arabia. For example, Egypt imports approximately 200,000 ruminants by
road, and 30,000 by sea from the Horn of Africa (Figure Y in Appendix). Saudi Arabia reported
import of 6,037,580 ruminants from the east Source (CDSI, 2013).
Table 2: Overview of reported trade flows into the Region Concerned
Importing
country
Import from the west source
Import from the east source
Data
source
Official
trade
2012*
UN
Comtrade
2009-11+
AU-IBAR/
PAFLEC
FAOSTAT
2005-10*
Official
trade
2012*
UN
Comtrade
2009-11+
AU-IBAR/
PAFLEC
FAOSTAT
2005-10*
Morocco
0
3
7000
5
0
NR
0
NR
Algeria
0
NR
0
NR
0
35
0
NR
Tunisia
0
NR
0
NR
0
NR
0
NR
Libya
NR
NR
130000
NR
NR
NR
0
NR
Israel
0
NR
0
NR
0
NR
0
NR
Palestinian
Territories
0
NR
0
NR
0
NR
0
NR
Jordan
0
NR
0
NR
0
16884
0
11675
Syria
NR
NR
0
12391
NR
NR
0
12595
Lebanon
NR
53
0
15
NR
2809
0
NR
TOTALS
0
56
167000
12410
0
19728
0
24269
*Official trade reported by Veterinary Services of the RC
+ Average number of animals imported per year reported to UN COMTRADE from 2009 to 2011
*Average number of animals imported per year reported to FAOSTAT from 2005 to 2010
AU-IBAR/ PAFLEC: Regional workshop on trade of Livestock and Animal Products Hammamet - Tunisia April 11th and
12th 2012; NR: Not Reported
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 21
Figure 2: Total number of large ruminant movements to the region concerned, reported by
FAOSTAT between 2005 and 2010
Prevalences of RVF
A narrative review looking into prevalence studies resulted in a list of references, which can be found
in Table 3. The reported prevalences vary largely according to a vast number of variables, such as the
country and region, the target of the test (IgG or IgM, or RVFV detection), the species tested, whether
vaccination was applied in the area, whether samples were taken during or in the period short after
outbreaks, the type of the diagnostic test, etc.
Table 3. RVF prevalence studies
Outbreak
Target
Species
Sero-
Prevalence
Country
Year
Reference
no
IgG
LR
0.00
Saudi Arabia
NR
Al-Afaleq 2012
no
IgG
SR
0.00
Saudi Arabia
NR
Al-Afaleq 2012
no
IgG
humans
0.06
Saudi Arabia
2008
Al-Azraqi 2012
no
IgM
humans
0.00
Saudi Arabia
2008
Al-Azraqi 2012
no
IgG
SR
0.00
Saudi Arabia
2007
Al-Qabati 201
no
IgG
SR
0.01
Saudi Arabia
2007
Al-Qabati 201
no
IgM
LR
0.00
Saudi Arabia
2007
Al-Qabati 201
no
IgM
SR
0.00
Saudi Arabia
2007
Al-Qabati 201
no
IgG
LR
0.00
Saudi Arabia
2007
Al-Qabati 2010
no
IgG
LR
0.12
Mayotte
2006
Cêtre-Sossah 2012
no
IgG
LR
0.13
Mayotte
2003
Cêtre-Sossah 2012
no
IgM
LR
0.00
Mayotte
2003
Cêtre-Sossah 2012
yes
IgG
LR
0.31
Mayotte
2003
Cêtre-Sossah 2012
yes
IgM
LR
0.00
Mayotte
2003
Cêtre-Sossah 2012
yes
IgM
SR
0.01
Mayotte
2003
Cêtre-Sossah 2012
yes
IgG
LR
0.28
Madagascar
2009
Chevalier 2011
yes
IgM
LR
0.01
Madagascar
2009
Chevalier 2011
no
Antibodies
SR
0.08
Saudi Arabia
2003-2004
Elfadil 2006
no
IgG
SR
0.00
Saudi Arabia
2003-2005
Elfadil 2006
no
IgM
SR
0.00
Saudi Arabia
2003-2006
Elfadil 2006
no
IgG
SR
0.16
Mozambique
2012
Engström 2012
no
Antibodies
wildlife
0.04
Senegal
1999
Go ra 2000
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 22
yes
IgG
humans
0.05
Tanzania
2008
Heinrich 2012
yes
IgG
LR
0.27
Madagascar
2008
Jeanmaire 2011
yes
IgG
SR
0.25
Madagascar
2008
Jeanmaire 2011
yes
IgM
LR
0.00
Madagascar
2008
Jeanmaire 2011
yes
IgM
SR
0.03
Madagascar
2008
Jeanmaire 2011
no
IgG
humans
0.13
Kenya
2006
LaBeaud 2008
yes
IgG
humans
0.05
Senegal
1999
Marrama 2005
no
IgG
humans
0.02
Saudi Arabia
2010
Memish 2011
no
IgM
humans
0.05
Saudi Arabia
2010
Memish 2011
yes
Antibodies
humans
0.13
Kenya
2007
Nguku 2010
yes
IgG
humans
0.19
Kenya
2007
Nguku 2010
no
IgG
humans
0.03
Gabon
2008
Pourrut 2010
yes
IgG
SR
0.34
Comoros
2009
Roger 2011
yes
IgG
LR
0.31
Comoros
2009
Roger 2011
no
IgG
SR
0.14
Kenya
1999-2006
Rostal 2010
no
IgM
SR
0.00
Kenya
1999-2006
Rostal 2010
no
IgG
SR+LR
0.03
Somalia
2001
Soumare 2007
no
IgG
SR+LR
0.07
Somalia
2003
Soumare 2007
no
IgG
SR+LR
0.15
Somalia
2004
Soumare 2007
no
IgM
SR+LR
0.00
Somalia
2003
Soumare 2007
no
IgM
SR+LR
0.00
Somalia
2004
Soumare 2007
no
IgM
SR
0.00
Somalia
2001
Soumare 2007
no
IgG
humans
0.04
Tanzania
2004
Swai 2009
no
IgM
humans
0.00
Tanzania
2004
Swai 2009
no
Antibodies
SR+LR
0.40
Egypt
1994
Tayler 1996
no
Antibodies
SR
0.10
Egypt
1994
Tayler 1996
yes
IgM
humans
0.09
Kenya and
Somalia
1998
Weekly Epidem Rec 10 Apr
1998
yes
IgM
humans
0.15
Kenya
1997-1998
Woods 2002
yes
IgG
humans
0.15
Kenya
1997-1999
Woods 2002
no
Antibodies
LR
0.07
Senegal
1993
Zeller 1997
no
Antibodies
SR
0.00
Senegal
1993
Zeller 1997
no
Antibodies
SR
0.02
Senegal
1994
Zeller 1997
no
IgG
humans
0.03
Senegal
1993
Zeller 1997
no
IgG
LR
0.05
Senegal
1993
Zeller 1997
no
IgG
SR
0.03
Senegal
1993
Zeller 1997
no
IgG
SR
0.04
Senegal
1993
Zeller 1997
no
IgG
SR
0.05
Senegal
1994
Zeller 1997
no
IgG
SR
0.06
Senegal
1994
Zeller 1997
no
IgM
LR
0.00
Senegal
1993
Zeller 1997
no
IgM
SR
0.00
Senegal
1993
Zeller 1997
no
IgM
SR
0.00
Senegal
1994
Zeller 1997
LR: large ruminants; SR: small ruminants; NR: not reported; IgG; immunoglobulin G; IgM ; immunoglobulin M
Disease related parameters
Table 4: parameters used for the elicitation
Parameter
Range
Units
Reference
Intrinsic incubation period
1-6
Days
Erasmus and Coetzer, 1981
Infectious period livestock
1-5
Days
Erasmus and Coetzer, 1981
EFSA, 2005
Mortality rate
0.025-0.1
1/days
Erasmus and Coetzer, 1981; Peters and
Linthicum, 1994
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 23
REFERENCES
Abdo-Salem S, Waret-Szkuta A, Roger F, Olive MM, Saeed K, Chevalier V. 2011. Risk assessment of
the introduction of Rift Valley fever from the Horn of Africa to Yemen via legal trade of small
ruminants. Trop Anim Health Prod. 2011 Feb;43(2):471-80.
ACERA (Australian Centre of Excellence for Risk Analysis), 2006. Process Manual. Elicitation Tool,
p 40.
ACERA (Australian Centre of Excellence for Risk Analysis), 2010. ACERA Project 0611, Eliciting
Expert Judgments, Report 1: Literature Review, p71.
EFSA (The European Food Safety Authority), 2005. Opinion of the Scientific Panel on Animal Health
and Welfare (AHAW) on a request from the Commission related to ―The Risk of a Rift Valley
Fever Incursion and its Persistence within the Community‖. EFSA Journal 238, p. 1-128. Available
from http://www.efsa.europa.eu/en/efsajournal/pub/238.htm
El-Harrak, M., R. Martin-Folgar, F. Llorente, P. Fernandez-Pacheco, A. Brun, J. Figuerola and M.A.
Jimenez-Clavero, 2011: Rift Valley and West Nile virus antibodies in camels, North Africa. Emerg
Infect Dis 17, 2372-4.
Erasmus B. J. and J. A. W. Coetzer. The symptomatology and pathology of Rift Valley fever in
domestic animals. In T. A. Swartz, M. A. Klingberg, N. Goldblum, and C. M. Papier, editors,
Contr. Epidem. Biostatist., volume 3, pages 7782, 1981.
Gad, A.M., F.M. Feinsod, I.H. Allam, A.N. Hassan, B.A. Soliman, S. el Said and A.J. Saah, 1986: A
possible route for the introduction of Rift Valley fever virus into Egypt during 1977. J Trop Med
Hyg 89, 233236.
Peters C. J. and K. J. Linthicum. Rift Valley fever. In G. W. Beran, editor, Handbook of Zoonoses, B:
Viral, pages 125138. CRC Press, second edition, 1994.
AU-IBAR/ PAFLEC, 2012: Regional workshop on trade of Livestock and Animal Products
Hammamet - Tunisia April 11th and 12th 2012
Al-Afaleq AI, Hussein MF, Al-Naeem AA, Housawi F and KabatiI AG, 2012. Seroepidemiological
study of Rift Valley fever (RVF) in animals in Saudi Arabia. Trop Anim Health Prod.
Al-Azraqi TA, El Mekki AA and Mahfouz AA, 2012. Rift Valley fever in south western Saudi Arabia:
A sero-epidemiological study seven years after the outbreak of 2000-2001. Acta Trop, 123, 111-6.
Al-Qabati AG and Al-Afaleq AI, 2010. Cross-Sectional, Longitudinal and Prospective
Epidemiological Studies of Rift Valley fever in Al-Hasa Oasis, Saudi Arabia. Journal of Animal
and Veterinary Advances, 9, 258-265.
Cetre-Sossah C, Pedarrieu A, Guis H, Defenez C, Bouloy M, Favre J, Girard S, Cardinale E and
Albina E, 2012. Prevalence of Rift Valley fever among Ruminants, Mayotte. Emerging Infectious
Diseases, 18, 972-5.
Chevalier V, Rakotondrafara T, Jourdan M, Heraud JM, Andriamanivo HR, Durand B, Ravaomanana
J, Rollin PE and Rakotondravao R, 2011. An unexpected recurrent transmission of Rift Valley
Fever virus in cattle in a temperate and mountainous area of Madagascar. Plos Neglected Tropical
Diseases, 2011, 19.
Elfadil AA, Hasab-Allah, KA. and Dafa-Allah, OM, 2006. Factors associated with Rift Valley fever in
south-west Saudi Arabia. Revue Scientifique Et Technique-Office International Des Epizooties, 25,
1137-1145.
Gora D, Yaya, T, Jochelyn T, Didier F, Maoulouth, D, Amadou, S., Ruel, TD and Gonzalez, JP, 2000.
The potential role of rodents in the enzootic cycle of Rift Valley fever virus in Senegal. Microbes
and Infection, 2, 343-346.
AHAW Network-Rift Valley fever
Supporting publications 2013:EN-416 24
Heinrich, N, Saathoff E, Weller N, Clowes P, Kroids I, Ntinginya E, Machibya H, Maboko L, Loesher
T, Dobler G and Hoeslscher M, 2012. High Seroprevalence of Rift Valley fever and Evidence for
Endemic Circulation in Mbeya Region, Tanzania, in a Cross-Sectional Study. Plos Neglected
Tropical Diseases, 6.
Jeanmaire EM, Rabenarivahiny R, Biarmann M, Rabibosoa L, Ravaomana F, Randriamparany T,
Andreamandimby SF, Diaw CS, Fenozara P, De la Rocque S. and Reynes J-M, 2011. Prevalence of
Rift Valley fever Infection in Ruminants in Madagascar After the 2008 Outbreak. Vector-Borne
and Zoonotic Diseases, 11, 395-402.
Labeaud AD, Cross PC, Getz WM and King CH, 2008. Rift Valley Fever virus infection in African
Buffalo (Syncercus caffer) Herds in rural South Africa-evidence of inter-epizootic transmission.
American Journal of Tropical Medicine and Hygiene, 79, 332-332.
Marrama L, Spiegel A, Ndiaye K, Sall AA, Gomes E, Diallo M, Thiongane Y, Mathiot C annd
Gonzalez JP, 2005. Domestic transmission of Rift Valley fever virus in Diawara (Senegal) in 1998.
The Southeast Asian journal of tropical medicine and public health, 36, 1487-95.
Memish ZA, Albarrak A, Almazroa MA, Al-Omar I, Alhakeem R, Assiri A, Fagbo, S, Macneil A,
Rollin PE, Abdullah N and Step[hens, G. 2011. Seroprevalence of Alkhurma and Other
Hemorrhagic Fever Viruses, Saudi Arabia. Emerging Infectious Diseases, 17, 2316-2318.
Nguku PM, Sharif SK, Mutonga D, Amwayi S, Omolo J, Mohammed O, Farnon, EC, Gould LH,
Lederman E, Rao C, Sang R, Schnabel D, Feikin DR, Hightower A, Njenga MK and Breiman RF,
2010. An Investigation of a Major Outbreak of Rift Valley fever in Kenya: 2006-2007. American
Journal of Tropical Medicine and Hygiene, 83, 5-13.
Pourrut X, Nkoghhe D, Souris M, Paupy C, Paweska J, Padilla C, MOUSSAVOU, G. & LEROY, E.
M. 2010. Rift Valley fever Virus Seroprevalence in Human Rural Populations of Gabon. Plos
Neglected Tropical Diseases, 4.
Roger M, Girard S, Faharoudine A, Halifa M, Bouloy M, Cetre-Sossah C. and Cardinale E. 2011. Rift
Valley fever in Ruminants, Republic of Comoros, 2009. Emerging Infectious Diseases, 17, 1319-
1320.
Rostal MK, Evans AL, Sang R, Gikundi S, Wakhule L, Munyua P, Macharia J, Feikin DR, Breiman
RF and Njenga MK, 2010. Identification of potential vectors of and detection of antibodies against
Rift Valley fever virus in livestock during interepizootic periods. Am J Vet Res, 71, 522-6.
Soumare B, Tempia S, Cagnolati V, Mohamoud A., Van Huylenbroeck G and Berkvenss D. 2007.
Screening for Rift Valley fever infection in northern Somalia: A GIS based survey method to
overcome the lack of sampling frame. Veterinary Microbiology, 121, 249-256.
Swai, ES. and Schoonman L, 2009. Prevalence of Rift Valley fever Immunoglobulin G Antibody in
Various Occupational Groups Before the 2007 Outbreak in Tanzania. Vector-Borne and Zoonotic
Diseases, 9, 579-582.
Taylor K, Arthur R, Soliman A, Calamaio C, Hussein H and Berry J, 1996. Surveillance of Rift Valley
fever in Egypt, using sentinel animals. Laboratory Animal Science, 46, 453.
Woods CW, Karpati AM, Grein T, Mccarthy N, Gatutuku P, Muchiri E, Dunster L, Henderson A,
Khan AS, Swanepoel R, Bonmarin I, Martin L, Mannn P, Smoak BL, Ryam M, Ksiakez, TG,
Arthur RR, Ndikuyeze A, Agata NN, Peters, et al., 2002. An outbreak of Rift Valley fever in
northeastern Kenya, 1997-98. Emerging Infectious Diseases, 8, 138-144.
Zeller HG, Fontenille D, Traore-Lamizana M, Thiongane Y and Digoutte J-P, 1997. Enzootic activity
of Rift valley fever virus in Senegal. American Journal of Tropical Medicine and Hygiene 56, 265
272.
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
A cross-sectional and longitudinal serological study was conducted on domestic ruminants in Al-Hasa Oasis to clarify the presence, prevalence and distribution of Rift Valley Fever (RVF). A total of 598 serum samples were collected from sheep, goats, cattle and camel during the year 2007. Enzyme Linked Immuno-Sorbent Assay (ELISA) was used to detect the presence of anti-RVF IgG and IgM antibodies in sheep, goats and cattle sera. Camel sera were tested by isotype-nonspecific inhibition ELISA. Two out of 225 sheep sera were IgG, but not IgM, seropositive, other sera were IgG and IgM seronegative. In a single sentinel herd of 40 sheep, which was established in the oasis, no seroconversion was detected during the period from July 2005 to May 2008. The low inrra-herd prevalence, the scattered distribution of the two seropositives, the absence anti-RVF IgM antibody and the absence of RVF-incidence in the sentinel herd, all suggest that the seropositive animals were introduced from outside of the oasis rather than infected inside the oasis. The prospective study shows that readiness of the region to RVF outbreak is possible.
Article
Full-text available
Rift Valley fever threatens human and animal health. After a human case was confirmed in Comoros in 2007, 4 serosurveys among ruminants in Mayotte suggested that Rift Valley fever virus had been circulating at low levels since 2004, although no clinical cases occurred in animals. Entomologic and ecologic studies will help determine outbreak potential.
Article
Full-text available
The Rift Valley fever virus (RVFV) is an arthropod-borne phlebovirus. RVFV mostly causes outbreaks among domestic ruminants with a major economic impact. Human infections are associated with these events, with a fatality rate of 0.5-2%. Since the virus is able to use many mosquito species of temperate climates as vectors, it has a high potential to spread to outside Africa. We conducted a stratified, cross-sectional sero-prevalence survey in 1228 participants from Mbeya region, southwestern Tanzania. Samples were selected from 17,872 persons who took part in a cohort study in 2007 and 2008. RVFV IgG status was determined by indirect immunofluorescence. Possible risk factors were analyzed using uni- and multi-variable Poisson regression models. We found a unique local maximum of RVFV IgG prevalence of 29.3% in a study site close to Lake Malawi (N = 150). The overall seroprevalence was 5.2%. Seropositivity was significantly associated with higher age, lower socio-economic status, ownership of cattle and decreased with distance to Lake Malawi. A high vegetation density, higher minimum and lower maximum temperatures were found to be associated with RVFV IgG positivity. Altitude of residence, especially on a small scale in the high-prevalence area was strongly correlated (PR 0.87 per meter, 95% CI = 0.80-0.94). Abundant surface water collections are present in the lower areas of the high-prevalence site. RVF has not been diagnosed clinically, nor an outbreak detected in the high-prevalence area. RVFV is probably circulating endemically in the region. The presence of cattle, dense vegetation and temperate conditions favour mosquito propagation and virus replication in the vector and seem to play major roles in virus transmission and circulation. The environmental risk-factors that we identified could serve to more exactly determine areas at risk for RVFV endemicity.
Article
Full-text available
Rift Valley fever is an acute, zoonotic viral disease of domestic ruminants, caused by a phlebovirus (Bunyaviridae family). A large outbreak occurred in Madagascar in 2008-2009. The goal of the present study was to evaluate the point prevalence of antibodies against Rift Valley Fever Virus (RVFV) in cattle in the Anjozorobe district, located in the wet and temperate highland region of Madagascar and yet heavily affected by the disease, and analyse environmental and trade factors potentially linked to RVFV transmission. A serological study was performed in 2009 in 894 bovines. For each bovine, the following variables were recorded: age, location of the night pen, minimum distance from the pen to the nearest water point and the forest, nearest water point type, and herd replacement practices. The serological data were analyzed using a generalized linear mixed model. The overall anti-RVFV IgG seroprevalence rate was 28% [CI95% 25-31]. Age was statistically linked to prevalence (p = 10(-4)), being consistent with a recurrent RVFV circulation. Distance from the night pen to the nearest water point was a protective factor (p = 5.10(-3)), which would be compatible with a substantial part of the virus transmission being carried out by nocturnal mosquito vectors. However, water point type did not influence the risk of infection: several mosquito species are probably involved. Cattle belonging to owners who purchase animals to renew the herd were significantly more likely to have seroconverted than others (p = 0.04): cattle trade may contribute to the introduction of the virus in this area. The minimum distance of the night pen to the forest was not linked to the prevalence. This is the first evidence of a recurrent transmission of RVFV in such an ecosystem that associates a wet, temperate climate, high altitude, paddy fields, and vicinity to a dense rain forest. Persistence mechanisms need to be further investigated.
Article
Full-text available
A 2009 deployment of military units from several Saudi Arabian provinces to Jazan Province, Saudi Arabia, enabled us to evaluate exposure to Alkhurma, Crimean-Congo, dengue, and Rift Valley hemorrhagic fever viruses. Seroprevalence to all viruses was low; however, Alkhurma virus seroprevalence was higher (1.3%) and less geographically restricted than previously thought.
Article
Full-text available
TO THE EDITOR: Different arboviral diseases have expanded their geographic range in recent times. Of them, Rift Valley fever, West Nile fever, and African horse sickness are of particular concern. They are endemic in sub-Saharan Africa but occasionally spread beyond this area. Trade and transport of animals and animal products, along with wildlife movements, are considered the driving factors in the spread of these pathogens.
Article
Full-text available
To the Editor: Rift Valley fever (RVF) is caused by a Phlebovirus (family Bunyaviridae) transmitted by a wide range of mosquitoes (1). This zoonotic disease is present in Africa, the Middle East, and Madagascar. Infections by RVF virus (RVFV) in ruminants cause massive abortions in livestock and high death rates in young animals, which result in major economic consequences. Humans are infected by mosquito bites, contact, or inhalation of aerosols. RVF is frequently unapparent or mild for humans, inducing an influenza-like illness that occasionally leads to more serious complications such as hemorrhage, meningoencephalitis, retinopathy, or even death (2).
Article
The objective of the present study was to measure seroepidemiology of Rift Valley Fever virus infection in the Southwestern regions of Saudi Arabia and to determine the potential risk factors leading to Rift Valley Fever virus infection. Through a series of field trips to the study area (Jizan, Aseer and Al-Qunfuda), a random sample of the general population (patients and their relatives) attending the outpatients' clinics for any reasons were included. Through questionnaire interviews, data were collected regarding their sociodemographic status, housing conditions, animal contact and other relevant information. Blood samples were taken and tested for RVF-specific IgG and IgM utilizing commercially available enzyme-linked immunosorbent assays (ELISAs). Out of 2322 persons included in the study, only 139 were positive for RVF-specific IgG thus giving an overall prevalence of 6.0%. On the other hand, none of the study samples were found to be sero-positive to RVF-specific IgM. The study revealed zero prevalence of specific IgM and IgG among pre-school children born after the 2000-2001 outbreaks. Using multivariate binary logistic regression analysis to identify potential risk factors associated with sero-positive RVF IgG, the following significant risk factors were identified: lack of electricity, having animals in the house, history of slaughtering animals, contact with or transporting aborted animals. The study documented the lack of recent RVF activity among humans in the study areas since the outbreak of 2000 and therefore, the rigorous control measures undertaken together with fostering public health messages in the region should be maintained to reduce the risk of animal-to-human transmission as a result of unsafe animal husbandry and slaughtering practices.
Article
Serological prevalence of IgG antibodies against Rift Valley fever (RVFV) virus was investigated in 22 major localities in five different regions of Saudi Arabia where vaccination against RVF virus (RVFV) is not practiced. The study excludes the southwestern region where a major outbreak of RVF occurred in 2000 and where annual vaccination of ruminants is practiced. Sheep and goat IgG-sandwich ELISA were used to test serum samples from sheep and goats, and bovine IgG-sandwich ELISA was used to test cattle sera. A nonspecies-specific, nonantibody isotype-specific ELISA was used to test camel sera. A total of 3,480 sheep, goats, cattle and camels with no previous history of vaccination against RVFV were randomly tested. All tested animals were negative for IgG class antibodies against the virus except four out of 1,508 sheep and three out of 913 goats, which tested positive. All animals were clinically normal and no evidence was found of virus activity in the studied areas. It is, therefore, most likely that those rare positive cases, which constituted 0.002% of the total animals tested, were either false positives or vaccinates smuggled from the outbreak zone. The need for regular monitoring of animals both within the outbreak zone of 2000 and other parts of the kingdom is strongly emphasized.