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Estimating Spatio-Temporal Dynamics of Aedes Albopictus Dispersal to Guide Control Interventions in Case of Exotic Arboviruses in Temperate Regions


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The increasing number of exotic arbovirus cases imported in Europe and the 2017 chikungunya outbreak in central/southern Italy highlight the urgency of evidence-based outbreak management plans to predict, prevent or interrupt spreading of these arboviruses to non-endemic countries in temperate regions. We here present the results of three mark-release-recapture experiments conducted in a peri-urban area of North-East Italy to estimate the spatio-temporal dynamics of the dispersal of Aedes albopictus females looking for oviposition sites. The Flight Range of 90% of the mosquito population (FR90) was found to exceed 200 m, consistently with data obtained from a previous study conducted in a highly urbanised area in Rome (Central Italy). Modelling results showed that dispersal can be so rapid that insecticide spraying within a 200m-radius around a potential infected case leaves >10% probability that a potentially infected mosquito escapes the treatment, even if this is carried out after only 2–3 days since the importation of a viremic case. These data provide evidence in favour of an update of guidelines for the control of exotic autochthonous arbovirus transmission in temperate areas and highlight the need of effective surveillance approaches and rapid response to contain the risks associated to imported viremic cases.
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SCIENTIFIC REPORTS | (2019) 9:10281 |
Estimating Spatio-Temporal
Dynamics of Aedes Albopictus
Dispersal to Guide Control
Interventions in Case of Exotic
Arboviruses in Temperate Regions
Francesca Marini
1,7, Beniamino Caputo1, Marco Pombi
1, Manuela Travaglio2,
Fabrizio Montarsi3, Andrea Drago4, Roberto Rosà5,6, Mattia Manica5 & Alessandra della Torre
The increasing number of exotic arbovirus cases imported in Europe and the 2017 chikungunya
outbreak in central/southern Italy highlight the urgency of evidence-based outbreak management plans
to predict, prevent or interrupt spreading of these arboviruses to non-endemic countries in temperate
regions. We here present the results of three mark-release-recapture experiments conducted in a peri-
urban area of North-East Italy to estimate the spatio-temporal dynamics of the dispersal of Aedes
albopictus females looking for oviposition sites. The Flight Range of 90% of the mosquito population
(FR90) was found to exceed 200 m, consistently with data obtained from a previous study conducted in
a highly urbanised area in Rome (Central Italy). Modelling results showed that dispersal can be so rapid
that insecticide spraying within a 200m-radius around a potential infected case leaves >10% probability
that a potentially infected mosquito escapes the treatment, even if this is carried out after only 2–3 days
since the importation of a viremic case. These data provide evidence in favour of an update of guidelines
for the control of exotic autochthonous arbovirus transmission in temperate areas and highlight the
need of eective surveillance approaches and rapid response to contain the risks associated to imported
viremic cases.
Knowledge about the spatio-temporal dynamics of dispersal of adult mosquito vectors of diseases is instrumental
for understanding mosquito-borne disease transmission dynamics and for eectively calibrating control inter-
vention in order to prevent or interrupt pathogen transmission. Active dispersal of adult mosquitoes is triggered
by the need to nd mates, sugar sources, resting sites and, in the case of females, hosts for blood-meals and
oviposition sites and is highly aected by intrinsic species-specic ight capability, as well as by ecological (e.g.
abundance and location of sugar sources, hosts, resting sites and oviposition sites) and climatic (e.g. temperature,
rainfall, light intensity, wind speed and direction at ground level) conditions1. Reliable estimates of active mos-
quito dispersal and ight ranges are thus very hard to obtain. is is even more challenging in the case of exo-
phagic and exophilic species which are particularly dicult to recapture in the frame of Mark–Release–Recapture
(MRR) studies1.
For the above reasons, little is known about the ight range of Aedes albopictus, the Asian Tiger Mosquito,
the species which in the last 30 years has invaded all continents (except Antarctica) thanks to the passive trans-
portation of its eggs mostly inside used tires and lucky bamboos, and has stably colonized not only tropical, but
1Dipartimento di Sanità Pubblica e Malattie Infettive, “Sapienza” Università di Roma, Piazzale Aldo Moro 5, 00185,
Rome, Italy. 2Dipartimento di Biologia, Università di Padova, Viale G. Colombo 3, 35121, Padua, Italy. 3Istituto
Zooprolattico Sperimentale delle Venezie, Viale dell’Università 10, 35020, Legnaro, (PD), Italy. 4ENTOSTUDIO
srl, Viale del Lavoro 66, 35020, Ponte San Nicolò, (PD), Italy. 5Department of Biodiversity and Molecular Ecology,
Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010, San Michele all’Adige, Italy.
6Center Agriculture Food Environment, University of Trento, 38010, San Michele all’Adige, Trento, Italy. 7Present
address: Biotechnology and Biological Control Agency (BBCA) Onlus, Via Angelo Signorelli 105, 00123, Rome, Italy.
Correspondence and requests for materials should be addressed to A.d. (email:
Received: 21 August 2018
Accepted: 3 June 2019
Published: xx xx xxxx
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SCIENTIFIC REPORTS | (2019) 9:10281 |
also temperate regions due to the capacity to overcome the cold months in a state of embryonic hibernation2.
ese capacities have turned the species into one of the most successful invasive animal species worldwide3 and
in a global public health threat due to its competence to transmit a large number of exotic arboviruses (such as
Chikungunya (CHIKV), Dengue (DENV),4 and Zika5). is is already testied by Ae. albopictus central role in
large CHIKV epidemics in Indian Ocean in 2006–076 and in the Caribbean and Americas since 20157 and in
several cases of autochthonous transmission of CHIKV and DENV in temperate countries8.
Few MRR studies have been carried out to investigate the capacity to disperse of both host-seeking gravid
Ae. albopictus females looking for a host and blood-fed females looking for oviposition sites. In the former case,
most marked host-seeking females were collected within 100 m from the release site (Hawaii9, Missouri10, La
Réunion Island11), while investigation carried out in Texas, on host-seeking females emerged from larvae marked
with stable isotopes, showed that approximately 79% of them were found within 250 m from their natal site and
all of them remained within a 1 km distance12. However, females released in the forest were shown to ight up
to 1 km to reach an urban area with high densities of possible hosts13. In the case of oviposition-associated dis-
persal, studies exploiting the release of Rb-labelled females and recapture of Rb-marked eggs reported presence
of Rb-marked eggs in ovitraps throughout the whole 160 m radius urban area sampled in Singapore14, while in
Brazil most Rb-marked eggs and uorescent dusted females were found within 100–200 m from a release site13,15.
In Florida, Davis et al.16 showed that self-marked gravid Ae. albopictus female dispersal increased with time, but
seemed to stabilize around 90 m from the initial marking site.
In 2008, we carried out 3 MRR experiments within a highly urbanised area in the city of Rome (central Italy)
to analyse dispersal of orescent dusted Ae. albopictus females released aer blood-meal and recaptured by sticky
traps (STs), and obtained ight ranges of 90% of the released females ranging between 168 and 236 m17. e rst
aim of the present study - carried out with the same design, but in a peri-urban area in north-east Italy - was
to understand whether the ight ranges assessed in Rome could represent a common feature of Ae. albopictus
female dispersal associated to search of an oviposition site in temperate regions. In addition, we exploited the
data to model the temporal dynamics of the dispersal. is parameter has been largely neglected in previous
studies, despite its high relevance for models estimating the dynamics of spread of autochthonous transmission
of exotic arboviruses in temperate regions, as well as for the calibration of the spatial/temporal scale of insec-
ticide treatments to be implemented to prevent or interrupt spread of arbovirus outbreaks. In fact, the recent
cases of autochthonous CHIKV and DENV transmission in Europe8 highlight the urgency and timeliness to
improve preparedness to predict, prevent or interrupt spreading of these and other exotic tropical arboviruses to
non-endemic northern countries.
Mark-release-recapture experiments. A total of 356 marked Ae. albopictus females were collected
out of the 3,959 released ones (MRR1 = 101/1,149, MRR2 = 214/1,600; MRR3 = 41/1,210; Supplementary
TableS2). In addition, 16,938 wilds Ae. albopictus were collected: 79.3% females (MRR1 = 3,607; MRR2 = 7,065;
MRR3 = 2,754), 14.4% males (MRR1 = 669; MRR2 = 1,533; MRR3 = 234), while for the remaining 6.4%
(MRR1 = 250; MRR2 = 401; MRR3 = 425) was not possible to determine the gender, due to bad preservation of
carcasses glued on the STs. Some specimens, mostly females, of Culex sp., Culiseta sp.. and Aedes caspius were also
found in the STs but not counted.
e recapture rates at 11 days from release were 8.8% (MRR1), 12.9% (MRR2), 3.0% (MRR3) and signicantly
dierent among the three experiments (Supplementary TableS1; comparison between GLMs with or without
releases as covariate: GLM deviance = 96.5, df = 2, P < 0.0001). Recapture rates observed in MRR1 and MRR2
were higher than those observed in the study carried out with a similar experimental design in a smaller study
area (i.e. 250 m radius vs 500 m radius, 55 STs vs 96 STs) in Rome (i.e. the odds of recapturing a marked mosquito
was 0.45 lower in Rome with a condence interval of 0.39–0.59; Binomial GLM: deviance 39.1, p-value < 0.001).
is may be due to the larger sampling area and the higher number of STs used in the present study as opposed
to Rome and/or to an inherent bias in using STs as recapture method (i.e. the power of recapture is dependent
on the competition with other natural oviposition sites in the study area, usually quite abundant in urban areas).
However, it is worth to note that the recapture rates obtained in both studies are generally higher than those
obtained in MRR studies on Ae. albopictus females dispersal aer blood-meal carried out with dierent recapture
approaches9,10,13. ese results conrm that STs are a valuable tool for MRR studies on Ae. albopictus ovipositing
or resting females (see also Marini et al.17 for a detailed discussion on pros and cons of using STs in the context
of MRR studies).
Notably, more than 70% of recaptured marked females were collected within 150 m from release site (Figs1B–
D, 2A; Supplementary TableS2) and during the rst 6 days of sampling (Fig.2B; Supplementary TableS2).
Table1 summarizes the mean distance travelled (MDT), maximum observed distance travelled (maxODT)
and ight range of 90% (FR90) and 50% (FR50) of marked females in each MRR experiment. Cumulative MDTs
were 110 m (days 2–11), 77 m (days 2–16) and 68 m (days 2–16) in MRR1, MRR2 and MRR3, respectively.
Daily MDTs were statistically dierent between the rst two MRRs and MRR3 (Mann Whitney test MRR1 vs
MRR3: U = 4, P = 0.03; MRR2 vs MRR3: U = 1, P = 0.01), but not between MRR1 and MRR2 (Mann Whitney
test U = 27.5, P = 0.19). e maxODTs were 463 m (day-4), 433 (day-5) and 375 (day-6) in MRR1, MRR2 and
MRR3, respectively. e ight ranges were always 50 m for FR50 and 252 m for FR90 (Table1) and statis-
tically dierent among the three MRR experiments (i.e. the interaction eect between log10(annulus median
distance + 1) and release was signicant as shown by a Likelihood ratio test P < 0.01, so the three lines were not
parallel between them: MRR1 vs MRR2: t = 4.98, P < 0.01; MRR1 vs MRR3: t = 4.08, P < 0.01; MRR2 vs MRR3:
t = 9.06, P < 0.01).
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Flight ranges estimates were on average in agreement with results of Gamma GLM and ZAG models, as shown
in Fig.3, which shows model results for the 90% percentiles of the distance up to which mosquitoes are expected
to travel, a proportion chose in compliance to allow comparison with the estimated FR90. e 90% percentile
values reached about 250 m aer 2 (MRR1) and 14 (MRR2) days since release (this estimate was not reached
during the sampling period in MRR3). On average, the 90% percentile of the distance up to which mosquitoes are
expected to y was stable in MRR1, but it was predicted to increase with time in MRR2 (from <150 m at day-2
to ~250 m at day-14) and in MRR3 (from <100 m at day-2 to ~200 m at day-14), although with shorter estimates
and wider condence intervals due to the lower numbers of mosquito recaptured (Fig.3).
Result of the Bernoulli GLM model allows to estimate the distance up to which 90% of marked mosquito
is expected to be detected. is estimate was stable in MRR1 and MRR2, ranging on average between 170 and
300 m, while a shorter range (between 100 and 200 m) was estimated for MRR3 (Fig.3). Similar to ight range
estimates, also the 50% percentiles of the distance up to which mosquitoes are expected to y were computed for
all three models (see Supplementary Material and Supplementary Fig.S1).
Effect of fluorescent dye marking on mosquito survival. The survival of marked Ae. albopictus
females kept under semi-eld conditions for the duration of the experiments was shown not to be aected by the
uorescent dyes. In fact, no dierences in survival between marked (N = 56, 43 and 43) and unmarked (N = 49,
48 and 48) females were recorded in MRR1, MRR2 and MRR3, respectively (MRR1: log-rank test χ2 = 0.15,
df = 1, p = 0.70; MRR2: log-rank test χ2 = 0.26, df = 1, p = 0.61; MRR3: χ2 = 0.10, df = 1, p = 0.76).
Figure 1. (A) Study area in Piove di Sacco (north-east Italy), where 96 sticky traps (yellow dots) were located
into concentric annuli of 50 up to maximum of 500 m radius around the release point (red star). Map layout
generation were done using QGIS 2.18 (QGIS Development Team (2017). QGIS Geographic Information
System. Open Source Geospatial Foundation Project. free and open source soware
for geographic information system. e base layer “Regione del Veneto – L.R. n. 28/76 – Formazione della
Carta Tecnica Regionale” was obtained from the Veneto Region Geoportal (
condizioni_utilizzo_geoportale/) distributed under Italian Open Data License 2.0 (IODL 2.0 http://www.dati. (B–D) Distribution of recaptured Aedes albopictus females in the sticky-traps during the three
mark-release-recapture experiments (MRR1, MRR2 and MRR3).
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Oviposition pattern under semi-field conditions. A positive correlation was observed in MRR2
(Spearman’s rank correlation: r = 0.92; t = 5.38, df = 5, p < 0.01) between the frequency of recaptured Ae. albopictus
females and the oviposition pattern of blood-fed females simultaneously to the released ones and kept under
semi-natural conditions for the entire length of the experiments (Fig.4). No correlation was observed in MRR3
(Spearman’s rank correlation: r = 0.42; t = 1.05, df = 5, p = 0.34), when a strong thunderstorm and heavy rainfall
occurred few hours aer the release, likely aecting more the released females than those kept under semi-natural
(and “sheltered”) conditions. Consistently with the temperature drop aer MRR3 (Supplementary TableS3), the
oviposition dynamics of marked females in MRR2 and MRR3 showed a 2-day shi in the peak of oviposition
e rst aim of the present work was to study active dispersal of blood-fed Ae. albopictus females in a peri-urban
habitats in order to conrm or dispute that evidence obtained in a similar study carried out in a highly urbanized
study area in Rome17 can be generalised and represent a reliable estimate of Ae. albopictus female dispersal asso-
ciated to search of an oviposition site in other temperate regions.
e results obtained showed that 90% of marked Ae. albopictus blood-fed females were recaptured within
250 m from the release site (FR90 = 177–252 m), a range consistent with estimates from the results obtained in
Rome (FR90 = 168–23617). Moreover, the comparison between the oviposition patterns of females kept under
semi-eld conditions and the recapture rates in MRR2 supports the hypothesis that the observed dispersal was
mostly triggered by the need of Ae. albopictus females released at the blood-fed stage to nd a suitable oviposition
site aer blood-meal digestion (Fig.4). erefore, 250 m may represent a consistent and possibly generalizable
estimate of FR90 of blood-fed Ae. albopictus females in Italy, and possibly in temperate regions, as this value did
not signicantly dier in relation to the ecology (peri-urban/rural vs urban) or the size (500 m vs 250 m radius) of
Figure 2. Cumulative proportion of recaptured Aedes albopictus females on total of recaptured across the study
area (A) and during the rst 11 days aer release (B), in the three mark-release-recapture experiments (MRR1,
MRR2 and MRR3).
Days aer
release MRR1 MRR2 MRR3
Daily MDT (Daily maxODT)
2 75 (73) 95 (114) — —
3 80 (287) 46 (275) — —
4 171 (463) 72 (388) 58 (71)
5 104 (436) 97 (433) 35 (71)
6 106 (333) 72 (131) 78 (375)
7–11 107 (352) 121 (333) 25 (168)
12–16 132 (433) 25 (192)
FR90 252 209 177
FR50 50 31 21
Table 1. Mean distance travelled (MDT), maximum observed distance travelled (maxODT) and ight ranges of
90% (FR90) and 50% (FR50) of recaptured Aedes albopictus females in three mark-release-recapture experiments
(MRR1, MRR2 and MRR3). All parameters are expressed in meters.
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the two study areas tested. However, it is important to highlight that the results obtained are based on mosquitoes
reared under optimal conditions, while adult tness and behaviour in nature are certainly aected by several
features such as competition for trophic resources at the larval stage and climatic conditions. For instance, Mori18
reported that Ae. albopictus emerging from larvae reared under crowded conditions dispersed further than those
reared in uncrowded conditions. Also, increased skip oviposition was reported in adults exposed to low-quality/
crowded versus high-quality/uncrowded larval habitats16. ese observations imply that gravid females will
move greater distances when larval habitat quality decreases and competition for resources increases. On the
other hand, extreme climatic conditions negatively aect survival and dispersal. In fact, compared to results from
MRR1 and MRR2 (which were carried out under optimal climatic conditions), results from MRR3 (which was
aected by heavy rainfall and a severe drop in temperature) show a much lower recapture rate, a delayed oviposi-
tion dynamics between released females and females kept in sheltered cages, and lower-distance dispersal.
e second aim of the study was to model the temporal dynamics of the dispersal, a parameter to our knowl-
edge previously analysed only in a study carried out in Florida showing that the dispersal of gravid Ae. albopictus
females increased with time, but seemed to stabilize around 90 m from the initial marking site16. Our analyses of
the temporal patterns of dispersal revealed that the distance travelled by blood-fed females is longer and does not
always increase over time. In fact, results from MRR1 showed that the potential exists for a very rapid dispersal,
as it is predicted that about 90% of marked mosquitoes have own within 250 m in 72 hours since release and
the remaining 10% have own even longer (Fig.3). Both in Padua and in Rome single females were found at the
limits of the study areas only 4 days since the release (maxODT Padua = 464 m; maxODT Rome = 290 m). In
particular, Bernoulli GLM model showed that the detection probability was not aected by the day of the release
in MRR1 and MRR2, suggesting that some individual mosquitoes could rapidly disperse in very few days aer
release (see Supplementary TableS2, day 4).
e obtained results are very relevant for the planning of control activities to prevent autochthonous transmis-
sion of exotic arboviruses in temperate areas, an occurrence which is likely to become recurrent, as testied by the
Chikungunya outbreak occurred in central Italy in summer 2017 with almost 500 human infected cases19, as well
as in France20 and Croatia21, and by the models predicting future patterns of transmission under climate change
scenarios22,23. e delayed application of peridomestic/perifocal space spray treatments with insecticides around
households where human arbovirus infection has been reported is a critical issue concerning their eectiveness in
reducing transmission risk. Despite that, guidelines from the Italian and French Ministries of Health24,25 recom-
mend insecticide treatments in a 200 m buer area around residence of conrmed infected patient independently
from the delay between notication and symptom onset. Based on our results and the model’s predictions over
time, however, the recommended 200 m buer does not appear to be sucient to target 90% of the mosquito
population which may have been in contact with the infected case in her/his household. First, the FR90 was found
to exceed 200 m in some of the MRR experiments carried both in Rome and in Padua. Second, modelling results
showed that dispersal can be so rapid that insecticide spraying within a 200 m radius around a potential infected
Figure 3. Distance up to which 90% of mosquitoes are expected to travel estimated by three models (Bernoulli
GLM, Gamma GLM, Zero Altered Gamma model). On the x-axis the days aer release, on the y-axis the
distance from the release site. Dots represent the mean distance value; vertical lines represent the 95%
condence intervals obtained by non-parametric bootstrap. e horizontal solid black lines represent the ight
ranges of 90% marked Aedes albopictus (FR90, calculated according to Lillie et al.29, White & Morris30, and
Morris et al.31). Each panel identies a mark-release-recapture experiment (MRR1, MRR2 and MRR3).
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SCIENTIFIC REPORTS | (2019) 9:10281 |
case could fail to reduce below 10% the probability that a potentially infected mosquito escapes the treatment,
even if this is carried out aer 2–3 days since the arrival of a viremic case (i.e. the shortest plausible time-interval
for activation of mosquito control activities aer the report of suspect case of arbovirosis to health authorities).
In conclusion, the above results suggest that insecticide treatments aimed to prevent risk of autochthonous
outbreaks of exotic arboviruses in temperate regions may fail to reach a non-neglectable part of the potential
vector population even if implemented in a 200-m buer aer reports of an infected case to health authorities,
considering an average of 6 days delay between symptom onset and detection26. Overall, this reinforce the claim
that control activities carried out around the place of residence of infected cases are not sucient to control an
emerging arbovirus outbreak, not only due to the importance of outdoor activities in the spread of Aedes-borne
diseases in temperate countries27, but also due to operational constraints in intervening in an adequate area in
due time.
Study area. e study area (80 hectares) lies within the municipality of Piove di Sacco (Padua province,
north-east Italy) and is characterized by either peri-urban or rural habitats (Fig.1A). e peri-urban habitat is
mostly characterized by two-story residential buildings with small gardens and includes football and recreational
grounds, small stores, schools, a fuel station and a church. e rural habitat comprises large corn and alfalfa cul-
tivations, small vineyards, horse and sheep pastures, and irrigation canals. A highway delimits the northern and
southern extremes of the study area.
Mark-release-recapture experiments. ree MRR experiments were performed in August 3rd (MRR1)
and 24th (MRR2), and in September 9th (MRR3) 2009, with the agreement of Piove di Sacco municipality.
Temperature data during the experiments (Supplementary TableS3) were obtained from the ARPAV agrome-
teorological station of Legnaro (45°2051N, 11°5708E), located about 10 km northwest from the centre of the
study area (45°1821N, 12°0149E). Rainfall was absent/very low during all MRRs (0.2 mm), except for a few
days of moderate rain in MRR1 (i.e. 9.2 mm on day-7 and 3.8 mm on both day-10 and day-11 since release) and
a strong thunderstorm (170 mm of rain) occurred few hours aer release in MRR3 (Supplementary TableS3).
Mark-release-recapture experiments were carried out using the same approach described in Marini et al.17 in
Figure 4. Frequencies of marked Aedes albopictus females collected (grey bar) in the second (MRR2, (A) and
third (MRR3, (B) mark-release-recapture experiment versus frequencies of ovipositing females kept in semi-
natural conditions (single ovipositions, black line) during the same interval.
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Aedes albopictus females released were obtained from eggs collected by >20 ovitraps located in Padua prov-
ince. Eggs were le to hatch and larvae were reared in plastic basins (35 × 28 × 8 cm) at larval density 1 larva/
mL with cat pellets as food (Friskies® Adults). Pupae were transferred to 40 cm cubic cages, where adults emerged
and were maintained with 10% sugar solution until the day of release. Eggs, larvae and adults were always kept
outdoors in a site sheltered from direct sunlight and wind.
In the morning of each release, 2–4 days-old females were fed with debrinated fresh bovine blood by a
hand-made membrane feeding system28. Blood-fed females were transferred into paper-cups closed by a net in
groups of 20, and marked by gently dropping orange uorescent dust (Day-Glo Color Corp., Cleveland, OH,
U.S.A.) into the cup. Marked females were then transferred back into the cages and provided with a 5% sugar
solution. In the evening, cages were brought by car to the release site in the centre of the study area inside paper
boxes. At 10 PM - when Ae. albopictus is known to be inactive2 - marked females were released by opening the
cages, which were le open all night long, in order to leave time to mosquitoes to y away. Alive and dead indi-
viduals found in the cages the following morning were counted and excluded from the total number of released
Collections of adult mosquitoes were performed using 96 sticky-traps (STs)29 located at ground level in shel-
tered positions and geo-referenced, using a global positioning system device (Garmin GPSMAP 60CSx). In order
to have the same collection-power at every distance from the release site, the study area was virtually subdivided
into 10 concentric annuli (from 50 to 500 m radius) around the release site, with the number of STs/annulus
increased from the centre to extremes of the sampling area to maintain the proportion ST/area to an average
density of 1 ST/8,200 m in each annulus (Fig.1A). All STs were activated by adding 500 ml of tap-water and
adhesive sheets approximately 12 h aer release (day-1); only the ST located on the release site was activated 24 h
later (day-2), to avoid collecting individuals which did not disperse immediately aer release. Hereaer, the 12 h
between release and STs activation are indicated as “day-0”. STs were monitored daily for the rst 6 days and at
days 11 (MRR1, MRR2 and MRR3) and -16 (MRR2 and MRR3) aer release, as described in Marini et al.17. All
collected mosquitoes were counted and morphologically subdivided by genus/species and gender under a dissect-
ing microscope; the presence of uorescent dust was checked under UV light.
Recapture rates were calculated for each MRR experiment as the proportion of the number of recaptured
marked mosquitoes over the total number of released ones. Recapture rates in the three MRRs experiments were
compared by a Bernoulli GLM, with the number of mosquitoes recaptured within the rst 11 days as response
variable and the MRR experiment as covariate. ese and the following statistical analyses were carried out using
the statistical soware R30.
To allow direct comparison of the results obtained in the present study and those previously obtained in
Rome, dispersal of the released mosquitoes was analysed as in Marini et al.17, i.e. estimating: (i) the Mean
Distance Travelled during the entire sampling period (MDT, a parameter not inherently biased by trap loca-
tion or size of study area3133); (ii) the daily MDTs for the rst 6 days aer release; (iii) the maximum Observed
Distance Travelled (max ODT), corresponding to the linear distance from the release site to the farthest positive
ST (i.e. where at least one marked mosquito female was collected); and iv) the Flight Ranges (FRs) based on the
linear regression of the cumulative number of expected recaptures (ERs) from each annulus (x-axis) on the log10
(annulus median distance +1). FR50 and FR90 values were calculated from the equation of regression line as 50%
and 90% of the largest ER value, respectively3133. Additionally, the linear regression of the cumulative number
of expected recaptures (ERs) was also computed considering the log10 (annulus median distance +1), the release
and their interaction to test the dierence between ight ranges in each release (by comparing the slopes of the
three regression lines).
To provide estimates of the distance up to which marked Ae. albopictus females are expected to be found con-
ditional to the time of release, dispersal data were further analysed by means of the following three models: (1) a
GLM with Bernoulli distribution and logit link to model the probability to detect a marked mosquito condition-
ally to days and distance from release, and therefore to estimate the probability to detect a marked mosquito at
a given distance. e response variable in the model is the presence/absence of marked mosquitoes into the STs,
while covariates are the distances of STs from the release site and the days aer release; (2) a GLM with Gamma
distribution and log link (hereaer Gamma GLM) to model the distance travelled by marked mosquitoes con-
ditional to the days aer release and to compute the percentile of the distance travelled by recaptured marked
mosquitoes. e response variable in this model is the distance from the release site at which marked mosquitoes
were captured; in compliance with the Gamma distribution constrain, only strictly positive distances are consid-
ered. Covariate are the days aer release; (3) a Zero Altered Gamma model (hereaer ZAG34), which accounts
for the recaptured mosquitoes into the ST located on the release site (zero distance) and allows to estimate the
percentile of the distance at which mosquitoes are expected to be found, weighted for the probability that marked
mosquitoes collected actually moved from the release site. erefore, in this model the distance travelled is mod-
elled conditional to the days aer release by means of a two-step model. First, a Bernoulli model with a binary
response variable (i.e. value of 0 for mosquitoes recaptured on the release site and of 1 for mosquitoes recaptured
in another ST) is applied to evaluate the probability that a marked mosquito moves away from the release site.
Second, a Gamma GLM is tted on distances from the release site at which marked mosquitoes were captured.
Covariate was the days aer release for both sub-models. In all the three models, condence intervals for the
estimated quantities are computed by non-parametric bootstrap applied to original data.
Eect of uorescent dye marking on mosquito survival. Before each MRR experiment, Ae. albopictus
blood-fed females were removed from the cages by manual aspiration before (“unmarked group”; N = 50) and
aer (“marked group”; N = 50) the marking procedure described above. Both groups were kept in 25 cm cubic
cages kept outdoors in sites sheltered from direct sunlight and wind and provided with water bowl for egg-laying
and 5% sugar solution ad libitum.
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SCIENTIFIC REPORTS | (2019) 9:10281 |
Number of dead mosquitoes was recorded daily for the entire duration of the MRR experiment. Mortality rates
in the two groups were analysed using the Kaplan-Meier method and comparing survival curves by Log-rank test.
Oviposition pattern under semi-field conditions. During MRR2 and MRR3, individual marked
blood-fed females (N = 48 and 24, respectively) reared and handled as described above, were kept in plastic cups
closed with mosquito net and lined with lter paper, kept in sheltered sites outdoors. Oviposition activity was
monitored daily for the entire length of the MRR experiments, by counting the number of eggs deposited on the
lter paper in each cup. e correlation between the number of marked mosquito females collected in MRR2 and
MRR3 and the number of the ovipositing females during the same intervals was assessed by Pearsons correlation.
Data Availability
All data generated or analysed during this study are included in this published article (and its Supplementary
Information Files).
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We thank Luca Delucchi for providing the map used in Figure 1A.
Author Contributions
F.M., B.C., M.P. and A.d.T. designed the study. F.M., B.C., M.P., M.T., M.F. and A.D. carried out the eld studies.
M.M., F.M., B.C. and R.R. carried out the statistical analyses. F.M., B.C., M.M. and A.d.T. wrote the manuscript.
Additional Information
Supplementary information accompanies this paper at
Competing Interests: e authors declare no competing interests.
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... Policymakers use these outputs as a proxy of MBVDs risk (e.g., Peterson, 2008Peterson, , 2014Dhingra et al., 2016;Escobar and Craft, 2016;Kraemer et al., 2015a;Acharya et al., 2018;Tjaden et al., 2021) and adopt them for the planning and evaluation of disease mitigation measures (Purse and Golding, 2015). Mathematical mechanistic models, instead, have the advantage to make explicit the causal links between the biology of the target species/disease system and the environment, by directly modelling the fitness of the population/individual as a function of a given environmental factor (e.g., the temperature-dependent mortality rate for mosquitoes; Poletti et al., 2011;Marini et al., 2019a). This is particularly relevant when the study aims to assess the boundaries of an organism distribution or to project its distribution onto novel environmental conditions (e.g., when forecasting species range shifts under future climate change or when modelling the spread of invasive alien species; Kearney, 2006;Maino et al., 2016;Fig. ...
... aegypti and Ae. albopictus (Roche et al. 2015;Marcantonio et al. 2019a;Marini et al. 2019a;Müller et al. 2020; Appendix B Tab. B4 for dispersal parameters). Beside to active dispersal, the model also considers dispersal aided by cars along the main road network (a matrix containing the coordinates of the grid cells of the landscape intersecting the road network must be provided, see the "Spatial scales of the model and temperature data sources" section), defined as the "hitchhiking" probability of a female to enter in a car and to be driven and released further away. ...
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Understanding the causal processes determining the geographical distribution of species is a fundamental question in ecology but has relevant implications in epidemiology. Infectious diseases are a public health concern for humans, livestock, and wildlife, and their relevance has fostered the interest in tools allowing the delineation of areas at risk for pathogen transmission. In the past two decades, the prompt availability of new spatio-temporal explicit datasets and coding environments has led to extensive use of modelling tools to infer the geographical distribution of the species involved in infectious disease systems. However, the validity of these models was questioned, underlining the lack of biological realism and causal-based reasoning as the main limitations. In this doctoral dissertation, I tried to include biological realism and a causal-based perspective on correlative and mechanistic modelling approaches aiming to infer the spatio-temporal distribution of vector and host species involved in vector-borne disease systems. I first applied the modelling relation framework in a species distribution modelling exercise through the Structural Equation Modelling approach, a methodology that includes and evaluates causal pathways within a linear modelling framework. I moved towards mechanistic models and built dynamAedes, a spatially-explicit model inferring the population dynamic of four Aedes mosquito species at different spatial scales. I then explored how the choice of the model parameters and spatial scales affect the outcomes of an epidemiological model estimating the number of Chikungunya’s secondary cases. Finally, since host abundance is an epidemiological parameter as substantial as vector abundance, I presented a downscaling methodology to disaggregate livestock censuses aggregated at different administrative unit levels. The results highlighted how a causal-based approach increases the biological realism and predictive accuracy of the modelling approaches tested. However, the knowledge of essential biological parameters is scattered, fragmented and not standardized, affecting the models’ outcome quality and reliability. The choice of the spatial scale affects as well the models' outputs, as coarser training and testing datasets produce, on average, better results because of the effects of the Modifiable Areal Unit Problem. To amend such limitations and promote the effective use of spatial-explicit model outputs for public health decisions, clear communication and dialogue with policymakers are essential to enable them to understand the assumptions of the models and the uncertainty of their predictions.
... On the other hand, some studies found non-significant associations with precipitation (n = 2), urbanisation, and relative humidity (n = 1). Wealth [124] Life expectancy [124] Greenhouse gas emissions [71] Light Intensity [103] Mean sunshine duration [125] Direction at ground level [103] Geocoded Twitter data-Geolocated activity data and computed mobility patterns of users [127] GDP-Gross domestic product [124] Agriculture [80] [61] ...
... On the other hand, some studies found non-significant associations with precipitation (n = 2), urbanisation, and relative humidity (n = 1). Wealth [124] Life expectancy [124] Greenhouse gas emissions [71] Light Intensity [103] Mean sunshine duration [125] Direction at ground level [103] Geocoded Twitter data-Geolocated activity data and computed mobility patterns of users [127] GDP-Gross domestic product [124] Agriculture [80] [61] ...
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Mosquito-borne infections are increasing in endemic areas and previously unaffected regions. In 2020, the notification rate for Dengue was 0.5 cases per 100,000 population, and for Chikungunya <0.1/100,000. In 2019, the rate for Malaria was 1.3/100,000, and for West Nile Virus, 0.1/100,000. Spatial analysis is increasingly used in surveillance and epidemiological investigation, but reviews about their use in this research topic are scarce. We identify and describe the methodological approaches used to investigate the distribution and ecological determinants of mosquito-borne infections in Europe. Relevant literature was extracted from PubMed, Scopus, and Web of Science from inception until October 2021 and analysed according to PRISMA-ScR protocol. We identified 110 studies. Most used geographical correlation analysis (n = 50), mainly applying generalised linear models, and the remaining used spatial cluster detection (n = 30) and disease mapping (n = 30), mainly conducted using frequentist approaches. The most studied infections were Dengue (n = 32), Malaria (n = 26), Chikungunya (n = 26), and West Nile Virus (n = 24), and the most studied ecological determinants were temperature (n = 39), precipitation (n = 24), water bodies (n = 14), and vegetation (n = 11). Results from this review may support public health programs for mosquito-borne disease prevention and may help guide future research, as we recommended various good practices for spatial epidemiological studies.
... Mean distance travelled, population survival and size. Mean distance travelled (MDT) was computed to estimate the dispersal of marked Ae. albopictus males from MRR experiments, taking into account the unequal trap densities within each annulus [61,62]. MDT is independent of the position of the traps or size of study area [63][64][65], and is defined by the following equation: ...
... However, the <60 m mean daily distance travelled by the males is in the range of values estimated for non-irradiated Ae. albopictus males in Switzerland [88] and La Reunion Island [87], and lower than values estimated for Ae. albopictus females in Italy [61,89] and Switzerland [88]. This suggests that the flying capacity of the released males is not affected by manipulations, irradiation and transportation and highlights the need of planning multiple short-distance ground releases and/or aerial uniform releases within a future SIT intervention program. ...
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In the last decades, the colonization of Mediterranean Europe and of other temperate regions by Aedes albopictus created an unprecedented nuisance problem in highly infested areas and new public health threats due to the vector competence of the species. The Sterile Insect Technique (SIT) and the Incompatible Insect Technique (IIT) are insecticide-free mosquito-control methods, relying on mass release of irradiated/manipulated males, able to complement existing and only partially effective control tools. The validation of these approaches in the field requires appropriate experimental settings, possibly isolated to avoid mosquito immigration from other infested areas, and preliminary ecological and entomological data. We carried out a 4-year study in the island of Procida (Gulf of Naples, Italy) in strict collaboration with local administrators and citizens to estimate the temporal dynamics, spatial distribution, and population size of Ae. albopictus and the dispersal and survival of irradiated males. We applied ovitrap monitoring, geo-spatial analyses, mark-release-recapture technique, and a citizen-science approach. Results allow to predict the seasonal (from April to October, with peaks of 928-9,757 males/ha) and spatial distribution of the species, highlighting the capacity of Ae. albopictus population of Procida to colonize and maintain high frequencies in urban as well as in sylvatic inhabited environments. Irradiated males shown limited ability to disperse (mean daily distance travelled
... This hypothesis is supported by previous evidences reported by Samson et al., 2013 [42] showing that Ae. albopictus rests during the daytime in the vegetation around residential areas, thus demonstrating that landscape can influence spatial distribution and behavior. Moreover, previous studies showed the importance of vegetation in urban areas also for what concerns to outdoor resting preferences [40,43], high plasticity in feeding behaviour [44] and rapid active dispersal [45] of Ae. albopictus. In contrast with Rome, Anzio is characterized by a homogenous presence of townhouses and villas with small gardens, which represent an ideal habitat for Aedes mosquito species. ...
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Background: Outbreaks of Aedes-borne diseases in temperate areas are not frequent, and limited in number of cases. We investigate the associations between habitat factors and temperature on individuals' risk of chikungunya (CHIKV) in a non-endemic area by spatially analyzing the data from the 2017 Italian outbreak. Methodology/principal findings: We adopted a case-control study design to analyze the association between land-cover variables, temperature, and human population density with CHIKV cases. The observational unit was the area, at different scales, surrounding the residence of each CHIKV notified case. The statistical analysis was conducted considering the whole dataset and separately for the resort town of Anzio and the metropolitan city of Rome, which were the two main foci of the outbreak. In Rome, a higher probability for the occurrence of CHIKV cases is associated with lower temperature (OR = 0.72; 95% CI: 0.61-0.85) and with cells with higher vegetation coverage and human population density (OR = 1.03; 95% CI: 1.00-1.05). In Anzio, CHIKV case occurrence was positively associated with human population density (OR = 1.03; 95% CI: 1.00-1.06) but not with habitat factors or temperature. Conclusion/significance: Using temperature, human population density and vegetation coverage data as drives for CHIKV transmission, our estimates could be instrumental in assessing spatial heterogeneity in the risk of experiencing arboviral diseases in non-endemic temperate areas.
... Notice that, for large enough values of a (corresponding to large values of Λ, see (13)), equation (17) has no positive solution, and pM˚˚, F˚˚q defined in (16) is the only equilibrium point of (12). ...
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The Sterile Insect Technique (SIT) is a promising technique to control mosquitoes, vectors of diseases, like dengue, chikungunya or Zika. However, its application in the field is not easy, and its success hinges upon several constraints, one of them being that the treated area must be sufficiently isolated to limit migration or re-invasion by mosquitoes from the outside. In this manuscript we study the impact of males and (fertile) females migration on SIT. We show that a critical release rate for sterile males exists for every migration level, in the context of continuous or periodic releases. In particular, when (fertile) females migration is sufficiently low, then SIT can be conducted successfully using either open-loop control or closed-loop control (or a combination of both methods) when regular measurements of the wild population are completed. Numerical simulations to illustrate our theoretical results are presented and discussed. Finally, we derive a threshold value for the females migration rate, when viruses are circulating, under which it is possible to lower the epidemiological risk in the treated area, according to the size of the human population.
... Additionally, in the study reported here, the quality of the flower resource, such as nectar quality and quantity, was not considered, although this is highly variable in nature [52]. Given the flight range of Ae. albopictus (> 200 m; [53,54]), it is likely that Ae. albopictus on Masig Island opportunistically access sugar sources beyond the plants in the census. Mosquitoes obtain sugar by feeding on a wide range of sources including floral and extrafloral nectar, fruit and seedpods, plant tissues, honeydew and ant regurgitate [11][12][13][14]55]. ...
Full-text available
Background Sugar feeding is a fundamental behaviour of many mosquito species. For Aedes albopictus, an important vector of dengue virus and chikungunya virus, little is known about its sugar-feeding behaviour, and no studies have been conducted on this in the southern hemisphere. This knowledge is pivotal for determining the potential of attractive targeted sugar baits (ATSBs) to control this important vector. Methods The prevalence of sugar was assessed in 1808 Ae. albopictus from Masig Island, Torres Strait, Australia collected between 13 and 25 March 2020. Fructose presence and content in field-collected Ae. albopictus were quantified using the cold anthrone assay. Results Significantly more male (35.8%) than female (28.4%) Ae. albopictus were sugar fed. There was a significant interaction between sex and time of day on the probability of capturing sugar-fed Ae. albopictus. For both sexes, fructose prevalence and content were higher in mosquitoes caught in the morning than in the afternoon. Female Ae. albopictus collected in the residential habitat were significantly more likely to be sugar fed than those collected in the woodland habitat. Conclusions These findings provide baseline information about the sugar-feeding patterns of Ae. albopictus and provide essential information to enable an assessment of the potential of ATSBs for vector suppression and control on Masig Island, with relevance to other locations where this species occurs. Graphical abstract
Full-text available
Mosquito species belonging to the genus Aedes have attracted the interest of scientists and public health officers because of their capacity to transmit viruses that affect humans. Some of these species were brought outside their native range by means of trade and tourism and then colonised new regions thanks to a unique combination of eco-physiological traits. Considering mosquito physiological and behavioural traits to understand and predict their population dynamics is thus a crucial step in developing strategies to mitigate the local densities of invasive Aedes populations. Here, we synthesised the life cycle of four invasive Aedes species (Ae. aegypti, Ae. albopictus, Ae. japonicus and Ae. koreicus) in a single multi-scale stochastic modelling framework which we coded in the R package dynamAedes. We designed a stage-based and time-discrete stochastic model driven by temperature, photo-period and inter-specific larval competition that can be applied to three different spatial scales: punctual, local and regional. These spatial scales consider different degrees of spatial complexity and data availability by accounting for both active and passive dispersal of mosquito species as well as for the heterogeneity of the input temperature data. Our overarching aim was to provide a flexible, open-source and user-friendly tool rooted in the most updated knowledge on the species’ biology which could be applied to the management of invasive Aedes populations as well as to more theoretical ecological inquiries. Graphical Abstract
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Infections due to chikungunya and other mosquito-borne viruses, such as dengue and Zika, represent an area of significant unmet medical need. There are currently no approved medicines for prophylaxis or treatment of these diseases, and the development and implementation of vaccines against these viruses has proved problematic. Although antiviral molecules with treatment and prophylactic potential against chikungunya virus have been identified, no successful field trials have been reported. Chemoprophylaxis may be attractive for unvaccinated at-risk populations, but performing a successful chemoprophylaxis trial during a chikungunya outbreak will require a clearly identifiable at-risk population. We propose the application of a household transmission model, as used in testing drugs against respiratory viruses. Current evidence on household clustering of chikungunya and other Aedes mosquito-borne viral infections is supportive. We suggest that this model may improve prophylaxis trial feasibility, as well as focusing research and future treatment on a population likely to benefit.
In the summer of 2007, an outbreak of Chikungunya virus (CHIKV) started in the urban areas of Castiglione di Cervia (Latitude 44°15′35.70" N, Longitude 12°15′47.08" E) and Castiglione di Ravenna (Latitude 44°15′33.97" N, Longitude 12°15′17.97" E), Italy, with secondary foci in other Emilia-Romagna urban areas. At the end of the outbreak a total of 217 confirmed cases were reported (45.6% males, 54.4% females). Aedes albopictus was identified as the mosquito vector species responsible of the outbreak. To estimate the dispersion of infected female mosquitoes, a spatio-temporal analysis on geocoded human case residences was performed using a Geographic Information System (QGIS 3.10). The mean distance between the primary and secondary cases after 7–14 days from the start of the outbreak ranged from 71.58 m (± 32.26 SD) to 83.07 m (± 32.26 SD) while the maximum distance ranged from 130.50 m to 174.93 m. The results obtained from this analysis can be useful to better understand the dynamics of the outbreak and to provide evidence-based data for planning emergence vector control activities focused on imported cases, to avoid the spread of the virus.
Dispersal is an important driver for animal population dynamics. Insect dispersal is conventionally assessed by Mark-Release-Recapture (MRR) experiments, whose results are usually analyzed by regression or Bayesian approaches which do not incorporate relevant parameters affecting this behavior, such as time dependence and mortality. Here we present an advanced mathematical-statistical method based on partial differential equations (PDEs) to predict dispersal based on MRR data, taking into consideration time, space, and daily mortality. As a case study, the model is applied to estimate the dispersal of the mosquito vector Aedes albopictus using data from three field MRR experiments. We used a two-dimensional PDE heat equation, a normal bivariate distribution, where we incorporated the survival and capture processes. We developed a stochastic model by specifying a likelihood function, with Poisson distribution, to calibrate the model free parameters, including the diffusion coefficient. We then computed quantities of interested as function of space and time, such as the area travelled in unit time. Results show that the PDE approach allowed to compute time dependent measurement of dispersal. In the case study, the model well reproduces the observed recapture process as 86%, 78% and 84% of the experimental observations lie within the 95% CI of the model predictions in the three releases, respectively. The estimated mean values diffusion coefficient are 1,800 (95% CI: 1,704–1 896), 960 (95% CI: 912- 1 128), 552 (95% CI 432–1 080) m²/day for MRR1, MRR2 and MRR3, respectively. The incorporation of time, space, and daily mortality in a single equation provides a more realistic representation of the dispersal process than conventional Bayesian methods and can be easily adapted to estimate the dispersal of insect species of public health and economic relevance. A more realistic prediction of vector species movement will improve the modelling of diseases spread and the effectiveness of control strategies against vectors and pests.
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Autochthonous outbreaks of chikungunya and dengue during the past decade showed that continental Europe is vulnerable to Aedes albopictus–borne infections. Ae. albopictus has spread geographically, resulting in more people exposed to risk. Timely application of adequate mosquito suppression measures may delay, or even prevent, the vector population from crossing the potential epidemic abundance threshold should a pathogen be introduced. Health authorities should be on alert to detect early cases to prevent autochthonous outbreaks.
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Climate change has already impacted the transmission of a wide-range of vector-borne diseases in Europe, and it will continue to do so in the coming decades. Climate change has been implicated in the observed shift of ticks to elevated altitudes and latitudes, notably including the Ixodes ricinus tick species which is a vector for Lyme borreliosis and tick-borne encephalitis. Climate change is also thought to have been a factor in the expansion of other important disease vectors in Europe: Aedes albopictus (the Asian tiger mosquito), which transmits diseases such as Zika, dengue, and chikungunya, and Phlebotomus sandfly species, which transmits diseases including Leishmaniasis. In addition, highly elevated temperatures in the summer of 2010 have been associated with an epidemic of West Nile Fever in Southeast Europe and subsequent outbreaks have been linked to summer temperature anomalies. Future climate-sensitive health impacts are challenging to project quantitatively, in part due to the intricate interplay between non-climatic and climatic drivers, weather-sensitive pathogens, and climate change adaptation. Moreover, globalisation and international air travel contribute to pathogen and vector dispersion internationally. Nevertheless, monitoring forecasts of meteorological conditions can help detect epidemic precursors of vector-borne disease outbreaks and serve as early warning systems for risk reduction.
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Zika virus (ZIKV) is an arthropod-borne virus (arbovirus) that recently caused outbreaks in the Americas. Over the past 60 years, this virus has been observed circulating among African, Asian, and Pacific Island populations, but little attention has been paid by the scientific community until the discovery that large-scale urban ZIKV outbreaks were associated with neurological complications such as microcephaly and several other neurological malformations in fetuses and newborns. This paper is a systematic review intended to list all mosquito species studied for ZIKV infection or for their vector competence. We discuss whether studies on ZIKV vectors have brought enough evidence to formally exclude other mosquitoes than Aedes species (and particularly Aedes aegypti) to be ZIKV vectors. From 1952 to August 15, 2017, ZIKV has been studied in 53 mosquito species, including 6 Anopheles, 26 Aedes, 11 Culex, 2 Lutzia, 3 Coquillettidia, 2 Mansonia, 2 Eretmapodites, and 1 Uranotaenia. Among those, ZIKV was isolated from 16 different Aedes species. The only species other than Aedes genus for which ZIKV was isolated were Anopheles coustani, Anopheles gambiae, Culex perfuscus, and Mansonia uniformis. Vector competence assays were performed on 22 different mosquito species, including 13 Aedes, 7 Culex, and 2 Anopheles species with, as a result, the discovery that A. aegypti and Aedes albopictus were competent for ZIKV, as well as some other Aedes species, and that there was a controversy surrounding Culex quinquefasciatus competence. Although Culex, Anopheles, and most of Aedes species were generally observed to be refractory to ZIKV infection, other potential vectors transmitting ZIKV should be explored.
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An autochthonous chikungunya outbreak is ongoing near Anzio, a coastal town in the province of Rome. The virus isolated from one patient and mosquitoes lacks the A226V mutation and belongs to an East Central South African strain. As of 20 September, 86 cases are laboratory-confirmed. The outbreak proximity to the capital, its late summer occurrence, and diagnostic delays, are favouring transmission. Vector control, enhanced surveillance and restricted blood donations are being implemented in affected areas.
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In August 2017, an autochthonous chikungunya case was reported in south-east France. By mid-September, eight additional autochthonous cases were found in the index case’s neighbourhood, where the chikungunya virus vector Aedes albopictus was observed. Genomic characterisation identified an East-Central South African (ECSA) lineage strain, probably from the Central African region and carrying an adaptive mutation facilitating transmission by Ae. albopictus. The event confirms we need early case detection and response to contain chikungunya in Europe.
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Background Zika virus transmission dynamics in urban environments follow a complex spatiotemporal pattern that appears unpredictable and barely related to high mosquito density areas. In this context, human activity patterns likely have a major role in Zika transmission dynamics. This paper examines the effect of host variability in the amount of time spent outdoors on Zika epidemiology in an urban environment. Methodology/Principal findings First, we performed a survey on time spent outdoors by residents of Miami-Dade County, Florida. Second, we analyzed both the survey and previously published national data on outdoors time in the U.S. to provide estimates of the distribution of the time spent outdoors. Third, we performed a computational modeling evaluation of Zika transmission dynamics, based on the time spent outdoors by each person. Our analysis reveals a strong heterogeneity of the host population in terms of time spent outdoors–data are well captured by skewed gamma distributions. Our model-based evaluation shows that in a heterogeneous population, Zika would cause a lower number of infections than in a more homogenous host population (up to 4-fold differences), but, at the same time, the epidemic would spread much faster. We estimated that in highly heterogeneous host populations the timing of the implementation of vector control measures is the major factor for limiting the number of Zika infections. Conclusions/Significance Our findings highlight the need of considering host variability in exposure time for managing mosquito-borne infections and call for the revision of the triggers for vector control strategies, which should integrate mosquito density data and human outdoor activity patterns in specific areas.
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In recent years, several European countries reported cases of imported chikungunya infection. We present the first imported clinically manifested chikungunya fever in Croatia. A 27-year-old woman returned to Croatia on 21 March 2016, after she stayed in Costa Rica for two months where she had noticed a mosquito bite on her left forearm. Five days after the mosquito bite she developed severe arthralgias, fever and erythematous papular rash. In next few days symptoms gradually subsided. After ten days she felt better, but arthralgias re-appeared accompanied with morning stiffness. Two weeks after the onset of the disease she visited the infectious diseases outpatient department. The physical examination revealed rash on the trunk, extremities, palms and soles. Laboratory findings showed slightly elevated liver transaminases. Serological tests performed on day 20 after disease onset showed a high titer of chikungunya virus (CHIKV) IgM and IgG antibodies which indicated CHIKV infection. CHIKV-RNA was not detected. Serology to dengue and Zika virus was negative. The patient was treated with nonsteroid anti-inflammatory drugs and paracetamol. Her symptoms ameliorated, however, three months later she still complaint of arthralgias. The presented case highlights the need for inclusion of CHIKV in the differential diagnosis of arthralgia in all travelers returning from countries with documented CHIKV transmission.
Chikungunya virus (CHIKV) is transmitted by Aedes aegypti and Aedes albopictus mosquitoes and causes febrile illness with severe arthralgia in humans. There are 3 circulating CHIKV genotypes, Asia, East/Central/South Africa, and West Africa. CHIKV was first reported in 1953 in Tanzania, and up until the early 2000s, a few outbreaks and sporadic cases of CHIKV were mainly reported in Africa and Asia. However, from 2004 to 2005, a large epidemic spanned from Kenya over to the southwestern Indian Ocean region, India, and Southeast Asia. Identified in 2005, the E1 glycoprotein A226V mutation of the East/Central/South Africa genotype conferred enhanced transmission by the A. albopictus mosquito and has been implicated in CHIKV's further spread in the last decade. In 2013, the Asian CHIKV genotype emerged in the Caribbean and quickly took the Americas by storm. This review will discuss the history of CHIKV as well as its expanding geographic distribution.