Rift Valley Fever Vectors Research Articles

Correlation of Probiotic synthesis nanoparticles against Rift Valley Fever Vector, Culex antennatus Becker (Diptera: Culicidae)

Application of Probiotic bacteria for biosynthesis of nanoparticles could be a good ecofriendly alternative to chemical and physical method. The present research was pointed to the biosynthesis of silver (AgNPs) and cooper (CuNPs) nanoparticles using Lactobacillus reuteri and evaluating their effect against Rift Valley Fever Vector, Culex antennatus Becker (Diptera: Culicidae). The cell free supernatant of Lactobacillus reuteri was used for silver and copper nanoparticle biosynthesis from AgNO3 and CuSO4 solutions. The NPs production were confirmed and characterization by UV-visible spectroscopy and transmission electron microscopy analysis. TEM images were used for determination NPs size, shape and distribution of nanoparticles. Results confirmed that AgNPs and CuNPs from Lactobacillus reuterishowed larvicidal activity against mortality of Culex antennatus 3rd larval instar recorded 98.67 and 89.33% by AgNPs and CuNPsat 500 µM, respectively. Lethal concentrations (LC25, LC50 and LC75) of AgNPs and CuNPs prolonged C. antennatus both larval and pupal times as compared with untreated groups. Also, AgNPs and CuNPssignificantly decreased the mean number of eggs laid by females resulted from treated larvae. At LC75 of AgNPs and CuNPs, number of eggs laid by females recorded 39.91 and 52.10 eggs/♀, respectively vs. 104.13 eggs/♀ for the control.The highest sterility index (91.87 and 78.21%) attained by LC75 of AgNPs and CuNPs, respectively. Generally, AgNPs was more effective against tested larvae, as well as reproductive potential of resulted females than CuNPs.

Spatiotemporal distribution of rift valley fever and malaria vectors in Baringo County, Kenya: Implications on vector control

Rift Valley Fever and malaria are zoonotic and human diseases respectively that pose major production and health challenges to pastoralists. This study aimed to determine the spatiotemporal distribution of mosquito vectors of these two diseases in Baringo County, Kenya. A longitudinal study design was used to collect mosquitoes from twenty four sites. Rainfall seasonality was determined using rainfall data from the WorldClim database. Negative binomial and zero-inflated negative binomial regression models were used to determine the effect of rainfall seasonality and ecogeographical conditions on vector distribution. Spatio-temporal maps showing vector distribution were made using the sf package in R. Four Rift Valley Fever vector species and four malaria vector species were collected and were predominantly found in the lowland and riverine zones. Vector control interventions against the two diseases should therefore target these two zones. The study also recommends integrated vector management methods targeting both larval and adult stages.

Epidemiological patterns of Rift Valley Fever from diverse habitats during an extreme unprecedented flooding of Lake Baringo basin, Kenya, 2012-2013

Mosquitoes’ ecology and associated arboviruses are heavily influenced by precipitation and retention of water in the environment. In 2011 and 2014, unprecedented floods occurred in the Lake Baringo basin inundating approximately 88 km2 of the shoreline land. This caused abrupt environmental changes raising fears of an outbreak of Rift Valley Fever (RVF) disease. This study was carried out to determine the situation of RVF disease in livestock from diverse habitats during the extreme unprecedented flooding phenomenon that occurred in the Lake Baringo basin, in 2012-2013. Blood was drawn from the ear vein of livestock selected randomly from the three study areas (lakeshore land, swamp marshy, and dry rangeland habitats). Mosquitoes were trapped using CDC light traps and identified morphologically. From a total of 77 blood samples, eight were positive for RVF virus (RVFV) representing an overall infection of 12%. RVF prevalence from livestock residents in flooded lakeshore land habitat was 2.6% (N=77) compared to the swamp marshy habitat at 7.8% (N=77). No infections were recorded from dry rangeland (0%). Mosquitoes of genus Mansonia dominated the catches in flooded lakeshore (98%). Highest individual catches of mosquitoes of genus Aedes was from swamp marshy area whose abundance was 96.8% and below 2% in other habitats. The Simpson’s Diversity Index for mosquitoes from swamp marshy habitat was 0.56, dry rangeland 0.57, and lakeshore land 0.13. The flooded lakeshore land was the most affected by the unprecedented floods resulting in uneven mosquito diversity and subsequently low prevalence of RVF in this habitat. This could be attributed to prolonged disruption of biotic and abiotic factors creating unfavorable breeding sites of multiple species of primary vectors of RVF in flooded lakeshore land unlike in other habitats.

Larvicidal Activity of Menthe longifolia (Lamiaceae) Different Extracts against Culex pipiens L. and Culex antennatus Becker (Diptera: Culicidae)

Larvicidal activity of Menthe longifolia different extracts against lymphatic filariasis vector, Culex pipiens and Rift Valley Fever vector, C. antennatuswas tested. The extraction was carried out using methanol, acetone, chloroform and petroleum ether solvents. Obtained results revealed that petroleum ether extraction from leaves of M. longifolia was more effective against 3rd instar larvae of C. pipiens and C. antennatus than those of chloroform, acetone and methanol extractions. Methanol, acetone, chloroform and petroleum ether extracts from leaves of M. longifolia recorded LC50 values of 1741.5, 1322.0, 702.4 and 379.5 ppm against C. pipiens third larval instar and 1064.6, 850.3, 459.9 and 250.4 ppm against C. antennatusthird larval instar, respectively. In addition, LC90 values recorded 2282.0, 1897.7, 1300.3 and 511.9 ppm by methanol, acetone, chloroform and petroleum ether extract from leaves of M. longifolia against C. pipiens third larval instar and 1596.5, 1388.6, 979.4 and 388.2 ppm against C. antennatusthird larval instar, respectively. Also, both C. pipiens and C. antennatus larval and pupal periods were prolonged by all tested extracts at all concentrations used as compared with the untreated groups. Menthe longifolia tested extracts are considered as new promising controlling agents against C. pipiens and C. antennatus, however, more studies are necessary to reach the active ingredient in the tested extracts.

Larvicidal activities of local Bacillus thuringiensis isolates and toxins from nematode bacterial symbionts against the Rift Valley fever vector, Aedes caspius (Diptera: Culicidae)

Mosquito resistance to insecticides has recently increased the burden of the majority of mosquito-borne diseases, and controlling the spread of these diseases should mainly rely on vector control measures. The present study aimed to investigate the toxicity of locally isolated mosquitocidal Bacillus thuringiensis (Bt) isolates and toxin complexes (TCs) from the two nematode bacterial symbionts Photorhabdus luminescens akhurstii (HRM1) and Photorhabdus luminescens akhurstii (HS1) on Aedes caspius. Out of sixty-eight local Bt isolates, four showed LC50 values ranging from 13.8–15.6 ppm, similar to LC50 recorded against the reference Bacillus thuringiensis israelensis (Bti-H14) (13.0 ppm). Seventeen isolates were more toxic than the Bti-H14 by 1.3–11.1 fold (LC50 values 1.17–9.9 ppm vs 13.0 ppm). Two isolates were less toxic than Bti-H14, showing LC50 values of 39.4 and 24.1 ppm, respectively. Additionally, the TCs from HRM1 and HS1 showed promising larvicidal toxicity, with HS1 being 2.74 fold more toxic than HRM1. Larval morphological features and body size were altered upon HS1 toxin-treatment. This study suggests that there is a new effective local Bt strain, and TCs toxin complexes could be used as eco-friendly biocontrol agents that might contribute to controlling mosquito-borne diseases. The synergistic effect of the Bt-TCs combination on mosquito larvae should be further investigated.

Disregarding reservoirs of disease vectors: A surveillance paradox in Africa.

Disregarding reservoirs of disease vectors: A surveillance paradox in Africa.

Risk assessment for the Rift Valley fever occurrence in China: Special concern in south-west border areas.

Rift Valley fever (RVF) is a mosquito-borne zoonotic disease. Since its first outbreak in 1930, RVF epidemics have caused huge economic losses and public health impacts in Africa. In 2000, RVF became a disease of global concern as it spread to the Arabian Peninsula. In our study, a Geographic Information System-based risk assessment for the occurrence of Rift Valley fever in China was established by means of ecological niche modelling. Based on occurrence records (RVF records from FAO EMPRES-i, vector records from literatures and GBIF) and high-resolution environmental layers, the prediction maps of RVF occurrence probability and distribution of five potential RVF vectors in China were modelled using Maxent. An internal validation was adopted for model verification, and high AUC values were obtained (0.918 for RVF and 0.837-0.992 for vectors). By overlaying the RVF prediction map with the combined RVF vector prediction map using Fuzzy overlay tool ('AND' operator) of ArcMap 10.2, we got the first risk map of possible RVF vector transmission. This map was further overlaid with the latest livestock distribution map ('AND' operator) to generate the second risk map of possible RVF threat to domestic livestock. The south-west border provinces in China, Yunnan, Guangxi and Tibet were predicted to have a high possibility of RVF occurrence. Conditions conducive to the local amplification of RVF also exist in these areas. Temperature seasonality, mean temperature of dry season and precipitation of the driest month were considered as key environmental variables for RVF, and common environmental conditions were found conductive for vectors. It is suggested to establish proper surveillance systems in south-west border areas to minimize the possibility of RVF invasion. Our findings can serve as a valuable reference for prevention measures to be implemented.

Larvicidal and Repellent Activities of Cestrum nocturnum (leaves) Extracts against the Mosquito Vector, Culex antennatus Becker (Diptera: Culicidae)

The present study investigated the larvicidal and repellent activities of Cestrum nocturnum (leaves) different extracts against Rift Valley Fever vector, Culex antennatus. The obtained results showed that the petroleum ether extract was the most effective extract against Cx. antennatus larvae followed by chloroform, acetone, and ethanolic extracts. The LC50 values of petroleum ether extract recorded 179.4, 164.2, and 148.7 ppm against Cx. antennatus third larval instar after 24, 48, and 72 h., respectively. On the other hand, at 6.67, 3.33, and 1.67 mg/cm2, ethanolic extract induced a degree of repellency equal to 93.1, 90.1, and 60.2% within the 4h post-treatment, respectively. Generally, petroleum ether extract proved high efficacy as repellents. At 3.33mg/cm2 petroleum ether extract produced the highest protection (100.0%) during the entire testing period of 4h post-treatment. Moreover, the protection (93.3, 90.7 and 80.8%) obtained at 2.67, 1.67 and 0.833 mg/cm2, respectively, compared with 100.0% repellency for DEET at a dose1.8 mg/cm2. So, Ce. nocturnum tested extracts can be considered as new promising controlling agents against the mosquito vector, Cx. antennatus.

Larval species diversity, seasonal occurrence and larval habitat preference of mosquitoes transmitting Rift Valley fever and malaria in Baringo County, Kenya

BackgroundBaseline information that is essential for determining the areas to target with larval control includes estimates of vector diversity and larval habitat preferences. Due to a lack of such information in Baringo County, Kenya, this study assessed species diversity and larval habitat preference of potential mosquito vectors of Rift Valley fever (RVF) and malaria.MethodsMosquito larvae were sampled from nine types of larval habitats and were identified morphologically. Species diversity was estimated by the Shannon’s diversity index while larval habitat preference by RVF and malaria vectors was determined by ANOVA.ResultsA total of 7724 immature mosquitoes comprising 17 species belonging to four genera, namely Anopheles, Culex, Aedes and Mansonia, were identified. Among the 17 species, three Anopheles species are responsible for malaria transmission: An. gambiae (s.l.), An. funestus (s.l.) and An. pharoensis. Rift Valley fever vectors included Mansonia spp. and Culex spp. The highest Shannon's diversity index was observed during the cold dry season (H = 2.487) and in the highland zone (H = 2.539) while the lowest diversity was recorded during the long rain season (H = 2.354) and in the riverine zone (H = 2.085). Ditches had the highest mean number of Anopheles larvae (16.6 larvae per sample) followed by swamp (12.4) and seasonal riverbed (10.7). Water pit and water pan had low mean numbers of Anopheles larvae (1.4 and 1.8, respectively) but relatively high mean numbers of culicines (16.9 and 13.7, respectively). Concrete tank was the least sampled type of habitat but had highest mean number of culicine larvae (333.7 l) followed distantly by water spring (38.9) and swamp (23.5). Overall, larval habitats were significantly different in terms of larval density (F(8,334) = 2.090, P = 0.036).ConclusionsTo our knowledge, the present study reports culicine larval species diversity in Baringo for the first time and the most preferred habitats were concrete tanks, water springs and swamps. Habitats preferred by Anopheles were mainly riverbed pools, ditches and swamps. Environmental management targeting the habitats most preferred by potential vectors can be part of integrated vector control in Baringo, especially during dry seasons.

Host species and site of collection shape the microbiota of Rift Valley fever vectors in Kenya.

The composition and structure of microbial communities associated with mosquitoes remain poorly understood despite their important role in host biology and potential to be harnessed as novel strategies for mosquito-borne disease control. We employed MiSeq sequencing of the 16S rRNA gene amplicons to characterize the bacterial flora of field-collected populations of Aedes mcintoshi and Aedes ochraceus, the primary vectors of Rift Valley fever (RVF) virus in Kenya. Proteobacteria (53.5%), Firmicutes (22.0%) and Actinobacteria (10.0%) were the most abundant bacterial phyla accounting for 85.5% of the total sequences. Non-metric multi-dimensional scaling plots based on Bray-Curtis dissimilarities revealed a clear grouping of the samples by mosquito species, indicating that the two mosquito species harbored distinct microbial communities. Microbial diversity, richness and composition was strongly influenced by the site of mosquito collection and overall, Ae. ochraceus had significantly higher microbial diversity and richness than Ae. mcintoshi. Our findings suggest that host species and site of collection are important determinants of bacterial community composition and diversity in RVF virus vectors and these differences likely contribute to the spatio-temporal transmission dynamics of RVF virus.

Spatial Modeling of Mosquito Vectors for Rift Valley Fever Virus in Northern Senegal: Integrating Satellite-Derived Meteorological Estimates in Population Dynamics Models

Mosquitoes are vectors of major pathogen agents worldwide. Population dynamics models are useful tools to understand and predict mosquito abundances in space and time. To be used as forecasting tools over large areas, such models could benefit from integrating remote sensing data that describe the meteorological and environmental conditions driving mosquito population dynamics. The main objective of this study is to assess a process-based modeling framework for mosquito population dynamics using satellite-derived meteorological estimates as input variables. A generic weather-driven model of mosquito population dynamics was applied to Rift Valley fever vector species in northern Senegal, with rainfall, temperature, and humidity as inputs. The model outputs using meteorological data from ground weather station vs satellite-based estimates are compared, using longitudinal mosquito trapping data for validation at local scale in three different ecosystems. Model predictions were consistent with field entomological data on adult abundance, with a better fit between predicted and observed abundances for the Sahelian Ferlo ecosystem, and for the models using in-situ weather data as input. Based on satellite-derived rainfall and temperature data, dynamic maps of three potential Rift Valley fever vector species were then produced at regional scale on a weekly basis. When direct weather measurements are sparse, these resulting maps should be used to support policy-makers in optimizing surveillance and control interventions of Rift Valley fever in Senegal.

Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania

Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania

Bionomik Mansonia uniformis dan Mansonia dives sebagai Vektor Filariasis pada Beberapa Wilayah di Kalimantan

Mansonia mosquitoes spread across the globe and several species as a vector. Ma. uniformis were known a vectors of Rift Valley Fever (RVF) and filariasis, while Ma. dives is vector of filariasis. This research aims to behavior of Ma. uniformis and Ma. dives in the form habits of blood sucking activity, resting behaviour and fluctuations density in several areas of Borneo. Natural population of Ma. uniformis and Ma. dives were collected by human landing collection and resting collection from 18:00 to 06:00 outdoor and indoor. The results showed bite activities. Ma. uniformis and Ma. dives in all areas of research are exophagic, while the rest conduct Ma. uniformis in the village Dadahup, Pulau Ku’u and Bangkal Ulu is indoor resting, while in Mandomai is outdoor resting. Behavior breaks Ma. dives in the area a lot more research that is indoor resting namely Mandomai and Bangkal Ulu Village, while the Dadahup village is exophilic. Highest fluctuations activity suck blood and rest on Ma. Uniformis in and out the house generally at 19.00 - 22.00, while at Ma. dives at 23.00 - 01.00. The behavior of mosquitoes is a difference, so the controlling method is also different.

Distribution and abundance of key vectors of Rift Valley fever and other arboviruses in two ecologically distinct counties in Kenya.

BackgroundRift Valley fever (RVF) is a mosquito-borne viral zoonosis of ruminants and humans that causes outbreaks in Africa and the Arabian Peninsula with significant public health and economic consequences. Humans become infected through mosquito bites and contact with infected livestock. The virus is maintained between outbreaks through vertically infected eggs of the primary vectors of Aedes species which emerge following rains with extensive flooding. Infected female mosquitoes initiate transmission among nearby animals, which amplifies virus, thereby infecting more mosquitoes and moving the virus beyond the initial point of emergence. With each successive outbreak, RVF has been found to expand its geographic distribution to new areas, possibly driven by available vectors. The aim of the present study was to determine if RVF virus (RVFV) transmission risk in two different ecological zones in Kenya could be assessed by looking at the species composition, abundance and distribution of key primary and secondary vector species and the level of virus activity.MethodologyMosquitoes were trapped during short and long rainy seasons in 2014 and 2015 using CO2 baited CDC light traps in two counties which differ in RVF epidemic risk levels(high risk Tana-River and low risk Isiolo),cryo-preserved in liquid nitrogen, transported to the laboratory, and identified to species. Mosquito pools were analyzed for virus infection using cell culture screening and molecular analysis.FindingsOver 69,000 mosquitoes were sampled and identified as 40 different species belonging to 6 genera (Aedes, Anopheles, Mansonia, Culex, Aedeomyia, Coquillettidia). The presence and abundance of Aedes mcintoshi and Aedes ochraceus, the primary mosquito vectors associated with RVFV transmission in outbreaks, varied significantly between Tana-River and Isiolo. Ae. mcintoshi was abundant in Tana-River and Isiolo but notably, Aedes ochraceus found in relatively high numbers in Tana-River (n = 1,290), was totally absent in all Isiolo sites. Fourteen virus isolates including Sindbis, Bunyamwera, and West Nile fever viruses were isolated mostly from Ae. mcintoshi sampled in Tana-River. RVFV was not detected in any of the mosquitoes.ConclusionThis study presents the geographic distribution and abundance of arbovirus vectors in two Kenyan counties, which may assist with risk assessment for mosquito borne diseases.

Rift Valley fever vector diversity and impact of meteorological and environmental factors on Culex pipiens dynamics in the Okavango Delta, Botswana.

BackgroundIn Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes cohabitate around permanent waters of the Okavango Delta. As in other regions of sub-Saharan Africa, Rift Valley Fever (RVF) virus is known to circulate in that area among wild and domestic animals. However, the diversity and composition of potential RVF mosquito vectors in that area are unknown as well as the climatic and ecological drivers susceptible to affect their population dynamics.MethodsUsing net traps baited with carbon dioxide, monthly mosquito catches were implemented over four sites surrounding cattle corrals at the northwestern border of the Okavango Delta between 2011 and 2012. The collected mosquito species were identified and analysed for the presence of RVF virus by molecular methods. In addition, a mechanistic model was developed to assess the qualitative influence of meteorological and environmental factors such as temperature, rainfall and flooding levels, on the population dynamics of the most abundant species detected (Culex pipiens).ResultsMore than 25,000 mosquitoes from 32 different species were captured with an overabundance of Cx. pipiens (69,39 %), followed by Mansonia uniformis (20,67 %) and a very low detection of Aedes spp. (0.51 %). No RVF virus was detected in our mosquito pooled samples. The model fitted well the Cx. pipiens catching results (ρ = 0.94, P = 0.017). The spatial distribution of its abundance was well represented when using local rainfall and flooding measures (ρ = 1, P = 0.083). The global population dynamics were mainly influenced by temperature, but both rainfall and flooding presented a significant influence. The best and worst suitable periods for mosquito abundance were around March to May and June to October, respectively.ConclusionsOur study provides the first available data on the presence of potential RVF vectors that could contribute to the maintenance and dissemination of RVF virus in the Okavango Delta. Our model allowed us to understand the dynamics of Cx. pipiens, the most abundant vector identified in this area. Potential predictions of peaks in abundance of this vector could allow the identification of the most suitable periods for disease occurrence and provide recommendations for vectorial and disease surveillance and control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1712-1) contains supplementary material, which is available to authorized users.

Plant resting site preferences and parity rates among the vectors of Rift Valley Fever in northeastern Kenya.

BackgroundMosquito lifespan can influence the circulation of disease causing pathogens because it affects the time available for infection and transmission. The life-cycle of mosquitoes is determined by intrinsic and environmental factors, which can include the availability of hosts and suitable resting environments that shelter mosquitoes from extreme temperature and desiccating conditions. This study determined the parity rates (an indirect measure of survival) and plant resting preference of vectors of Rift Valley fever (RVF) in northeastern Kenya.MethodsResting mosquitoes were trapped during the rainy and the dry season using a Prokopack aspirator from vegetation, whereas general adult populations were trapped using CDC light traps. At each site, sampling was conducted within a 1 km2 area, subdivided into 500 × 500 m quadrants and four 250 × 250 m sub-quadrants from which two were randomly selected as sampling units. In each sampling unit, plants were randomly selected for aspiration of mosquitoes. Only Aedes mcintoshi and Ae. ochraceus were dissected to determine parity rates while all mosquito species were used to assess plant resting preference.ResultsOverall, 1124 (79 %, 95 % CI = 76.8–81.1 %) mosquitoes were parous. There was no significant difference in the number of parous Ae. mcintoshi and Ae. ochraceus. Parity was higher in the rainy season than in the dry season. Daily survival rate was estimated to be 0.93 and 0.92 among Ae. ochraceus and Ae. mcintoshi, respectively. Duosperma kilimandscharicum was the most preferred plant species with the highest average capture of primary (3.64) and secondary (5.83) vectors per plant, while Gisekia africana was least preferred.ConclusionSurvival rate of each of the two primary vectors of RVF reported in this study may provide an indication that these mosquitoes can potentially play important roles in the circulation of diseases in northern Kenya. Resting preference of the mosquitoes in vegetation may influence their physiology and enhance longevity. Thus, areas with such vegetation may be associated with an increased risk of transmission of arboviruses to livestock and humans.

Mosquito host choices on livestock amplifiers of Rift Valley fever virus in Kenya.

BackgroundAnimal hosts may vary in their attraction and acceptability as components of the host location process for assessing preference, and biting rates of vectors and risk of exposure to pathogens. However, these parameters remain poorly understood for mosquito vectors of the Rift Valley fever (RVF), an arboviral disease, and for a community of mosquitoes.MethodsUsing three known livestock amplifiers of RVF virus including sheep, goat and cattle as bait in enclosure traps, we investigated the host-feeding patterns for a community of mosquitoes in Naivasha, an endemic area of Rift Valley fever (RVF), in a longitudinal study for six months (June–November 2015). We estimated the incidence rate ratios (IRR) where mosquitoes chose cow over the other livestock hosts by comparing their attraction (total number collected) and engorgement rate (proportion freshly blood-fed) on these hosts.ResultsOverall, significant differences were observed in host preference parameters for attraction (F2,15 = 4.1314, P = 0.037) and engorgement (F2,15 = 6.24, P = 0.01) with cow consistently attracting about 3-fold as many mosquitoes as those engorged on sheep (attraction: IRR = 2.9, 95 % CI 1.24–7.96; engorgement: IRR = 3.2, 95 % CI = 1.38–7.38) or goat (attraction: IRR = 2.7, 95 % CI 1.18–7.16; engorgement: IRR = 3.28, 95 % CI 1.47–7.53). However, there was no difference between the attraction elicited by sheep and goat (IRR = 1.08; 95 % CI 0.35–3.33 or engorgement rate (IRR = 0.96, 95 % CI 0.36–2.57).ConclusionDespite the overall attractive pattern to feed preferentially on cows, the engorgement rate was clearly independent of the number attracted for certain mosquito species, notably among the flood water Aedes spp., largely incriminated previously as primary vectors of RVF. Our findings suggest that insecticide treated cattle (ITC) can be exploited in enclosure traps as contact bait in the monitoring and control of disease-causing mosquitoes in RVF endemic areas.

Modelling hotspots of the two dominant Rift Valley fever vectors (Aedes vexans and Culex poicilipes) in Barkédji, Sénégal.

BackgroundClimatic and environmental variables were used successfully by using models to predict Rift Valley fever (RVF) virus outbreaks in East Africa. However, these models are not replicable in the West African context due to a likely difference of the dynamic of the virus emergence. For these reasons specific models mainly oriented to the risk mapping have been developed. Hence, the areas of high vector pressure or virus activity are commonly predicted. However, the factors impacting their occurrence are poorly investigated and still unknown. In this study, we examine the impact of climate and environmental factors on the likelihood of occurrence of the two main vectors of RVF in West Africa (Aedes vexans and Culex poicilipes) hotspots.MethodsWe used generalized linear mixed models taking into account spatial autocorrelation, in order to overcome the default threshold for areas with high mosquito abundance identified by these models. Getis’ Gi*(d) index was used to define local adult mosquito abundance clusters (hotspot).ResultsFor Culex poicilipes, a decrease of the minimum temperature promotes the occurrence of hotspots, whereas, for Aedes vexans, the likelihood of hotspot occurrence is negatively correlated with relative humidity, maximum and minimum temperatures. However, for the two vectors, proximity to ponds would increase the risk of being in an hotspot area.ConclusionsThese results may be useful in the improvement of RVF monitoring and vector control management in the Barkedji area.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1399-3) contains supplementary material, which is available to authorized users.

Linalool oxide: generalist plant based lure for mosquito disease vectors.

BackgroundLack of effective vaccines and therapeutics for important arboviral diseases such as Rift Valley fever (RVF) and dengue, necessitates continuous monitoring of vector populations for infections in them. Plant-based lures as surveillance tools has the potential of targeting mosquitoes of both sexes and females of varied physiological states; yet such lures are lacking for vectors of these diseases. Here, we present evidence of the effectiveness of linalool oxide (LO), a single plant-based lure previously developed for malaria vectors in trapping RVF vectors, Aedes mcintoshi and Aedes ochraceus, and dengue vector, Aedes aegypti.MethodsFor RVF vectors, we used CDC traps to evaluate the performance of LO against three vertebrate-based lures: CO2 (dry ice), BioGent (BG) lure, and HONAD (a blend of aldehydes) in 2 experiments with Completely Randomized design: 1) using unlit CDC traps baited separately with LO, HONAD and BG-lure, and unlit CDC trap + CO2 and lit CDC trap as controls, 2) similar treatments but with inclusion of CO2 to all the traps. For dengue vectors, LO was evaluated against BG lure using BG sentinel traps, in a 3 × 6 Latin Square design, first as single lures and then combined with CO2 and traps baited with CO2 included as controls. Trap captures were compared between the treatments using Chi square and GLM.ResultsLow captures of RVF vectors were recorded for all lures in the absence of CO2 with no significant difference between them. When combined with CO2, LO performance in trapping these vectors was comparable to BG-lure and HONAD but it was less effective than the lit CDC trap. In the absence of CO2, LO performed comparably with the BG-lure in trapping female Ae. aegypti, but with significantly higher males recorded in traps baited with the plant-based lure. When CO2 was added, LO was significantly better than the BG-lure with a 2.8- fold increase in captures of male Ae. aegypti.ConclusionsThese results highlight the potential of LO as a generalist plant-based lure for mosquito disease vectors, pending further assessment of possible specificity in their response profile to the different stereoisomers of this compound.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1184-8) contains supplementary material, which is available to authorized users.

A Stochastic Model to Study Rift Valley Fever Persistence with Different Seasonal Patterns of Vector Abundance: New Insights on the Endemicity in the Tropical Island of Mayotte.

Rift Valley fever (RVF) is a zoonotic vector-borne disease causing abortion storms in cattle and human epidemics in Africa. Our aim was to evaluate RVF persistence in a seasonal and isolated population and to apply it to Mayotte Island (Indian Ocean), where the virus was still silently circulating four years after its last known introduction in 2007. We proposed a stochastic model to estimate RVF persistence over several years and under four seasonal patterns of vector abundance. Firstly, the model predicted a wide range of virus spread patterns, from obligate persistence in a constant or tropical environment (without needing vertical transmission or reintroduction) to frequent extinctions in a drier climate. We then identified for each scenario of seasonality the parameters that most influenced prediction variations. Persistence was sensitive to vector lifespan and biting rate in a tropical climate, and to host viraemia duration and vector lifespan in a drier climate. The first epizootic peak was primarily sensitive to viraemia duration and thus likely to be controlled by vaccination, whereas subsequent peaks were sensitive to vector lifespan and biting rate in a tropical climate, and to host birth rate and viraemia duration in arid climates. Finally, we parameterized the model according to Mayotte known environment. Mosquito captures estimated the abundance of eight potential RVF vectors. Review of RVF competence studies on these species allowed adjusting transmission probabilities per bite. Ruminant serological data since 2004 and three new cross-sectional seroprevalence studies are presented. Transmission rates had to be divided by more than five to best fit observed data. Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission. Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions.