Potential West Nile Virus Vectors Research Articles

First record of West Nile Virus detection inside wild mosquitoes in Khartoum capital of Sudan using PCR.

This study aimed to explore the presence of West Nile Virus (WNV) inside four species of mosquitoes: Culex univittatus (Theobald), Culex quinquefasciatus (Say) Aedes vittatus (Bigot) and Aedes vexans (Meigen). Adult wild mosquitoes were collected from different sites: Soba West, Hellat Kuku, Shambat, and Khartoum North Central Live Stock Market (KCLM). Surveys were carried out at Khartoum State during two phases: pre to the rainy season and post to the rainy season. Mosquito specimens were identified using classical keys then preserved at −80 °C freezer for two weeks till the virus examination using polymerase chain reaction (PCR) were carried out. WNV has been detected inside the three species of mosquitoes: A. vexans, C. univittatus, and C. quinquefasciatus. The species were collected from Hellat Kuku, (Shambat and Hellat Kuku), and (Shambat and KCLM) respectively. Two species of mosquitoes were positive for the virus: C. quinquefasciatus and C. univittatus. Positive results for the virus during the first phase of the study; males of C. quinquefasciatus and C. univittatus collected during the second phase of the study were also tested for the existence of the virus and they were positive. For our knowledge this study represents first record of WNV inside wild mosquitoes in Sudan. PCR technique provided reliable information because specific primer-probe sets were used for the detection of the virus. Extra studies are required to incriminate these species of mosquitoes as potential vectors of WNV.

Pilot longitudinal mosquito surveillance study in the Danube Delta Biosphere Reserve and the first reports of Anopheles algeriensis Theobald, 1903 and Aedes hungaricus Mihályi, 1955 for Romania.

BackgroundMosquito-borne viruses (moboviruses) are of growing importance in many countries of Europe. In Romania and especially in the Danube Delta Biosphere Reserve (DDBR), mosquito and mobovirus surveillance are not performed on a regular basis. However, this type of study is crucially needed to evaluate the risk of pathogen transmission, to understand the ecology of emerging moboviruses, or to plan vector control programmes.MethodsWe initiated a longitudinal mosquito surveillance study with carbon dioxide-baited Heavy Duty Encephalitis Vector Survey traps at four sampling sites to analyse the spatio-temporal pattern of the (i) mosquito species composition and diversity, (ii) functional groups of mosquitoes (oviposition sites, overwintering stage, and number of generations), and (iii) the occurrence of potential West Nile virus (WNV) vectors.ResultsDuring 2014, a total of 240,546 female mosquitoes were collected. All species were identified using morphological characteristics and further confirmed by mitochondrial cytochrome c oxidase subunit I (COI) gene analysis of selected specimens. The two most common taxa were Coquilettidia richiardii (40.9 %) and Anopheles hyrcanus (34.1 %), followed by Culex pipiens (sensu lato) (s.l.)/Cx. torrentium (7.7 %), Aedes caspius (5.7 %), Cx. modestus (4.0 %), An. maculipennis (s.l.) (3.9 %), and Ae. vexans (3.0 %). A further seven species were less common in the area studied, including two new records for Romania: An. algeriensis and Ae. hungaricus. Phylogenetic analysis of COI gene demonstrated the evolutionary relatedness of most species with specimens of the same species collected in other European regions, except Ae. detritus and An. algeriensis, which exhibited high genetic diversity. Due to the dominance of Cq. richiardii and An. hyrcanus (75 % of all collected specimens), the overall phenology and temporal pattern of functional groups basically followed the phenology of both species. A huge proportion of the mosquito population in the course of the entire sampling period can be classified as potential WNV vectors. With 40 % of all collected specimens, the most frequent species Cq. richiardii is probably the most important vector of WNV in the DDBR.ConclusionThis is the first DNA-barcoding supported analysis of the mosquito fauna in the DDBR. The detection of two new species highlights the lack of knowledge about the mosquito fauna in Romania and in the DDBR in particular. The results provide detailed insights into the spatial-temporal mosquito species composition, which might lead to a better understanding of mobovirus activity in Romania and thus, can be used for the development of vector control programs.

Review of West Nile virus circulation and outbreak risk in Madagascar: Entomological and ornithological perspectives.

West Nile fever (WNF) is a zoonotic disease, occurring nearly globally. In Madagascar, West Nile virus (WNV) was first detected in 1978 from wild birds and the virus is currently distributed across the island, but no epidemic or epizootic period has been recorded. One fatal human case of WNV infection was reported in 2011, suggesting a “tip of the iceberg” phenomenon of a possible WNF epidemic/epizootic on the island. The main objective of this literature-based survey is to review patterns of WNV circulation in Madagascar from the entomological and ornithological points of view. Among the 235 mosquito species described from Madagascar, 29 species are widely associated with WNV infection; 16 of them are found naturally infected with WNV on the island and categorized into major, candidate, and potential vectors of WNV according to their vector capacity. This study upholds the hypothesis that WNV enzooticity is independent of annual movements of migratory birds passing through Madagascar. Moreover, the lack of regular migratory bird flux between Africa and Madagascar would reduce the probability of transmission and the subsequent reintroduction of the virus into locally occurring mosquito species. Given that Palearctic migratory birds are strongly implicated in the transmission of WNV, we highlight notable differences in the movements and species diversity of these birds in Madagascar as compared to eastern and northern Africa. Risk factors from this two-pronged approach are presented for the emergence of WNF outbreak.

Abundance and Diversity of Mosquito Species Collected From a Rural Area of Central Mississippi: Implications for West Nile Virus Transmission in Mississippi.

To determine abundance and seasonality of potential West Nile virus (WNV) mosquito vectors in a forested area of central Mississippi, mosquitoes were collected weekly from a wildlife management area located approximately 10 mi from a local urban area known to have numerous human WNV cases. We were particularly interested in the presence or absence of Culex quinquefasciatus, the primary vector of WNV in Mississippi, although other Culex species were assayed. Two Centers for Disease Control and Prevention light traps baited with CO2 were set once a week from 2005 through 2006 in the Pearl River Wildlife Management Area (PRWMA), which consists of 6,925 acres primarily composed of bottomland hardwood forest with wetland areas. Traps were placed midafternoon and picked up the following morning. A total of 199,222 mosquitoes were collected during the 2-year study. No Cx. quinquefasciatus were collected throughout the entire study, although other health department surveys have indicated they are abundant just a few miles away. As for other potential WNV vectors, 1,325 (0.6%) Cx. nigripalpus, 1,804 (0.9%) Cx. restuans, and 6,076 (3.1%) Cx. salinarius were collected in the PRWMA over the 2-year period. These data suggest that Cx. quinquefasciatus is not usually found in remote forested environments, but is more associated with human habitation.

Variation in adult longevity of Culex pipiens f. pipiens, vector of the West Nile Virus.

The common house mosquito, Culex pipiens (Diptera: Culicidae), which is considered the primary bridge vector of West Nile Virus (WNV) to humans, is a wide spread insect pest with medical importance and consists of two distinct bioforms, Cx. pipiens f. pipiens and Cx. pipiens f. molestus. Here, we consider the adult lifespan of male and female Cx. pipiens f. pipiens under controlled conditions at five constant temperature regimes (15, 20, 25, 27.5, and 30 °C). Our results show that adult longevity was affected by temperature, as it significantly decreased with increase in temperature. At the highest tested temperature, mean adult longevity did not exceed 12 days for both sexes and thus makes impossible the risk of WNV transmission. On the other hand at the lowest temperature, longevity was extremely high with some individuals surviving up to 129 and 132 days, males and females, respectively, and thus enable them to function as potential vectors of WNV for a prolonged period of time. As far as sex is concerned, adult females displayed a 1.2-1.4-fold longer longevity compared to the male ones. However, this difference was significant only at the lowest and highest tested temperature regime. This information is useful in determining the critical temperatures which may affect the distribution of Cx. pipiens and consequently the risk of WNV transmission. Moreover, the effect of environmental temperature should be considered when evaluating the abundance of these species.

Infection and dissemination of West Nile virus in China by the potential vector, Culex pipiens pallens.

The distribution of the West Nile virus (WNV) in the organs and tissues of the mosquito Culex pipiens pallens, a potential vector of WNV in China, was investigated up to 14 days after oral infection. The WNV antigen was detected in paraffin-embedded mosquitoes using immunocytochemistry and viral titers of post-infected mosquitoes determined by plaque assay. Viral titers sharply decreased 24 h post-infection, were undetectable for the first few days, then rose over the course of infection. The first midgut infection appeared after one day, and the overall infection rate (based on midgut infection) was 43.9%. Other tissues, including hindgut, foregut, ovarian follicles, Malpighian tubules, and ommatidia, showed weak WNV antigens as early as three days post-infection. Staining in the salivary glands first appeared after seven days, and the salivary gland infection rate on the 14th day was 37.5%. Specimens with no detectable WNV antigens in any tissues, and with positive results confined to the midgut, anterior midgut, and hindgut, were observed on the 14th day. The route of viral dissemination from the midgut, and the relative importance of amplifying tissues in mosquitoes' susceptibility to infection, were evaluated. The results indicate that Cx. p. pallens has the ability to harbor WNV throughout its alimentary system and that midgut epithelial cells may be the initial site of the replication of this virus in this species.

West Nile virus epidemiology and factors triggering change in its distribution in Europe

West Nile virus (WNV) has historically been considered among the least virulent members of the Japanese serogroup complex (family Flaviviridae, genus Flavivirus). The WNV natural cycle involves birds as the main amplifying hosts and several species of mosquito as vectors. Many outbreaks occurred during the past decade, causing severe human encephalitis in the Old World, and the virus has become established in many European countries. Emergence of WNV is difficult to predict and even more difficult to prevent. In this review, the latest information on the epidemiology, transmission dynamics and clinical aspects of WNV is presented, with particular focus on specific factors likely to trigger changes in the distribution of the disease in Europe, such as climate changes and their consequences on the potential vectors of WNV or bird migration routes. The control of some anthropogenic and environmental factors could help prevent extension and re-emergence of WNV epidemics.

Feeding Patterns of Potential West Nile Virus Vectors in South-West Spain

BackgroundMosquito feeding behaviour determines the degree of vector–host contact and may have a serious impact on the risk of West Nile virus (WNV) epidemics. Feeding behaviour also interacts with other biotic and abiotic factors that affect virus amplification and transmission.Methodology/Principal FindingsWe identified the origin of blood meals in five mosquito species from three different wetlands in SW Spain. All mosquito species analysed fed with different frequencies on birds, mammals and reptiles. Both ‘mosquito species’ and ‘locality’ explained a similar amount of variance in the occurrence of avian blood meals. However, ‘season of year’ was the main factor explaining the presence of human blood meals. The differences in diet resulted in a marked spatial heterogeneity in the estimated WNV transmission risk. Culex perexiguus, Cx. modestus and Cx. pipiens were the main mosquito species involved in WNV enzootic circulation since they feed mainly on birds, were abundant in a number of localities and had high vector competence. Cx. perexiguus may also be important for WNV transmission to horses, as are Cx. pipiens and Cx. theileri in transmission to humans. Estimates of the WNV transmission risk based on mosquito diet, abundance and vector competence matched the results of previous WNV monitoring programs in the area. Our sensitivity analyses suggested that mosquito diet, followed by mosquito abundance and vector competence, are all relevant factors in understanding virus amplification and transmission risk in the studied wild ecosystems. At some of the studied localities, the risk of enzootic circulation of WNV was relatively high, even if the risk of transmission to humans and horses was less.Conclusions/SignificanceOur results describe for first time the role of five WNV candidate vectors in SW Spain. Interspecific and local differences in mosquito diet composition has an important effect on the potential transmission risk of WNV to birds, horses and humans.

New distribution information for Coquillettidia perturbans (Walker) (Diptera, Culicidae) in northern British Columbia, Canada

The detection of West Nile virus (WNV) in North America in 1999 (Jia et al. 1999) prompted an increased interest in the biology of mosquito species throughout Canada, including the province of British Columbia. Increased funding for research was further fueled by the presence of WNV in neighboring provinces and states. Recent surveys of mosquito diversity have been carried out primarily to determine the geographic distributions of potential WNV vectors and, therefore, to help estimate the risk of WNV infection in human and other populations in various regions of the province (Stephen et al. 2006). While WNV has been the arbovirus emphasized in recent years, improved understanding of mosquito distributions and biology may prove invaluable if other pathogens become threats in the future. In BC, prior to 2003, surveys of mosquito species had been largely restricted to the southern half of the province (Hearle 1927, Belton and Belton 1981). Early results from surveys conducted by the British Columbia Centre for Disease Control (BCCDC) suggested that the estimated geographic ranges for several species in BC were in need of revision. In particular, Coquillettidia (=Mansonia) perturbans, has been described by most authors as having a southerly distribution (Hearle 1927, Wood et al. 1979, Belton and Belton 1981, Belton 1983). This species was trapped as far north as Prince George (53.9°N, 122.8°W) in 2004 (BCCDC 2005). The larvae attach their siphons to the roots of wetland plants, such as cattails (Typha latifolia L.) and obtain oxygen from the root aerenchyma; this habit makes the larvae difficult to catch, monitor or manage (Belton 1983). The cattail marsh habitat type is common throughout British Columbia, especially at low elevations in areas with warm summers (Mackenzie and Moran 2004), suggesting that Cq. perturbans may be far more widely distributed than previously thought. In 2005, 2007, and 2010, surveys were conducted in northern British Columbia (Figure 1) with CDC (Center for Disease Control) miniature light traps fitted with incandescent light bulbs and using dry ice as a source of carbon dioxide for the primary attractant. Traps were placed

Nationwide Surveillance of West Nile Virus Targeting Mosquitoes and Dead Birds from April 2004 through March 2007 in Japan

We conducted nationwide West Nile virus (WNV) surveillance targeting mosquitoes and dead birds to reveal whether the virus and its potential vectors are present in Japan. A total of 12 766 mosquitoes and 230 dead birds were collected in April 2004-March 2005 (the 2004-2005 period), 10 755 mosquitoes and 267 dead birds in April 2005-March 2006 (the 2005-2006 period), and 8624 mosquitoes and 245 dead birds in April 2006-March 2007 (the 2006-2007 period). The species of most of the mosquitoes collected over the 3 years were Culex tritaeniorhynchus (47.82%) and Anopheles sinensis (28.49%), and other species included Aedes albopictus (6.75%), the Culex pipiens group (Cx. pipiens pallens and Cx. pipiens molestus: 5.37%), Aedes vexans nipponii (2.54%), Armigeres subalbatus (1.08%), and Aedes japonicus (0.95%). As for the dead birds, most were Passeriformes (456 specimens), which included several crow species, and the other orders included Anseriformes, Columbiformes and Ciconiiformes (78, 66 and 36 specimens, respectively). All the specimens tested negative for WNV RNA by reverse-transcriptase polymerase chain reaction (RT-PCR) in the 2004-2005 period and by real-time RT-PCR in the 2005-2006 and the 2006-2007 periods, respectively. Our surveillance provided no evidence for WNV in Japan as of the end of the surveillance period, but on the other hand, it revealed that several species of potential WNV vectors are distributed widely in Japan, which suggests that WNV in principle could be transmitted by the potential vectors if introduced. Thus, it is essential to take continued precautions against WNV introduction.

Evaluation of Potential West Nile Virus Vectors in Volgograd Region, Russia, 2003 (Diptera: Culicidae): Species Composition, Bloodmeal Host Utilization, and Virus Infection Rates of Mosquitoes

Potential West Nile virus (family Flaviviridae, genus Flavivirus, WNV) vectors were assessed during 2003 at indoor and outdoor collection sites in urban Volgograd, Russia, and in three nearby towns and surrounding rural areas. In total, 9,182 female mosquitoes comprising 13 species in six genera were collected. Relative abundance and bloodmeal host utilization differed temporarily and spatially. During June and July in Volgograd, Aedes vexans (Meigen) (85.4%) and Culex p. pipiens L. (7.6%) were the two most abundant species collected indoors, whereas during August, Cx. p. pipiens was the dominant species, accounting for 87.9% of specimens collected. Two WNV-positive mosquito pools were detected in August: one pool was composed of Cx. p. pipiens and the other pool of Culex modestus Ficalbi. Anopheles messeae Falleroni, Aedes caspius (Pallas), Ae. vexans, Cx. modestus, and Cx. p. pipiens used both humans and birds as bloodmeal sources. In urban areas, 20.4% of the Cx. p. pipiens fed on humans, 58.1% fed on chickens, and six specimens were positive for both chicken and human blood. Culex p. pipiens collected from flooded basements were predominantly autogenous (91.7%), whereas adult females resting in buildings with dry basements were composed of 67.5% anautogenous and 32.5% autogenous specimens. Our data suggest that the primary WNV vectors in the Volgograd region were Cx. p. pipiens and Cx. modestus and that intense transmission of WNV to humans in urban areas during the epidemic of 1999 may have been facilitated by the abundance and concentration of anautogenous Cx. p. pipiens in multistory buildings. The role of autogenous Cx. p. pipiens in urban transmission remains unresolved.

Evaluation of Potential West Nile Virus Vectors in Volgograd Region, Russia, 2003 (Diptera: Culicidae): Species Composition, Bloodmeal Host Utilization, and Virus Infection Rates of Mosquitoes

Evaluation of Potential West Nile Virus Vectors in Volgograd Region, Russia, 2003 (Diptera: Culicidae): Species Composition, Bloodmeal Host Utilization, and Virus Infection Rates of Mosquitoes

Telephonic Survey of Surveillance and Control Procedures for the Mosquito Vectors of West Nile Virus Near Naval Installations in the Eastern United States

Surveillance and control procedures for the mosquito vectors of West Nile virus (WNV) and other arboviruses are described in response plans that vary among states. To ensure that naval installations in the eastern United States follow WNV response plan criteria similar to those of their host states, we conducted a telephone survey of 25 personnel who directed surveillance and control procedures in areas near these installations. For adult mosquito surveillance, 76% of respondents used Centers for Disease Control and Prevention miniature light traps baited with dry ice; 68% of respondents used these and baited Centers for Disease Control and Prevention gravid traps. We report a summary of the mosquito species that were most problematic among states. In the eastern United States, these species have tested positive for WNV and some have been reported as potential vectors of WNV and other arboviruses. Among respondents, numerical thresholds or the presence of WNV-positive mosquito pools facilitated decision-making (i.e., whether to increase surveillance or to initiate control procedures). The presence of mosquito larvae, abiotic variables, and historical databases were also important. Reports of dead birds and human serology data were used by 92% and 64% of respondents, respectively. Adult control was accomplished with synthetic pyrethroids; larvae were controlled with microbial insecticides and growth regulators. Geographic information systems and public awareness/education were used by 60% and 88% of respondents, respectively. We discuss our results in light of response plan variability and implications for the future.

Potential transmission of West Nile virus in the British Isles: an ecological review of candidate mosquito bridge vectors

West Nile virus (WNV) transmitted by mosquitoes (Diptera: Culicidae) infects various vertebrates, being pathogenic for birds, horses and humans. After its discovery in tropical Africa, sporadic outbreaks of WNV occurred during recent decades in Eurasia, but not the British Isles. WNV reached New York in 1999 and spread to California by 2003, causing widespread outbreaks of West Nile encephalitis across North America, transmitted by many species of mosquitoes, mainly Culex spp. The periodic reappearance of WNV in parts of continental Europe (from southern France to Romania) gives rise to concern over the possibility of WNV invading the British Isles. The British Isles have about 30 endemic mosquito species, several with seasonal abundance and other eco-behavioural characteristics predisposing them to serve as potential WNV bridge vectors from birds to humans. These include: the predominantly ornithophilic Culex pipiens L. and its anthropophilic biotype molestus Forskal; tree-hole adapted Anopheles plumbeus Stephens; saltmarsh-adapted Ochlerotatus caspius Pallas, Oc. detritus Haliday and Oc. dorsalis (Meigen); Coquillettidia richiardii Ficalbi, Culiseta annulata Schrank and Cs. morsitans (Theobald) from vegetated freshwater pools; Aedes cinereus Meigen, Oc. cantans Meigen and Oc. punctor Kirby from seasonal woodland pools. Those underlined have been found carrying WNV in other countries (12 species), including the rarer British species Aedes vexans (Meigen), Culex europaeus Ramos et al., Cx. modestus Ficalbi and Oc. sticticus (Meigen) as well as the Anopheles maculipennis Meigen complex (mainly An. atroparvus van Thiel and An. messeae Falleroni in Britain). Those implicated as key vectors of WNV in Europe are printed bold (four species). So far there is no proof of any arbovirus transmission by mosquitoes in the British Isles, although antibodies to Sindbis, Tahyna, Usutu and West Nile viruses have been detected in British birds. Neighbouring European countries have enzootic WNV and human infections transmitted by mosquito species that are present in the British Isles. However, except for localized urban infestations of Cx. pipiens biotype molestus that can be readily eliminated, there appear to be few situations in the British Isles where humans and livestock are exposed to sustained risks of exposure to potential WNV vectors. Monitoring of mosquitoes and arbovirus surveillance are required to guard the British Isles against WNV outbreaks and introduction of more anthropophilic mosquitoes such as Stegomyia albopicta (Skuse) and Ochlerotatus japonicus (Theobald) that have recently invaded Europe, since they transmit arboviruses elsewhere.

Potential vectors of West Nile virus following an equine disease outbreak in Italy.

In the late summer of 1998, an outbreak of equine encephalomyelitis due to West Nile virus (WNV) occurred in the Tuscany region of central Italy. The disease was detected in 14 race horses from nine localities in four Provinces: Firenze, Lucca, Pisa and Pistoia. The outbreak area included Fucecchio wetlands (1800 ha), the largest inland marsh in Italy, and the adjacent hilly Cerbaie woodlands with farms breeding horses. To detect potential vectors of WNV, entomological surveys of Fucecchio and Cerbaie were undertaken during 1999-2002 by collecting mosquito larvae from breeding sites and adult mosquitoes by several methods of sampling. Among 6023 mosquitoes (Diptera: Culicidae) collected, 11 species were identified: Aedes albopictus (Skuse), Ae. vexans (Meigen), Anopheles atroparvus Van Thiel, An. maculipennis Meigen s.s., An. plumbeus Stephens, Culex impudicus Ficalbi, Cx. pipiens L., Culiseta longiareolata Macquart), Ochlerotatus caspius (Pallas), Oc. detritus (Haliday) and Oc. geniculatus (Olivier). In Fucecchio marshes, Cx. impudicus predominated with seasonal peak densities in spring and autumn: its greatest abundance during early spring coincides with arrival of migratory birds from Africa. In Cerbaie hills, Cx. pipiens predominated with peak population density in late summer. No viruses were isolated from 665 mosquitoes processed. These findings, plus other data on Italian mosquito bionomics, suggest a possible mode of WNV transmission involving the most abundant Culex in the Fucecchio-Cerbaie areas. Culex impudicus, being partly ornithophilic, might transmit WNV from migratory to non-migratory birds during springtime; Cx. pipiens, having a broader host range, would be more likely to transmit WNV from birds to horses and, perhaps, to humans by late summer.

Scientific Note Culex quinquefasciatus (Diptera: Culicidae) as a potential West Nile virus vector in Tucson, Arizona: Blood meal analysis indicates feeding on both humans and birds

Most reports from the United States suggest Culex quinquefasciatus mosquitoes feed minimally on humans. Given the abundance of C. quinquefasciatus in residential Tucson and parts of metropolitan Phoenix, and the arrival of West Nile virus to this area, discovering the blood meal hosts of the local population is important. Using a sandwich ELISA technique, the local C. quinquefasciatus were found to feed on both humans and birds. This suggests they should be considered potential West Nile virus vectors.