A multi-year study of mosquito feeding patterns on avian hosts in a southeastern focus of eastern equine encephalitis virus

Emerging and Novel Viruses in Passerine Birds

There is growing interest in emerging viruses that can cause serious or lethal disease in humans and animals. The proliferation of cloacal virome studies, mainly focused on poultry and other domestic birds, reveals a wide variety of viruses, although their pathogenic significance is currently uncertain. Analysis of viruses detected in wild birds is complex and often biased towards waterfowl because of the obvious interest in avian influenza or other zoonotic viruses. Less is known about the viruses present in the order Passeriformes, which comprises approximately 60% of extant bird species. This review aims to compile the most significant contributions on the DNA/RNA viruses affecting passerines, from traditional and metagenomic studies. It highlights that most passerine species have never been sampled. Especially the RNA viruses from Flaviviridae, Orthomyxoviridae and Togaviridae are considered emerging because of increased incidence or avian mortality/morbidity, spread to new geographical areas or hosts and their zoonotic risk. Arguably poxvirus, and perhaps other virus groups, could also be considered "emerging viruses". However, many of these viruses have only recently been described in passerines using metagenomics and their role in the ecosystem is unknown. Finally, it is noteworthy that only one third of the viruses affecting passerines have been officially recognized.

Spatiotemporal Environmental Drivers of Eastern Equine Encephalitis Virus in Central Florida: Towards a Predictive Model for a Lethal Disease

Eastern equine encephalitis virus (EEEV) is a mosquito-borne virus that affects humans and horses, with a high case fatality rate in both species. The virus can be transmitted by several mosquito species and maintained in multiple reservoir hosts, making EEEV dynamics difficult to anticipate. In this study, we identified spatial and temporal factors that precede EEEV detection using sentinel chicken surveillance data from Orange County, Florida, from 2003 to 2017. We first examined the land cover and mosquito species composition associated with sentinel chicken sites. We then fit distributed lag nonlinear models of EEEV detection at the county scale, using monthly temperature, precipitation, and Southern Oscillation Index values, and at the sentinel flock-scale, using remotely sensed temperature and wetness indicators. We found positive associations between the percent wooded wetlands and the count of EEEV detections. We found Culiseta melanura (Diptera: Culicidae) were more abundant at positive sites in winter and summer, but Coquillettidia perturbans (Walker) were more abundant at positive sites in spring. In the county-wide model, precipitation, temperature, and Southern Oscillation Index values at lags of two, nine, and twelve months were significant, respectively, while temperature and wetness were significant at lags of eight and six months in the flock-specific models.

Field Analysis of Biological Factors Associated With Sites at High and Low to Moderate Risk for Eastern Equine Encephalitis Virus Winter Activity in Florida

Eastern equine encephalitis virus (EEEV) is the most pathogenic arbovirus endemic to the United States. Studies have demonstrated Florida's role as a regional reservoir for the virus and its ability to support year-round transmission. Previous research has developed risk index models for mapping locations most at risk for EEEV transmission. We compared vector abundance, vector feeding behavior, potential host species, and fauna presence at high versus low-moderate risk sites during the winter and spring. Predicted high-risk sites had a significantly greater abundance of mosquitoes overall, including Culiseta melanura (Coquillett) (Diptera: Culicidae), the primary enzootic vector of EEEV. Twenty host species were identified from Cs. melanura bloodmeals, with the majority taken from avian species. Culiseta melanura largely fed upon the Northern Cardinal (Cardinalis cardinalis (Passeriformes: Cardinalidae)), which accounted for 20-24.4% of the bloodmeals obtained from this species in years 1 and 2, respectively. One EEEV-positive mosquito pool (Cs. melanura) and nine EEEV seropositive sentinel chickens were confirmed during winter-spring collections from high-risk sites; no seropositive chickens nor mosquito pools were found at the low-moderate risk sites. These results suggest that high-risk sites for EEEV activity are characterized by habitats that support populations of Cs. melanura and which may also provide ample opportunities to feed upon Northern Cardinals. The overall low level of mosquito populations during the winter also suggests that control of Cs. melanura populations in winter at high-risk sites may prove effective in reducing EEEV transmission during the peak summer season.

The transmission ecology of Tahyna orthobunyavirus in Austria as revealed by longitudinal mosquito sampling and blood meal analysis in floodplain habitats

Background

Tahyna orthobunyavirus (TAHV) is a mosquito-borne virus that may cause mild flu-like symptoms or neurological symptoms in humans. It is historically associated with floodplain habitats in Central Europe, and the mammalophilic floodwater mosquito, Aedes vexans, is thought to be the principal vector. There are few contemporary reports of TAHV transmission ecology within mosquitoes or their vertebrate hosts, and virus infections are rarely reported (and probably seldom diagnosed). The objectives of this study were to survey the mosquito population for TAHV in three floodwater habitats and describe host usage by the predominant floodwater mosquito species to potentially define TAHV transmission at these foci.

Methods

We performed longitudinal mosquito sampling along three major rivers in eastern Austria to characterize the mosquito community in floodplain habitats, and tested for the presence of TAHV in pools of mosquitoes. We characterized TAHV rescued from mosquito pool homogenate by sequencing. We surveyed mosquito host selection by analyzing mosquito blood meals.

Results

We identified TAHV in two pools of Ae. vexans captured along the Leitha River. This mosquito, and other floodwater mosquitoes, used large mammals (red deer, roe deer, wild boar) as their hosts. The sequence of the rescued virus was remarkably similar to other TAHV isolates from the region, dating back to the first isolate of TAHV in 1958.

Conclusions

In general, we confirmed that TAHV is most likely being transmitted by Ae. vexans, although the precise contribution of vertebrate-amplifying hosts to the ecological maintenance of the virus is unclear. The pattern of host selection matches the estimated exposure of the same large mammal species in the region to TAHV based on a recent serosurvey, but hares were also hosts at the site where TAHV was detected. We also confirm humans as hosts of two floodwater mosquito species, providing a potential mechanism for spillover of TAHV or other mosquito-borne viruses.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05061-1.

Arboviral diseases and poverty in Alabama, 2007-2017

Mosquito-borne viruses cause diseases of great public health concern. Arboviral disease case distributions have complex relationships with socioeconomic and environmental factors. We combined information about socio-economic (population, and poverty rate) and environmental (precipitation, and land use) characteristics with reported human cases of arboviral disease in the counties of Alabama, USA, from 2007–2017. We used county level data on West Nile virus (WNV), dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), California serogroup virus, Eastern equine encephalitis virus, and Saint Louis encephalitis virus to provide a detailed description of their spatio-temporal pattern. We found a significant spatial convergence between incidence of WNV and poverty rate clustered in the southern part of Alabama. DENV, CHIKV and ZIKV cases showed a different spatial pattern, being mostly located in the northern part, in areas of high socioeconomic status. The results of our study establish that poverty-driven inequities in arboviral risk exist in the southern USA, and should be taken into account when planning prevention and intervention strategies.

Mosquito-borne arboviruses like West Nile virus (WNV), dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), California serogroup virus (CSV), Eastern equine encephalitis virus (EEE), and Saint Louis encephalitis virus (SLE) are on the rise globally. Socioeconomic and environmental conditions have played a role in directing in this expansion by creating conditions ideal for mosquito vectors and transmission. In this study, we used 10 years (2007–2017) of county level human arboviral case data from the US state of Alabama to better understand the roles socioeconomics (poverty rate) and environmental (land use, precipitation, land cover) conditions may play in driving patterns of arboviral disease in the southern US. We found a significant association between poverty rate and incidence of WNV, an arbovirus primarily transmitted by Culex spp. mosquitoes, which are known for thriving in contaminated water sources and sewage overflow. Conversely, cases of DENV, CHIKV, and ZIKV, arboviruses primarily transmitted by Aedes spp. mosquitoes, were reported in areas of high socioeconomic status. These findings suggest differential distribution of arboviruses relevant to human health in Alabama, and that poverty in the southern US is a significant factor that should be considered when planning WNV prevention and intervention strategies.

Molecular Analysis of the Bloodmeals of Culex spp. Mosquitoes at Natural Habitats in Singapore to Investigate the Potential Risk of Japanese Encephalitis Virus and West Nile Virus Transmission

Japanese encephalitis virus (JEV) and West Nile virus (WNV) are arboviruses primarily transmitted by Culex spp. mosquitoes. Birds are the primary hosts for JEV and WNV. Recent WNV outbreaks in Europe and United States and their association with migratory birds highlight the importance of understanding the feeding host preference of potential vectors for outbreak preparedness, especially in nonendemic settings. Singapore is nonendemic to JEV and WNV, but is a stopover site for migratory birds of the East Asian-Australasian Flyway. Therefore, we elucidated the feeding host range of Culex spp. mosquitoes captured in four natural (bird) habitats in Singapore from January 2011 to December 2012. We characterized feeding host DNA in field-caught mosquitoes using a PCR sequencing-based assay targeting the mitochondrial gene regions. Of 22,648 mosquitoes captured, 21,287 belonged to the Culex vishnui subgroup. The host DNA analysis showed that mosquitoes from the Cx. vishnui subgroup are opportunistic biters, feeding on a range of birds and mammals. Cx. vishnui subgroup, Culex sitiens and Culex bitaeniorhynchus, was primarily ornithophagic, although they fed opportunistically on mammals, including humans. Culex gelidus and Culex quinquefasciatus, in contrast, fed mainly on mammals. The presence of ornitho- and anthropophilic mosquito vectors and susceptible avian and mammalian hosts poses a risk spill-over transmission of JEV and WNV among humans, should these viruses be introduced through migratory birds and establish persistent transmission in resident birds and animal hosts in Singapore.

Seasonal Changes of Host Use by Culiseta melanura (Diptera: Culicidae) in Central Florida

The mosquito Culiseta melanura (Coquillett) is the primary enzootic vector of eastern equine encephalitis virus (EEEV), a zoonotic Alphavirus endemic to eastern North America. In its northern range, Cs. melanura is considered a strict avian biter, transmitting EEEV among susceptible birds in a cycle of enzootic amplification. In its southern range, however, Cs. melanura is more general in host use, feeding heavily upon birds but also reptiles and mammals. The goal of this study was to better understand how host use of Cs. melanura changes throughout the year in Florida, where year-round EEEV transmission is observed. Mosquitoes were sampled in 2018 from nine sites across three central Florida counties. In total, 213 Cs. melanura bloodmeals were identified by PCR consisting of 39 species of birds, reptiles, and mammals. Avian bloodmeals were prominent throughout the year (range = 30-85%), and songbirds were a large portion of identified bloodmeals (37.1%). Reptiles surpassed birds only in spring (April-June), and brown anole (Anolis sagrei Duméril and Bibron, 1837 [Reptilia: Dactyloidae]) was the most commonly detected single host species (22.1% overall). Mammalian bloodmeals were mainly observed in summer, with humans being the most fed on mammal (12.7% overall). This study reveals that in southern foci of EEEV transmission, Cs. melanura host use varies throughout the year with reptiles providing the majority of blood meals in spring (51.3%), and birds are fed on more than other host groups during all other seasons (50.6-70.1%). In addition, feeding on mammals increases during summer months, which may implicate Cs. melanura in epizootic transmission in Florida.

Epidemic Alphaviruses: Ecology, Emergence and Outbreaks

Over the past century, the emergence/reemergence of arthropod-borne zoonotic agents has been a growing public health concern. In particular, agents from the genus Alphavirus pose a significant risk to both animal and human health. Human alphaviral disease presents with either arthritogenic or encephalitic manifestations and is associated with significant morbidity and/or mortality. Unfortunately, there are presently no vaccines or antiviral measures approved for human use. The present review examines the ecology, epidemiology, disease, past outbreaks, and potential to cause contemporary outbreaks for several alphavirus pathogens.

National Seroprevalence and Risk Factors for Eastern Equine Encephalitis and Venezuelan Equine Encephalitis in Costa Rica

Eastern equine encephalitis and Venezuelan equine encephalitis are endemic neglected tropical diseases in the Americas, causing encephalitis in both horses and humans. In 2013, a cross-sectional study was performed in 243 horses located in the highlands and lowlands throughout Costa Rica. Serum samples were analyzed with an IgG ELISA and confirmed by the plaque-reduction neutralization test (PRNT80). Venezuelan equine encephalitis virus (VEEV) and Eastern equine encephalitis virus (EEEV) overall seroprevalences by the PRNT80 were 36% (95% confidence interval [CI]: 29.9-42.5; 78/217 horses) and 3% (95% CI: 1.3-5.9; 6/217 horses), respectively. Both the viruses occurred in the lowlands and highlands. Rainfall and altitude were associated with VEEV seropositivity in the univariate analysis, but only altitude <100 meters above sea level was considered a risk factor in the multivariate analysis. No risk factors could be identified for the EEEV in the multivariate analysis. This is the first study that estimates the seroprevalence of the EEEV and VEEV in Costa Rican horses. The VEEV is widely distributed, whereas the EEEV occurs at a much lower frequency and only in specific areas. Clinical cases and occasional outbreaks of both viruses are to be expected.

Using Bloodmeal Analysis to Assess Disease Risk to Wildlife at the New Northern Limit of a Mosquito Species

The historically southeastern mosquito species Culex erraticus has over the last 30 years undergone a marked expansion north. We evaluated this species' potential to participate in local disease cycles in the northeastern USA by identifying the vertebrate sources of blood in Cx. erraticus specimens from New Jersey. We found that the majority of bloodmeals (92.6%) were derived from birds, followed by 6.8% from mammals (of which half were human), and a single amphibian bloodmeal from a spring peeper (0.56%). Medium- and large-sized water birds from the order Pelecaniformes made up 60.4% of the bird species and 55.9% of all identified hosts. This group of birds is known enzootic hosts of arboviruses such as eastern equine encephalitis virus, for which Cx. erraticus is a competent vector. Additionally, we screened blooded mosquitoes for avian malaria parasites and identified three different lineages of Plasmodium, including what may represent a new Plasmodium species (likely a wetland bird specialist) in bloodmeals from Green Herons, a Great Egret, and a Double-Crested Cormorant. Our results support the utility of mosquito bloodmeals as sources of information about circulating wildlife pathogens and reveal the potential of range-expanding species to intensify local zoonoses and bridge enzootic pathogens to humans.

Detection of Aedes (Stegomyia) aegypti (Diptera: Culicidae) Populations in Southern Alabama Following a 26-yr Absence and Public Perceptions of the Threat of Zika Virus

With the establishment of Zika virus in the Americas, an accurate understanding of the geographic range of its primary vector, Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae), is vital to assessing transmission risk. In an article published in June 2016, Hahn and colleagues compiled county-level records in the United States for the presence of Ae. aegypti and Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) reported between January 1995 and March 2016. Despite ecological suitability for both mosquito species along the Gulf Coast, Ae. aegypti was not reported in Alabama during the time interval, a result consistent with research suggesting that interactions between these two species often result in displacement of Ae. aegypti. Herein, we report the detection of Ae. aegypti populations in Mobile, Alabama, after a 26-yr absence and present findings on human perceptions of Zika virus relevant to transmission. It is unclear whether the specimens (69 out of 1074) represent a recent re-introduction or belong to a previously undetected remnant population. Sequencing of mtDNA from identified Ae. aegypti matched closest to a specimen collected in Kerala, India. A survey of residents in the surveillance area suggests high encounter rates with mosquitoes in and around homes. Despite high self-reported knowledge about Zika virus, the survey revealed gaps in knowledge regarding its transmission cycle and relative degrees of vulnerability to serious illness among segments of the human population. These findings highlight the importance of continued surveillance, vector control, and public-health education in Gulf Coast states, as well as the potential threat of Ae. Aegypti-transmitted pathogens in southern Alabama.

Cryptic etiopathological conditions of equine nervous system with special emphasis on viral diseases

The importance of horse (Equus caballus) to equine practitioners and researchers cannot be ignored. An unevenly distributed population of equids harbors numerous diseases, which can affect horses of any age and breed. Among these, the affections of nervous system are potent reason for death and euthanasia in equids. Many episodes associated with the emergence of equine encephalitic conditions have also pose a threat to human population as well, which signifies their pathogenic zoonotic potential. Intensification of most of the arboviruses is associated with sophisticated interaction between vectors and hosts, which supports their transmission. The alphaviruses, bunyaviruses, and flaviviruses are the major implicated groups of viruses involved with equines/humans epizootic/epidemic. In recent years, many outbreaks of deadly zoonotic diseases such as Nipah virus, Hendra virus, and Japanese encephalitis in many parts of the globe addresses their alarming significance. The equine encephalitic viruses differ in their global distribution, transmission and main vector species involved, as discussed in this article. The current review summarizes the status, pathogenesis, pathology, and impact of equine neuro-invasive conditions of viral origin. A greater understanding of these aspects might be able to provide development of advances in neuro-protective strategies in equine population.

Wetland characteristics linked to broad-scale patterns in Culiseta melanura abundance and eastern equine encephalitis virus infection

BACKGROUND

Eastern equine encephalitis virus (EEEV) is an expanding mosquito-borne threat to humans and domestic animal populations in the northeastern United States. Outbreaks of EEEV are challenging to predict due to spatial and temporal uncertainty in the abundance and viral infection of Cs. melanura, the principal enzootic vector. EEEV activity may be closely linked to wetlands because they provide essential habitat for mosquito vectors and avian reservoir hosts. However, wetlands are not homogeneous and can vary by vegetation, connectivity, size, and inundation patterns. Wetlands may also have different effects on EEEV transmission depending on the assessed spatial scale. We investigated associations between wetland characteristics and Cs. melanura abundance and infection with EEEV at multiple spatial scales in Connecticut, USA.

RESULTS

Our findings indicate that wetland vegetative characteristics have strong associations with Cs. melanura abundance. Deciduous and evergreen forested wetlands were associated with higher Cs. melanura abundance, likely because these wetlands provide suitable subterranean habitat for Cs. melanura development. In contrast, Cs. melanura abundance was negatively associated with emergent and scrub/shrub wetlands, and wetland connectivity to streams. These relationships were generally strongest at broad spatial scales. Additionally, the relationships between wetland characteristics and EEEV infection in Cs. melanura were generally weak. However, Cs. melanura abundance was strongly associated with EEEV infection, suggesting that wetland-associated changes in abundance may be indirectly linked to EEEV infection in Cs. melanura. Finally, we found that wet hydrological conditions during the transmission season and during the fall/winter preceding the transmission season were associated with higher Cs. melanura abundance and EEEV infection, indicating that wet conditions are favorable for EEEV transmission.

CONCLUSIONS

These results expand the broad-scale understanding of the effects of wetlands on EEEV transmission and help to reduce the spatial and temporal uncertainty associated with EEEV outbreaks.

Avian phenotypic traits related to feeding preferences in two Culex mosquitoes

Host choice by mosquitoes affects the transmission dynamics of vector-borne infectious diseases. Although asymmetries in mosquito attraction to vertebrate species have been reported, the relative importance of host characteristics in mosquito blood-feeding behavior is still poorly studied. Here, we investigate the relationship between avian phenotypic traits-in particular, morphometry, plumage coloration, and nesting and roosting behavior-and the blood-feeding patterns in two common Culex mosquito species on a North American avian community. Forage ratios of the mosquito species were unrelated to the phylogenetic relationships among bird species. Culex pipiens fed preferably on birds with lighter-colored plumage and longer tarsi; furthermore, solitary roosting avian species were both bitten by Cx. pipiens and Cx. restuans more often than expected. These associations may be explained by greater mosquito attraction towards larger birds with a greater color contrast against the background. Although communally roosting birds may release more cues and attract more mosquitoes, individuals may in fact receive fewer bites due to the encounter-dilution effect. Mosquito feeding behavior is a highly complex phenomenon, and our results may improve understanding of the non-random interaction between birds and mosquitoes in natural communities.

Mosquito Vectors of Avian Malaria in Mississippi: A First Look

The vectors of avian malaria (Haemosporida) are an understudied component of wildlife disease ecology. Most studies of avian malaria have focused on the intermediate bird hosts. This bias leaves a significant gap in our knowledge and understanding of the insect hosts. This study investigates the diversity of malaria parasites carried by mosquitoes (Diptera, Culicidae) in the state of Mississippi. With the use of molecular techniques, haemosporidian infection rates were determined and parasites were identified. A total of 27,157 female mosquitoes representing 15 species were captured. Five of those species tested positive for malaria parasites with an overall infection rate of 4 per 1,000 mosquitoes infected. Mosquitoes were shown to harbor Plasmodium and Haemoproteus ( Parahaemoproteus) parasites. A unique lineage of parasites was discovered in Anopheles mosquitoes, potentially representing a new genus of haemosporidian parasites, reinforcing the need to continue investigating this diverse group of parasites.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): equine encephalomyelitis (Eastern and Western)

Equine encephalomyelitis (Eastern and Western) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of equine encephalomyelitis (Eastern and Western) to be listed, Article 9 for the categorisation of equine encephalomyelitis (Eastern and Western) according to disease prevention and control rules as in Annex IV, and Article 8 on the list of animal species related to equine encephalomyelitis (Eastern and Western). The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, equine encephalomyelitis (Eastern and Western) can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Section 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in point (e) of Article 9(1). The assessment here performed on compliance with the criteria as in Section 4 of Annex IV referred to in point (d) of Article 9(1) is inconclusive. The animal species to be listed for equine encephalomyelitis (Eastern and Western) according to Article 8(3) criteria are several species of mammals, birds, reptiles and amphibians as susceptible species; rodents, lagomorphs and several bird species as reservoirs and at least four mosquito species (family Culicidae) as vectors.

Evaluating the feeding preferences of West Nile virus mosquito vectors using bird-baited traps

Background

The total contact rates (TCRs) between mosquito vectors and their potential hosts have a serious impact on disease transmission dynamics. Culex pipiens (sensu stricto) (s.s.) is considered the main vector of the West Nile Virus (WNV) in Europe and birds are the reservoir hosts. The results of our previous study showed that WNV seroreactors are significantly more prevalent among raptors compared to a range of other wild avian groups. The current study aims to assess the role of bird type (raptor vs others) and bird size on mosquito feeding preferences in a free-choice experiment using bird-baited traps.

Methods

From July to September 2014, a battery of six bird-baited traps was operated in twelve mosquito capture sessions. Eight bird species, belonging to five different orders, including raptors, were used. After each session, the trapped mosquitoes were collected and identified using standard keys. Two sets of independent generalized linear mixed models (GLMM) were used to assess mosquito vector feeding preferences (MFp) among different bird species and types.

Results

A total of 304 mosquitoes belonging to seven taxa were collected, C. pipiens being by far the most abundant (84.2 % of the total mosquito catch). Most C. pipiens were engorged (83.59 %). The selected model showed that 25.6 % of the observed variability of MFp is explained by the interaction between bird size and bird type, with C. pipiens preferring to feed on large birds, especially raptors. The proportion of engorged mosquitoes was 1.9-fold higher in large (22.88 %; range 0–42 %) than in medium-sized raptors (11.71 %; range 0–33 %), and was nearly the same in medium-sized (9.08 %; range 0–26 %) and large (8.5 %; 6–24 %) non-raptor species.

Conclusion

Culex pipiens showed an obvious preference for large raptors, which concurs with the higher seroprevalence to WNV in our previous study. The appreciable feeding by C. pipiens on large raptors makes them useful alternative sentinels to poultry for WNV surveillance. Thus, wildlife parks and rehabilitation centers can contribute to surveillance efforts to a greater extent.

Host associations of mosquitoes at eastern equine encephalitis virus foci in Connecticut, USA

Background

Eastern equine encephalitis virus (EEEV) is a highly pathogenic mosquito-borne arbovirus, with active transmission foci in freshwater hardwood swamps in eastern North America, where enzootic transmission is maintained between the ornithophilic mosquito, Culiseta melanura, and wild passerine birds. The role of other locally abundant mosquito species in virus transmission and their associations with vertebrate hosts as sources of blood meals within these foci are largely unknown but are of importance in clarifying the dynamics of enzootic and epidemic/epizootic transmission.

Methods

Blood-engorged mosquitoes were collected from resting boxes at four established EEEV foci in Connecticut during 2010–2011. Mosquitoes were identified to species, and the identity of vertebrate hosts was determined based on mitochondrial cytochrome b and/or cytochrome c oxidase subunit I gene sequences of polymerase chain reaction products.

Results

The vertebrate hosts of 378 (50.3 % of engorged mosquitoes) specimens, representing 12 mosquito species, were identified. Culiseta morsitans (n = 54; 67.5 %), Culex restuans (n = 4; 66.7 %), and Cx. pipiens (n = 2; 100 %) acquired blood meals exclusively from avian hosts, whereas Aedes cinereus (n = 6; 66.7 %), Ae. canadensis (n = 2; 100 %), and Ae. stimulans (n = 1; 100 %) obtained blood meals solely from mammals. Species that fed opportunistically on both avian and mammalian hosts included: Ae. thibaulti (n = 21 avian, and n = 181 mammalian; 57.2 %), Anopheles punctipennis (n = 8 and n = 40; 44.0 %), An. quadrimaculatus (n = 1 and n = 23; 35.7 %), Coquillettidia perturbans (n = 3 and n = 3; 46.2 %) and Ae. abserratus (n = 1 and n = 2; 23.1 %). Culex territans obtained blood meals from avian and amphibian hosts (n = 18 and n = 5; 26.6 %). Mixed blood meals originating from both avian and mammalian hosts were identified in An. quadrimaculatus (n = 1), and Cx. territans (n = 2).

Conclusions

Our findings indicate that wood thrush, tufted titmouse, and a few other avian species serve as hosts for mosquitoes, and likely contribute to amplification of EEEV. Our study supports the role of Cs. morsitans in enzootic transmission of EEEV among avian species. Culex territans will seek blood from multiple vertebrate classes, suggesting that this species may contribute to epizootic transmission of the virus. Our findings support roles for Cq. perturbans and An. quadrimaculatus as epidemic/epizootic vectors to humans, horses, and white-tailed deer. Despite its abundance, the potential of Ae. thibaulti to serve as a “bridge vector” for EEEV remains unclear in the absence of any definitive knowledge on its competency for the virus. The contribution of white-tailed deer to the dynamics of EEEV transmission is not fully understood, but findings indicate repeated exposure due to frequent feeding by vector competent mosquito species.

Vector Competence and Capacity of Culex erraticus (Diptera: Culicidae) for Eastern Equine Encephalitis Virus in the Southeastern United States

Field studies of the ecology of eastern equine encephalitis virus (EEEV; family Togaviridae, genus Alphavirus) in the southeastern United States have demonstrated that Culex erraticus (Dyar and Knab) is the most common mosquito at many enzootic sites and is often infected with the virus. However, the competence of Cx. erraticus for EEEV has not been explored in detail. Culex erraticus females were collected from the field and fed upon EEEV-infected chicks. The infected mosquitoes were provided honey for nutrition and to monitor for time to infectiveness. Of the mosquitoes that survived the 14-d postfeeding period, 89% were infected and 84% had evidence of a disseminated infection, though titers were generally low. EEEV was first detected in honey 6 d postinfection and was detected in samples collected from 94% of the mosquitoes with a disseminated infection overall. These data and others were then employed to estimate the relative vectorial capacity of Cx. erraticus at an EEEV enzootic site in Alabama. The vectorial capacity of Cx. erraticus at this site was 44% of Culiseta melanura (Coquillett), the accepted enzootic vector, suggesting Cx. erraticus may play a role in transmitting EEEV in areas where it is abundant and Cs. melanura rare.

Mayaro virus and dengue virus 1 and 4 natural infection in culicids from Cuiabá, state of Mato Grosso, Brazil

This study aimed to verify the diversity of Culicidae species and their frequency of infection with flaviviruses and alphaviruses in Cuiabá, state of Mato Grosso, Brazil. Mosquitoes were captured with Nasci aspirators and hand net in 200 census tracts, identified alive at species level and pooled in one-20 (11,090 mosquitoes, 14 species). Female pools (n = 610) were subjected to multiplex seminested-reverse transcription-polymerase chain reaction (RT-PCR) for 11 flavivirus and five alphavirus. Positive pools were tested by single RT-PCR followed by nucleotide sequencing, by RT-PCR for E1 gene [Mayaro virus (MAYV)] and by inoculation in Vero cells (MAYV) or C6/36 cells (flaviviruses). One/171 Aedes aegypti was positive for dengue virus (DENV)-1, 12/403 Culex quinquefasciatus, and four/171Ae. aegypti for MAYV, which was isolated from two pools containing two nonengorged females of Ae. aegypti and two of Cx. quinquefasciatus. DENV-4 was detected in 58/171 pools of Ae. aegytpi, 105/403 Cx. quinquefasciatus, two/five Psorophora sp., two/11 Psorophora varipes/Psorophora albigenu, one/one Sabethes chloropterus, two/five Culex bidens/Culex interfor, and one/one Aedes sp. DENV-4 was isolated from two pools containing three and 16 nonengorged Cx. quinquefasciatus females. Phylogenetic analysis revealed MAYV belongs to genotype L, clustering with human samples of the virus previously identified in the city. Cuiabá has biodiversity and ecosystem favourable for vector proliferation, representing a risk for arbovirus outbreaks.

Insights into the recent emergence and expansion of eastern equine encephalitis virus in a new focus in the Northern New England USA

BACKGROUND

Eastern equine encephalomyelitis virus (EEEV) causes a highly pathogenic zoonosis that circulates in an enzootic cycle involving the ornithophagic mosquito, Culiseta melanura, and wild passerine birds in freshwater hardwood swamps in the northeastern U.S. Epidemic/epizootic transmission to humans/equines typically occurs towards the end of the transmission season and is generally assumed to be mediated by locally abundant and contiguous mammalophagic "bridge vector" mosquitoes.

METHODS

Engorged mosquitoes were collected using CDC light, resting box, and gravid traps during epidemic transmission of EEEV in 2012 in Addison and Rutland counties, Vermont. Mosquitoes were identified to species and blood meal analysis performed by sequencing mitochondrial cytochrome b gene polymerase chain reaction products. Infection status with EEEV in mosquitoes was determined using cell culture and RT-PCR assays, and all viral isolates were sequenced and compared to other EEEV strains by phylogenetic analysis.

RESULTS

The host choices of 574 engorged mosquitoes were as follows: Cs. melanura (n = 331, 94.3 % avian-derived, 5.7 % mammalian-derived); Anopheles quadrimaculatus (n = 164, 3.0 % avian, 97.0 % mammalian); An. punctipennis (n = 56, 7.2 % avian, 92.8 % mammalian), Aedes vexans (n = 9, 22.2 % avian, 77.8 % mammalian); Culex pipiens s.l. n = 6, 100 % avian); Coquillettidia perturbans (n = 4, 25.0 % avian, 75.0 % mammalian); and Cs. morsitans (n = 4, 100 % avian). A seasonal shift in blood feeding by Cs. melanura from Green Heron towards other avian species was observed. EEEV was successfully isolated from blood-fed Cs. melanura and analyzed by phylogenetic analysis. Vermont strains from 2012 clustered with viral strains previously isolated in Virginia yet were genetically distinct from an earlier EEEV isolate from Vermont during 2011.

CONCLUSIONS

Culiseta melanura acquired blood meals primarily from birds and focused feeding activity on several competent species capable of supporting EEEV transmission. Culiseta melanura also occasionally obtained blood meals from mammalian hosts including humans. This mosquito species serves as the primary vector of EEEV among wild bird species, but also is capable of occasionally contributing to epidemic/epizootic transmission of EEEV to humans/equines. Other mosquito species including Cq. perturbans that feed more opportunistically on both avian and mammalian hosts may be important in epidemic/epizootic transmission under certain conditions. Phylogenetic analyses suggest that EEEV was independently introduced into Vermont on at least two separate occasions.

Mapping eastern equine encephalitis virus risk for white-tailed deer in Michigan

Eastern equine encephalitis (EEE) is a mosquito-borne viral disease that is often fatal to humans and horses. Some species including white-tailed deer and passerine birds can survive infection with the EEE virus (EEEV) and develop antibodies that can be detected using laboratory techniques. In this way, collected serum samples from free ranging white-tailed deer can be used to monitor the presence of the virus in ecosystems. This study developed and tested a risk index model designed to predict EEEV activity in white-tailed deer in a three-county area of Michigan. The model evaluates EEEV risk on a continuous scale from 0.0 (no measurable risk) to 1.0 (highest possible risk). High risk habitats are identified as those preferred by white-tailed deer that are also located in close proximity to an abundance of wetlands and lowland forests, which support disease vectors and hosts. The model was developed based on relevant literature and was tested with known locations of infected deer that showed neurological symptoms. The risk index model accurately predicted the known locations, with the mean value for those sites equal to the 94th percentile of values in the study area. The risk map produced by the model could be used refine future EEEV monitoring efforts that use serum samples from free-ranging white-tailed deer to monitor viral activity. Alternatively, it could be used focus educational efforts targeted toward deer hunters that may have elevated risks of infection.

Vector-Host Interactions of Culiseta melanura in a Focus of Eastern Equine Encephalitis Virus Activity in Southeastern Virginia

Eastern equine encephalitis virus (EEEV) causes a highly pathogenic mosquito-borne zoonosis that is responsible for sporadic outbreaks of severe illness in humans and equines in the eastern USA. Culiseta (Cs.) melanura is the primary vector of EEEV in most geographic regions but its feeding patterns on specific avian and mammalian hosts are largely unknown in the mid-Atlantic region. The objectives of our study were to: 1) identify avian hosts of Cs. melanura and evaluate their potential role in enzootic amplification of EEEV, 2) assess spatial and temporal patterns of virus activity during a season of intense virus transmission, and 3) investigate the potential role of Cs. melanura in epidemic/epizootic transmission of EEEV to humans and equines. Accordingly, we collected mosquitoes at 55 sites in Suffolk, Virginia in 2013, and identified the source of blood meals in engorged mosquitoes by nucleotide sequencing PCR products of the mitochondrial cytochrome b gene. We also examined field-collected mosquitoes for evidence of infection with EEEV using Vector Test, cell culture, and PCR. Analysis of 188 engorged Cs. melanura sampled from April through October 2013 indicated that 95.2%, 4.3%, and 0.5% obtained blood meals from avian, mammalian, and reptilian hosts, respectively. American Robin was the most frequently identified host for Cs. melanura (42.6% of blood meals) followed by Northern Cardinal (16.0%), European Starling (11.2%), Carolina Wren (4.3%), and Common Grackle (4.3%). EEEV was detected in 106 mosquito pools of Cs. melanura, and the number of virus positive pools peaked in late July with 22 positive pools and a Maximum Likelihood Estimation (MLE) infection rate of 4.46 per 1,000 mosquitoes. Our findings highlight the importance of Cs. melanura as a regional EEEV vector based on frequent feeding on virus-competent bird species. A small proportion of blood meals acquired from mammalian hosts suggests the possibility that this species may occasionally contribute to epidemic/epizootic transmission of EEEV.

Ecology of Culiseta Melanura and Other Mosquitoes (Diptera: Culicidae) from Walton County, FL, During Winter Period 2013-2014

Winter ecology of putative vectors of eastern equine encephalomyelitis virus (EEEV) in northern Florida was investigated at field locations with evidence of historic EEEV winter transmission. Light traps and resting shelters were used to sample the mosquito community in the vicinity of eight sentinel flocks throughout the winter period (November-April) of 2013 and 2014 in Walton County, FL. Overall mosquito activity was relatively low, although mosquitoes were captured during each week of the study period. Mosquito activity was linked to morning temperature, and females were captured when ambient morning temperatures were quite low (1-5°C). Anopheles crucians Wiedemann, Culex erraticus (Dyar and Knab), Culex territans Walker, and Culiseta melanura (Coquillett) were the most commonly collected mosquito species (of 20 total species). Analysis of blood-engorged mosquitoes revealed a number of mosquito species feeding upon chickens, other birds, amphibians, and domestic and wild mammals. Cs. melanura fed primarily upon chickens and songbirds (Passeriformes), suggesting that this mosquito species is the likely winter vector of EEEV to sentinel chickens in northern Florida. Both resident and nonresident songbird species were fed upon, constituting 63.9 and 36.1% of total songbird meals, respectively. Our results suggest important roles for Cs. melanura and songbird hosts for the winter transmission of EEEV in northern Florida.

Complete coding sequences of eastern equine encephalitis virus and venezuelan equine encephalitis virus strains isolated from human cases

We obtained the complete coding genome of an eastern equine encephalitis virus (EEEV) strain, EEEV V105-00210, and the complete genome of a Venezuelan equine encephalitis virus (VEEV) strain, VEEV INH-9813. They were obtained from human cases and are proposed as reference challenge strains for vaccine and therapeutic development in animal models.

West nile virus and equine encephalitis viruses: new perspectives

Mosquito-borne diseases affect horses worldwide. Mosquito-borne diseases generally cause encephalomyelitis in the horse and can be difficult to diagnose antemortem. In addition to general disease, and diagnostic and treatment aspects, this review article summarizes the latest information on these diseases, covering approximately the past 5 years, with a focus on new equine disease encroachments, diagnostic and vaccination aspects, and possible therapeutics on the horizon.

Field investigations of winter transmission of eastern equine encephalitis virus in Florida

Studies investigating winter transmission of Eastern equine encephalitis virus (EEEV) were conducted in Hillsborough County, Florida. The virus was detected in Culiseta melanura and Anopheles quadrimaculatus in February 2012 and 2013, respectively. During the winter months, herons were the most important avian hosts for all mosquito species encountered. In collections carried out in the summer of 2011, blood meals taken from herons were still common, but less frequently encountered than in winter, with an increased frequency of mammalian- and reptile-derived meals observed in the summer. Four wading bird species (Black-crowned Night Heron [Nycticorax nycticorax], Yellow-crowned Night Heron [Nyctanassa violacea], Anhinga [Anhinga anhinga], and Great Blue Heron [Ardea herodias]) were most frequently fed upon by Cs. melanura and Culex erraticus, suggesting that these species may participate in maintaining EEEV during the winter in Florida.

Innate preference or opportunism: mosquitoes feeding on birds of prey at the Southeastern Raptor Center

The amplification of mosquito-borne pathogens is driven by patterns of host use by vectors. While each mosquito species is innately adapted to feed upon a particular group of hosts, this "preference" is difficult to assess in field-based studies, because factors such as host defenses and spatial and temporal overlap of mosquitoes and hosts affect which host animals actually get bitten. Here we examined patterns of host use by mosquitoes feeding on caged raptors at a rehabilitation and education center for birds of prey in Alabama, U.S.A. PCR-based techniques were used to determine the host species fed upon. Of 19 raptor species at the facility, seven were found to be fed upon by mosquitoes. Feeding indices and linear regression indicated that no species or family of raptor were significantly preferred over another (R(2)=0.46). Relative abundance adjusted for bird size explained a statistically significant amount of the variation in relative host use (R(2)=0.71), suggesting that bird size is an important component of host selection by mosquitoes. These findings support the hypothesis that traits of host animals drive patterns of host use by mosquitoes in nature, an interaction that leads to amplification of mosquito-borne viruses.

Zoonotic encephalitides caused by arboviruses: transmission and epidemiology of alphaviruses and flaviviruses

In this review, we mainly focus on zoonotic encephalitides caused by arthropod-borne viruses (arboviruses) of the families Flaviviridae (genus Flavivirus) and Togaviridae (genus Alphavirus) that are important in both humans and domestic animals. Specifically, we will focus on alphaviruses (Eastern equine encephalitis virus, Western equine encephalitis virus, Venezuelan equine encephalitis virus) and flaviviruses (Japanese encephalitis virus and West Nile virus). Most of these viruses were originally found in tropical regions such as Africa and South America or in some regions in Asia. However, they have dispersed widely and currently cause diseases around the world. Global warming, increasing urbanization and population size in tropical regions, faster transportation and rapid spread of arthropod vectors contribute in continuous spreading of arboviruses into new geographic areas causing reemerging or resurging diseases. Most of the reemerging arboviruses also have emerged as zoonotic disease agents and created major public health issues and disease epidemics.

Risk of exposure to eastern equine encephalomyelitis virus increases with the density of northern cardinals

For a variety of infectious diseases, the richness of the community of potential host species has emerged as an important factor in pathogen transmission, whereby a higher richness of host species is associated with a lowered disease risk. The proposed mechanism driving this pattern is an increased likelihood in species-rich communities that infectious individuals will encounter dead-end hosts. Mosquito-borne pathogen systems potentially are exceptions to such “dilution effects” because mosquitoes vary their rates of use of vertebrate host species as bloodmeal sources relative to host availabilities. Such preferences may violate basic assumptions underlying the hypothesis of a dilution effect in pathogen systems. Here, we describe development of a model to predict exposure risk of sentinel chickens to eastern equine encephalitis virus (EEEV) in Walton County, Florida between 2009 and 2010 using avian species richness as well as densities of individual host species potentially important to EEEV transmission as candidate predictor variables. We found the highest support for the model that included the density of northern cardinals, a highly preferred host of mosquito vectors of EEEV, as a predictor variable. The highest-ranking model also included Culiseta melanura abundance as a predictor variable. These results suggest that mosquito preferences for vertebrate hosts influence pathogen transmission.

Alphaviruses: population genetics and determinants of emergence

Alphaviruses are responsible for several medically important emerging diseases and are also significant veterinary pathogens. Due to the aerosol infectivity of some alphaviruses and their ability to cause severe, sometimes fatal neurologic diseases, they are also of biodefense importance. This review discusses the ecology, epidemiology and molecular virology of the alphaviruses, then focuses on three of the most important members of the genus: Venezuelan and eastern equine encephalitis and chikungunya viruses, with emphasis on their genetics and emergence mechanisms, and how current knowledge as well as gaps influence our ability to detect and determine the source of both natural outbreaks and potential use for bioterrorism. This article is one of a series in Antiviral Research on the genetic diversity of emerging viruses.

Winter severity predicts the timing of host shifts in the mosquito Culex erraticus

In temperate regions, seasonal epidemics of many mosquito-borne viruses are triggered when mosquito populations shift from feeding on avian to mammalian hosts. We investigated effects of temperature on the timing of bird-to-mammal shifts using an 8 year dataset of blood-meals from a mosquito (Culex erraticus) in Alabama, USA. As expected, Cx. erraticus shifted from avian to mammalian hosts each year. The timing of the shift, however, varied considerably among years. Harshness of the preceding winter (chill accumulation) explained 93 per cent of the variation in the timing of bird-to-mammal shifts, with shifts occurring later in years following harsher winters. We hypothesize that winter temperatures drive the timing of bird-to-mammal shifts through effects on host reproductive phenology. Because mosquitoes target birds during the nesting season, and bird nesting occurs later in years following colder winters, later nesting dates result in a concomitant delay in the timing of bird-to-mammal host shifts. Global increases in winter temperatures could cause significant changes in the timing of seasonal host shifts by mosquitoes, with prolonged periods of epidemic transmission of mosquito-borne diseases.

Developing models for the forage ratios of Culiseta melanura and Culex erraticus using species characteristics for avian hosts

Studies of mosquito preferences for avian hosts have found that some bird species are at greater risk than others of being fed upon by mosquitoes. The ecological factors that determine this interspecific variation in avian host use by mosquitoes have been little studied, despite the possibility that such variation may influence spatial and temporal patterns of the occurrence of mosquito-borne pathogens. Our objective was to identify ecological variables associated with the avian host forage ratios estimated from a previous study of mosquito feeding patterns in Tuskegee National Forest, AL. We used species' characteristics derived from the literature to develop multiple linear regression models for the forage ratios of Culiseta melanura (Coquillett) and Culex erraticus (Dyar & Knab) for avian hosts. We found that habitat-edge association and body mass of avian host species were the best predictors of forage ratios of Cx. erraticus for avian hosts. Although no avian host traits were inferred to be strong predictors of forage ratios of Cs. melanura, body mass had the greatest importance weight among those considered. Our results suggest that characteristics of avian hosts may predict their levels of use by some mosquito species.