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.
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.
A simple inexpensive trap (Esperanza window trap) was shown recently to collect significant numbers of Simulium ochraceum sensu lato, a major vector of Onchocerca volvulus in Mesoamerica. Here, we report studies optimizing this trap for the collection of Simulium damnosum s.l., the major vector of O. volvulus in Africa. A shortened, blue and black striped version of the Esperanza window trap, when baited with a combination of CO2 and worn trousers, rivalled human landing collections in the number of S. damnosum s.l. females collected. Traps baited with a commercially available human skin lure and CO2 resulted in collections that were not significantly different than those obtained from traps baited with worn trousers and CO2. This suggests that the Esperanza window trap may offer a replacement for human landing collections for monitoring onchocerciasis transmission in Africa.
The resting sites of tropical American mosquitoes are poorly documented, and the few reports that do exist are largely from opportunistic collections. Since blood-engorged females (used in determining host associations) are more efficiently collected from resting sites than attractive traps, information on resting site utilization has practical value. To investigate differences in the resting sites utilized by tropical mosquitoes, we collected and identified female mosquitoes from one man-made (resting shelter) and three natural (buttress tree roots, hollow trees, and understory vegetation) resting environments at a tropical dry forest location in western Costa Rica. All of the most common species collected demonstrated associations with one or more resting environments. Females of five species (blood-engorged Anopheles albimanus, Uranotaenia apicalis, Uranotaenia lowii, Uranotaenia orthodoxa, and blood-engorged Mansonia titillans) were collected in significantly greater numbers from understory vegetation than other resting environments. Culex erraticus and other members of the subgenus Melanoconion were encountered more often in resting shelters, hollow trees, and buttress roots, while Culex restrictor (blood-engorged) females were associated with hollow trees. Similarity indices indicate that buttress tree roots, hollow trees, and resting shelters are similar with respect to the mosquito communities that utilize them as resting sites, while understory vegetation has a resting fauna that is different than the other environments surveyed here. These results add to the body of information regarding resting sites utilized by tropical American mosquitoes.
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.
Human landing collections are currently the standard method for collecting onchocerciasis vectors in Africa and Latin America. As part of the efforts to develop a trap to replace human landing collections for the monitoring and surveillance of onchocerciasis transmission, comprehensive evaluations of several trap types were conducted to assess their ability to collect Simulium ochraceum sensu lato, one of the principal vectors of Onchocerca volvulus in Latin America.
At temperate latitudes, vectors and pathogens must possess biological mechanisms for coping with cold temperatures and surviving from one transmission season to the next. Mosquitoes that overwinter in the adult stage have been proposed as winter maintenance hosts for certain arboviruses. In the cases of West Nile virus (family Flaviviridae, genus Flavivirus) and St. Louis encephalitis virus (family Flaviviridae, genus Flavivirus), discovery of infected overwintering females lends support to this hypothesis, but for other arboviruses, in particular Eastern equine encephalomyelitis virus (family Togaviridae, genus Alphavirus, EEEV), overwintering of the virus in mosquito hosts as not been demonstrated. In the current study, we collected overwintering mosquitoes from a focus of EEEV transmission in the southeastern United States to determine whether mosquitoes serve as winter maintenance hosts for EEEV and to document overwintering biologies of suspected vectors. No virus was detected via reverse transcription-polymerase chain reaction of > 500 female mosquitoes collected during three winters. Investigation into the winter biologies indicated that Anopheles punctipennis (Say), Culex erraticus (Dyar & Knab), Culex peccator Dyar & Knab, and Uranotaenia sapphirina (Osten Sacken) overwinter as females. Females of these species were collected from hollow trees and emergence traps placed over ground holes. Southern magnolia, Magnolia grandiflora L., trees were preferred overwintering sites of culicine mosquitoes. Emergence from underground overwintering sites peaked in mid-March, when air temperatures reached 18-22 degrees C, and the first blood-engorged females of Cx. erraticus and Cx. peccator were collected during this same period. Blood-fed Culex territans Walker females were collected as early as mid-February. This work provides insight into the overwintering biologies of suspected virus vectors at a site of active EEEV transmission and provides limited evidence against the hypothesis that EEEV persists through intertransmission periods in overwintering mosquitoes.
Collecting resting mosquitoes is important for studies of the bloodfeeding patterns of medically important mosquitoes. We developed a novel resting shelter, called a wire-frame resting shelter, for collecting resting mosquitoes and evaluated its efficacy at sites in Alabama and the Florida Panhandle. The shelter is made of a 1 x 2-m section of galvanized metal-wire field fencing rolled into a cylinder and placed inside a heavy-duty black plastic bag. In the field evaluation, the wire-frame shelters were comparable to other artificial resting shelters (trash cans) in the number of Culex (Melanoconion) females collected. While a number of other resting shelter designs are available, the wire-frame shelter has a number of beneficial attributes, including being easily assembled in the field, lightweight, inexpensive, and easily modified.
Eastern equine encephalitis virus (EEEV) is a mosquito-borne pathogen that cycles in birds but also causes severe disease in humans and horses. We examined patterns of avian host use by vectors of EEEV in Alabama from 2001 to 2009 using blood-meal analysis of field-collected mosquitoes and avian abundance surveys. The northern cardinal (Cardinalis cardinalis) was the only preferred host (fed on significantly more than expected based on abundance) of Culiseta melanura, the enzootic vector of EEEV. Preferred hosts of Culex erraticus, a putative bridge vector of EEEV, were American robin (Turdus migratorius), Carolina chickadee (Poecile carolinensis), barred owl (Strix varia), and northern mockingbird (Mimus polyglottis). Our results provide insight into the relationships between vectors of EEEV and their avian hosts in the Southeast and suggest that the northern cardinal may be important in the ecology of EEEV in this region.
Circadian patterns of flight activity in mosquitoes can influence pathogen transmission by regulating dispersal potential of vectors and contact rates between vectors and reservoir and/or dead-end hosts. We investigated circadian activity patterns of Culex erraticus (Dyar and Knab) at a wetland field site in central Alabama, by aspirating resting adults and questing females in the morning and evening hours, respectively. Mosquitoes were aspirated at regular time intervals to determine the time of day during which peak resting site-seeking and host-seeking activities occurred. Day-to-day variation in activity patterns due to wind, humidity, and temperature was examined using stepwise linear regression. We found a distinct peak in flight activity during the morning hours (2 h before and 2 h after sunrise) for females and males of Culex erraticus, the most commonly encountered species at the site. The exact time of the peak varied from day to day, and was largely a function of temperature. A less distinct peak in activity was observed for questing females in the evening, although flights generally commenced just after sunset and peaked 30-60 min after sunset. A significant amount of day-to-day variation in the number of questing females was attributable to relative humidity. Our study demonstrates predictable patterns of circadian activity for Cx. erraticus, a suspected bridge vector of eastern equine encephalitis virus. Moreover, these patterns are modulated by environmental conditions. This information may be used to develop vector control strategies and make predictions about factors that affect the spread of mosquito-vectored pathogens.
Host blood meals in seven mosquito species previously shown to be infected with eastern equine encephalitis virus at a site in the Tuskegee National Forest in southcentral Alabama were investigated. Of 1374 blood meals derived from 88 different host species collected over 6 years from these seven mosquito species, 1099 were derived from Culex erraticus. Analysis of the temporal pattern of Cx. erraticus meals using a Runs test revealed that the patterns of feeding upon avian and mammalian hosts from March to September of each year were not randomly distributed over time. Similarly, meals taken from the three most commonly targeted host species (yellow-crowned night heron, great blue heron, and white-tailed deer) were not randomly distributed. A Tukeys two-way analysis of variance test demonstrated that although the temporal pattern of meals taken from avian hosts were consistent over the years, the patterns of meals taken from the individual host species were not consistent from year to year.
Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early- and late-season breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs).
Patterns of mosquito dispersal are important for predicting the risk of transmission of mosquito-borne pathogens to vertebrate hosts. We studied dispersal behavior of Culex erraticus (Dyar & Knab), a potentially significant vector of eastern equine encephalitis virus (EEEV) that is often associated with foci of this pathogen in the southeastern United States. Using data on the relative density of resting adult female Cx. erraticus around known emergence sites in Tuskegee National Forest, Alabama, we developed a model for the exponential decay of the relative density of adult mosquitoes with distance from larval habitats through parameterization of dispersal kernels. The mean and 99th percentile of dispersal distance for Cx. erraticus estimated from this model were 0.97 and 3.21 km per gonotrophic cycle, respectively. Parameterized dispersal kernels and estimates of the upper percentiles of dispersal distance of this species can potentially be used to predict EEEV infection risk in areas surrounding the Tuskegee National Forest focus in the event of an EEEV outbreak. The model that we develop for estimating the dispersal distance of Cx. erraticus from collections of adult mosquitoes could be applicable to other mosquito species that emerge from discrete larval sites.
The hypothesis that nestlings are a significant driver of arbovirus transmission and amplification is based upon findings that suggest nestlings are highly susceptible to being fed upon by vector mosquitoes and to viral infection and replication. Several previous studies have suggested that nestlings are preferentially fed upon relative to adults in the nest, and other studies have reported a preference for adults over nestlings. We directly tested the feeding preference of nestling and adult birds in a natural setting, introducing mosquitoes into nesting boxes containing eastern bluebirds (Sialia sialis), collecting blood-fed mosquitoes, and matching the source of mosquito blood meals to individual birds using microsatellite markers. Neither nestlings nor adults were fed upon to an extent significantly greater than would be predicted based upon their relative abundance in the nests, although feeding upon mothers decreased as the age of the nestlings increased.
A site near Tuskegee, Alabama was examined for vector-host activities of eastern equine encephalomyelitis virus (EEEV). Land cover maps of the study site were created in ArcInfo 9.2 from QuickBird data encompassing visible and near-infrared (NIR) band information (0.45 to 0.72 microm) acquired July 15, 2008. Georeferenced mosquito and bird sampling sites, and their associated land cover attributes from the study site, were overlaid onto the satellite data. SAS 9.1.4 was used to explore univariate statistics and to generate regression models using the field and remote-sampled mosquito and bird data. Regression models indicated that Culex erracticus and Northern Cardinals were the most abundant mosquito and bird species, respectively. Spatial linear prediction models were then generated in Geostatistical Analyst Extension of ArcGIS 9.2. Additionally, a model of the study site was generated, based on a Digital Elevation Model (DEM), using ArcScene extension of ArcGIS 9.2.
The role that different age classes of birds play in the amplification of arthropod-borne viruses depends critically on the feeding choices made by mosquitoes. To determine if mosquitoes are more likely to feed on nestling or adult birds, we introduced Culex quinquefasciatus mosquitoes into eastern bluebird Sialia sialis nest boxes after dark and recaptured them the following morning. We collected blood from each nestling and brooding mother and used molecular genotyping methods to trace the blood meals of individual mosquitoes to the individual bird fed upon (mothers or chicks). Of the 14 recaptured mosquitoes, whose blood meals were identified to the species level, 10 fed only on nestlings, three fed only on an adult, and one mosquito fed on an adult and two nestlings. These preliminary data show that microsatellite genotyping may be used to answer important questions concerning mosquito feeding patterns on different age classes of birds.
Determining the structure of ectoparasite-host networks will enable disease ecologists to better understand and predict the spread of vector-borne diseases. If these networks have consistent properties, then studying the structure of well-understood networks could lead to extrapolation of these properties to others, including those that support emerging pathogens. Borrowing a quantitative measure of network structure from studies of mutualistic relationships between plants and their pollinators, we analyzed 29 ectoparasite-vertebrate host networks--including three derived from molecular bloodmeal analysis of mosquito feeding patterns--using measures of nestedness to identify non-random interactions among species. We found significant nestedness in ectoparasite-vertebrate host lists for habitats ranging from tropical rainforests to polar environments. These networks showed non-random patterns of nesting, and did not differ significantly from published estimates of nestedness from mutualistic networks. Mutualistic and antagonistic networks appear to be organized similarly, with generalized ectoparasites interacting with hosts that attract many ectoparasites and more specialized ectoparasites usually interacting with these same "generalized" hosts. This finding has implications for understanding the network dynamics of vector-born pathogens. We suggest that nestedness (rather than random ectoparasite-host associations) can allow rapid transfer of pathogens throughout a network, and expand upon such concepts as the dilution effect, bridge vectors, and host switching in the context of nested ectoparasite-vertebrate host networks.
The role of non-avian vertebrates in the ecology of eastern equine encephalomyelitis virus (EEEV) is unresolved, but mounting evidence supports a potential role for snakes in the EEEV transmission cycle, especially as over-wintering hosts. To determine rates of exposure and infection, we examined serum samples from wild snakes at a focus of EEEV in Alabama for viral RNA using quantitative reverse transcription polymerase chain reaction. Two species of vipers, the copperhead (Agkistrodon contortrix) and the cottonmouth (Agkistrodon piscivorus), were found to be positive for EEEV RNA using this assay. Prevalence of EEEV RNA was more frequent in seropositive snakes than seronegative snakes. Positivity for the quantitative reverse transcription polymerase chain reaction in cottonmouths peaked in April and September. Body size and sex ratios were not significantly different between infected and uninfected snakes. These results support the hypothesis that snakes are involved in the ecology of EEEV in North America, possibly as over-wintering hosts for the virus.
Eastern Equine Encephalitis virus (EEEV; family Togaviridae, genus Alphavirus) a highly pathogenic mosquito-borne virus is endemic to eastern North America. The ecology of EEEV in Florida differs from that in other parts of the United States; EEEV in the northeastern United States is historically associated with freshwater wetlands. No formal test of habitat associations of EEEV in Florida has been reported. Geographical Information Sciences (GIS) was used in conjunction with sentinel chicken EEEV seroconversion rate data as a means to examine landscape features associated with EEEV transmission in Walton County, FL. Sentinel sites were categorized as enzootic, periodically enzootic, and negative based on the number of chicken seroconversions to EEEV from 2005 to 2009. EEEV transmission was then categorized by land cover usage using Arc GIS 9.3. The land classification data were analyzed using the Kruskal-Wallis test for each land use class to determine which habitats may be associated with virus transmission as measured by sentinel chicken seroconversion rates. The habitat class found to be most significantly associated with EEEV transmission was tree plantations. The ecological factor most commonly associated with reduced levels of EEEV transmission was vegetated nonforest wetlands. Culiseta melanura (Coquillett), the species generally considered to be the major enzootic EEEV vector, was relatively evenly distributed across all habitat classes, while Aedes vexans (Meigen) and Anopheles crucians Weidemann were most commonly associated with tree plantation habitats.
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.
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.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.