Encephalitis virus persistence in California birds: experimental infections in mourning doves (Zenaidura macroura)

After-hatching and hatching year, mourning doves were infected by inoculation with either western equine encephalomyelitis (WEE) or St. Louis encephalitis (SLE) viruses; some birds in each group also were treated with the immunosuppressant cyclophosphamide before and during infection. Cyclophosphamide treatment significantly increased the WEE viremia but did not alterthe antibody response. In contrast, cyclophosphamide-treated and -untreated doves did not develop a detectable SLE viremia but became antibody positive. Antibody peaked at 10 wk after inoculation for both viruses and remained detectable in most birds throughout the 26-wk study. When treated with cyclophosphamide the following spring, birds did not relapse and develop a detectable viremia. Previously infected birds were protected when challenged with conspecific virus (i.e., none produced a detectable viremia), but there was no anamnestic antibody response to reinfection. In agreement with our failure to detect relapses, all birds were negative for viral RNA when sera, spleen, lung, and kidney tissues were tested by reverse transcriptase-polymerase chain reaction after necropsy. Our results indicated that adult mourning doves were an incompetent host for SLE virus and probably do not serve as a suitable overwintering or dispersal host for either WEE and SLE viruses.

Emergence and virulence of encephalitogenic arboviruses

Each arbovirus that causes encephalitis is geographically restricted by the availability of appropriate vectors and reservoir hosts. These viruses evolve regionally by recombination, reassortment and point mutation and can "emerge" as causes of human encephalitis through extension to new geographic regions or by selection of more virulent or more efficiently transmitted virus variants. The properties of arboviruses that result in encephalitis involve efficient replication in peripheral tissues after initiation of infection, production of a viremia, entry into the central nervous system and efficient replication in neurons with spread to additional populations of neurons. Many of these steps are determined by properties of the envelope glycoproteins responsible for cellular attachment, but changes in noncoding regions of the genome, as well as in other structural and nonstructural proteins, also contribute to neurovirulence.

Experimental infection of California birds with western equine encephalomyelitis and St. Louis encephalitis viruses

A total of 27 bird species from the San Joaquin and Coachella valleys of California were inoculated subcutaneously with sympatric strains of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses. Overall, 133 of 164 birds inoculated with WEE virus developed a viremia detected by plaque assay; significantly greater than 72 of 163 birds inoculated with SLE virus. Host competence was calculated as the average number of days that each avian species had a viremia > or = 2 log10 plaque-forming units per 0.1 ml, the threshold for infecting susceptible Culex tarsalis Coquillett, the primary vector of these viruses in California. Eleven of 20 species inoculated with WEE virus had a value > or = 1 and were considered to be competent hosts, whereas only six of 22 species inoculated with SLE virus had a value > or = 1. Overall, 133 of 164 birds inoculated with WEE virus and 105 of 163 inoculated with SLE virus produced antibody detectable by enzyme immunoassay and/or plaque reduction neutralization test. Six birds infected with WEE virus (one house finch, three mourning doves, one Brewer's sparrow, and one white-crowned sparrow) and nine birds infected with SLE virus (two house finches, three white-crowned sparrows, one song sparrow, two Western scrub-jays, and one orange crowned warbler) contained viral RNA detected by reverse transcription-polymerase chain reaction at necropsy > 6 wk postinoculation; infectious WEE and SLE viruses were only recovered from three mourning doves and an orange-crowned warbler, respectively, after blind passage in mosquito cells. Our study indicated that birds with elevated field antibody prevalence rates may not be the most competent hosts for encephalitis viruses and that relatively few birds developed chronic infections that could be important in virus persistence and dispersal.

Transmission patterns of African horse sickness and equine encephalosis viruses in South African donkeys

African horse sickness (AHS) and equine encephalosis (EE) viruses are endemic to southern Africa. AHS virus causes severe epidemics when introduced to naive equine populations, resulting in severe restrictions on the movement of equines between AHS-positive and negative countries. Recent zoning of South Africa has created an AHS-free zone to facilitate equine movement, but the transmission dynamics of these viruses are not fully understood. Here, we present further analyses of serosurveys of donkeys in South Africa conducted in 1983-5 and in 1993-5. Age-prevalence data are used to derive estimates of the force of infection, A. For both viruses, A was highest in the northeastern part of the country and declined towards the southwest. In most of the country, EE virus had a higher transmission rate than AHS. The force of infection increased for EE virus between 1985 and 1993, but decreased for AHS virus. Both viruses showed high levels of variation in transmission between districts within the same province, particularly in areas of intermediate transmission. These data emphasize the focal nature of these viruses, and indicate areas where further data will assist in understanding the geographical variation in transmission.

Tonate virus infection in French Guiana: clinical aspects and seroepidemiologic study

Two recent cases of human infection with Tonate virus, one of which was a fatal case of encephalitis, have renewed interest in these viruses in French Guiana. The clinical aspects of confirmed and probable cases of infection with this virus indicate that it has pathogenic properties in humans similar to those of other viruses of the Venezuelan equine encephalitis complex. To determine the prevalence of antibodies to Tonate virus in the various ethnic groups and areas of French Guiana, 3,516 human sera were tested with a hemagglutination inhibition test. Of these, 11.9% were positive for the virus, but significant differences in seroprevalence were found by age, with an increase with age. After adjustment for age, significant differences were found between places of residence. The prevalence of antibody to Tonate virus was higher in savannah areas, especially in the Bas Maroni (odds ratio [OR] = 22.2, 95% confidence interval [CI] = 15.2-32.4) and Bas Oyapock areas (OR = 13.4; 95% CI = 9.8-18.4). The ethnic differences observed in this study were due mainly to differences in place of residence, except that whites were significantly less frequently infected than other ethnic groups. This study indicates that Tonate virus infection is highly prevalent in French Guiana, especially in savannah areas.

Effect of eastern equine encephalomyelitis virus on the survival of Aedes albopictus, Anopheles quadrimaculatus, and Coquillettidia perturbans (Diptera: Culicidae)

The effect of eastern equine encephalomyelitis (EEE) virus on the survivorship of Aedes albopictus (Skuse), Anopheles quadrimaculatus Say, and Coquillettidia perturbans (Walker) was determined experimentally. Female mosquitoes were allowed to feed on EEE viremic chicks, and survival rates were compared for infected and uninfected mosquitoes. Additionally, the survival of female Cq. perturbans and An. quadrimaculatus intrathoracically (i.t.) inoculated with EEE was compared with controls receiving diluent inoculations. Infection with EEE significantly reduced survival in Cq. perturbans compared with uninfected individuals in per os infection experiments. I.t. infections of Cq. perturbans did not reduce survival when compared with diluent inoculated groups. In contrast, infection with EEE did not affect the survival of Ae. albopictus after per os infection or An. quadrimaculatus after either i.t. or per os infections.

Application of geographic information technology in determining risk of eastern equine encephalomyelitis virus transmission

Geographic information system (GIS) technology and remote sensing were used to identify landscape features determining risk of eastern equine encephalomyelitis virus (EEE) transmission as defined by the abundance of Culiseta melanura (the enzootic vector) and 6 putative epidemic-epizootic vectors in Massachusetts. Landsat Thematic Mapper data combined with aerial videography data were used to generate a map of landscape elements at epidemic-epizootic foci in southeastern Massachusetts. Geographic information system technology was used to determine the proportion of landscape elements surrounding 15 human and horse case sites where abundance data were collected for Culiseta melanura, Aedes canadensis, Aedes vexans, Culex salinarius, Coquillettidia perturbans, Anopheles quadrimaculatus, and Anopheles punctipennis. The relationships between vector abundance and landscape proportions were analyzed using stepwise linear regression. Stepwise regression indicated wetlands as the most important major class element, which accounted for up to 72.5% of the observed variation in the host-seeking populations of Ae. canadensis, Ae. vexans, and Cs. melanura. Moreover, stepwise linear regression demonstrated deciduous wetlands to be the specific wetland category contributing to the major class models. This approach of utilizing GIS technology and remote sensing in combination with street mapping can be employed to identify deciduous wetlands in neighborhoods at risk for EEE transmission and to plan more efficient schedules of pesticide applications targeting adults.

Method of infection does not alter response of chicks and house finches to western equine encephalomyelitis and St. Louis encephalitis viruses

The effects of method of infection and virus dose on the viremia and antibody responses of 1-wk-old chicks and after-hatching-year house finches to infection with western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were studied under laboratory conditions. Using a capillary tube technique, females from 2 strains of Culex tarsalis Coquillett mosquitoes were estimated to expectorate from 1.0 to 1.7 log10 plaque forming units (PFU) of WEE and from 1.9 to 2.2 log10 PFU of SLE. Based on the proportion of parenterally infected females that transmitted and the number that blood fed during each experiment, virus doses per bird were estimated to be 1.0-1.9 log10 PFU for WEE and 1.4-2.3 log10 PFU for SLE. When infected with comparable doses of WEE by subcutaneous inoculation, there was no significant difference in the duration or magnitude of the viremia response between birds infected by mosquito bite or syringe; few birds developed a viremia response after infection with SLE, precluding analysis. In chickens, increasing the syringe dose of WEE from 0.3 to 1.7 log10 PFU/0.1 ml shortened the time when viremia first appeared from 3 to 1 d postinfection and increased the duration of the viremia period from 1 to 3 d, but did not alter the maximum viremia titer. In house finches, increasing the syringe dose of WEE from 2.6 to 3.3 log10 PFU/0.1 ml did not alter markedly the viremia response. Most birds developed antibody detected by enzyme immunoassay (EIA) or plaque reduction neutralization test (PRNT). In chickens, WEE EIA levels and PRNT titers were higher for birds infected by syringe than by mosquito bite, whereas in house finches the pattern was reversed. For birds infected with SLE, there was overlap among groups infected by mosquito bite or syringe. These results indicate that subcutaneous syringe inoculation provides a biologically sound mode of infection that did not alter viremia and antibody responses when compared with infection by mosquito bite.

Toward the incrimination of epidemic vectors of eastern equine encephalomyelitis virus in Massachusetts: abundance of mosquito populations at epidemic foci

Putative epidemic/epizootic eastern equine encephalomyelitis virus (EEE) vector populations were compared at 15 recent (1982-90) human and horse case sites in Bristol and Plymouth counties in southeastern Massachusetts. Carbon dioxide-baited American Biophysics Corporation light traps were used for trapping adult mosquitoes to estimate biting risk in these foci of known transmission. Population data suggest that Coquillettidia perturbans, Aedes canadensis, and Culex salinarius are more likely vectors of EEE in Massachusetts than Aedes vexans, Anopheles punctipennis, and Anopheles quadrimaculatus.

Eastern equine encephalitis virus in birds: relative competence of European starlings (Sturnus vulgaris)

To determine whether eastern equine encephalitis (EEE) virus infection in starlings may be more fulminant than in various native candidate reservoir birds, we compared their respective intensities and durations of viremia. Viremias are more intense and longer lasting in starlings than in robins and other birds. Starlings frequently die as their viremia begins to wane; other birds generally survive. Various Aedes as well as Culiseta melanura mosquitoes can acquire EEE viral infection from infected starlings under laboratory conditions. The reservoir competence of a bird is described as the product of infectiousness (proportion of feeding mosquitoes that become infected) and the duration of infectious viremia. Although starlings are not originally native where EEE is enzootic, a starling can infect about three times as many mosquitoes as can a robin.

Molecular epidemiological studies of veterinary arboviral encephalitides

Recent studies using molecular genetic approaches have made important contributions to our understanding of the epidemiology of veterinary arboviral encephalitides. Viruses utilizing avian enzootic hosts, such as Western equine encephalitis virus (WEEV) and North American Eastern equine encephalitis virus (EEEV), evolve as relatively few, highly conserved genotypes that extend over wide geographic regions; viruses utilizing mammalian hosts with more limited dispersal evolve within multiple genotypes, each geographically restricted. Similar findings have been reported for Australian alphaviruses. This difference may be related to vertebrate host relationships and the relative mobility of mammals and avians. Whereas EEEV and Venezualan equine encephalitis virus (VEEV) utilize small mammalian hosts in the tropics, most WEEV genotypes probably utilize avian hosts in both North and South America. The ability of mobile, infected avian hosts to disperse alphaviruses may result in continual mixing of virus populations, and thus limit diversification. This high degree of genetic conservation is also exhibited by EEE and Highlands J viruses in North America, where passerine birds serve as amplifying hosts in enzootic transmission foci. Most equine arboviral pathogens, including EEEV, WEEV and Japanese encephalitis virus (JEV), occur in a naturally virulent enzootic state and require only appropriate ecological conditions to cause epizootics and epidemics. However, VEE epizootics apparently require genetic changes to convert avirulent enzootic strains into distinct epizootic serotypes. All of these arboviruses have the potential to cause severe disease of veterinary and human health importance, and further molecular epidemiological studies will undoubtedly improve our ability to understand and control future emergence.

Impact of naled on the mosquito vectors of eastern equine encephalitis virus

This letter questions the appropriateness of methodology used in a study by Howard and Oliver (J. Am. Mosq. Control Assoc. 13:315-325; 1988). Two independent data sets, collected for different purposes by 2 different groups, were subjected to statistical analysis to determine if the data sets differed. The experimental "design," as described by the authors, is an example of pseudoreplication, which arises when replicates are collected at a scale finer than the one for which conclusions of statistical testing are intended to be drawn. All of the components of a properly designed field experiment (control, replication, randomization, and interspersion) are missing from this study. The authors proceed to draw a series of conclusions from the data presented. Few, if any, of the conclusions can be supported by the evidence presented. The assertions put forward in this paper could have a severe negative impact on efforts to prevent transmission of arboviruses or other pathogens to humans and domestic animals.

Vector competence of Aedes dorsalis (Diptera: Culicidae) from Morro Bay, California, for western equine encephalomyelitis virus

In laboratory vector competence studies, Aedes dorsalis (Meigen) collected from Morro Bay, CA, did not vertically transmit sympatric strains of western equine encephalomyelitis virus (WEE). This population of Ae. dorsalis was highly susceptible to oral infection and was a competent horizontal vector of WEE. The E2 region of the viral genome of the 3 virus strains isolated from Ae. dorsalis in Morro Bay were closely related genetically to a strain of WEE isolated in 1953 from a geographically separate location that is used regularly in the laboratory. These laboratory findings support recent field research and indicate that Ae. dorsalis probably does not play a significant role in WEE persistence in coastal California.

Monitoring the abundance of Aedes (Ochlerotatus) albifasciatus (Macquart 1838) (Diptera: Culicidae) to the south of Mar Chiquita Lake, central Argentina, with the aid of remote sensing

Surges in the size of adult populations of the flood-water mosquito Aedes albifasciatus can produce important economical losses because of the way this species irritates livestock. Although this species is also the main vector of west equine encephalitis in Argentina, little is known about the factors affecting its population dynamics, as it is difficult to obtain data on its abundance over a large area. However, the results of intensive study of the mosquito in a few sites might reasonably be extrapolated to a regional scale by the use of remotely sensed data. The adult, larval and pupal stages of Ae. albifasciatus were sampled at five field sites to the south of Mar Chiquita Lake, either once a month (during the dry, cold season) or once a fortnight (during the warm, rainy season), between August 1992 and April 1993. The measured abundance of adults or pre-adults and a meteorological coefficient useful for the estimation of larval abundance each showed significant correlation with various statistics derived from normalized-difference, vegetation indices (NDVI) calculated from satellite (NOAA-AVHRR) imagery. A linear discriminant analysis, using data on NDVI, rainfall and temperature, accurately identified periods with and without pre-adults. The satellite imagery was also useful in the estimation of larval abundance and consequently could be used to predict adult abundance 7 days in advance. Even though the satellite data employed have poor spatial resolution, their high temporal resolution makes them very useful in studies of the population dynamics of mosquitoes in general, at least once the relevant variables and their relationships with mosquito breeding and survival have been identified.

Prevalence of antibodies to western equine encephalomyelitis and St. Louis encephalitis viruses in residents of California exposed to sporadic and consistent enzootic transmission

Sera from outpatients attending county health department clinics in areas of California with consistent (Imperial Valley) and sporadic (Sacramento Valley) enzootic transmission of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses exhibited neutralizing antibody prevalence rates of 1.3% (n = 690) and 0.5% (n = 1,066) for WEE and 11.0% and 0.8% for SLE, respectively. Seroprevalence for SLE virus in Imperial County increased as a function of both age and years of residence, indicating that this virus was endemic with a low rate of annual infection. Of 26 sera that tested positive for SLE virus antibody by an enzyme immunoassay, but were negative by plaque reduction neutralization test, 14 (53%) had neutralizing antibody that reacted with > or = one type of dengue (DEN) virus. The DEN virus infections presumably were acquired elsewhere because neither the vectors nor DEN virus transmission occurs in California. The low prevalence of neutralizing antibody for WEE and SLE in the California human population indicated that despite recent increases in enzootic transmission, contact between humans and infectious mosquitoes have remained low.

Time of host-seeking by Culex tarsalis (Diptera:Culicidae) in California

Factors altering the pattern of Culex tarsalis Coquillett host-seeking activity were studied in Kern and Riverside counties of California using an automatic time-segregated sampler baited with bottled CO2 gas released at 0.5 or 1.0 liters/min. Host-seeking always commenced shortly after sunset and usually peaked during the succeeding 1-3 h, the hottest and driest time of the night. The time of maximal activity varied over time and space, because of increased mosquito abundance (presumably reduced blood feeding success), distance of the sampler from resting sites, adulticide applications, and perhaps weather.

Eastern equine encephalitis transmission to emus (Dromaius novaehollandiae) in Volusia County, Florida: 1992 through 1994

From May 1992 through October 1994, sera were collected from 204 domestic emus (Dromaius novaehollandiae) at a ranch in Volusia County, FL, and tested for antibody evidence of arboviral infection. Hemagglutination-inhibition (HI) and neutralizing (NT) antibodies to eastern equine encephalitis (EEE) virus were identified in sera collected during each year. In addition, HI and NT antibodies to St. Louis encephalitis virus were detected in 3 naturally infected emus. Isolations of EEE virus were made from emu blood and tissues collected in 1992 and 1994, when EEE-related mortality in emus was 14% and 1%, respectively. A total of 259 mosquito pools was collected and tested for arbo-viruses during the 3-year study. The EEE virus was isolated from 4 of 140 mosquito pools (2 Anopheles crucians and 2 Culex erraticus pools) in 1992 and 3 of 10 pools (all Culex nigripalpus) in 1994. Emus vaccinated against EEE virus showed evidence of short-term HI antibody acquisition. Evidence of EEE antibody transfer from naturally infected hens to their offspring is reported.

Evidence for multiple foci of eastern equine encephalitis virus (Togaviridae:Alphavirus) in central New York State

A regional surveillance system for eastern equine encephalitis (EEE) virus was established in central New York in 1984 after the 2nd human EEE fatality occurred in 1983. Extensive mosquito surveillance activities were coordinated with the rapid laboratory processing of mosquito specimens for EEE virus. Active surveillance for EEE infections in humans and equines also was initiated. Results of long-term surveillance detected the presence of multiple Culiseta breeding swamps. A 6-yr interepizootic period (1984-1989) was followed by 2 yr of equine EEE. In 1990, there were 7 equine cases and a record number of EEE virus isolations from mosquitoes (n = 86), wild birds (n = 27), and sentinel pheasants (n = 7). In 1991, 7 equine cases also occurred, although there were fewer isolations from mosquitoes (n = 40). The sequence to the appearance of EEE virus at swamps and upland sites and at individual swam complexes, and the spatial and temporal distribution of equine cases provide evidence for multiple foci of EEE virus in central New York. The role of infected Culiseta melanura (Coquillett) in the transfer of EEE virus between swamp and upland areas and among swamp complexes is advanced.

Dual host infections: enhanced infectivity of eastern equine encephalitis virus to Aedes mosquitoes mediated by Brugia microfilariae

When mosquitoes feed on a vertebrate host that is infected concurrently with virus and microfilariae (mf), both pathogens are ingested. If mf penetrate the mosquito midgut, a small portion of the ingested virus may disseminate directly into the mosquito hemocoel. This phenomenon, termed microfilarial enhancement of arboviral transmission, has the potential to enhance the infectivity of arboviruses to mosquitoes. We investigated whether concurrent ingestion of Brugia mf and eastern equine encephalitis virus would enhance the infectivity and subsequent transmissibility of the virus by Aedes mosquitoes. Trials with Ae. triseriatus and B. pahangi mf indicated that microfilarial enhancement was dose dependent. Both a sufficient number of penetrating mf and a sufficient viremia were required for enhancement to occur. Furthermore, studies with B. malayi and three species of Aedes indicated that under comparable conditions of host viremia and microfilaremia, microfilarial enhancement occurred in some mosquito species (i.e., Ae. aegypti and Ae. taeniorhynchus) but not in others (Ae. triseriatus). We suggest that certain key parameters determine whether dual virus/mf host infections will enhance arboviral infectivity to mosquitoes. These include species differences in the capacity of mf to penetrate the mosquito midgut, the amount of virus passing into the hemocoel during mf penetration, and the innate susceptibility of mosquitoes to hemocoelomically introduced virus.

Landscape ecology of arboviruses in southern California: patterns in the epizootic dissemination of western equine encephalomyelitis and St. Louis encephalitis viruses in Coachella Valley, 1991-1992

Temporal and spatial patterns in the initiation and dissemination of western equine encephalomyelitis and St. Louis encephalitis virus activity in Coachella Valley during 1991 and 1992 were detected by testing pools of host-seeking Culex tarsalis Coquillett for virus infection and sentinel chickens for seroconversions. Both viruses repeatedly were detected first at a salt marsh adjacent to the Salton Sea in the southeastern corner of the study area and then disseminated to the northwest to freshwater marsh, agricultural, and residential habitats. Virus dissemination was relatively slow (< 1 km/d) and may have been accomplished by dispersive host-seeking mosquitoes. Repeated early-season recovery of virus activity indicated that both viruses may persist interseasonally in salt marsh habitat.

Bionomics of Culex tarsalis (Diptera: Culicidae) in relation to arbovirus transmission in southeastern California

Population dynamics and bionomics of host-seeking Culex tarsalis Coquillett were studied in the Imperial and Coachella valleys of California during periods in 1991 and 1992 when western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were transmitted to sentinel chickens. Female abundance was greatest during the spring and fall, before and after most virus transmission occurred and was not correlated with temperature, humidity, or rainfall. Parity rates were highest during late summer when virus activity peaked and were lowest during December when females may enter a short-term reproductive diapause. Although most likely underestimated, the proportion of older multiparous females were collected at a consistent, but low level throughout the year. Changes in the parity rate seemed to be influenced primarily by the proportions of 1-parous females. Survivorship estimated from the parity rate (adjusted to account for autogeny) was highest in winter; however, the proportion of females surviving to potentially transmit either WEE or SLE virus was highest in summer and early fall. Wing length decreased in summer as an inverse correlate of temperature and increased as a function of female age, implying that larger females lived longest. However, autogenous females were larger than anautogenous females at emergence and only parous autogenous females were collected host seeking, thereby confounding the relationship between size and age. The proportion of females testing positive for fructose was greatest during winter and lowest during summer, perhaps affecting survivorship and blood-feeding avidity. The vector competence (infection, dissemination and transmission rates, and ID50) of females collected host seeking or emerging from field-collected pupae for WEE or SLE viruses remained similar over time, even though the wing length of females used in these experiments differed among samples. We conclude that in nature virus transmission progressed efficiently during midsummer because elevated temperatures shortened the extrinsic incubation period without markedly decreasing survivorship resulting in an increased proportion of females surviving extrinsic incubation to become infective.

Landscape ecology of arboviruses in southern California: temporal and spatial patterns of vector and virus activity in Coachella Valley, 1990-1992

Consistent temporal and spatial patterns in the activity of Culex tarsalis Coquillett and western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses were delineated that were useful in developing a stratified surveillance program. Vernal increases in Cx. tarsalis abundance typically were associated with flooding of saline marshes along the north shore of the Salton Sea and were followed 6-8 wk later by the onset of WEE and SLE virus activity. Viruses then spread to managed marsh (duck club) and agricultural habitats in the Whitewater Channel flood plain and, depending upon the intensity of amplification, to agricultural and residential areas in the more elevated northwestern portion of the valley. Mean annual Cx. tarsalis abundance was correlated inversely with elevation and distance from the Salton Sea. Abundance was greatest at managed marsh habitats. Although spatially correlated with vector abundance among sites, virus transmission rates to sentinel chickens were asynchronous temporally with vector abundance. Seroconversion rates were related to flock location but not flock size (10 versus 20 chickens). Human cases were not detected during the study period, despite elevated transmission rates of both WEE and SLE viruses to sentinel chickens positioned in peridomestic habitats.

Experimental transmission of eastern equine encephalitis virus and Highlands J virus via semen of infected tom turkeys

Tom turkeys were experimentally inoculated with eastern equine encephalitis (EEE) virus or Highlands J (HJ) virus; semen was examined for presence of virus and ability to transmit infection by artificial insemination. Mild depression and inappetence were observed in tom turkeys inoculated with either EEE virus or HJ virus. Toms were viremic on days 1-2 postinoculation (PI), and virus was shed in semen on days 1-5 PI. Semen collected from EEE-virus-inoculated or HJ-virus-inoculated toms on days 1-2 PI and inseminated into turkey breeder hens transmitted the infection. EEE virus was detected in one of 10 hens after insemination with semen from EEE-virus-inoculated toms, and HJ virus was detected in three of 10 hens after insemination with semen from HJ-virus-inoculated toms. These results indicate that semen is a potential vehicle for transmission of EEE virus and HJ virus.