Eastern Equine Encephalitis Virus Infection Research Articles

Eastern Equine Encephalitis Virus: High Seroprevalence in Horses from Southern Quebec, Canada, 2012

Eastern equine encephalitis virus (EEEV) is a highly pathogenic arbovirus that infects humans, horses, and other animals. There has been a significant increase in EEEV activity in southeastern Canada since 2008. Few data are available regarding nonlethal EEEV infections in mammals, and consequently the distribution and pathogenicity spectrum of EEEV infections in these hosts is poorly understood. This cross-sectional study focuses on the evaluation of viral activity in southern Quebec's horses by seroprevalence estimation. A total of 196 horses, 18 months and older, which had never been vaccinated against EEEV and have never traveled outside Canada, were sampled from 92 barns distributed throughout three administrative regions of southern Quebec. Blood samples were taken from each horse and titrated for EEEV antibodies by plaque reduction neutralization test (PRNT). Equine population vaccination coverage was estimated by surveying horse owners and equine practitioners. PRNT results revealed an EEEV seroprevalence up to 8.7%, with 95% confidence limits ranging from 4.4% to 13.0%. Vaccination coverage was estimated to be at least 79%. Our study reveals for the first time in Canada a measure of EEEV seroprevalence in horses. High seroprevalence in unvaccinated animals challenges the perception that EEEV is a highly lethal pathogen in horses. Monitoring high-risk vector-borne infections such as EEEV in animal populations can be an important element of a public health surveillance strategy, population risk assessment and early detection of epidemics.

Snakes May Be Winter Reservoir for Encephalitis Virus

Snakes harbor Eastern equine encephalitis virus (EEEV), apparently accounting for how this virus survives during cold winters, according to Thomas Unnasch and his collaborators at the University of Southern Florida in Tampa and also at Auburn University in Auburn, Ala. The viruses emerge to cause a surge in EEEV infections during summers, when mosquitoes transmit the virus, mainly to horses but also to humans. “So far, we've shown that snakes have the circulating virus,” he says. “We need to confirm the rest of the cycle.”

Estimation of dispersal distances of Culex erraticus in a focus of eastern equine encephalitis virus in the southeastern United States.

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.

Pathogenesis of aerosolized Eastern Equine Encephalitis virus infection in guinea pigs

Mice and guinea pigs were experimentally exposed to aerosols containing regionally-distinct strains (NJ1959 or ArgM) of eastern equine encephalitis virus (EEEV) at two exclusive particle size distributions. Mice were more susceptible to either strain of aerosolized EEEV than were guinea pigs; however, clinical signs indicating encephalitis were more readily observed in the guinea pigs. Lower lethality was observed in both species when EEEV was presented at the larger aerosol distribution (> 6 μm), although the differences in the median lethal dose (LD50) were not significant. Virus isolation and immunohistochemistry indicated that virus invaded the brains of guinea pigs within one day postexposure, regardless of viral strain or particle size distribution. Immunohistochemistry further demonstrated that neuroinvasion occurred through the olfactory system, followed by transneuronal spread to all regions of the brain. Olfactory bipolar neurons and neurons throughout the brain were the key viral targets. The main microscopic lesions in infected guinea pigs were neuronal necrosis, inflammation of the meninges and neuropil of the brain, and vasculitis in the brain. These results indicate that guinea pigs experimentally infected by aerosolized EEEV recapitulate several key features of fatal human infection and thus should serve as a suitable animal model for aerosol exposure to EEEV.

Prevalence of Antibodies to West Nile Virus and Other Arboviruses among Crested Caracaras (Caracara cheriway) in Florida

We documented the antibody prevalence to three arboviruses, St. Louis encephalitis virus (SLEV), eastern equine encephalitis virus (EEEV), and West Nile virus (WNV), in Crested Caracaras (Caracara cheriway; n = 80) in Florida from 2007 to 2008. Antibody prevalence to WNV was higher (9%) than for the other viruses. Most seropositive birds were adults (< or =3 yr of age), with 55% of adults testing positive for antibodies to at least one virus. Adults were significantly more likely to have antibodies to WNV than nonadults (P<0.001). Prevalence of SLEV and EEEV antibodies among Crested Caracaras was 3% for each virus, and three adult caracaras had indistinguishable anti-flavivirus antibodies. The susceptibility of Crested Caracaras to adverse effects of WNV, SLEV, or EEEV infection remains unknown; however, we observed that some free-ranging individuals survived infection and successfully fledged young. Knowledge of arboviral infection among Florida's Crested Caracara, which is both state and federally threatened, is valuable considering increasing pressure on this population from rapid and extensive habitat alterations.

EASTERN EQUINE ENCEPHALITIS VIRUS INFECTION AND HEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS IN A 5-MONTH-OLD INFANT

Eastern equine encephalitis virus infection is a rare sporadic central nervous system infection transmitted by a mosquito vector. Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening disease associated with the inability of an overactive immune system to effectively respond to infections. Many viruses are known to trigger primary, as well as secondary, HLH. We report a pediatric case of eastern equine encephalitis virus-associated HLH which caused severe neurologic injury and death.

AN OUTBREAK OF EASTERN EQUINE ENCEPHALITIS VIRUS IN FREE-RANGING WHITE-TAILED DEER IN MICHIGAN

Eastern equine encephalitis (EEE) virus has been recognized as affecting horses and humans in the eastern United States for 70 yr. Evidence of exposure with EEE virus has been reported in a variety of free-ranging wild birds and mammals but cases of clinical disease are much less commonly reported. In Michigan, reports of outbreaks of EEE virus in equine species extend back more than a half century. We report diagnosis of EEE virus infection of multiple free-ranging white-tailed deer (Odocoileus virginianus) from three Michigan counties during late summer of 2005. Infection was confirmed in seven of 30 deer collected based on reported neurologic signs and results from immunohistochemistry, polymerase chain reaction, and/or virus isolation. One of the deer also was infected with West Nile virus and an eighth deer had microscopic lesions in the cerebrum consistent with those reported for EEE. To our knowledge, this is the first report of multiple cases of EEE in free-ranging white-tailed deer, and highlights several issues of significance to wildlife managers and public health officials.

HUMAN EASTERN EQUINE ENCEPHALITIS IN MASSACHUSETTS: PREDICTIVE INDICATORS FROM MOSQUITOES COLLECTED AT 10 LONG-TERM TRAP SITES, 1979–2004

Human eastern equine encephalitis (EEE) is a life-threatening mosquito-borne disease. To determine whether mosquito abundance and EEE virus infection rates are associated with human EEE disease, we evaluated retrospectively a total of 592,637 mosquitoes and onset dates for 20 confirmed human cases over 26 years in Massachusetts. Annual Culiseta melanura populations at 10 defined sites decreased over the study period (P = 0.002). Weekly infection rates and number of infected Culiseta melanura captured per trap night were positively associated EEE cases (P < 0.023 and P < 0.001, respectively), whereas abundance was not (P = 0.077). The infection rate for Culiseta melanura of 0.39 per 1,000 tested mosquitoes identified human cases with a sensitivity of 0.87, a specificity of 0.82, a positive predictive value of 0.14, and a negative predictive value of 0.995. Timely mosquito testing and infection rate calculation are critical for disease risk estimation and outbreak control efforts.

A dynamic transmission model of eastern equine encephalitis virus

Eastern equine encephalitis virus (EEEV) is one of several arthropod-borne viruses (arboviruses) endemic to the United States. Interactions between arthropod (mosquito) vectors and avian amplification host populations play a significant role in the dynamics of arboviral transmission. Recent data have suggested the hypothesis that an increased rate of successful feeding on young-of-the-year (YOY) birds might play a role in the dynamics of EEEV transmission. To test this hypothesis, we developed a model to explore the effect of the interactions of the vectors and avian host populations on EEEV transmission. Sensitivity analyses conducted using this model revealed eleven parameters that were capable of disproportionately affecting the predicted level of EEEV infection in the vertebrate reservoir and vector populations. Of these, four parameters were related to the interaction of the vector with young-of-the-year birds. Furthermore, adult birds could not substitute for young-of-the-year in initiating and maintaining a predicted enzootic outbreak of EEEV. Taken together, the model predicted that young-of-the-year birds play a key role in establishing and maintaining enzootic outbreaks of EEEV.

Eastern Equine Encephalitis in a Free-ranging White-tailed Deer (Odocoileus virginianus)

Eastern equine encephalitis (EEE) was diagnosed in a free-ranging, adult, male white-tailed deer (Odocoileus virginianus) from Houston County, Georgia, USA, in July 2001. The yearling buck had neurologic disease and died during transport to our diagnostic facility. Eastern equine encephalitis virus (EEEV) was isolated in Vero cell culture and identified by reverse-transcriptase polymerase chain reaction; as well, EEEV antigen was detected in brain by immunohistochemistry. This is the first report of fatal EEEV infection in a white-tailed deer. Antibodies to EEEV were demonstrated by microtiter neutralization in 14 of 99 (14%) of the white-tailed deer from Georgia sampled in fall 2001. Most antibody-positive deer originated from the Coastal Plain physiographic region. Eastern equine encephalitis virus should be considered a possible cause of neurologic disease in white-tailed deer where it may occur.

Evaluation of outbreaks of disease attributable to eastern equine encephalitis virus in horses

Objectives To evaluate outbreaks of disease attributable to eastern equine encephalitis virus (EEEV) in horses in Michigan, and the associated environmental patterns and weather conditions, so that factors could be identified that may have predisposed horses in specific areas of the state to infections with EEEV. Design Epidemiologic retrospective records analysis. Animals Data on EEEV vectors, wild-bird reservoir hosts, and incidental hosts, including horses and human beings, obtained from census reports and medical records compiled between 1942 and 1991. Procedure Patterns detected during outbreaks of disease attributable to EEEV infections in horses were compared to associated water drainage patterns, distributions of EEEV vectors, wild-bird reservoir and incidental hosts, and weather conditions. Results Michigan has all of the elements required to sustain EEEV on a state-wide basis. Outbreaks of disease attributable to EEEV in horses have recurred in a similar regional distribution in Michigan. Regions of Michigan that have specific patterns for water drainage, specific mosquito species, and areas with higher than expected amounts of precipitation have been associated with outbreaks of disease attributable to EEEV in horses. Clinical Implications Evaluation of environmental patterns, weather conditions, and vector and reservoir host distributions may be useful to identify areas in Michigan and elsewhere in which horses and human beings are at increased risk for an outbreak of disease attributable to EEEV. (J Am Vet Med Assoc 1996;208:1988-1997)

Pathology of Eastern Equine Encephalitis in Emus (Dromaius novaehollandiae)

Pathology of Eastern Equine Encephalitis in Emus (<i>Dromaius novaehollandiae</i>)

High Mortality of Domestic Turkeys Associated with Highlands J Virus and Eastern Equine Encephalitis Virus Infections

High mortality occurred in two flocks of commercial turkey hens placed in southern North Carolina in fall 1991. Daily mortality peaked at 3.19% in Flock 1 and 3.79% in Flock 2. Clinical signs included restlessness, somnolence, vocalization, and acute death. Gross lesions included atrophy of the bursa of Fabricius, thymus, and spleen, and watery intestinal contents. Microscopic changes included moderate to marked lymphocyte necrosis and depletion in the bursa, thymus, and spleen, widely scattered necrosis of pancreatic acinar cells, and mild villous atrophy and fusion in the jejunum and ileum with cuboidal to low columnar epithelial cells covering the villous tips. In Flock 1, at 27 days of age, reovirus and picornavirus particles were detected in the feces. One week later, togavirus-like particles were observed in fecal contents, and two of seven serum samples showed seroconversion to Highlands J virus. Eleven days later, five of six serum samples were positive for antibodies against Highlands J virus, with a fourfold increase in the geometric mean titer. In Flock 2, seroconversion to eastern equine encephalitis virus was observed in four of 10 serum samples 11 days after the onset of clinical signs. Based on the above observations, it is suspected that these alphaviruses were the cause of the clinical syndrome.

Epizootiology of eastern equine encephalitis virus in upstate New York, USA. VII. Virus surveillance 1978-85, description of 1983 outbreak, and series conclusions.

Mosquito and arbovirus surveillance activities have been routinely conducted in upstate New York since 1971. This report details the surveillance results during 1978–85. Minimal virus activity was detected in the first 4 yr of concentrated surveillance at Toad Harbor Swamp, Oswego County. In 1983, an outbreak of eastern equine encephalitis (EEE) resulted in one human and nine equine cases. The outbreak was preceded by an epiornitic of Highlands J (HJ) virus in 1982; this was the first evidence of HJ virus activity in the region. Isolations of EEE virus from mosquitoes in 1983 incriminated Culiseta melanura (Coquillett) and Cs. morsitans (Dyar) as epiornitic vectors and Aedes canadensis (Theobald) as an epizootic vector. Mosquito collection data from two endemic foci indicated substantial and significant differences in EEE virus infection rates. The occurrence of HJ virus, the differences in mosquito infection rates, and widespread epizootic disease during a year of low mosquito densities are used to develop a hypothesis on the distribution of multiple endemic foci of EEE virus in upstate New York.

Eastern equine encephalitis in the United States, 1971: Past and prologue

During 1971, surveillance for equine encephalitis in the United States was increased due to an epizootic of Venezuelan equine encephalomyelitis. Of 1,982 specimens from 1,551 equines, 76 isolates of eastern equine encephalitis (EEE) virus were recovered from 67 individuals. The virus was isolated from 50/176 brains, 8/74 spleens, 14/1,127 sera, and 4/147 whole bloods from infected equines in 12 of the 31 states bounded by or east of the Mississippi River and in Texas and Iowa; no specimens were received from 9 of these 31 states. Thus, EEE virus was isolated from equines in 12 of 22 of these states. Determinations of antibody to EEE and western equine encephalitis (WEE) viruses indicated a relatively high prevalence of infection with EEE virus in the eastern USA and similarly high prevalence of antibody to WEE virus in the western USA. These data indicate that equine infections with EEE virus in the eastern USA are considerably more common than previous surveillance data have suggested. Increased surveillance and submission of specimens to diagnostic laboratories for diagnosis of EEE virus infections in equines are suggested so that a greater proportion of the thousands of unspecified equine encephalitis cases occurring in the United States each year can be laboratory confirmed.

Eastern equine encephalitis virus infection: Electron microscopic studies of mouse central nervous system

Eastern equine encephalitis (EEE) virus infection of the central nervous system of newborn mice was examined by light and electron microscopy. Initial changes in brain architecture were due to interstitial and perivascular edema formation; the resulting extracellular space increased throughout the course of infection. Neuronal damage consisted of disruption of cytoplasmic organization and terminated in crenation, vacuolation, and membrane breakdown. Virus nucleoids (28 nm in diameter) were formed in the cytoplasmic matrix of all types of brain cells except endothelium, and viral maturation took place via nucleoid budding primarily through plasma membranes. Virus particles were 55 nm in diameter and were similar in morphology to other group A arboviruses.