Venezuelan equine encephalitis virus, southern Mexico

Equine epizootics of Venezuelan equine encephalitis (VEE) occurred in the southern Mexican states of Chiapas in 1993 and Oaxaca in 1996. To assess the impact of continuing circulation of VEE virus (VEEV) on human and animal populations, serologic and viral isolation studies were conducted in 2000 to 2001 in Chiapas State. Human serosurveys and risk analyses indicated that long-term endemic transmission of VEEV occurred among villages with seroprevalence levels of 18% to 75% and that medical personnel had a high risk for VEEV exposure. Seroprevalence in wild animals suggested cotton rats as possible reservoir hosts in the region. Virus isolations from sentinel animals and genetic characterizations of these strains indicated continuing circulation of a subtype IE genotype, which was isolated from equines during the recent VEE outbreaks. These data indicate long-term enzootic and endemic VEEV circulation in the region and continued risk for disease in equines and humans.     

Postepizootic persistence of Venezuelan equine encephalitis virus, Venezuela

Five years after the apparent end of the major 1995 Venezuelan equine encephalitis (VEE) epizootic/epidemic, focal outbreaks of equine encephalitis occurred in Carabobo and Barinas States of western Venezuela. Virus isolates from horses in each location were nearly identical in sequence to 1995 isolates, which suggests natural persistence of subtype IC VEE virus (VEEV) strains in a genetically stable mode. Serologic evidence indicated that additional outbreaks occurred in Barinas State in 2003. Field studies identified known Culex (Melanoconion) spp. vectors and reservoir hosts of enzootic VEEV but a dearth of typical epidemic vectors. Cattle serosurveys indicated the recent circulation of enzootic VEEV strains, and possibly of epizootic strains. Persistence of VEEV subtype IC strains and infection of horses at the end of the rainy season suggest the possibility of an alternative, cryptic transmission cycle involving survival through the dry season of infected vectors or persistently infected vertebrates.     

Experimental Everglades virus infection of cotton rats (Sigmodon hispidus)

Everglades virus (EVEV), an alphavirus in the Venezuelan equine encephalitis (VEE) serocomplex, circulates among rodents and vector mosquitoes and infects humans, causing a febrile disease sometimes accompanied by neurologic manifestations. EVEV circulates near metropolitan Miami, which indicates the potential for substantial human disease, should outbreaks arise. We characterized EVEV infection of cotton rats in South Florida, USA, to validate their role in enzootic transmission. To evaluate whether the viremia induced in cotton rat populations regulates EVEV distribution, we also infected rats from a non-EVEV-endemic area. Viremia levels developed in rats from both localities that exceeded the threshold for infection of the vector. Most animals survived infection with no signs of illness, despite virus invasion of the brain and the development of mild encephalitis. Understanding the mechanisms by which EVEV-infected cotton rats resist clinical disease may be useful in developing VEE therapeutics for equines and humans.     

委内瑞拉马脑炎的研究进展

委内瑞拉马脑炎（Venezuelan equine encephalitis,VEE）是由委内瑞拉马脑炎病毒复合物（VEEV复合物）引起的自然疫源性疾病,历史上引起了多次暴发流行。VEEV还是一种潜在的、可以用于战争和恐怖活动的生物武器。本文就VEE的病原学、流行病学、临床表现、实验室检测、治疗和预防等方面予以综述。     

Venezuelan equine encephalitis virus vaccine candidate (V3526) safety, immunogenicity and efficacy in horses

A new vaccine, V3526, is a live-attenuated virus derived by site-directed mutagenesis from a virulent clone of the Venezuelan equine encephalitis virus (VEEV) IA/B Trinidad donkey (TrD) strain, intended for human use in protection against Venezuelan equine encephalitis (VEE). Two studies were conducted in horses to evaluate the safety, immunogenicity, ability to boost and protective efficacy of V3526 against challenges of TrD and VEEV IE 64A99. Horses were vaccinated subcutaneously (SC) with 10(7), 10(5), 10(3) or 10(2) plaque-forming units (pfu) of V3526. Control horses were sham immunized. In the first study, challenge viruses (TrD or 64A99) were administered SC 28 days post-vaccination (PV). No viremia and only mild fluctuation in white blood cell counts were observed PV. None of the V3526 vaccinated horses showed clinical signs of disease or pathology of VEE post-challenge (PC). In contrast, control horses challenged SC with 10(4)pfu TrD became viremic and showed classical signs of VEE beginning on Day 3 PC, including elevated body temperature, anorexia, leukopenia and malaise. Moderate to severe encephalitis was found in three of five control horses challenged with TrD. Control horses challenged with 64A99 failed to develop detectable viremia, but did exhibit a brief febrile episode at 1-3 days PC. None of the 10 immunized horses challenged with 64A99 became pyrexic. Twenty four of 25 horses immunized with V3526 in the first study developed serum neutralizing antibody to TrD and 64A99 within 14 days PV. Vaccinations with V3526, at doses as low as 10(2)pfu, were safe and efficacious in protecting horses against a virulent TrD virus challenge. The second study supported that repeat dosing resulted in an increase in serum neutralizing antibody to TrD.     

Arbovirus vector ecology studies in Mexico during the 1972 Venezuelan equine encephalitis outbreak.

Virus vector studies were conducted in the States of Durango, Chihuahua, and Tamaulipas, Mexico, in June and July 1972. Apparently only a low level of Venzuelan equine encephalitis (VEE) virus transmission to equines occured at the time of the study, and the infection was restricted to areas which had not experienced overt activity during the preceding year. The low level of infection was associated with a scarcity of mosquitoes. The IB (epidemic) strain of VEE virus was isolated from two pools of Anopheles pseudopunctipennis (Theo.) and the blood of one symptomatic equine. The low mosquito population, the relatively few equine cases observed, and the absence of reports of VEE human disease from the outbreak area suggested VEE virus persistence through a low-level mosquito-equine transmission cycle. Other studies have already indicated that wild vertebrates play no more than a minor role in outbreaks of epidemic VEE. Mosquito collections made in areas of the states of Durango, Chihuahua, and Tamaulipas, where considerable epidemic activity of VEE had occurred in 1971, failed to reveal evidence of VEE virus persistence. Twenty-nine ioslations of other arboviruses were also made in these studies: including 22 of St. Louis encephalitis virus (SLE), 2 of Flanders virus, 1 of Turlock virus, 1 of Trivittatus virus of the California Group, 1 of western equine encephalitis virus (VEE), and 2 (from Santa Rose) which possibly represent a hitherto unknown virus in the Bunyamwera Group. These are the first reports of SLE virus isolations from mosquitoes in Mexico, and the first demonstration of Trivittatus, VEE Turlock and Flanders viruses in Mexico from any source.     

Venezuelan Equine Encephalitis and 2 Human Deaths,Peru

Studies have suggested that enzootic strains of Venezuelan equine encephalitis (VEE) subtype ID in the Amazon region, Peru, may be less pathogenic to humans than are epizootic variants. Deaths of 2 persons with evidence of acute VEE virus infection indicate that fatal VEEV infection in Peru is likely. Cases may remain underreported.     

Venezuelan equine encephalitis virus infection of spiny rats

Enzootic strains of Venezuelan equine encephalitis virus (VEEV) circulate in forested habitats of Mexico, Central, and South America, and spiny rats (Proechimys spp.) are believed to be the principal reservoir hosts in several foci. To better understand the host-pathogen interactions and resistance to disease characteristic of many reservoir hosts, we performed experimental infections of F1 progeny from Proechimys chrysaeolus collected at a Colombian enzootic VEEV focus using sympatric and allopatric virus strains. All animals became viremic with a mean peak titer of 3.3 log10 PFU/mL, and all seroconverted with antibody titers from 1:20 to 1:640, which persisted up to 15 months. No signs of disease were observed, including after intracerebral injections. The lack of detectable disease and limited histopathologic lesions in these animals contrast dramatically with the severe disease and histopathologic findings observed in other laboratory rodents and humans, and support their role as reservoir hosts with a long-term coevolutionary relationship to VEEV.     

Expression, processing, and immunogenicity of the structural proteins of Venezuelan equine encephalitis virus from recombinant baculovirus vectors

Recombinant baculoviruses expressing the structural proteins of Venezuelan equine encephalitis virus (VEE) have been constructed and the intracellular processing, antigenicity, and immunogenicity of the expression products have been assessed. Baculoviruses expressing the entire structural protein region (C-E3-E2-6K-E1), or the complete glycoprotein region (E3-E2-6K-E1), generated products in Sf9 cells that were accurately and completely processed, and resulted in mature proteins that were antigenically and electrophoretically indistinguishable from authentic viral proteins. These products were highly immunogenic in BALB/c mice, induced efficient VEE neutralizing responses, and protected these animals against challenge with virulent VEE. Expression of individual glycoprotein regions (E3-E2 and 6K-E1) generated products that were accurately but incompletely processed, and induced non-neutralizing antibodies that reacted more efficiently with denatured than native VEE proteins. Nonetheless, immunization with the 6K-E1 expression product provided complete protection against VEE challenge.     

Molecular epidemiology of eastern equine encephalitis virus, New York

Perpetuation, overwintering, and extinction of eastern equine encephalitis virus (EEEV) in northern foci are poorly understood. We therefore sought to describe the molecular epidemiology of EEEV in New York State during current and past epizootics. To determine whether EEEV overwinters, is periodically reintroduced, or both, we sequenced the E2 and partial NSP3 coding regions of 42 EEEV isolates from New York State and the Eastern Seaboard of the United States. Our phylogenetic analyses indicated that derived subclades tended to contain southern strains that had been isolated before genetically similar northern strains, suggesting southern to northern migration of EEEV along the Eastern Seaboard. Strong clustering among strains isolated during epizootics in New York from 2003-2005, as well as from 1974-1975, demonstrates that EEEV has overwintered in this focus. This study provides molecular evidence for the introduction of southern EEEV strains to New York, followed by local amplification, perpetuation, and overwintering.     

Recombinant RNA replicons derived from attenuated Venezuelan equine encephalitis virus protect guinea pigs and mice from Ebola hemorrhagic fever virus

RNA replicons derived from an attenuated strain of Venezuelan equine encephalitis virus (VEE), an alphavirus, were configured as candidate vaccines for Ebola hemorrhagic fever. The Ebola nucleoprotein (NP) or glycoprotein (GP) genes were introduced into the VEE RNA downstream from the VEE 26S promoter in place of the VEE structural protein genes. The resulting recombinant replicons, expressing the NP or GP genes, were packaged into VEE replicon particles (NP-VRP and GP-VRP, respectively) using a bipartite helper system that provided the VEE structural proteins in trans and prevented the regeneration of replication-competent VEE during packaging. The immunogenicity of NP-VRP and GP-VRP and their ability to protect against lethal Ebola infection were evaluated in BALB/c mice and in two strains of guinea pigs. The GP-VRP alone, or in combination with NP-VRP, protected both strains of guinea pigs and BALB/c mice, while immunization with NP-VRP alone protected BALB/c mice, but neither strain of guinea pig. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge. However, the complete protection achieved with active immunization with VRP, as well as the unique characteristics of the VEE replicon vector, warrant further testing of the safety and efficacy of NP-VRP and GP-VRP in primates as candidate vaccines against Ebola hemorrhagic fever.     

Venezuelan equine encephalitis vaccination survey in Arizona and New Mexico, 1972.

Field studies were conducted in 1972 to determine the immunization status of equines along the Mexico, Arizona, and New Mexico borders. Interviews with horse owners were conducted along roads selected at random in the counties of Santa Cruz and Yuma, Ariz., and in Dona Ana County, N. Mex. At least 450 horse owners in each county were asked about the vaccination status of their animals, and information was taken on 1,260 animals. Blood specimens were obtained from every third equine, regardless of stated vaccination status, and tested for the presence of Venezuelan equine encephalitis (VEE), western equine encephalomyelitis (WEE), and eastern equine encephalomyelitis (EEE) neutralization antibodies. Serum samples were collected from 446 equines in the 3-county area; only 227 (50.7 percent) had both a history of VEE vaccination in 1971 (including 20 vaccinated in 1972) and serum neutralization antibody against VEE. Of the remaining 220 with no detectable neutralization antibody to VEE, 197 (89.5 percent) had a history of VEE vaccination in 1971 (including 5 revaccinated in 1972), 14 (6.4 percent) had no history of vaccination, and 9 (4.1 percent) had an unknown vaccination status. Eighty-two percent (160 of 1971) of the equines with a history of VEE vaccination and presence of dectectable WEE or EEE antibodies, or both, had no detectable levels of VEE antibody. Therefore, the results of this study suggest that the presence of WEE or EEE antibodies, or both, may suppress the development of dectable vaccine-induced VEE antibody response in the equine. As a result of this investigation, the U.S. Department of Agriculture, as an added precaution, recommended the revaccination of equines in areas of the United States bordering Mexico.     

Experimental Infection of Potential Reservoir Hosts with Venezuelan Equine Encephalitis Virus, Mexico

In 1993, an outbreak of encephalitis among 125 affected equids in coastal Chiapas, Mexico, resulted in a 50% case-fatality rate. The outbreak was attributed to Venezuelan equine encephalitis virus (VEEV) subtype IE, not previously associated with equine disease and death. To better understand the ecology of this VEEV strain in Chiapas, we experimentally infected 5 species of wild rodents and evaluated their competence as reservoir and amplifying hosts. Rodents from 1 species (Baiomys musculus) showed signs of disease and died by day 8 postinoculation. Rodents from the 4 other species (Liomys salvini, Oligoryzomys fulvescens, Oryzomys couesi, and Sigmodon hispidus) became viremic but survived and developed neutralizing antibodies, indicating that multiple species may contribute to VEEV maintenance. By infecting numerous rodent species and producing adequate viremia, VEEV may increase its chances of long-term persistence in nature and could increase risk for establishment in disease-endemic areas and amplification outside the disease-endemic range.Keywords: Zoonoses, vector-borne infections, bioterrorism agents and preparedness, encephalomyelitis virus, alphaviruses, transmission, Mexico, strains, wild rodents, researchVenezuelan equine encephalitis (VEE) is a potentially fatal, reemerging disease in tropical America (the portions of North, South, and Central America between the tropics of Cancer and Capricorn) that can cause outbreaks involving hundreds of thousands of humans and equids. VEE virus (VEEV; Togaviridae: Alphavirus) strains are categorized as either epizootic (associated with equine disease and major epidemics of human disease through equine amplification), or enzootic (not known to cause equine disease). Most VEEV strains, both epizootic and enzootic, have been associated with human disease (1). VEEV is also of biodefense importance; it has been developed as a biological weapon, mainly because it is highly infectious by aerosol transmission and can infect humans with a relatively low dose (2).During the mid-1990s, 2 epizootic equine outbreaks occurred in coastal Oaxaca and Chiapas states in Mexico; the causative agent was determined to be VEEV subtype IE (VEEV-IE), which was previously considered to be not virulent for equids (1). On the basis of the spread of a VEEV subtype IAB epizootic/epidemic through Mexico and into Texas in 1971 (3), the 1993 and 1996 outbreaks were considered to have the potential to spread to other regions of Mexico or the United States. To prevent, detect, and evaluate potential reemergence of this virus in the United States, we need to understand the factors that govern circulation and persistence of this virus in its enzootic foci and epizootic cycles.Enzootic strains of VEEV are maintained naturally by transmission between mosquitoes of the subgenus Culex (Melanoconion) and wild rodents (4). These viruses are thought to circulate continuously among mosquitoes and their principal vertebrate amplifying hosts, whereas horses and humans are considered spillover, dead-end hosts not required for maintenance of the natural cycle. Several studies have shown that terrestrial mammals of 5 genera (Didelphis, Oryzomys, Proechimys, Sigmodon, and Zygodontomys) are susceptible to VEEV-IE infection; they develop viremia sufficient to infect mosquito vectors, yet they usually survive infection (5–10).Several species of wild rodents captured in coastal Chiapas have VEEV-specific antibodies (11). To address which of these species are likely to play a role as reservoir and/or amplification hosts, we captured rodents from 5 genera (Baiomys, Liomys, Oligoryzomys, Oryzomys, and Sigmodon) and transported them to the laboratory for experimental infection studies. Our goals were to evaluate the role of various vertebrate species in VEEV-IE maintenance and to help interpret seroprevalence data gathered in the field.     

Antigenic variation of equine (Heq2Neq2) influenzavirus

Influenza equine (Heq2Neq2) strains isolated during the course of epizootics observed in Guanabara (Rio de Janeiro) and São Paulo, Brazil, in July—October 1969 were shown to differ antigenically from earlier strains of the same subtype (A/equine/Miami/1/63 (Heq2Neq2)). The difference could be clearly demonstrated in haemagglutination inhibition tests performed with postinfection horse or ferret sera but not with hyperimmune rooster sera. Antibody responses of diseased horses were higher and more frequent against current isolates than against strain equine/Miami/1/63. Some animals also showed antibody responses to the Hong Kong variant of human influenzavirus A.     

Venezuelan equine encephalitis virus infection of cotton rats

Venezuelan equine encephalitis virus (VEEV) is an emerging pathogen of equids and humans, but infection of its rodent reservoir hosts has received little study. To determine whether responses to infection vary among geographic populations, we inoculated 3 populations of cotton rats with 2 enzootic VEEV strains (Co97-0054 [enzootic ID subtype] and 68U201 [enzootic IE subtype]). The 3 populations were offspring from wild-caught cotton rats collected in a VEE-enzootic area of south Florida, USA; wild-caught cotton rats from a non-VEE-enzootic area of Texas, USA; and commercially available (Harlan) colony-reared cotton rats from a non-VEE-enzootic region. Although each population had similar early viremia titers, no detectable disease developed in the VEE-sympatric Florida animals, but severe disease and death affected the Texas and Harlan animals. Our findings suggest that the geographic origins of cotton rats are important determinants of the outcome of VEE infection and reservoir potential of these rodents.     

Alphavirus replicon particles expressing the two major envelope proteins of equine arteritis virus induce high level protection against challenge with virulent virus in vaccinated horses

Replicon particles derived from a vaccine strain of Venezuelan equine encephalitis (VEE) virus were used as vectors for expression in vivo of the major envelope proteins (G(L) and M) of equine arteritis virus (EAV), both individually and in heterodimer form (G(L)/M). The immunogenicity of the different replicons was evaluated in horses, as was their ability to protectively immunize horses against intranasal and intrauterine challenge with a virulent strain of EAV (EAV KY84). Horses immunized with replicons that express both the G(L) and M proteins in heterodimer form developed neutralizing antibodies to EAV, shed little or no virus, and developed only mild or inapparent signs of equine viral arteritis (EVA) after challenge with EAV KY84. In contrast, unvaccinated horses and those immunized with replicons expressing individual EAV envelope proteins (M or G(L)) shed virus for 6-10 days in their nasal secretions and developed severe signs of EVA after challenge. These data confirm that replicons that co-express the G(L) and M envelope proteins effectively, induce EAV neutralizing antibodies and protective immunity in horses.     

Weather factors in the prediction of western equine encephalitis epidemics in Manitoba.

Cases of western equine encephalitis in horses in 1987 in western USA and Manitoba, Canada were examined by backward trajectory analysis of winds. Culex tarsalis mosquitoes infected with western equine encephalitis virus could have been carried on southerly winds from Texas and Oklahoma to northern USA and from there to Manitoba. The presence of the Polar front over North Dakota and Minnesota at the end of July would have led to the landing of Cx. tarsalis in Montana and Wisconsin and prevented further carriage into Manitoba. Temperatures in southern Texas during the winter months (average daily maximum temperatures 19.7 degrees C and higher) would have permitted continuous transmission of western equine encephalitis virus by Cx. tarsalis in this area. Weather factors involved in outbreaks from 1975-88 were analysed to see if epidemics in Manitoba (23 or more cases in horses) could be predicted. The conditions for epidemics could be defined as follows: (a) the number of cases in horses in USA was 98 or more, (b) winds were southerly with speeds 45 kmh-1 or higher, and (c) counts of Cx. tarsalis females/light trap per day were 3.2 or higher. There were 3 or fewer cases in Manitoba, when the number of cases in USA was 27 or less, even when Cx. tarsalis counts were higher than 3.2. With Cx. tarsalis counts below 3 and/or unsuitable winds, or the Polar front further south, the number of cases in Manitoba was between 0 and 17, even when the number of cases in USA was from 38-172. Without information on the extent of infection further south, the weather variables would probably be more useful in excluding the possibility of an epidemic in Manitoba than in predicting one.     

Hendra virus and Nipah virus animal vaccines

Hendra virus (HeV) and Nipah virus (NiV) are zoonotic viruses that emerged in the mid to late 1990s causing disease outbreaks in livestock and people. HeV appeared in Queensland, Australia in 1994 causing a severe respiratory disease in horses along with a human case fatality. NiV emerged a few years later in Malaysia and Singapore in 1998–1999 causing a large outbreak of encephalitis with high mortality in people and also respiratory disease in pigs which served as amplifying hosts. The key pathological elements of HeV and NiV infection in several species of mammals, and also in people, are a severe systemic and often fatal neurologic and/or respiratory disease. In people, both HeV and NiV are also capable of causing relapsed encephalitis following recovery from an acute infection. The known reservoir hosts of HeV and NiV are several species of pteropid fruit bats. Spillovers of HeV into horses continue to occur in Australia and NiV has caused outbreaks in people in Bangladesh and India nearly annually since 2001, making HeV and NiV important transboundary biological threats. NiV in particular possesses several features that underscore its potential as a pandemic threat, including its ability to infect humans directly from natural reservoirs or indirectly from other susceptible animals, along with a capacity of limited human-to-human transmission. Several HeV and NiV animal challenge models have been developed which have facilitated an understanding of pathogenesis and allowed for the successful development of both active and passive immunization countermeasures.     

Immune interference after sequential alphavirus vaccine vaccinations

We compared the effect of order of administration of investigational alphavirus vaccines on neutralizing antibody response. Volunteers who received the inactivated eastern and western equine encephalitis (EEE and WEE) vaccines before live attenuated Venezuelan (VEE) vaccine had significantly lower rates of antibody response than those receiving VEE vaccine before EEE and WEE vaccines (66.7% vs. 80.6%; p = 0.026). The odds of having a VEE antibody non-response among those initially receiving EEE and WEE vaccines, adjusted for gender, were significant (odds ratio [OR] = 2.20; 95% CI = 1.2–4.1 [p = 0.0145]) as were the odds of non-response among females adjusted for group (OR = 1.81; 95% CI = 1.2–2.7 [p = 0.0037]). Antibody interference and gender effect have major implications for vaccine strategy among those receiving multiple alphavirus vaccines and those developing next generation vaccines for these threats.