Western Equine Encephalitis (WEE) is a viral disease affecting horses, caused by the Western Equine Encephalitis virus, which is transmitted primarily through mosquito bites. The virus can lead to neurological symptoms in horses, such as fever, depression, ataxia, and encephalitis, which may progress to more severe neurological impairment or death. Diagnosis of WEE is typically based on clinical signs, serological testing, and virus isolation. Preventative measures include mosquito control and vaccination programs to reduce the risk of transmission. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, pathogenesis, clinical presentation, and management strategies for Western Equine Encephalitis in horses.
Pennington MV, Zoller JL, White-Springer SH, Harlin JF, Huseman CJ, Leatherwood JL, O'Reilly CL.Competition stress is a common factor influencing the success of performing athletes. However, few studies have quantified the physiological stress responses in horses and riders surrounding an equestrian event. Objective: The objectives of the current study were to determine salivary cortisol concentrations (SCC) as an indicator of stress in fifteen horse and rider pairs competing in western stock horse events and to investigate the relationship between SCC and performance. Methods: Subjects included male and female Quarter horses aged 3-15 years and equestrians aged 18-22 years. Salivary sam...
Wang L, Zheng R, Li Z, Zhang L.Recent increases in cases of western equine encephalitis (WEE) in South America have raised significant concerns about the virus's potential to cause an endemic disease due to its adaptation to mosquito vectors. Currently, there are no effective vaccines or treatments for WEEV, despite ongoing research into various biochemical products in animal models. The virus presents different pathological effects depending on the host. In humans, WEEV infection leads to central nervous system damage, resulting in encephalitis and severe neurological sequelae, which underscores the need for further resear...
Frabasile S, Morel N, Pérez R, Marrero LM, Burgueño A, Cortinas MN, Bassetti L, Negro R, Rodríguez S, Bórmida V, Gayo V, de Souza VC, Naveca FG....We report the genomic analysis from early equine cases of the Western equine encephalitis virus outbreak during 2023-2024 in Uruguay. Sequences are related to a viral isolate from an outbreak in 1958 in Argentina. A viral origin from South America or continuous enzootic circulation with infrequent spillover is possible.
Vissani MA, Alamos F, Tordoya MS, Minatel L, Schammas JM, Dus Santos MJ, Trono K, Barrandeguy ME, Balasuriya UBR, Carossino M.Western equine encephalitis virus (WEEV) is a mosquito-borne arbovirus (genus , family ) that has re-emerged in South America in late 2023, causing severe disease in both horses and humans after a nearly 40-year intermission period. We here describe the virological, serological, pathological, and molecular features of WEEV infection in horses during the 2023-2024 outbreak in Argentina. WEEV-infected horses developed neurological signs with mild to severe encephalitis associated with minimal to abundant WEEV-infected cells, as demonstrated by WEEV-specific in situ hybridization. The distributio...
Campos AS, Franco AC, Godinho FM, Huff R, Candido DS, da Cruz Cardoso J, Hua X, Claro IM, Morais P, Franceschina C, de Lima Bermann T, Dos Santos FM....Western equine encephalitis virus (WEEV) is a mosquitoborne virus that reemerged in December 2023 in Argentina and Uruguay, causing a major outbreak. We investigated the outbreak using epidemiologic, entomological, and genomic analyses, focusing on WEEV circulation near the Argentina‒Uruguay border in Rio Grande do Sul state, Brazil. During November 2023‒April 2024, the outbreak in Argentina and Uruguay resulted in 217 human cases, 12 of which were fatal, and 2,548 equine cases. We determined cases on the basis of laboratory and clinical epidemiologic criteria. We characterized 3 fatal equ...
Luethy D.The continued recognition and emergence of alphavirus and flavivirus diseases is a growing veterinary and public health concern. As the global environment continues to change, mosquito-borne diseases will continue to evolve and expand. Continued development of readily available vaccines for the prevention of these diseases in humans and animals is essential to controlling epizootics of these diseases. Further research into effective antiviral treatments is also sorely needed. This article describes equine encephalitis viruses with a focus on clinical and public health considerations.
Ogorek TJ, Golden JE.Venezuelan, western, and eastern equine encephalitic alphaviruses (VEEV, WEEV, and EEEV, respectively) are arboviruses that are highly pathogenic to equines and cause significant harm to infected humans. Currently, human alphavirus infection and the resulting diseases caused by them are unmitigated due to the absence of approved vaccines or therapeutics for general use. These circumstances, combined with the unpredictability of outbreaks-as exemplified by a 2019 EEE surge in the United States that claimed 19 patient lives-emphasize the risks posed by these viruses, especially for aerosolized V...
Desanti-Consoli H, Bouillon J, Chapuis RJJ.Vaccination against infectious diseases is a cornerstone of veterinary medicine in the prevention of disease transmission, illness severity, and often death in animals. In North American equine medicine, equine vaccines protecting against tetanus, rabies, Eastern and Western equine encephalomyelitis, and West Nile are core vaccines as these have been classified as having a heightened risk of mortality, infectiousness, and endemic status. Some guidelines differ from the label of vaccines, to improve the protection of patients or to decrease the unnecessary administration to reduce potential sid...
Calvert AE, Bennett SL, Hunt AR, Fong RH, Doranz BJ, Roehrig JT, Blair CD.Eastern equine encephalitis virus (EEEV), western equine encephalitis virus (WEEV) and Venezuelan equine encephalitis virus (VEEV) can cause fatal encephalitis in humans and equids. Some MAbs to the E1 glycoprotein are known to be cross-reactive, weakly neutralizing in vitro but can protect from disease in animal models. We investigated the mechanism of neutralization of VEEV infection by the broadly cross-reactive E1-specific MAb 1A4B-6. 1A4B-6 protected 3-week-old Swiss Webster mice prophylactically from lethal VEEV challenge. Likewise, 1A4B-6 inhibited virus growth in vitro at a pre-attachm...
Bantle CM, Rocha SM, French CT, Phillips AT, Tran K, Olson KE, Bass TA, Aboellail T, Smeyne RJ, Tjalkens RB.Viral infection of the central nervous system (CNS) can cause lasting neurological decline in surviving patients and can present with symptoms resembling Parkinson's disease (PD). The mechanisms underlying postencephalitic parkinsonism remain unclear but are thought to involve increased innate inflammatory signaling in glial cells, resulting in persistent neuroinflammation. We therefore studied the role of glial cells in regulating neuropathology in postencephalitic parkinsonism by studying the involvement of astrocytes in loss of dopaminergic neurons and aggregation of α-synuclein protein fo...
Nunes JDSDSS, Casseb LMN, Guimarães RJPS, Reis WDM, de Barros BCV, Ferreira MS, Chiang JO, Pinheiro HHC, Vasconcelos PFDC, Cruz ACR.Serum samples from 89 equids were analyzed (75 horses, 9 donkeys, and 5 mules) from the municipality of Viseu, Pará state, Brazil. Samples were collected in November 2014 and August 2015. The antibody prevalence against the following alphaviruses was estimated: Eastern equine encephalitis virus, Western equine encephalitis virus, Mucambo virus, and Mayaro virus. Seroprevalence was determined by the hemagglutination inhibition (HI) technique. Sera that exhibited HI antibodies with heterotypic reactions for the analyzed viruses were subjected to the 90% plaque reduction neutralization test (PRN...
Robb LL, Hartman DA, Rice L, deMaria J, Bergren NA, Borland EM, Kading RC.Western equine encephalitis (WEE) was once prevalent and routinely isolated from mosquitoes in Colorado; however, isolations of Western equine encephalitis virus (WEEV) have not been reported from mosquito pools since the early 1990s. The objective of the present study was to test pools of Culex tarsalis (Coquillett) mosquitoes sampled from Weld County, CO, in 2016 for evidence of WEEV infection. Over 7,000 mosquitoes were tested, but none were positive for WEEV RNA. These data indicate that WEEV either was not circulating enzootically in Northern Colorado, was very rare, and would require muc...
Borland EM, Ledermann JP, Powers AM.Highlands J virus (HJV) is an alphavirus closely related to western equine encephalitis virus (WEEV) and eastern equine encephalitis virus (EEEV). HJV is an avian pathogen with the potential for disruption of poultry operations, but is not known to cause human or equine disease. HJV has only been identified in the eastern United States and is thought to have a transmission cycle similar to that of EEEV involving Culiseta melanura mosquitoes and birds. However, HJV is more genetically similar to WEEV and it remains unclear if it may be transmitted by Culex species mosquitoes like WEEV. Seven st...
Amaya M, Keck F, Lindquist M, Voss K, Scavone L, Kehn-Hall K, Roberts B, Bailey C, Schmaljohn C, Narayanan A.Many viruses have been implicated in utilizing or modulating the Ubiquitin Proteasome System (UPS) to enhance viral multiplication and/or to sustain a persistent infection. The mosquito-borne Venezuelan equine encephalitis virus (VEEV) belongs to the Togaviridae family and is an important biodefense pathogen and select agent. There are currently no approved vaccines or therapies for VEEV infections; therefore, it is imperative to identify novel targets for therapeutic development. We hypothesized that a functional UPS is required for efficient VEEV multiplication. We have shown that at non-tox...
Davis EG, Bello NM, Bryan AJ, Hankins K, Wilkerson M.Protection from infectious disease requires antigen-specific immunity. In foals, most vaccine protocols are delayed until 6 months to avoid maternal antibody interference. Susceptibility to disease may exist prior to administration of vaccination at age 4-6 months. Objective: The aim of this investigation was to characterise immune activation among healthy foals in response to a multivalent vaccine protocol and compare immune responses when foals were vaccinated at age either 90 or 180 days. Methods: Randomised block design. Methods: Twelve healthy foals with colostral transfer were blocked fo...
Reed DS, Glass PJ, Bakken RR, Barth JF, Lind CM, da Silva L, Hart MK, Rayner J, Alterson K, Custer M, Dudek J, Owens G, Kamrud KI, Parker MD, Smith J.Alphavirus replicons were evaluated as potential vaccine candidates for Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), or eastern equine encephalitis virus (EEEV) when given individually or in combination (V/W/E) to mice or cynomolgus macaques. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in mice to their respective alphavirus. Protection from either subcutaneous or aerosol challenge with VEEV, WEEV, or EEEV was demonstrated out to 12 months after vaccination in mice. Individual replicon v...
Delekta PC, Dobry CJ, Sindac JA, Barraza SJ, Blakely PK, Xiang J, Kirchhoff PD, Keep RF, Irani DN, Larsen SD, Miller DJ.Neurotropic alphaviruses, including western, eastern, and Venezuelan equine encephalitis viruses, cause serious and potentially fatal central nervous system infections in humans for which no currently approved therapies exist. We previously identified a series of thieno[3,2-b]pyrrole derivatives as novel inhibitors of neurotropic alphavirus replication, using a cell-based phenotypic assay (W. Peng et al., J. Infect. Dis. 199:950-957, 2009, doi:http://dx.doi.org/10.1086/597275), and subsequently developed second- and third-generation indole-2-carboxamide derivatives with improved potency, solub...
Chung DH, Jonsson CB, Tower NA, Chu YK, Sahin E, Golden JE, Noah JW, Schroeder CE, Sotsky JB, Sosa MI, Cramer DE, McKellip SN, Rasmussen L, White EL....Alphaviruses present serious health threats as emerging and re-emerging viruses. Venezuelan equine encephalitis virus (VEEV), a New World alphavirus, can cause encephalitis in humans and horses, but there are no therapeutics for treatment. To date, compounds reported as anti-VEEV or anti-alphavirus inhibitors have shown moderate activity. To discover new classes of anti-VEEV inhibitors with novel viral targets, we used a high-throughput screen based on the measurement of cell protection from live VEEV TC-83-induced cytopathic effect to screen a 340,000 compound library. Of those, we identified...
Durand B, Lecollinet S, Beck C, Martínez-López B, Balenghien T, Chevalier V.Live animal trade is considered a major mode of introduction of viruses from enzootic foci into disease-free areas. Due to societal and behavioural changes, some wild animal species may nowadays be considered as pet species. The species diversity of animals involved in international trade is thus increasing. This could benefit pathogens that have a broad host range such as arboviruses. The objective of this study was to analyze the risk posed by live animal imports for the introduction, in the European Union (EU), of four arboviruses that affect human and horses: Eastern and Western equine enc...
Mossel EC, Ledermann JP, Phillips AT, Borland EM, Powers AM, Olson KE.Western equine encephalitis virus (WEEV) is a naturally occurring recombinant virus derived from ancestral Sindbis and Eastern equine encephalitis viruses. We previously showed that infection by WEEV isolates McMillan (McM) and IMP-181 (IMP) results in high (∼90-100%) and low (0%) mortality, respectively, in outbred CD-1 mice when virus is delivered by either subcutaneous or aerosol routes. However, relatively little is known about specific virulence determinants of WEEV. We previously observed that IMP infected Culex tarsalis mosquitoes at a high rate (app. 80%) following ingestion of an in...
Thompson NN, Auguste AJ, Coombs D, Blitvich BJ, Carrington CV, da Rosa AP, Wang E, Chadee DD, Drebot MA, Tesh RB, Weaver SC, Adesiyun AA.Seroprevalence rates of selected arboviruses in animal populations in Trinidad were determined using serum samples collected between 2006 and 2009 from horses (n=506), cattle (n=163), sheep (n=198), goats (n=82), pigs (n=184), birds (n=140), rodents (n=116), and other vertebrates (n=23). The sera were screened for antibodies to West Nile virus (WNV), St. Louis encephalitis virus (SLEV), Ilheus virus (ILHV), Bussuquara virus (BSQV), Venezuelan equine encephalitis virus (VEEV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV), using hemagglutination inhibiti...
Toth AM, Geisler C, Aumiller JJ, Jarvis DL.In an effort to produce processed, soluble Western equine encephalitis virus (WEEV) glycoproteins for subunit therapeutic vaccine studies, we isolated twelve recombinant baculoviruses designed to express four different WEEV glycoprotein constructs under the transcriptional control of three temporally distinct baculovirus promoters. The WEEV glycoprotein constructs encoded full-length E1, the E1 ectodomain, an E26KE1 polyprotein precursor, and an artificial, secretable E2E1 chimera. The three different promoters induced gene expression during the immediate early (ie1), late (p6.9), and very lat...
Swayze RD, Bhogal HS, Barabé ND, McLaws LJ, Wu JQ.Western equine encephalitis virus (WEEV) is a mosquito-borne RNA virus which causes lethal infection in humans and equines. There are no commercial vaccines or anti-WEEV drugs available for humans. We used replication-defective, human adenovirus serotype-5 (HAd5) as a delivery vector for developing WEEV vaccine. Our previous study found delivery of both E1 and E2 envelope proteins of WEEV by HAd5 vector offers complete protection against lethal challenge of WEEV. In this paper, we constructed a HAd5-vectored E1 vaccine, Ad5-E1. Mice given single-dose vaccination of Ad5-E1 were completely prote...
Steele KE, Twenhafel NA.The encephalitides caused by Venezuelan (VEEV), eastern (EEEV), and western (WEEV) equine encephalitis viruses are important natural diseases of horses and humans and potential agents of biowarfare or bioterrorism. No licensed vaccines or specific therapies exist to prevent or treat human infections with VEEV, EEEV, or WEEV. Well-characterized animal models are needed to support the development of such medical countermeasures under the United States Food and Drug Administration's "Animal Rule." This review focuses on the pathological features and pathogenetic mechanisms of these alphaviral enc...
Reichert E, Clase A, Bacetty A, Larsen J.The New World alphaviruses Venezuelan equine encephalitis virus (VEEV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV) pose a significant threat to human health as the etiological agents of serious viral encephalitis through natural infection as well as through their potential use as a biological weapon. At present, there is no FDA-approved medical treatment for infection with these viruses. The Defense Threat Reduction Agency, Joint Science and Technology Office for Chemical and Biological Defense (DTRA/JSTO), is currently funding research aimed at deve...
Gauci PJ, Wu JQ, Rayner GA, Barabé ND, Nagata LP, Proll DF.DNA vaccines encoding different portions of the structural proteins of western equine encephalitis virus were tested for the efficacy of their protection in a 100% lethal mouse model of the virus. The 6K-E1 structural protein encoded by the DNA vaccine conferred complete protection against challenge with the homologous strain and limited protection against challenge with a heterologous strain.
Forrester NL, Kenney JL, Deardorff E, Wang E, Weaver SC.The incidence of Western Equine Encephalitis (WEE) in humans and equids peaked during the mid-20th century and has declined to fewer than 1-2 human cases annually during the past 20 years. Using the mouse model, changes in WEE virus (WEEV) virulence were investigated as a potential explanation for the decline in the number of cases. Evaluation of 10 WEEV strains representing a variety of isolation locations, hosts, and all decades from the 1940's to the 1990's yielded no evidence of a decline in virulence. These results suggest that ecological factors affecting human and equine exposure should...
Reisen WK, Fang Y, Brault AC.Historically, western equine encephalomyelitis virus (WEEV) caused large equine and human epidemics in the Americas from Canada into Argentina. Despite recent enhanced surveillance for West Nile virus, there have been few reports of equine or human cases and little documented enzootic activity of WEEV. During the past three years, WEEV has been active again in California, but without human or equine cases. In the current study, we compared host and vector competence of representative WEEV isolates made during each decade over the past 60 years using white-crowned sparrows, house sparrows, and ...
Hu WG, Chau D, Wong C, Masri SA, Fulton RE, Nagata LP.The genes encoding envelope proteins E1 and E2 of western equine encephalitis virus (WEEV) were respectively cloned into a prokaryotic T7 RNA polymerase-regulated expression vector. The recombinant C-terminal 6xHis-tagged WEEV E1 and E2 were expressed in bacteria as inclusion bodies that were subsequently solubilized with 8M urea, purified by immobilized metal ion affinity chromatography and finally refolded using an arginine system. The purified 6xHis-tagged proteins showed 50kDa bands as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, consistent with the expected size...
Calisher CH.Of more than 500 arboviruses recognized worldwide, 5 were first isolated in Canada and 58 were first isolated in the United States. Six of these viruses are human pathogens: western equine encephalitis (WEE) and eastern equine encephalitis (EEE) viruses (family Togaviridae, genus Alphavirus), St. Louis encephalitis (SLE) and Powassan (POW) viruses (Flaviviridae, Flavivirus), LaCrosse (LAC) virus (Bunyaviridae, Bunyavirus), and Colorado tick fever (CTF) virus (Reoviridae, Coltivirus). Their scientific histories, geographic distributions, virology, epidemiology, vectors, vertebrate hosts, transm...
Steele KE, Twenhafel NA.The encephalitides caused by Venezuelan (VEEV), eastern (EEEV), and western (WEEV) equine encephalitis viruses are important natural diseases of horses and humans and potential agents of biowarfare or bioterrorism. No licensed vaccines or specific therapies exist to prevent or treat human infections with VEEV, EEEV, or WEEV. Well-characterized animal models are needed to support the development of such medical countermeasures under the United States Food and Drug Administration's "Animal Rule." This review focuses on the pathological features and pathogenetic mechanisms of these alphaviral enc...
Reisen WK, Meyer RP, Presser SB, Hardy JL.The extrinsic incubation rate (inverse of the time in days from infection to median transmission) of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses by laboratory strains of Culex tarsalis Coquillett increased as a linear function of incubation temperatures from 10 to 30 degrees C. The estimated temperatures for zero transmission thresholds (intercept of the X axis) were 10.9 and 14.9 degrees C, and the number of degree days above these thresholds required for median transmission (inverse of the slope) was 67.6 and 115.2, respectively. Although the bodies of mos...
Reed DS, Glass PJ, Bakken RR, Barth JF, Lind CM, da Silva L, Hart MK, Rayner J, Alterson K, Custer M, Dudek J, Owens G, Kamrud KI, Parker MD, Smith J.Alphavirus replicons were evaluated as potential vaccine candidates for Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), or eastern equine encephalitis virus (EEEV) when given individually or in combination (V/W/E) to mice or cynomolgus macaques. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in mice to their respective alphavirus. Protection from either subcutaneous or aerosol challenge with VEEV, WEEV, or EEEV was demonstrated out to 12 months after vaccination in mice. Individual replicon v...
Reichert E, Clase A, Bacetty A, Larsen J.The New World alphaviruses Venezuelan equine encephalitis virus (VEEV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV) pose a significant threat to human health as the etiological agents of serious viral encephalitis through natural infection as well as through their potential use as a biological weapon. At present, there is no FDA-approved medical treatment for infection with these viruses. The Defense Threat Reduction Agency, Joint Science and Technology Office for Chemical and Biological Defense (DTRA/JSTO), is currently funding research aimed at deve...
Chung DH, Jonsson CB, Tower NA, Chu YK, Sahin E, Golden JE, Noah JW, Schroeder CE, Sotsky JB, Sosa MI, Cramer DE, McKellip SN, Rasmussen L, White EL....Alphaviruses present serious health threats as emerging and re-emerging viruses. Venezuelan equine encephalitis virus (VEEV), a New World alphavirus, can cause encephalitis in humans and horses, but there are no therapeutics for treatment. To date, compounds reported as anti-VEEV or anti-alphavirus inhibitors have shown moderate activity. To discover new classes of anti-VEEV inhibitors with novel viral targets, we used a high-throughput screen based on the measurement of cell protection from live VEEV TC-83-induced cytopathic effect to screen a 340,000 compound library. Of those, we identified...
Forrester NL, Kenney JL, Deardorff E, Wang E, Weaver SC.The incidence of Western Equine Encephalitis (WEE) in humans and equids peaked during the mid-20th century and has declined to fewer than 1-2 human cases annually during the past 20 years. Using the mouse model, changes in WEE virus (WEEV) virulence were investigated as a potential explanation for the decline in the number of cases. Evaluation of 10 WEEV strains representing a variety of isolation locations, hosts, and all decades from the 1940's to the 1990's yielded no evidence of a decline in virulence. These results suggest that ecological factors affecting human and equine exposure should...
Amaya M, Keck F, Lindquist M, Voss K, Scavone L, Kehn-Hall K, Roberts B, Bailey C, Schmaljohn C, Narayanan A.Many viruses have been implicated in utilizing or modulating the Ubiquitin Proteasome System (UPS) to enhance viral multiplication and/or to sustain a persistent infection. The mosquito-borne Venezuelan equine encephalitis virus (VEEV) belongs to the Togaviridae family and is an important biodefense pathogen and select agent. There are currently no approved vaccines or therapies for VEEV infections; therefore, it is imperative to identify novel targets for therapeutic development. We hypothesized that a functional UPS is required for efficient VEEV multiplication. We have shown that at non-tox...
Mossel EC, Ledermann JP, Phillips AT, Borland EM, Powers AM, Olson KE.Western equine encephalitis virus (WEEV) is a naturally occurring recombinant virus derived from ancestral Sindbis and Eastern equine encephalitis viruses. We previously showed that infection by WEEV isolates McMillan (McM) and IMP-181 (IMP) results in high (∼90-100%) and low (0%) mortality, respectively, in outbred CD-1 mice when virus is delivered by either subcutaneous or aerosol routes. However, relatively little is known about specific virulence determinants of WEEV. We previously observed that IMP infected Culex tarsalis mosquitoes at a high rate (app. 80%) following ingestion of an in...
Iversson LB, Silva RA, da Rosa AP, Barros VL.Neutralizing antibodies to EEE (6.7%), WEE (1.2%), ILH (26.6%), MAG (28.2%) and TCM (15.7%) viruses were found in sera of 432 equines of the Brazilian Pantanal, area where undiagnosed horse deaths are frequently observed. A 4-fold rise in CF titer to EEE virus was detected in acute and convalescent sera of an encephalitis horse sacrificed in 1992. Antibodies to EEE, ILH, MAG and TCM viruses were detected in horses less than 2 years old indicating recent circulation of these viruses in the Pantanal. The evidence of recent equine encephalitis associated with rising CF titer to EEE warrants a mor...
Barker CM, Reisen WK, Kramer VL.The California Mosquito-Borne Virus Surveillance and Response Plan recently was developed to provide a semi-quantitative means for assessing risk for western equine encephalomyelitis (WEE) or St. Louis encephalitis (SLE) viruses and to provide intervention guidelines for mosquito control and public health agencies during periods of heightened risk for human infection. West Nile virus recently has arrived in California, and the response plan also will provide a baseline for assessing the risk for human and equine infection with this virus. In the response plan, overall risk is calculated by ave...
Bantle CM, Rocha SM, French CT, Phillips AT, Tran K, Olson KE, Bass TA, Aboellail T, Smeyne RJ, Tjalkens RB.Viral infection of the central nervous system (CNS) can cause lasting neurological decline in surviving patients and can present with symptoms resembling Parkinson's disease (PD). The mechanisms underlying postencephalitic parkinsonism remain unclear but are thought to involve increased innate inflammatory signaling in glial cells, resulting in persistent neuroinflammation. We therefore studied the role of glial cells in regulating neuropathology in postencephalitic parkinsonism by studying the involvement of astrocytes in loss of dopaminergic neurons and aggregation of α-synuclein protein fo...
Mitchell CJ, Monath TP, Sabattini MS, Daffner JF, Cropp CB, Calisher CH, Darsie RF, Jakob WL.Mosquitoes were collected in Santa Fe and Rio Negro provinces, Argentina, in 1982-1983 during a western equine encephalitis (WEE) epizootic. Totals of 153,084 mosquitoes from Santa Fe Province and 484 from Rio Negro Province were tested for virus in 2,351 pools. Seventeen virus strains were isolated, all from Santa Fe collections, as follows: 4 WEE, 6 Venezuelan equine encephalitis, 1 St. Louis encephalitis, 2 Antequera, 1 Maguari, 1 Melao, 1 new vesiculovirus (Calchaqui), and 1 Gamboa. The WEE virus isolates were from Aedes albifasciatus, Anopheles albitarsis, Mansonia species, and Psorophora...
Thompson NN, Auguste AJ, Coombs D, Blitvich BJ, Carrington CV, da Rosa AP, Wang E, Chadee DD, Drebot MA, Tesh RB, Weaver SC, Adesiyun AA.Seroprevalence rates of selected arboviruses in animal populations in Trinidad were determined using serum samples collected between 2006 and 2009 from horses (n=506), cattle (n=163), sheep (n=198), goats (n=82), pigs (n=184), birds (n=140), rodents (n=116), and other vertebrates (n=23). The sera were screened for antibodies to West Nile virus (WNV), St. Louis encephalitis virus (SLEV), Ilheus virus (ILHV), Bussuquara virus (BSQV), Venezuelan equine encephalitis virus (VEEV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV), using hemagglutination inhibiti...
Reisen WK, Fang Y, Brault AC.Historically, western equine encephalomyelitis virus (WEEV) caused large equine and human epidemics in the Americas from Canada into Argentina. Despite recent enhanced surveillance for West Nile virus, there have been few reports of equine or human cases and little documented enzootic activity of WEEV. During the past three years, WEEV has been active again in California, but without human or equine cases. In the current study, we compared host and vector competence of representative WEEV isolates made during each decade over the past 60 years using white-crowned sparrows, house sparrows, and ...
Campos AS, Franco AC, Godinho FM, Huff R, Candido DS, da Cruz Cardoso J, Hua X, Claro IM, Morais P, Franceschina C, de Lima Bermann T, Dos Santos FM....Western equine encephalitis virus (WEEV) is a mosquitoborne virus that reemerged in December 2023 in Argentina and Uruguay, causing a major outbreak. We investigated the outbreak using epidemiologic, entomological, and genomic analyses, focusing on WEEV circulation near the Argentina‒Uruguay border in Rio Grande do Sul state, Brazil. During November 2023‒April 2024, the outbreak in Argentina and Uruguay resulted in 217 human cases, 12 of which were fatal, and 2,548 equine cases. We determined cases on the basis of laboratory and clinical epidemiologic criteria. We characterized 3 fatal equ...
Durand B, Lecollinet S, Beck C, Martínez-López B, Balenghien T, Chevalier V.Live animal trade is considered a major mode of introduction of viruses from enzootic foci into disease-free areas. Due to societal and behavioural changes, some wild animal species may nowadays be considered as pet species. The species diversity of animals involved in international trade is thus increasing. This could benefit pathogens that have a broad host range such as arboviruses. The objective of this study was to analyze the risk posed by live animal imports for the introduction, in the European Union (EU), of four arboviruses that affect human and horses: Eastern and Western equine enc...
Science (New York, N.Y.)February 4, 1994
Volume 263, Issue 5147 676-678 doi: 10.1126/science.8303276
Fulhorst CF, Hardy JL, Eldridge BF, Presser SB, Reeves WC.The mechanism by which western equine encephalomyelitis (WEE) virus and other mosquito-borne alphaviruses (Togaviridae) survive during periods of vector inactivity is unknown. Recently, three strains of WEE virus were isolated from adult Aedes dorsalis collected as larvae from a salt marsh in a coastal region of California. This provides evidence of vertical transmission of WEE virus in mosquitoes in nature. Vertical transmission in Ae. dorsalis and closely related mosquito species may be an important mechanism for the maintenance of WEE virus in temperate regions in North America where horizo...
Ulloa A, Langevin SA, Mendez-Sanchez JD, Arredondo-Jimenez JI, Raetz JL, Powers AM, Villarreal-Treviño C, Gubler DJ, Komar N.A serologic survey in domestic animals (birds and mammals) was conducted in four communities located in the Lacandón Forest region of northeastern Chiapas, Mexico, during June 29 to July 1, 2001, with the objective to identify zoonotic arboviruses circulating in this area. We collected 202 serum samples from healthy domestic chickens, geese, ducks, turkeys, horses and cattle. The samples were tested by plaque-reduction neutralization test for antibodies to selected mosquito-borne flaviviruses (family Flaviviridae), including St. Louis encephalitis (SLE), Rocio (ROC), Ilheus (ILH), Bussuquara ...
Toth AM, Geisler C, Aumiller JJ, Jarvis DL.In an effort to produce processed, soluble Western equine encephalitis virus (WEEV) glycoproteins for subunit therapeutic vaccine studies, we isolated twelve recombinant baculoviruses designed to express four different WEEV glycoprotein constructs under the transcriptional control of three temporally distinct baculovirus promoters. The WEEV glycoprotein constructs encoded full-length E1, the E1 ectodomain, an E26KE1 polyprotein precursor, and an artificial, secretable E2E1 chimera. The three different promoters induced gene expression during the immediate early (ie1), late (p6.9), and very lat...
Netolitzky DJ, Schmaltz FL, Parker MD, Rayner GA, Fisher GR, Trent DW, Bader DE, Nagata LP.The complete nucleotide sequence of the 71V-1658 strain of western equine encephalitis virus (WEE) was determined (minus 25 nucleotides from the 5' end). A 5' RACE reaction was used to sequence the 5' terminus from WEE strain CBA87. The deduced WEE genome was 11508 nucleotides in length, excluding the 5' cap nucleotide and 3' poly(A) tail. The nucleotide composition was 28% A, 25% C, 25% G and 22% U. Comparison with partial WEE sequences of strain 5614 (nsP2-nsP3 of the nonstructural region) and strain BFS1703 (26S structural region) revealed comparatively little variation; a total of 149 nucl...
Nagata LP, Hu WG, Masri SA, Rayner GA, Schmaltz FL, Das D, Wu J, Long MC, Chan C, Proll D, Jager S, Jebailey L, Suresh MR, Wong JP.The efficacy of a DNA vaccine against western equine encephalitis (WEE) infection in mice was evaluated. The 26S structural region was expressed, in vitro from an internal T7 promoter using a rabbit reticulysate transcription/translation system; and from a CMV promoter after transfection into Vero cell monolayers. The proteins synthesized were reactive with anti-WEE virus (WEEV) antibodies, both in western blot analysis and histochemical staining, respectively. When the DNA vaccine plasmid, pVHX-6, was administered intraepidermally to mice, followed by challenge in a lethal mouse model, the le...
Calisher CH, Sasso DR, Sather GE.During 1971, an epizootic of Venezuelan equine encephalitis (VEE) reached the United States. Laboratory tests were performed on a large number of sick, healthy, unvaccinated, and vaccinated horses. Neutralization (N) tests in cell cultures revealed that 153 of 193 (79.3%) equines outside the state of Texas and 175 of 204 (85.8%) within Texas (82.6% overall) had detectable N antibody to VEE virus a week or more after vaccination. Twenty-six of 40 (65%) non-Texas equines and 18 of 29 (62%) Texas equines which had no detectable antibody against VEE virus a week or more after vaccination had N ant...
Burgess EC, Mattison M.Infection with Borrelia burgdorferi was associated with encephalitis in a horse. The horse lived in an area of Wisconsin endemic for B burgdorferi infection. Borrelia burgdorferi was isolated from the brain, but rabies virus was not detected in the brain. Serum obtained from the horse had a B burgdorferi antibody titer of 1:2,048, but was negative for antibodies to eastern and western encephalomyelitis.
Karabatsos N, Lewis AL, Calisher CH, Hunt AR, Roehrig JT.A virus, strain 64A-1519, isolated from the brain of a horse dying of encephalitis in Florida in 1964, was identified as western equine encephalomyelitis (WEE) virus. Recently, we used polyclonal and monoclonal immune reagents to identify this isolate by comparing it to 2 strains of WEE virus and to Highlands J (HJ) virus in hemagglutination-inhibition, immunofluorescent antibody, and plaque-reduction neutralization tests. These tests demonstrate that strain 64A-1519 is a strain of HJ virus distinct from WEE virus.
Sponseller ML, Binn LN, Wooding WL, Yager RH.Four field strains of western encephalitis virus were inoculated subcutaneously or intracranially (i/c) into recently weaned ponies. After s/c inoculation, 3 of the 4 strains produced an inapparent infection with a short period of viraemia. The 4th strain produced viraemia, fever, and signs of central nervous system disease. Viraemia occurred after intracranial inoculation with each strain; however, a variation in clinical response occurred, ranging from an inapparent infection to death. The disease pattern was characterized by three successive phases: viraemia, increased body temperature, and...
