Encephalomyelitis in horses refers to inflammation of the brain and spinal cord, often caused by viral infections such as Eastern, Western, and Venezuelan equine encephalomyelitis viruses. These conditions can lead to neurological symptoms including fever, ataxia, and behavioral changes. The disease can be transmitted through mosquito vectors, with horses serving as dead-end hosts. Diagnosis typically involves serological testing and clinical evaluation. This page aggregates peer-reviewed research studies and scholarly articles that explore the etiology, pathogenesis, clinical presentation, and management strategies for encephalomyelitis in equine populations.
Cao X, Yang D, Parvathareddy J, Chu YK, Kim EJ, Fitz-Henley JN, Li X, Lukka PB, Parmar KR, Temrikar ZH, Dhole P, Adcock RS, Gabbard J, Bansal S....Venezuelan and eastern equine encephalitis viruses (VEEV and EEEV, respectively) are mosquito-borne, neuroinvasive human pathogens for which no FDA-approved therapeutic exists. Besides the biothreat posed by these viruses when aerosolized, arthropod transmission presents serious health risks to humans, as demonstrated by the 2019 outbreak of EEE disease in the United States that resulted in 38 confirmed cases, 19 deaths, and neurological effects in survivors. Here, we describe the discovery of a 2-pyrrolidinoquinazolinone scaffold, efficiently synthesized in two to five steps, whose structural...
Bonilla-Aldana DK, Bonilla Carvajal CD, Moreno-Ramos E, Barboza JJ, Rodriguez-Morales AJ.Eastern equine encephalitis virus (EEEV) and Venezuelan equine encephalitis virus (VEEV) viruses are zoonotic pathogens affecting humans, particularly equines. These neuroarboviruses compromise the central nervous system and can be fatal in different hosts. Both have significantly influenced Colombia; however, few studies analyse its behaviour, and none develop maps using geographic information systems to characterise it. To describe the temporal-spatial distribution of those viruses in Colombia between 2008 and 2019. Retrospective cross-sectional descriptive study, based on weekly reports by ...
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.
Ibrahim M.Rhinoestrus species larvae are considered obligatory parasites of the nasal cavities of equine. This type of myiasis is characterised by sneezing, coughing, olfactory nerve damage and encephalomyelitis. Also, it has a zoonotic importance as the larvae might cause ophthalmomyiasis and conjunctivitis in human. While few studies describing R. purpureus adult fly antennal sensillae are available, the R. usbekistanicus antennal sensillae have never been described. Also, scanty data are available on the adult flies of Rhinoestrus species morphology. For this reason, the current study aimed at identi...
Cardo MV, Carbajo AE, Mozzoni C, Kliger M, Vezzani D.Blood feeding patterns of mosquitoes are a key component in the dynamics of arboviral encephalitides transmission. In temperate Argentina, the members of the Culex pipiens complex include Cx. pipiens molestus, Cx. quinquefasciatus and their hybrids. To characterize their blood feeding patterns, adult resting mosquitoes were collected monthly during the warm season in urban and rural equestrian fields. The availability of birds and domestic mammals per site was characterized. The blood source and the complex member were successfully identified for 89 specimens using PCR. Blood of 19 vertebrate ...
Toribio RE.A number of viruses transmitted by biological vectors or through direct contact, air, or ingestion cause neurologic disease in equids. Of interest are viruses of the Togaviridae, Flaviviridae, Rhabdoviridae, Herpesviridae, Bornaviridae, and Bunyaviridae families. Many are classified as arboviruses because they use arthropod vectors, whereas others are transmitted directly via ingestion, inhalation, or integument damage. The goal of this article is to provide an overview on pathophysiologic and clinical aspects of arboviruses of equine importance, including alphaviruses (Togaviridae) and flaviv...
Ciota AT.Eastern equine encephalitis virus (EEEV; Togaviridae, Alphavirus) is an arthropod-borne virus (arbovirus) primarily maintained in an enzootic cycle between Culiseta melanura (Coquillett) and passerine birds. EEEV, which has the highest reported case- fatality rate among arbovirus in the Americas, is responsible for sporadic outbreaks in the Eastern and Midwest United States. Infection is associated with severe neurologic disease and mortality in horses, humans, and other vertebrate hosts. Here, we review what is known about EEEV taxonomy, functional genomics, and evolution, and identify gaps i...
Armstrong PM, Andreadis TG.In the current review, we examine the regional history, ecology, and epidemiology of eastern equine encephalitis virus (EEEV) to investigate the major drivers of disease outbreaks in the northeastern United States. EEEV was first recognized as a public health threat during an outbreak in eastern Massachusetts in 1938, but historical evidence for equine epizootics date back to the 1800s. Since then, sporadic disease outbreaks have reoccurred in the Northeast with increasing frequency and northward expansion of human cases during the last 20 yr. Culiseta melanura (Coquillett) (Diptera: Culicidae...
Stobierski MG, Signs K, Dinh E, Cooley TM, Melotti J, Schalow M, Patterson JS, Bolin SR, Walker ED.Eastern equine encephalomyelitis (EEE) is a mosquito-borne viral disease that is an emerging public health concern in the state of Michigan. Although Michigan has one of the highest incidence rates of EEE in the United States, much of the information known about cases in humans, equines, and other animals residing in Michigan is unpublished. This article summarizes such information and explores spatial trends in the historic distribution of EEE in Michigan. Outbreaks in Michigan have occurred over an 80-yr interval, involving only horses in 1942-1943 and 1973-1976, and then episodically from 1...
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...
Boos GS, Failing K, Colodel EM, Driemeier D, de Castro MB, Bassuino DM, Diomedes Barbosa J, Herden C.Like humans, horses are susceptible to neurotropic and neuroinvasive pathogens that are not always readily identified in histological sections. Instead, alterations in astrocytes and microglia cells can be used as pathological hallmarks of injured nervous tissue in a variety of infectious and degenerative diseases. On the other hand, equine glial cell alterations are poorly characterized in diseases. Therefore, in this study, we provide a statistically proved score system to classify astrogliosis and microgliosis in the central nervous system (CNS) of horses, based on morphological and quantit...
Hales EN, Aleman M, Marquardt SA, Katzman SA, Woolard KD, Miller AD, Finno CJ.To determine period prevalences of postmortem diagnoses for spinal cord or vertebral column lesions as underlying causes of ataxia (spinal ataxia) in horses. Methods: 2,861 client-owned horses (316 with ataxia [ataxic group] and 2,545 without ataxia [control group]). Methods: The medical records database of the University of California-Davis Veterinary Medical Teaching Hospital was searched to identify horses necropsied between January 1, 2005, and December 31, 2017. Results were compared between the ataxic and control groups and between various groups of horses in the ataxic group. Period pre...
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...
Metz MBC, Olufemi OT, Daly JM, Barba M.There is some evidence that West Nile virus (WNV), which causes encephalomyelitis in equids, is an emerging disease in Europe. The aim of this study was to perform a systematic review and meta-analysis to analyse seroprevalence studies of WNV in equids in European countries between 2001 and 2018. Two electronic databases, PubMed and Scopus, were searched for relevant publications published from 2001 to 2018 using predetermined keywords. A total of 1,484 papers were initially found. After applying the eligibility criteria, 39 papers were finally included in the systematic review. Analysis of 28...
Kutasi O, Fehér O, Sárdi S, Balogh N, Nagy A, Moravszki L, Bódai E, Szenci O.West Nile virus (WNV) is a zoonotic arbovirus transmitted by mosquitoes between wild birds (natural hosts) and other vertebrates. Horses and humans are incidental, dead-end hosts, but can develop severe neurological disorders. Owing to the close contact of cerebrospinal fluid (CSF) with the extracellular fluid of the brain, the analysis of CSF composition can reflect central nervous system (CNS) impairments enabling the diagnosis and understanding of various neurodegenerative CNS disorders. Our objective was to compare the findings from the CSF samples of horses with neuroinvasive WNV infectio...
Smith DR, Schmaljohn CS, Badger C, Ostrowski K, Zeng X, Grimes SD, Rayner JO.Venezuelan, eastern, and western equine encephalitis viruses (VEEV, EEEV, and WEEV) are mosquito-borne viruses in the Americas that cause central nervous system (CNS) disease in humans and equids. In this study, we directly characterized the pathogenesis of VEEV, EEEV, and WEEV in cynomolgus macaques following subcutaneous exposure because this route more closely mimics natural infection via mosquito transmission or by an accidental needle stick. Our results highlight how EEEV is significantly more pathogenic compared to VEEV similarly to what is observed in humans. Interestingly, EEEV appears...
León B, Käsbohrer A, Hutter SE, Baldi M, Firth CL, Romero-Zúñiga JJ, Jiménez C.Eastern equine encephalitis and Venezuelan equine encephalitis are endemic neglected tropical diseases in the Americas, causing encephalitis in both horses and humans. In 2013, a cross-sectional study was performed in 243 horses located in the highlands and lowlands throughout Costa Rica. Serum samples were analyzed with an IgG ELISA and confirmed by the plaque-reduction neutralization test (PRNT80). Venezuelan equine encephalitis virus (VEEV) and Eastern equine encephalitis virus (EEEV) overall seroprevalences by the PRNT80 were 36% (95% confidence interval [CI]: 29.9-42.5; 78/217 horses) and...
Avila VA, López-García Y, Hernández-Castro R, Salas-Garrido CG, Ramírez-Lezama J, Calderón-Villa R, Martínez-Chavarría LC.Aberrant nematode larval migration in the CNS of horses is rare but frequently fatal; one of the main etiological agents involved in this illness is Halicephalobus gingivalis. This soil nematode has been associated with several fatal equine meningoencephalitis reports worldwide; however, it had never been diagnosed in horses of Mexico. A 10 year-old Andalusian horse presented dysphagia, fever, weakness, prostration and ataxia; the patient expired during the medical attention. Post mortem examination was performed and no gross alterations were found. Histopathology revealed meningoencephalitis...
Barba M, Fairbanks EL, Daly JM.Members of several different virus families cause equine viral encephalitis, the majority of which are arthropod-borne viruses (arboviruses) with zoonotic potential. The clinical signs caused are rarely pathognomonic; therefore, a clinical diagnosis is usually presumptive according to the geographical region. However, recent decades have seen expansion of the geographical range and emergence in new regions of numerous viral diseases. In this context, this review presents an overview of the prevalence and distribution of the main viral causes of equine encephalitis and discusses their impact an...
Niazmand MH, Hirai T, Ito S, Habibi WA, Noori J, Hasheme R, Yamaguchi R.We performed postmortem examinations on seven Misaki feral horses () and evaluated Misaki feral horses, Japanese wild boars (), domestic pigs (), and wild Japanese macaques () from 2015 to 2017 in Cape Toi, Kushima, Miyazaki Prefecture, southern Japan, for antibodies against Japanese encephalitis virus (JEV). infection with severe arterial lesions and hemomelasma ilei was present in all necropsied horses. We frequently found intestinal ulcers, perihepatitis filamentosa, and poor body condition. We recorded degenerative arthropathy in metacarpophalangeal joints in two cases and a fracture of t...
Silva ASG, Matos ACD, da Cunha MACR, Rehfeld IS, Galinari GCF, Marcelino SAC, Saraiva LHG, Martins NRDS, Maranhão RPA, Lobato ZIP, Pierezan F....Mosquito-borne arboviruses are a major public health concern worldwide and are responsible for emerging and re-emerging diseases. Taken together, the arboviruses have a strong impact on public health and are the most common causes of equine encephalitis. In-depth diagnostic investigation of equine viral encephalitis is of utmost importance for the epidemiological surveillance and control of this disease. Regarding neurological disorders in equids, in April-May 2018, at least 12 cases of equid mortality with acute neurological signs were reported in six farms from Espirito Santo state, Brazil. ...
Certoma A, Lunt RA, Vosloo W, Smith I, Colling A, Williams DT, Tran T, Blacksell SD.Australian bat lyssavirus (ABLV) is closely related to the classical rabies virus and has been associated with three human fatalities and two equine fatalities in Australia. ABLV infection in humans causes encephalomyelitis, resulting in fatal disease, but has no effective therapy. The virus is maintained in enzootic circulation within fruit bats ( spp.) and at least one insectivorous bat variety ( ). Most frequently, laboratory testing is conducted on pteropodid bat brains, either following a potential human exposure through bites, scratches and other direct contacts with bats, or as opportun...
Tan Y, Lam TT, Heberlein-Larson LA, Smole SC, Auguste AJ, Hennigan S, Halpin RA, Fedorova N, Puri V, Stockwell TB, Shilts MH, Andreadis T....Eastern equine encephalitis virus (EEEV) has a high case-fatality rate in horses and humans, and Florida has been hypothesized to be the source of EEEV epidemics for the northeastern United States. To test this hypothesis, we sequenced complete genomes of 433 EEEV strains collected within the United States from 1934 to 2014. Phylogenetic analysis suggested EEEV evolves relatively slowly and that transmission is enzootic in Florida, characterized by higher genetic diversity and long-term local persistence. In contrast, EEEV strains in New York and Massachusetts were characterized by lower genet...
Chapman GE, Baylis M, Archer D, Daly JM.Equine populations worldwide are at increasing risk of infection by viruses transmitted by biting arthropods, including mosquitoes, biting midges (Culicoides), sandflies and ticks. These include the flaviviruses (Japanese encephalitis, West Nile and Murray Valley encephalitis), alphaviruses (eastern, western and Venezuelan encephalitis) and the orbiviruses (African horse sickness and equine encephalosis). This review provides an overview of the challenges faced in the surveillance, prevention and control of the major equine arboviruses, particularly in the context of these viruses emerging in ...
Ledermann W.With the apparition of the crazy cows disease at the end of twentieth century, great was the temptation for denominate "crazy horses disease" an ancient enzootic encephalo-myelitis, known from the 17th century and now named "Borna disease" in 1970, because severe outbreaks affecting horses in this city of Germany since 1885. But the sickness was not a prion disease but a viral one, causing also encephalopathy in several other animal species. After seventy years of investigation, the finding of the virus in human patients with psychiatric pathology in the eighties gave an incentive to work hard...
Kumar R, Patil RD.The importance of horse (Equus caballus) to equine practitioners and researchers cannot be ignored. An unevenly distributed population of equids harbors numerous diseases, which can affect horses of any age and breed. Among these, the affections of nervous system are potent reason for death and euthanasia in equids. Many episodes associated with the emergence of equine encephalitic conditions have also pose a threat to human population as well, which signifies their pathogenic zoonotic potential. Intensification of most of the arboviruses is associated with sophisticated interaction between ve...
More S, Bøtner A, Butterworth A, Calistri P, Depner K, Edwards S, Garin-Bastuji B, Good M, Gortázar Schmidt C, Michel V, Miranda MA, Nielsen SS....Equine encephalomyelitis (Eastern and Western) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of equine encephalomyelitis (Eastern and Western) to be listed, Article 9 for the categorisation of equine encephalomyelitis (Eastern and Western) according to disease prevention and control rules as in Annex IV, and Article 8 on the list of animal species related to equine encephalomyelitis (Eastern and Western). The assessment has been performed following a methodology compos...
Weaver SC, Salas R, Rico-Hesse R, Ludwig GV, Oberste MS, Boshell J, Tesh RB.Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic. Methods: Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera ...
Murray KO, Mertens E, Despres P.Zoonotic West Nile virus (WNV) circulates in natural transmission cycles involving certain mosquitoes and birds, horses, humans, and a range of other vertebrates are incidental hosts. Clinical infections in humans can range in severity from uncomplicated WNV fever to fatal meningoencephalitis. Since its introduction to the Western Hemisphere in 1999, WNV had spread across North America, Central and South America and the Caribbean, although the vast majority of severe human cases have occurred in the United States of America (USA) and Canada. By 2002-2003, the WNV outbreaks have involved thousa...
Garmashova N, Atasheva S, Kang W, Weaver SC, Frolova E, Frolov I.The encephalitogenic New World alphaviruses, including Venezuelan (VEEV), eastern (EEEV), and western equine encephalitis viruses, constitute a continuing public health threat in the United States. They circulate in Central, South, and North America and have the ability to cause fatal disease in humans and in horses and other domestic animals. We recently demonstrated that these viruses have developed the ability to interfere with cellular transcription and use it as a means of downregulating a cellular antiviral response. The results of the present study suggest that the N-terminal, approxima...
Carrera JP, Forrester N, Wang E, Vittor AY, Haddow AD, López-Vergès S, Abadía I, Castaño E, Sosa N, Báez C, Estripeaut D, Díaz Y, Beltrán D....The eastern equine encephalitis (EEE) and Venezuelan equine encephalitis (VEE) viruses are pathogens that infect humans and horses in the Americas. Outbreaks of neurologic disease in humans and horses were reported in Panama from May through early August 2010. Methods: We performed antibody assays and tests to detect viral RNA and isolate the viruses in serum samples from hospitalized patients. Additional cases were identified with enhanced surveillance. Results: A total of 19 patients were hospitalized for encephalitis. Among them, 7 had confirmed EEE, 3 had VEE, and 1 was infected with both ...
Castillo-Olivares J, Wood J.West Nile virus (WNV) is a flavivirus closely related to Japanese encephalitis and St. Louis encephalitis viruses that is primarily maintained in nature by transmission cycles between mosquitoes and birds. Occasionally, WNV infects and causes disease in other vertebrates, including humans and horses. West Nile virus has re-emerged as an important pathogen as several recent outbreaks of encephalomyelitis have been reported from different parts of Europe in addition to the large epidemic that has swept across North America. This review summarises the main features of WNV infection in the horse, ...
Arrigo NC, Adams AP, Weaver SC.The eastern equine encephalitis (EEE) complex consists of four distinct genetic lineages: one that circulates in North America (NA EEEV) and the Caribbean and three that circulate in Central and South America (SA EEEV). Differences in their geographic, pathogenic, and epidemiologic profiles prompted evaluation of their genetic diversity and evolutionary histories. The structural polyprotein open reading frames of all available SA EEEV and recent NA EEEV isolates were sequenced and used in evolutionary and phylogenetic analyses. The nucleotide substitution rate per year for SA EEEV (1.2 x 10(-4...
Cantile C, Di Guardo G, Eleni C, Arispici M.West Nile (WN) virus infection is a mosquito-borne flavivirosis endemic in Africa and Asia. Clinical disease is usually rare and mild and only in a few cases the infection causes encephalomyelitis in horses, fever and meningoencephalitis in man. We report here the clinical and pathological findings in an epidemic of the disease involving 14 horses from Tuscany, Italy. All cases were observed from August to October 1998. Affected horses showed ataxia, weakness paresis of the hindlimbs and, in 6 cases, there was paraparesis progressing to tetraplegia and recumbency within 2 to 9 days. Eight anim...
Hassan HK, Cupp EW, Hill GE, Katholi CR, Klingler K, Unnasch TR.An important variable in the amplification and escape from the enzootic cycle of the arboviral encephalitides is the degree of contact between avian hosts and mosquito vectors. To analyze this interaction in detail, blood-fed mosquitoes that were confirmed vectors of eastern equine encephalomyelitis (EEE) virus were collected in 2002 from an enzootic site in central Alabama during the time this virus was actively transmitted. Avian-derived blood meals were identified to the species level of the host, and the proportion derived from each species was compared with the overall composition of the ...
Weaver SC, Hagenbaugh A, Bellew LA, Gousset L, Mallampalli V, Holland JJ, Scott TW.Evolution of viruses in the eastern equine encephalomyelitis (EEE) complex was studied by analyzing RNA sequences and oligonucleotide fingerprints from isolates representing the North and South American antigenic varieties. By using homologous sequences of Venezuelan equine encephalomyelitis virus as an outgroup, phylogenetic trees revealed three main EEE virus monophyletic groups. A North American variety group included all isolates from North America and the Caribbean. One South American variety group included isolates from the Amazon basin in Brazil and Peru, while the other included strain...
Cantile C, Del Piero F, Di Guardo G, Arispici M.The pathologic and peroxidase immunohistochemical features of West Nile flavivirus (WNV) infection were compared in four horses from the northeastern United States and six horses from central Italy. In all 10 animals, there were mild to severe polioencephalomyelitis with small T lymphocyte and lesser macrophage perivascular infiltrate, multifocal glial nodules, neutrophils, and occasional neuronophagia. Perivascular hemorrhages, also noted macroscopically in two animals, were observed in 50% of the horses. In the four American horses, lesions extended from the basal nuclei through the brain st...
Baer A, Lundberg L, Swales D, Waybright N, Pinkham C, Dinman JD, Jacobs JL, Kehn-Hall K.Venezuelan equine encephalitis virus (VEEV) is a previously weaponized arthropod-borne virus responsible for causing acute and fatal encephalitis in animal and human hosts. The increased circulation and spread in the Americas of VEEV and other encephalitic arboviruses, such as eastern equine encephalitis virus and West Nile virus, underscore the need for research aimed at characterizing the pathogenesis of viral encephalomyelitis for the development of novel medical countermeasures. The host-pathogen dynamics of VEEV Trinidad donkey-infected human astrocytoma U87MG cells were determined by car...
Cupp EW, Klingler K, Hassan HK, Viguers LM, Unnasch TR.A site near Tuskegee, Alabama was examined for vector activity of eastern equine encephalomyelitis (EEE) virus in 2001. More than 23,000 mosquitoes representing 8 genera and 34 species were collected during a 21-week period, and five species, Culiseta melanura, Aedes vexans, Coquillettidia perturbans, Culex erraticus, and Uranotaenia sapphirina, were examined for the presence of virus using a nested reverse transcriptase-polymerase chain reaction for EEE virus. Each species was infected at various times of the mosquito season (May-September) with different minimum infection rates (MIRs). Culis...
Kutasi O, Bakonyi T, Lecollinet S, Biksi I, Ferenczi E, Bahuon C, Sardi S, Zientara S, Szenci O.The spread of lineage 2 West Nile virus (WNV) from sub-Saharan regions to Europe and the unpredictable change in pathogenicity indicate a potential public and veterinary health threat and requires scientific awareness. Objective: To describe the results of clinical and virological investigations of the 1st outbreak of a genetic lineage 2 WNV encephalomyelitis in horses. Methods: Seventeen horses with neurologic signs. Methods: Information regarding signalment, clinical signs, and outcome was obtained for each animal. Serology was performed in 15 cases, clinicopathological examination in 7 case...
Greene IP, Paessler S, Austgen L, Anishchenko M, Brault AC, Bowen RA, Weaver SC.Epidemics of Venezuelan equine encephalitis (VEE) result from high-titer equine viremia of IAB and IC subtype viruses that mediate increased mosquito transmission and spillover to humans. Previous genetic studies suggest that mutations in the E2 envelope glycoprotein allow relatively viremia-incompetent, enzootic subtype ID strains to adapt for equine replication, leading to VEE emergence. To test this hypothesis directly, chimeric VEEV strains containing the genetic backbone of enzootic subtype ID strains and the partial envelope glycoprotein genes of epizootic subtype IC and IAB strains, as ...
Aréchiga-Ceballos N, Aguilar-Setién A.Summary Alphaviral equine encephalomyelitis is a mosquito-borne infection that causes severe neurological disease and fatalities in horses and humans in the Americas. Consequently, the equine alphaviruses (Eastern, Western and Venezuelan) are of considerable concern worldwide and are notifiable to the World Organisation for Animal Health. In addition, these diseases are considered a potent potential biological weapon, emphasising the need to develop an effective vaccine. Alphaviral equine encephalomyelitis is caused by Eastern equine encephalomyelitis virus (EEEV), Western equine encephalomyel...
Bigler WJ, Lassing EB, Buff EE, Prather EC, Beck EC, Hoff GL.Research and surveillance programs relating to the circulation of eastern equine encephalomyelitis (EEE) virus in Florida between 1955 and 1974 are summarized. All available data suggest that EEE virus is 1) endemic in many Florida fresh water swamps and waterways, 2) active in a continuous cycle throughout the year with a peak between May and August, and 3) circulating in Culiseta melanura. It has been isolated also from eight other mosquito species.
Taylor KG, Paessler S.Equine encephalids have high mortality rates and represent a significant zoonotic public health threat. Of these the most pathogenic viruses to equids are the alphaviruses in the family Togaviridae. The focus of this review Venezualen equine encephalitis virus (VEEV) has caused the most widespread and recent epidemic outbreaks of disease. Circulation in naturally occuring rodent-mosquito cycles, results in viral spread to both human and equine populations. However, equines develop a high titer viremia and can transmit the virus back to mosquito populations. As such, the early recognition and c...
CASALS J.A study by hemagglutination-inhibition test showed that 19 strains of eastern equine encephalitis virus grouped themselves in two main types, which have been designated North American and South American. The former consists of ten strains from the eastern half of the United States, from Massachusetts to Florida; Jamaica, the Dominican Republic, and, subject to confirmation, Thailand. The South American type comprises nine strains from Panama, Trinidad, British Guiana, Brazil, and Argentina. The strains were isolated from different natural hosts over a period of 30 years.
Wilson TM, Ross PF, Rice LG, Osweiler GD, Nelson HA, Owens DL, Plattner RD, Reggiardo C, Noon TH, Pickrell JW.During the fall of 1989, an episode of equine leukoencephalomalacia involved 18 of 66 purebred Arabian horses at a breeding/training stable in Arizona. Of the 18 horses affected, the condition was fatal in 14. These horses, as well as 48 unaffected horses, had been fed a diet containing a substantial amount of white corn screenings. Gross pathologic findings included liquefactive necrosis in parts of the cerebral white matter and hemorrhagic foci of various sizes in the brain stem. Histopathologic findings included rarefied white matter with pyknotic nuclei and eosinophilic cytoplasm. Thin-lay...
Weaver SC, Powers AM, Brault AC, Barrett AD.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 alphaviruse...
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...
Magnarelli LA.Blood-engorged Coquillettidia perturbans, Psorophora ferox, Culex, Culiseta, and Aedes mosquitoes were collected principally by sweep net from salt marsh and woodland habitats in Connecticut. Of the 570 mosquitoes tested, precipitin tests identified the origins of 517 blood meals and revealed distinct host feeding patterns. Aedes mosquitoes fed chiefly on mammals; A. abserratus, A. cantator, and A. vexans showed selectivity for cattle and (or) horses. A. cantator also obtained blood from avian hosts and, in some instances, showed mixed passerine-mammal blood meals. These findings increase the ...
Sudia WD, Newhouse VF, Beadle ID, Miller DL, Johnston JG, Young R, Calisher CH, Maness K.A major epidemic of Venezuelan equine encephalitis occurred in south Texas in the summer of 1971. More than 1500 equines died of VEE in Texas, and 110 human cases with no deaths were reported. Vector studies in south Texas and northern Tamaulipas revealed that the overall mosquito infection rates during the peak of the epidemic were about 1:100, one of the highest rates observed for a major epidemic. Mosquito infection rates of this magnitude could easily explain the intensity of VEE outbreaks in both equines and man. A total of 943 VEE virus isolations were made from mosquitoes. Eight of the ...
Pauvolid-Corrêa A, Juliano RS, Campos Z, Velez J, Nogueira RM, Komar N.The Pantanal hosts diverse wildlife species and therefore is a hotspot for arbovirus studies in South America. A serosurvey for Mayaro virus (MAYV), eastern (EEEV), western (WEEV) and Venezuelan (VEEV) equine encephalitis viruses was conducted with 237 sheep, 87 free-ranging caimans and 748 equids, including 37 collected from a ranch where a neurologic disorder outbreak had been recently reported. Sera were tested for specific viral antibodies using plaque-reduction neutralisation test. From a total of 748 equids, of which 264 were immunised with vaccine composed of EEEV and WEEV and 484 had n...
