Encephalitis in horses refers to inflammation of the brain, which can be caused by various infectious agents, including viruses, bacteria, and parasites. This condition affects the central nervous system and can lead to neurological symptoms such as ataxia, seizures, and changes in behavior. Common viral causes of equine encephalitis include Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), and West Nile Virus (WNV). Diagnosis often involves clinical evaluation, serological testing, and sometimes cerebrospinal fluid analysis. This page compiles peer-reviewed research studies and scholarly articles that explore the etiology, pathogenesis, clinical presentation, and management of encephalitis in horses.
HAMMON WM, REEVES WC.In three cases of encephalitis in humans that occurred in the area where the newly described California virus was isolated from mosquitoes, serological evidence seemed to indict the California virus as the etiological agent. In the case of an infant with very severe disease, the serological evidence was convincing; the evidence was almost as strong in the case of a seven-year-old boy; the results in an adult were equivocal. Inapparent infection in man is quite common as indicated by neutralization tests on the sera of nearly 600 residents of California, but encephalitic manifestations of infec...
Fukushi N, Fukushi H.Equine herpesvirus type 1 (EHV-1) is a devastating pathogen of horses, their natural hosts, and causes fatal encephalitis in non-natural hosts. We previously demonstrated that acylation of the tegument protein UL11 is required for viral replication in cultured cells. We created a mutant virus (EHV-1 UL12 trunc UL11 G2AC7AC9A), in which glycyl and cysteinyl residues at positions 2, 7 and 9 of UL11 that are normally acylated were replaced with alanyl residues. This virus, designated the 2/7/9 mutant, has a limited-replication cycle (LRC), in which replication stops after just a few cycles. Here,...
Croser EL, Marsh GA.The Henipavirus genus represents a group of paramyxoviruses that are some of the deadliest of known human and veterinary pathogens. Hendra and Nipah viruses are zoonotic pathogens that can cause respiratory and encephalitic illness in humans with mortality rates that exceed 70%. Over the past several years, we have seen an increase in the number of cases and an altered clinical presentation of Hendra virus in naturally infected horses. Recent increase in the number of cases has also been reported with human Nipah virus infections in Bangladesh. These factors, along with the recent discovery of...
Marshall ID, Brown BK, Keith K, Gard GP, Thibos E.There was extensive and exuberant breeding of waterbirds before and during an epidemic of arboviral encephalitis in the Murray Valley of south eastern Australia in 1974. As estimated by haemagglutination inhibition tests on 432 bird sera collected between 4th and 13th February, 1974, infection with Murray Valley encephalitis virus, Kunjin virus and possibly other flaviviruses was concentrated in species of the Order Ciconiiformes (55% positive) and Pelecaniformes (41%), compared with only 5% in Anseriformes. Although Sindbis virus infections were also highest in these 2 Orders (56% and 46%, re...
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...
Shepard JJ, Andreadis TG, Thomas MC, Molaei G.Eastern equine encephalitis virus (EEEV) is a highly pathogenic mosquito-borne arbovirus, with active transmission foci in freshwater hardwood swamps in eastern North America, where enzootic transmission is maintained between the ornithophilic mosquito, Culiseta melanura, and wild passerine birds. The role of other locally abundant mosquito species in virus transmission and their associations with vertebrate hosts as sources of blood meals within these foci are largely unknown but are of importance in clarifying the dynamics of enzootic and epidemic/epizootic transmission. Blood-engorged mosqu...
Wozniak A, Dowda HE, Tolson MW, Karabatsos N, Vaughan DR, Turner PE, Ortiz DI, Wills W.Arboviruses isolated and identified from mosquitoes in South Carolina (USA) are described, including new state records for eastern equine encephalitis virus (EEE), St. Louis encephalitis virus (SLE), Flanders virus, Tensaw virus (TEN), and a variant of Jamestown Canyon virus (JC). Mosquitoes were collected at 52 locations in 30 of 46 South Carolina counties beginning in June 1996, and ending in October 1998, and tested for arboviruses. Of 1,329 mosquito pools tested by virus isolation (85,806 mosquitoes representing 34 mosquito species or complexes), 15 pools were positive. Virus isolations in...
Hill V, Koch RT, Bialosuknia SM, Ngo K, Zink SD, Koetzner CA, Maffei JG, Dupuis AP, Backenson PB, Oliver J, Bransfield AB, Misencik MJ, Petruff TA....Eastern equine encephalitis virus (EEEV) causes a rare but severe disease in horses and humans and is maintained in an enzootic transmission cycle between songbirds and Culiseta melanura mosquitoes. In 2019, the largest EEEV outbreak in the United States for more than 50 years occurred, centered in the Northeast. To explore the dynamics of the outbreak, we sequenced 80 isolates of EEEV and combined them with existing genomic data. We found that, similar to previous years, cases were driven by multiple independent but short-lived virus introductions into the Northeast from Florida. Once in the ...
Fares W, Gdoura M, Dhrif H, Touzi H, Hogga N, Hannachi N, Mhalla S, Kacem S, Karray H, Bougatef S, Ben-Alaya N, Triki H.West Nile Virus (WNV) is an arbovirus transmitted by mosquito bite involving birds as reservoirs, humans and equines as accidental hosts. Eight distinct lineages (WNV-1 to WNV-8) have been identified: WNV-1 and WNV-2 infect humans and animals, and WNV-3 to WNV-8 have been identified only in vectors. WNV has been implicated in neuroinvasives infections, especially meningitis and encephalitis. Tunisia experienced three epidemics in 1997, 2003 and 2012. Serological studies on humans, equines and birds as well as the detection of the virus in the vector favour a fairly frequent circulation in the ...
Ryder S, Bracho D.Antibodies against Venezuelan Equine Encephalitis Virus (VEEV) were studied in the human population of Mara District, Zulia State, Venezuela. Two hundred thirty nine blood samples were taken from the towns of San Rafael de Mara, Santa Cruz de Mara, La Sierrita-4 Bocas, Carrasquero, Isla de San Carlos e Isla de Toas, during june, july and september, 1988. Donors samples were classified by age, sex and serological titres. Eighty nine were less than 15 years old (37.2%) and 150, over 15 years old (62.7%). From the 239 samples, 224 were negative (93.7%) and 15 positive (6.3%). Our results indicate...
Knox J, Cowan RU, Doyle JS, Ligtermoet MK, Archer JS, Burrow JN, Tong SY, Currie BJ, Mackenzie JS, Smith DW, Catton M, Moran RJ, Aboltins CA....Murray Valley encephalitis virus (MVEV) is a mosquito-borne virus that is found across Australia, Papua New Guinea and Irian Jaya. MVEV is endemic to northern Australia and causes occasional outbreaks across south-eastern Australia. 2011 saw a dramatic increase in MVEV activity in endemic regions and the re-emergence of MVEV in south-eastern Australia. This followed significant regional flooding and increased numbers of the main mosquito vector, Culex annulirostris, and was evident from the widespread seroconversion of sentinel chickens, fatalities among horses and several cases in humans, res...
Wang H, Liu S, Lv Y, Wei W.Venezuelan equine encephalitis virus (VEEV) is an emerging zoonotic virus in the alphavirus genus. It can be transmitted to humans due to spillover from equid-mosquito cycles. The symptoms caused by VEEV include fever, headache, myalgia, nausea, and vomiting. It can also cause encephalitis in severe cases. The evolutionary features of VEEV are largely unknown. In this study, we comprehensively analyzed the codon usage pattern of VEEV by computing a variety of indicators, such as effective number of codons (ENc), codon adaptation index (CAI), relative synonymous codon usage (RSCU), on 130 VEEV ...
Arboviruses include mosquitoborne and tickborne agents that persist in nature in complex cycles involving birds or mammals, including humans. Arboviral infection can cause fever, headache, meningitis, encephalitis, and sometimes death. During 1996-1997, health departments in 19 states reported to CDC 286 confirmed or probable cases (eight fatal) of arboviral encephalitis in humans (132 cases in 1996 and 154 provisionally in 1997). Surveillance programs in 18 states detected enzootic arboviral activity in mosquito or sentinel or wild bird populations, and cases of arboviral disease were recogni...
Ryder S, Núñez-Camargo J, Rangel P, Añez F.With the purpose of determining antibodies prevalence against Venezuelan Equine Encephalitis Virus in the population of Puertos de Altagracia and Sabaneta de Palmas of Miranda county, Zulia State, Venezuela, 199 subjects were studied: 57 from Puertos de Altagracia and 142 from Sabaneta de Palmas. They were classified in older (42.78%) and younger (57.2%) than 15 years. The blood specimens were processed for Hemagglutination Inhibition Test using EEV antigen Goajira strain at pH 6.5. We found that all 57 specimens from Puertos de Altagracia were negative, whereas of 142 specimens from Sabaneta ...
Bingham AM, Burkett-Cadena ND, Hassan HK, McClure CJ, Unnasch TR.Studies investigating winter transmission of Eastern equine encephalitis virus (EEEV) were conducted in Hillsborough County, Florida. The virus was detected in Culiseta melanura and Anopheles quadrimaculatus in February 2012 and 2013, respectively. During the winter months, herons were the most important avian hosts for all mosquito species encountered. In collections carried out in the summer of 2011, blood meals taken from herons were still common, but less frequently encountered than in winter, with an increased frequency of mammalian- and reptile-derived meals observed in the summer. Four ...
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...
Gibney KB, Robinson S, Mutebi JP, Hoenig DE, Bernier BJ, Webber L, Lubelczyk C, Nett RJ, Fischer M.Eastern equine encephalitis (EEE) is one of the most severe arboviral encephalitides in North America. Before 2009, limited nonhuman EEE virus activity had been reported in Maine, all from the southernmost area of the state. No human case has been reported in a Maine resident. Methods: We review all EEE virus activity reported to Maine Centers for Disease Control in 2009 and describe current testing practices for possible human EEE cases. Results: In 2009, fatal cases of EEE were identified in 15 horses, 1 llama, and 3 flocks of pheasants in Maine, with activity extending into the central part...
McLean RG, Ubico SR, Bourne D, Komar N.WN virus is one of the most ubiquitous arboviruses occurring over a broad geographical range and in a wide diversity of vertebrate host and vector species. The virus appears to be maintained in endemic foci on the African continent and is transported annually to temperate climates to the north in Europe and to the south in South Africa. Reports of clinical disease due to natural WN virus infection in wild or domestic animals were much less common than reports of infection (virus isolation or antibody detection). Until recently, records of morbidity and mortality in wild birds were confined to ...
Hasan SS, Dey D, Singh S, Martin M.Alphaviruses are arboviruses that cause arthritis and encephalitis in humans. Eastern Equine Encephalitis Virus (EEEV) is a mosquito-transmitted alphavirus that is implicated in severe encephalitis in humans with high mortality. However, limited insights are available into the fundamental biology of EEEV and residue-level details of its interactions with host proteins. In recent years, outbreaks of EEEV have been reported mainly in the United States, raising concerns about public safety. This review article summarizes recent advances in the structural biology of EEEV based mainly on single-par...
Lobigs M, Pavy M, Hall RA, Lobigs P, Cooper P, Komiya T, Toriniwa H, Petrovsky N.Advax is a polysaccharide-based adjuvant that potently stimulates vaccine immunogenicity without the increased reactogenicity seen with other adjuvants. This study investigated the immunogenicity of a novel Advax-adjuvanted Vero cell culture candidate vaccine against Japanese encephalitis virus (JEV) in mice and horses. The results showed that, in mice, a two-immunization, low-dose (50 ng JEV antigen) regimen with adjuvanted vaccine produced solid neutralizing immunity comparable to that elicited with live ChimeriVax-JE immunization and superior to that elicited with tenfold higher doses of a ...
Arthropodborne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. Symptomatic infections most often manifest as a systemic febrile illness and, less commonly, as neuroinvasive disease (e.g., meningitis, encephalitis, or acute flaccid paralysis). West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the United States. However, several other arboviruses also cause seasonal outbreaks and sporadic cases. In 2011, CDC received reports of 871 cases of nationally notifiable arboviral diseases (excluding deng...
Reisen WK, Hardy JL, Presser SB, Chiles RE.The vector competence of Culex tarsalis Coquillett from the Coachella Valley of California for western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses was monitored monthly from February to November 1993. The concentration of WEE virus required to infect 50% of the females increased during summer coincidentally with ambient temperature and was highest during July. Transmission rates of WEE virus were high during March, low during May-June, and high again during July-September. Females expressed both mesenteronal escape and salivary gland barriers limiting WEE virus diss...
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...
Rossi SL, Guerbois M, Gorchakov R, Plante KS, Forrester NL, Weaver SC.Venezuelan equine encephalitis virus (VEEV) is an arbovirus that causes periodic outbreaks that impact equine and human populations in the Americas. One of the VEEV subtypes located in Mexico and Central America (IE) has recently been recognized as an important cause of equine disease and death, and human exposure also appears to be widespread. Here, we describe the use of an Internal Ribosome Entry Site (IRES) from encephalomyocarditis virus to stably attenuate VEEV, creating a vaccine candidate independent of unstable point mutations. Mice infected with this virus produced antibodies and wer...
Dürrwald R, Kolodziejek J, Oh DY, Herzog S, Liebermann H, Osterrieder N, Nowotny N.(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture...
Dauphin G, Legay V, Pitel PH, Zientara S.For over two centuries, Borna disease (BD) has been described as a sporadically occurring infectious meningoencephalomyelitis affecting horses and sheep in Central Europe. Over the last decade, the BD epidemiology has been discussed. Firstly, its geographical distribution seems larger than what was previously thought. Secondly, the disease can affect a large number of warm-blooded animal species, including humans. The aetiological agent is the Boma disease virus (BDV), an enveloped, nonsegmented negative-stranded RNA virus classified in the new virus family Bornaviridae (Mononegavirales order)...
de Heus P, Bagó Z, Weidinger P, Lale D, Trachsel DS, Revilla-Fernández S, Matiasek K, Nowotny N.As evidenced by sero-epidemiological studies, infections of horses with the tick-borne encephalitis virus (TBEV) occur frequently in TBEV-endemic areas. However, there are only very few reports of clinical cases. A possible underreporting may be due to a variety of diagnostic challenges. In this study, ELISA and neutralization tests were applied to serum samples. Brain tissue samples were investigated for the presence of nucleic acids of TBEV, Equid alphaherpesvirus 1, Borna disease virus 1, West Nile and Usutu viruses, rustrela virus, as well as Eastern, Western, and Venezuelan equine encepha...
