Topic:Mosquito-borne Diseases
Mosquito-borne diseases in horses encompass a range of illnesses transmitted by mosquito vectors, impacting equine health worldwide. These diseases include West Nile Virus (WNV), Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), and Venezuelan Equine Encephalitis (VEE). Each disease is caused by distinct viral pathogens, leading to varying clinical presentations, such as fever, neurological symptoms, and in severe cases, death. Understanding the epidemiology, transmission dynamics, and pathogenesis of these diseases is essential for effective prevention and control strategies. This page compiles peer-reviewed research studies and scholarly articles that explore the transmission, clinical manifestations, and management of mosquito-borne diseases in horses.
The transmission and geographical spread of African horse sickness and bluetongue viruses. African horse sickness virus (AHSV) and bluetongue virus (BTV) are dsRNA viruses within the genus Orbivirus. Both are able to cause non-contagious, infectious arthropod-borne diseases in their respective vertebrate hosts. AHSV infects equines and occasionally dogs, whereas BTV replicates in ruminants. The disease caused by AHSV is usually at its most severe in horses, whereas certain breeds of sheep are particularly sensitive to BTV infection. AHSV is endemic in sub-Saharan Africa but periodically makes brief excursions beyond this area. BTV occurs much more widely and can be found in a band a...
Emergence of eastern encephalitis in Massachusetts. The 20th century emergence in Massachusetts of zoonotic eastern encephalitis was interpreted in terms of recorded environmental change. The main mosquito vector of the infection, Cs. melanura, appears to have been scarce in eastern North America before the 1930s. Its relative scarcity resulted from destruction of the swamps that had been lumbered or drained for farming in the 18th and 19th centuries. When swamps matured once again early in the 1900s, the formation of subsurface pools of water beneath mature trees would have increased the availability of breeding sites for this mosquito. Transm...
Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and Culicidae) and control methods. The biology, veterinary importance and control of certain Nematocera are described and discussed. Culicoides spp. (family Ceratopogonidae) transmit the arboviruses of bluetongue (BT), African horse sickness (AHS), bovine ephemeral fever (BEF) and Akabane. Some other arboviruses have been isolated from these species, while fowl pox has been transmitted experimentally by Culicoides. These insects are vectors of the parasitic protozoans Leucocytozoon caulleryi and Haemoproteus nettionis, and the parasitic nematodes Onchocerca gutturosa, O. gibsoni and O. cervicalis. They also cause recurrent summ...
Eastern equine encephalomyelitis virus in relation to the avian community of a coastal cedar swamp. Eastern equine encephalomyelitis virus (EEEV) is perpetuated in eastern North America in a mosquito-wild bird maintenance cycle that involves Culiseta melanura (Coquillett) as the principal enzootic vector and passerine birds as the primary amplifying hosts. We examined the role of birds in the EEEV cycle at a site in southern New Jersey where EEEV cycles annually at high levels. Birds and mosquitoes were sampled during three epiornitics and one season of limited virus activity. We examined antibody prevalence in birds in relation to eight physical and natural history characteristics. Our goal...
Epizootiology and vectors of African horse sickness virus. African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and is enzootic in sub-Saharan Africa. The major vectors are species of Culicoides but mosquitoes and ticks may be involved. Periodically the virus makes excursions beyond its enzootic zones but until recently has not been able to maintain itself outside these areas for more than 2-3 consecutive years. This is probably due to a number of factors including the absence of a long term vertebrate reservoir, the prevalence and seasonal incidence of the vectors and the efficiency of control mea...
Experimental transmission of eastern equine encephalitis virus by strains of Aedes albopictus and A. taeniorhynchus (Diptera: Culicidae). The vector competence of Aedes taeniorhynchus (Wiedemann) and four strains of Aedes albopictus (Skuse) was assessed for eastern equine encephalitis (EEE) virus isolated from Ae. albopictus collected in Polk County, Florida. Both species became infected with and transmitted EEE virus by bite after feeding on 1-d-old chicks that had been inoculated with EEE virus (viremia = 10(10.1) plaque-forming units [PFU] per ml of blood). However, when fed on an older chick with a lower viremia (viremia = 10(6.1) PFU per ml of blood), Ae. albopictus was significantly more susceptible to infection (90%, n = ...
Natural vertical transmission of western equine encephalomyelitis virus in mosquitoes. 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...
Medically important arboviruses of the United States and Canada. 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...
Eastern equine encephalitis (EEE): a description of the 1989 outbreak, recent epidemiologic trends, and the association of rainfall with EEE occurrence. An Eastern equine encephalitis (EEE) outbreak in 1989 led to nine human and 196 equine cases, chiefly in coastal Atlantic and Gulf Coast counties. In the past two decades, EEE age-specific incidence and mortality rates have declined compared with earlier years. Analysis of rainfall patterns in areas where human EEE cases occurred between 1983 and 1989 revealed an association between occurrence of human cases and excess rainfall. The association was stronger with data from local weather stations than from statewide rainfall averages and the predictive models were best when applied to northern s...
A rapid diagnostic assay for eastern equine encephalomyelitis viral RNA. Eastern equine encephalomyelitis virus (EEEV) has been a low-frequency, but serious human and veterinary health problem. Increased frequency of this mosquito-borne virus is anticipated as wetlands are maintained and re-established. Control of EEEV has depended on mosquito abatement in response to increasing frequency of EEEV in the environment. A coupled reverse transcription/polymerase chain reaction assay was designed to rapidly, sensitively, and specifically detect EEEV RNA. The assay successfully detected the viral RNA in a single-blind study of a set of field samples composed of either po...
Immunogens of encephalitis viruses. The equine encephalitis viruses are members of the genus Alphavirus, in the family Togaviridae. Three main virus serogroups represented by western (WEE), eastern (EEE) and Venezuelan equine encephalitis (VEE) viruses cause epizootic and enzootic infection of horses throughout the western hemisphere. All equine encephalitis viruses are transmitted through the bite of an infected mosquito. The first equine encephalitis virus vaccines were produced by virus inactivation. Problems with inadequate inactivation, which may have caused a major epidemic/epizootic of VEE in central America and Texas in ...
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 dai...
Diversity within natural populations of eastern equine encephalomyelitis virus. We evaluated genetic and phenotypic diversity within natural populations of the alphavirus, Eastern equine encephalomyelitis (EEE) virus. RNA fingerprinting revealed that most populations within infected hosts (unpassaged isolates) contained a consensus genotype along with minority genotypes differing in one to three T1-resistant oligonucleotides. Mutation frequencies appeared to be similar to those reported for other RNA viruses, suggesting that the slow rate of EEE virus evolution is not limited by fidelity of genome replication. Within a given year, genetic diversity was generally greater a...
Circulation of eastern equine encephalitis, western equine encephalitis, Ilhéus, Maguari and Tacaiuma viruses in equines of the Brazilian Pantanal, South America. 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...
Laboratory transmission of eastern equine encephalomyelitis virus to chickens by chicken mites (Acari: Dermanyssidae). Pools of adult female chicken mites, Dermanyssus gallinae (De Geer), were allowed to feed on chicks that had been inoculated with eastern equine encephalomyelitis (EEE) virus and that had a viremia level of 10(6.2)-10(6.6) plaque-forming units per milliliter of blood. Virus remained detectable by plaque assay in samples of these mites for 30 d after the infectious blood meal. Virus was not recovered from any of 151 progeny of virus-exposed female mites. Mites that had fed on viremic chicks were allowed to feed on naive chicks 3, 7, 11, 15, or 30 d later. EEE virus was transmitted to chicks by ...
African horse sickness: transmission and epidemiology. African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and occasionally of dogs. The virus is widely distributed across sub-Saharan African where it is transmitted between susceptible vertebrate hosts by the vectors. These are usually considered to be species of Culicoides biting midges but mosquitoes and/or ticks may also be involved to a greater or lesser extent. Periodically the virus makes excursions beyond its sub-Saharan enzootic zones but until recently does not appear to have been able to maintain itself outside these areas for more t...
Eastern equine encephalitis virus in Ohio during 1991. During August and September of 1991, an epizootic of eastern equine encephalitis (EEE) virus in horses occurred in Wayne and Holmes countries, OH. This was the first recorded epizootic of EEE virus in the state. Twelve horses were confirmed positive for EEE virus through virus isolation or seroconversion, and seven additional horses with compatible symptoms were in close spatial and temporal proximity to the confirmed cases and were presumed to have died from EEE virus. The outbreak was centered around the Killbuck Wildlife Area, a 2,147-ha tract maintained by the state, half of which consists...
Effect of temperature on the transmission of western equine encephalomyelitis and St. Louis encephalitis viruses by Culex tarsalis (Diptera: Culicidae). 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...
Molecular evidence for the origin of the widespread Venezuelan equine encephalitis epizootic of 1969 to 1972. Venezuelan equine encephalitis (VEE) virus is a mosquito-borne pathogen that has caused encephalitis in equine species and humans during sporadic outbreaks in the western hemisphere. The last, and most widespread, VEE outbreak occurred in South America, Central America, Mexico and the U.S.A. (Texas) during 1969 to 1972. We have cloned and sequenced the genome of a virulent VEE subtype I-AB virus, strain 71-180, isolated in Texas in 1971. Thirty-four nucleotide differences were detected between the genome of 71-180 virus and that of the subtype I-AB Trinidad donkey (TRD) virus isolated during t...
[Epidemiology of encephalitis caused by arbovirus in the Brazilian Amazonia]. An overview of ecological, epidemiological and clinical findings of potential arthropod-borne encephalitis viruses circulating in the Amazon Region of Brazil are discussed. These viruses are the Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), St. Louis Encephalitis (SLE), Mucambo (MUC) and Pixuna (PIX). These last two are subtypes (III and IV) of Venezuelan Equine Encephalitis virus. The areas of study were the highways and projects of development, as well as places where outbreaks of human diseases caused by arboviruses had been detected. These viruses are widespread in ...
An assessment of the biological capacity of a Sacramento Valley population of Aedes melanimon to vector arboviruses. Daily survivorship, duration of the gonotrophic cycle, absolute abundance and season-long relative abundance were estimated for Aedes melanimon in the Sacramento Valley of California in 1987 and 1988 using mark-release-recapture (MRR) techniques and by monitoring changes in the abundance and parity rate of the native population. One objective of these studies was to determine the extent to which A. melanimon was biologically capable of serving as a horizontal arbovirus vector. Daily survivorship was estimated to be 0.90 and 0.84 in MRR studies conducted in September 1987 and August 1988, 0.89 ...
Isolations of African horse sickness virus from vector insects made during the 1988 epizootic in Spain. This paper describes the first isolations of African horse sickness virus (AHSV) from insects in Spain. Seven isolations of AHSV serotype 4 were made; four from Culicoides imicola a known vector of the virus elsewhere, two from mixed pools of Culicoides species not including C. imicola and one from blood engorged mosquitoes. Three further isolations of AHSV serotype 4 were also made from horses kept adjacent to the insect collecting sites. This work presents the first definitive identification of the vectors of AHSV in Spain during the 1987, 88 and 89 epizootics. Suggestions are also made conc...
Equine insect hypersensitivity: skin test and biopsy results correlated with clinical data. Forty-four seasonally pruritic horses and 21 asymptomatic horses in Florida, USA, were tested for insect, grass and mould hypersensitivity by intradermal injection of allergenic extracts. The affected horses ranged in age from 10 months to over 30 years and included a variety of breeds. Affected horses reacted to varying dilutions of extracts made from Culicoides, mosquitoes, horse flies and black flies. Reactions to Culicoides were more intense than those caused by injection of antigens from other arthropods. Mild pruritus existed from the end of February until the end of June when the condit...
Trajectory analysis of winds and eastern equine encephalitis in USA, 1980-5. Backward trajectories of winds were determined to identify possible sources of eastern equine encephalitis virus associated with isolation of virus from mosquitoes or birds or outbreaks in horses between 1980 and 1985 in Maryland, New Jersey, New York and Michigan, USA. The results of the trajectory analyses suggested that eastern equine encephalitis virus could have been carried by infected mosquitoes on surface winds at temperatures 13 degrees C or higher from North Carolina north-eastwards along the Atlantic Coast to Maryland and New Jersey and thence to upstate New York and from western Ke...
Veterinary use of ivermectin. Following the development of a unique claim structure encompassing both nematode and arthropod species, ivermectin was first introduced as a veterinary parasiticide in 1981. For cattle(c), sheep(s), horses(h) and pigs(p) injectable(c,s,p), oral(c,s,h) and topical(c) products are available delivering ivermectin at 200 to 500 micrograms/kg. Efficacy extends to nematodes of the gastrointestinal and respiratory tracts, conjunctival sac and soft tissues. Among the arthropod parasites claims have been established for the biting fly Haematobia irritans(c), the screw-worm Chrysomyia bezziana(c), larva...