Equine encephalosis virus

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Equine encephalosis virus
Equine Encephalosis Virus particle.jpg
Equine encephalosis virus virion particles
Virus classification OOjs UI icon edit-ltr.svg
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Duplornaviricota
Class: Resentoviricetes
Order: Reovirales
Family: Sedoreoviridae
Genus: Orbivirus
Species:
Equine encephalosis virus

Equine encephalosis virus (EEV) is a species of virus the Orbivirus genus, and a member of the Reoviridae family, related to African horse sickness virus (AHSV) and Bluetongue virus (BTV). [1]

Contents

First described in South Africa over a hundred years ago by Arnold Theiler, EEV is the causative agent of equine encephalosis (EE), an arthropod-borne disease transmitted by the Culicoides spp. midges affecting all equids. [2] Since then the disease has become both widespread and prevalent, taking on epidemic proportions in certain parts of the country. Serological studies estimated a presence of anti-EEV antibodies in over 75% of all South African horses. [3]

Prior to 2008, Equine encephalosis virus had been identified and isolated only in South Africa, where seven antigenetically distinct serotypes, EEV1-7, have been characterised. [1] In 2009, the outbreak of a febrile horse disease across Israel, later diagnosed as EEV, caused great concern primarily due to the similarity of EEV with the African horse sickness virus, one of the most devastating equine pathogens.

Clinical signs

The name equine encephalosis is misleading as the disease is not primarily a neurological disorder. Although the majority of infections result only in mild clinical signs, in more severe cases clinical signs include a short period (typically two to five days) of fluctuating fever, accompanied by varying degrees of inappetence. [4] Elevated heart and respiratory rates are also common, and occasionally as a result of nasal congestion, a red-brown discolouration of the mucous membranes may be observed. [4]

Although rare, more severe clinical signs may occur including facial swelling (lips and eyelids), respiratory distress, and petechial haemorrhages of the conjunctivae. [4] Pregnant mares may also abort during their first 5 months of gestation. [5]

Neurological signs are atypical, but in certain cases hindquarter ataxia, convulsions, hyperexcitability, and depression have been reported. [5] The mortality rate is normally low, accounting for only 5% of infected animals. [4]

Structure and genome

Equine encephalosis virus is an Orbivirus , and as such encodes 4 non-structural and 7 structural proteins derived from 10 linear dsRNA genome segments. [6] The smallest of those genome segments, segment-10, encodes the NS3 protein, which allows the release of the viral particles from the infected cell. [4] The second largest of those segments in turn codes for one of the outer capsid proteins, VP(2). [4]

By analogy with Bluetongue virus , both these proteins may then be used to determine the serotype of EEV, of which seven have been identified to date. [4] This is achieved by analysing the interaction between VP(2), and the antibodies generated by the host during infection. [7] The sequence variation between the proteins is then associated with various viral serotypes.[ citation needed ]

Epidemiology

First isolated in 1967, Equine encephalosis virus appeared until recently to be unique to the South African equidae . [5] As of 2008 however, evidence seems to suggest the virus has circulated beyond southern Africa, and outbreaks have been reported in a number of other countries including Israel, Ethiopia, Ghana, and Gambia. [5] Intriguingly, Morocco remains free of the epidemic, suggesting the Sahara desert may be acting as a natural barrier to the progression of the disease. [5] Such a progression is of major concern to the worldwide livestock industry, primarily due to the similarity between EEV and other more devastating equid pathogens, such as the African horse sickness virus.

As with all vector-borne diseases, EEV is not transmissible from host-to-host, rather infection requires another intermediate organism that will transmit the pathogen. In the case of Equine encephalosis virus, the transmission occurs via the Culicoides midges during a blood meal. [4]

Several studies have shown that between 50 and 75% of South African equids (notably horses, donkeys and zebras) are seropositive for EEV or have anti-EEV antibodies indicating a prior infection, with serotype 1 being the most prevalent. [3] Antibodies have also occasionally been reported in elephants. [3]

Treatment and prevention

Drug therapy

In the vast majority of cases (c. 90%) the animal will recover without further complications, and a course of anti-inflammatories or appetite stimulants may be administered. [3] Occasionally, antibiotics are prescribed in order to prevent the appearance of secondary infections. [3] Some equids show no clinical signs at all but are biliary carriers. [3] Although in this instance the animal is not in immediate danger, it must be treated in order to prevent the reemergence of the virus were the immune system to be challenged by another disease simultaneously.[ citation needed ]

Vector control

Due to the absence of an effective vaccine, vector control remains one of the primary methods of prevention. Control of the midges is usually only instigated for domesticated stabled horses, and includes precautionary measures such as the limited use of lights at night, as well as the use of fly repellents and fans.[ citation needed ]

Related Research Articles

<span class="mw-page-title-main">Bluetongue disease</span> Viral disease in animals

Bluetongue disease is a noncontagious, insect-borne, viral disease of ruminants, mainly sheep and less frequently cattle, yaks, goats, buffalo, deer, dromedaries, and antelope. It is caused by Bluetongue virus (BTV). The virus is transmitted by the midges Culicoides imicola, Culicoides variipennis, and other culicoids.

<span class="mw-page-title-main">Sedoreoviridae</span> Family of viruses

Sedoreoviridae is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layered capsids. Lack of a lipid envelope has allowed three-dimensional structures of these large complex viruses to be obtained, revealing a structural and likely evolutionary relationship to the cystovirus family of bacteriophage. There are currently 97 species in this family, divided among 15 genera in two subfamilies. Reoviruses can affect the gastrointestinal system and respiratory tract. The name "reo-" is an acronym for "respiratory enteric orphan" viruses. The term "orphan virus" refers to the fact that some of these viruses have been observed not associated with any known disease. Even though viruses in the family Reoviridae have more recently been identified with various diseases, the original name is still used.

<span class="mw-page-title-main">Culicomorpha</span> Infraorder of flies

The Culicomorpha are an infraorder of Nematocera, including mosquitoes, black flies, and several extant and extinct families of insects. They originated 176 million years ago, in the Triassic period. There are phylogenetic patterns that are used to interpret bionomic features such as differences in the nature of blood-feeding by adult females, daytime or nighttime feeding by adult females, and occurrence of immature stages in aquatic habitats.

<i>Orbivirus</i> Genus of viruses

Orbivirus is a genus of double-stranded RNA viruses in the family Reoviridae and subfamily Sedoreovirinae. Unlike other reoviruses, orbiviruses are arboviruses. They can infect and replicate within a wide range of arthropod and vertebrate hosts. Orbiviruses are named after their characteristic doughnut-shaped capsomers.

<i>Aphthovirus</i> Genus of viruses

Aphthovirus is a viral genus of the family Picornaviridae. Aphthoviruses infect split-hooved animals, and include the causative agent of foot-and-mouth disease, Foot-and-mouth disease virus (FMDV). There are seven FMDV serotypes: A, O, C, SAT 1, SAT 2, SAT 3 and Asia 1, and four non-FMDV serotypes belonging to three additional species Bovine rhinitis A virus (BRAV), Bovine rhinitis B virus (BRBV) and Equine rhinitis A virus (ERAV).

African horse sickness (AHS) is a highly infectious and often fatal disease caused by African horse sickness virus. It commonly affects horses, mules, and donkeys. It is caused by a virus of the genus Orbivirus belonging to the family Reoviridae. This disease can be caused by any of the nine serotypes of this virus. AHS is not directly contagious, but is known to be spread by insect vectors.

Epizootic hemorrhagic disease (EHD) is a hemorrhagic disease of white-tailed deer caused by an infection of a virus from the genus Orbivirus subsequently called Epizootic hemorrhagic disease virus (EHDV). It is an infectious, and sometimes fatal, virus that is characterized by extensive hemorrhages, and is found throughout the United States. Large-scale outbreaks in wild ruminants affect livestock and the production industry. EHD has been found in some domestic ruminants and many species of deer including white-tailed deer, mule deer, elk, and pronghorn antelope. Seropositive black-tailed deer, fallow deer, red deer, wapiti, and roe deer have also been found, which essentially means that they were exposed to the disease at some time in the past but may not be involved in transmission. Outbreaks of EHD have been reported in cattle, although they rarely develop disease or die. Sheep may develop clinical signs, but this is also rare. EHD is often called bluetongue, but this is incorrect. Bluetongue virus is closely related to EHDV, and has similar clinical signs, but it is a different disease. Bluetongue is a serious disease in cattle, as well as other ruminants, and can have a significant effect on international trade. Testing at animal health laboratories is necessary to distinguish between the viruses that cause bluetongue and EHD.

Erbovirus is a genus of viruses in the order Picornavirales, in the family Picornaviridae. Horses serve as natural hosts. There is only one species in this genus: Erbovirus A. Diseases associated with this genus include: upper respiratory tract disease with viremia and fecal shedding. Viruses belonging to the genus Erbovirus have been isolated in horses with acute upper febrile respiratory disease. The structure of the Erbovirus virion is icosahedral, having a diameter of 27–30 nm.

<i>Coltivirus</i> Genus of viruses

Coltivirus is a genus of viruses that infects vertebrates and invertebrates. It includes the causative agent of Colorado tick fever. Colorado tick fever virus can cause a fever, chills, headache, photophobia, myalgia, arthralgia, and lethargy. Children, in particular, may develop a hemorrhagic disease. Leukopenia with both lymphocytes and neutrophils is very common for Colorado tick fever virus. In either case, the infection can lead to encephalitis or meningitis.

<i>Culicoides</i> Genus of biting midges

Culicoides is a genus of biting midges in the family Ceratopogonidae. There are over 1000 species in the genus, which is divided into many subgenera. Several species are known to be vectors of various diseases and parasites which can affect animals. The genus has a long fossil record, with earliest known fossils being from Burmese amber, around 99 million years old.

<span class="mw-page-title-main">Double-stranded RNA viruses</span> Type of virus according to Baltimore classification

Double-stranded RNA viruses are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid. The double-stranded genome is used as a template by the viral RNA-dependent RNA polymerase (RdRp) to transcribe a positive-strand RNA functioning as messenger RNA (mRNA) for the host cell's ribosomes, which translate it into viral proteins. The positive-strand RNA can also be replicated by the RdRp to create a new double-stranded viral genome.

<i>Banna virus</i> Species of virus

Banna virus (BAV) is a virus belonging to Reoviridae, a family of segmented, non-enveloped, double-stranded RNA viruses. It is an arbovirus, being primarily transmitted to humans from the bite of infected mosquitoes of the genus Culex. Pigs and cattle have also been shown to become infected. The most common symptom of infection is fever, but in some cases encephalitis may occur. There is no specific treatment for infection, so treatment is aimed at alleviating the severity of symptoms until the immune system has cleared the infection.

Liao ning virus (LNV) is a virus belonging to the genus Seadornavirus within the family Reoviridae, a family of segmented, non-enveloped, double-stranded RNA viruses. LNV was first discovered in Aedes dorsalis populations in the Liaoning province of the People's Republic of China in 2006 from mosquito samples obtained in 1997. Its geographic distribution was previously thought to be limited to China, but it has since been found in mosquito populations in Australia. In addition to Aedes dorsalis, LNV has been isolated from Culex species.

Culicoides variipennis is a 1 millimetre (0.039 in) long biting midge. It is a part of the subgenus Monoculicoides and has many subspecies. Found in North America, C. variipennis transmits Bluetongue virus, African horse sickness virus, akabane virus, and epizootic hemorrhagic disease.

<i>Sedoreovirinae</i> Subfamily of viruses

Sedoreovirinae was a subfamily of the Reoviridae family of viruses. Viruses in this subfamily are distinguished by the absence of a turreted protein on the inner capsid to produce a smooth surface.

Culicoides bolitinos is an African species of bloodsucking fly that breeds in the dung of the African buffalo, the blue wildebeest, and cattle (Bosraces). It is considered a possible vector for African horse sickness. It is closely related to Culicoides imicola.

Epizootic hemorrhagic disease virus, often abbreviated to EHDV, is a species of the genus Orbivirus, a member of the family Reoviridae. It is the causative agent of epizootic hemorrhagic disease, an acute, infectious, and often fatal disease of wild ruminants. In North America, the most severely affected ruminant is the white-tailed deer, although it may also infect mule deer, black-tailed deer, elk, bighorn sheep, and pronghorn antelope. It is often mistakenly referred to as “bluetongue virus” (BTV), another Orbivirus that like EHDV causes the host to develop a characteristic blue tongue due to systemic hemorrhaging and lack of oxygen in the blood. Despite showing clinical similarities, these two viruses are genetically distinct.

The Peruvian horse sickness virus (PHSV) is a cause of the neurological disorder Peruvian horse sickness resulting in encephalitis in horses and other livestock. The disease has significantly affected livestock in areas of Peru and has also been documented in northern Australia.

Lubombo virus (LUBV) is an orbivirus that infects vertebrates and culicine mosquitoes, thought to be its arthropod vector. It is classified in the genus Orbivirus and the family Reoviridae. It is studied at biosafety level 2.

Umatilla virus(UMAV) is a dsRNA virus in the family Reoviridae, subfamily Sedoreovirinae, and the genus Orbivirus. This arbovirus was first isolated in 1969 in Umatilla County, Oregon in a group of Culex pipiens mosquitoes. The viral host is the Passer domesticus bird with the vectors being Culex mosquitoes.

References

  1. 1 2 Mertens PP, Maan S, Samuel A, Attoui H Orbivirus, Reoviridae (2005). Fauquet CM, Mayo MA, Maniloff J, Desselberger U, Ball LA (eds.). Virus taxonomy, VIIIth report of the ICTV. Vol. 1. London: Elsevier/Academic Press. pp. 466–83.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ↑ Venter GJ, Groenewald DM, Paweska JT, Venter EH, Howell PG (1999). "Vector competence of selected South African "Culicoides" species for the Bryanston serotype of Equine encephalosis virus". Med Vet Entomol . 13 (4): 393–400. doi:10.1046/j.1365-2915.1999.00188.x. PMID   10608228. S2CID   36530418.
  3. 1 2 3 4 5 6 Venter GJ, Koekemoer JJ, Paweska JT (2006). "Investigations on outbreaks of African horse sickness in the surveillance zone in South Africa". Rev Sci Tech Off Int Epiz . 25 (3): 1097–1109. doi: 10.20506/rst.25.3.1719 . PMID   17361773.
  4. 1 2 3 4 5 6 7 8 Karin Aharonson-Raz; Amir Steinman; Velizar Bumbarov; Sushila Maan; Narender Singh Maan; Kyriaki Nomikou; Carrie Batten; Christiaan Potgieter; Yuval Gottlieb; Peter Mertens; Eyal Klement (2011). "Isolation and Phylogenetic Grouping of Equine encephalosis virus in Israel". Emerging Infectious Diseases . 17 (10): 1883–1886. doi:10.3201/eid1710.110350. PMC   3310674 . PMID   22000361.
  5. 1 2 3 4 5 C. A. L. Oura; C. A. Batten; P. A. S. Ivens; M. BALCHA; A. ALHASSAN; D. GIZAW; M. ELHARRAK; D. B. JALLOW; M. SAHLE; N. Maan; P. C. Mertens; S. Maan (2012). "Equine encephalosis virus: evidence for circulation beyond southern Africa". Epidemiology and Infection . 140 (11): 1982–1986. doi: 10.1017/S0950268811002688 . PMID   22166372. S2CID   23269136.
  6. ↑ Roy P (1996). ""Orbivirus" Structure and Assembly". Virology . 216 (1): 1–11. doi: 10.1006/viro.1996.0028 . PMID   8614976.
  7. ↑ Maan S, Maan NS, Samuel AR, Rao S, Attoui H, Mertens PP (2007). "Analysis and phylogenetic comparisons of full-length VP2 genes of the 24 bluetongue virus serotypes". Journal of General Virology . 88 (2): 621–30. doi: 10.1099/vir.0.82456-0 . PMID   17251581.
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