Horse diseases-equine viral arteritis, Biology

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Equine viral arteritis


Equine viral arteritis (EVA) is a highly contagious disease of equines and is caused by equine arteritis virus (EAV), a RNA virus belonging to the genus Arterivirus in the family Arteriviridae. The disease is characterized by fever, depression, anorexia, dependent oedema especially of limbs, scrotum and prepuce in stallion, conjunctivitis, urticarial type skin reaction, abortion and rarely pneumonia or pneumoenteritis in young foals. The disease is also known as epizootic lymphangitis or pink eye. No clinical case of EAV infection has been reported from India. However, based on sero- surveillance some seropositive horses have been reported.


Epidemiology:
EAV is sheded in large amount from the acutely infected horses through respiratory route. It is transmitted by direct contact between horses by droplet infection. EVA is transmitted from infected mares through the placenta to their unborn foals. The virus is also excreted in urine and faeces. Infected saliva and nasal discharge  contaminates drinking water, mangers and straw, which are the sources of infection to other healthy horses. Virus is also sheded in semen of acutely infected stallions, some of which become long term carriers and constant semen shedder. The carrier state is found only in stallion and not in the mare. The virus can be transmitted via fresh- cooled or frozen semen used in artificial insemination.


Clinical signs:
There may be fever, swelling (edema) of the legs, scrotum sheath or mammary glands in infected horses. Loss of appetite (anorexia), depression, nasal discharge, initially watery, but becoming mucoids later are also observed in infected animals. The affected horse shows conjunctivitis (pink eye) that may be accompanied by tearing down the face and swelling above or around the eyes. Skin rash (urticaria), often localized to the cheeks or sides of the neck, but sometimes generalized over the body may also occur. Pneumonia or pneumonia with enteritis in very young foals is common. EVA causes contagious respiratory disease in horses and abortion in mares. A mild stomatitis may also be seen. Oedema of the ventral body wall, limbs extending up to prepuce of the stallion may be seen. Abortion due to EVA infection occurs late in the acute phase or early in the recovery phase of the infection, not months after the virus exposure has taken place.


Diagnosis: Diagnosis of abortion due to EAV is largely dependent on virus isolation from placenta or foetal tissues in RK13, horse kidney, Vero and BHK-21 cell lines. Serial 2-8 blind passages are required. Virus-specific antibody in serum of horses can be demonstrated by complement fixation (CF) and virus neutralization (VN) tests.


Prevention and control: Modified live virus vaccine is available that gives strong immunity. An inactivated vaccine developed in Japan has been reported to induce neutralizing antibodies and preventive to virus shedding through semen. Serum samples for EVA testing should be collected from all horses before breeding and virus isolation should be performed on imported semen before use.


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