Equine viral arteritis (EVA), is a notifiable disease of horses that occurs in outbreaks throughout the world, it is transmitted by close contact (racetracks, sales, etc.) or by crossbreeding (natural service and artificial insemination). with stallion carriers that eliminate the virus in their semen.

The causative agent of equine viral arteritis is an adenovirus type 1 virus that specifically infects the endothelial cells of small muscular arteries. This virus causes vascular lesions, extensive edema and hemodialysis in the extremities and ventral abdomen. It also causes respiratory distress, fever, and colic. and gastrointestinal upset. 

The clinical signs are reminiscent of other common infectious diseases such as equine infectious anemia and differential diagnosis should be made carefully when evaluating suspected cases of equine viral arteritis. Diagnosis is based on the detection of the virus in body fluids or tissues, visualization of the viral antigen and serology.

Symptoms

Equine viral arteritis is an acute and contagious disease that, like the infection caused by hendra virus, directly affects equids (horses, donkeys and mules), the disease affects the smallest blood vessels and is caused by a virus of the Arterivirus genus of the Arteriviridae family. The virus has a complement-fixing antigen but no hemagglutinin, is easily inactivated with lipid solvents and disinfectants, and is relatively thermolabile, but can persist for years at low temperatures. 

The infection is transmitted through respiratory secretions of acutely infected horses and is also spread through breeding (natural service or artificial insemination). During the course of infection, the virus replicates in the cells of the blood vessels and reticuloendothelial system.

Symptoms of equine viral arteritis are variable and can be quite severe and include: pyrexia lasting 1 to 5 days, depression, edema (swelling) of the legs (especially the hind legs), ventral abdomen, scrotum, foreskin, and mammary glands. , rhinitis and conjunctivitis with nasal or ocular discharge, photophobia, skin rash and anorexia.

Infection of pregnant mares with specific strains of the virus is associated with “abortion storms” in which up to 70% of affected mares abort; infected young foals are prone to developing progressive bronchointerstitial pneumonia, which in many cases is fatal.

Vascular lesions are characterized by the formation of indurated, firm and painless nodules in the blood vessels of affected animals, thrombosis is common in smaller arteries, especially of the cranial mesenteric artery and its branches, the vessel wall enlarged It is firm and fibrotic, with a profuse infiltration of inflammatory cells.

Persistently infected carrier stallions are the main natural reservoir of equine viral arteritis; these stallions persist in certain areas of the accessory sexual glands and serve as long-term carriers of the virus. 

The disease is not usually life-threatening in adult horses, but as it can cause abortions and deaths in young foals, this could have a negative and economically significant impact on breeders; most breeding farms are unaware of the presence of the disease. Equine viral arteritis and its importance, leading to a state of near panic when first entered, this can be overcome through education and greater attention to prevention.

Transmission

The virus that causes equine viral arteritis enters the lung in the form of droplets and initially replicates in bronchial and alveolar macrophages; These macrophages then transfer the virus to endothelial cells in the blood vessels of skeletal muscle, connective tissue, and internal organs, where it causes inflammation and damage through a mechanism that involves the synthesis of proinflammatory cytokines such as IL-6. 

This damage to the vascular endothelium leads to a state of hypercoagulability and vasculitis Systemic with prominent involvement of small muscular arteries, the affected arteries show macroscopic lesions characteristic of fibrinoid necrosis, mainly in the media, with extensive edema and pleural and pericardial effusions.

The persistently infected stallion carrier is the main natural reservoir of the virus and is responsible for perpetuating and maintaining viral arteritis in the equine population, the virus persists in certain accessory sexual glands, including the ampulla and to a lesser extent, the other accessory sexual glands of the stallion carrier, and continues to be constantly eliminated in his semen, even after recovery from clinical illness. 

Acutely infected stallions may show no signs of illness and still shed the virus through semen for prolonged periods; these stallions are the essential natural reservoir of the virus and have been responsible for many outbreaks of equine viral arteritis.

Immature mares, geldings and foals do not become carriers of the virus, persistence is mediated directly or indirectly by testosterone; Stallions with the susceptible CD3+ T cell phenotype in vitro are at increased risk of becoming persistently infected carriers and are more likely to transmit the virus to susceptible mares during artificial insemination.

If a mare becomes pregnant by an infected stallion, the foal may become clinically ill or have low titers of neutralizing antibodies to the virus and may subsequently infect other horses.

During outbreaks, equine viral arteritis virus is transmitted from horse to horse by contact with the secretions or excretions of acutely infected horses and by horizontal aerosol spread. The virus is also transmitted by venereal transmission and by crossing a susceptible mare with an infected stallion carrier.

Outbreaks of clinical disease are rare and occur mainly on breeding farms where up to 50% of affected mares abort. However, in most cases abortions are not associated with the presence of the virus, indicating that other factors play an important role in determining pregnancy outcomes.

Equine viral arteritis is highly contagious and is easily transmitted between animals in sales, shows, racetracks and breeding farms, adequate biosecurity and control programs are essential to prevent the introduction and spread of the virus in these types of facilities.

Diagnosis

The virus can be detected in nasal or conjunctival swabs, whole blood (on EDTA or sodium citrate anticoagulant), fetal tissue (placenta, lung and spleen) from abortions and in the semen of stallion carriers, the virus can also be found in the lungs, spleen, lymph nodes and thymus of horses that die from “pneumoenteric syndrome.”

Serological studies indicate that equine viral arteritis infection occurs worldwide, but the incidence of overt disease varies significantly, with some countries having major problems with a high prevalence of seropositive horses and frequent outbreaks of clinical disease, while others have low infection rates and few or no overt disease outbreaks.

treatment of arteritis

There is a vaccine against equine viral arteritis, but its effectiveness has not been demonstrated. The vaccine appears to be safe and probably increases humoral immunity in the horse. The presence of antibodies in the serum is the best evidence of vaccination.

Equine viral arteritis vaccine is available and the vaccine provides protection against both the disease and the causative virus, equine viral arteritis infection occurs primarily when horses are exposed to infectious material from an infected animal. This is often the case at horse sales and shows or on breeding farms. 

Mares should be tested and vaccinated against equian viral arteritis at least four weeks before breeding. Because immunity to the virus takes time to develop, mares vaccinated for the first time should be kept isolated from other horses to prevent them from transmitting the virus. to their non-immunized partners.

Prevention

To prevent equine viral arteritis and other diseases, it is important to maintain a healthy stableControl of equine viral arteritis outbreaks also depends on the identification of acute cases and asymptomatic carriers, isolation, quarantine, and use of disinfectants on fomites. Infected stallions should not be used for breeding until they have been isolated and eliminated from the virus by repeated testing. 

Stallions that remain asymptomatic are more likely to transmit the virus to susceptible mares and should be subject to breeding restrictions until this risk can be mitigated through castration or export.

Following the recommendations of the Horseracing Tax Board Code of Practice and BEVA biosecurity guidelines, if a stallion is confirmed to be infected with equine viral arteritis, he should be isolated and prevented from breeding unvaccinated mares. until his risk has been mitigated by neutering, exporting or repeated testing, indicating that he no longer has virus present, he should not be allowed to enter facilities that keep horses for breeding or semen collection, unless the facilities are authorized by the APHA.