Equine coital exanthema

Etiology

The causalagent of equine coital exanthema is equine alphaherpesvirus type 3, belongingto the order Herpesvirales, family Herpesviridae and genus Varicellovirus. The genomehas a size of 151,601 nucleotides that encode 76 genes. It is different bothgenetically and pathogenically from the rest of equine herpesviruses.

Epidemiology

It is a highly contagious disease. The virus has a worldwide distribution and only affects equids. The main form of transmission is venereal during mating, although it can also be transmitted through fomites or iatrogenically. The infection has a self-limiting character, subsequently producing a period of latency in which animals do not show clinical signs and act as reservoirs. In animals that are latently infected, periods of reactivation and re-excretion of the virus can occur, both with and without clinical signs, and act as a source of infection for other susceptible animals.

Pathogeny

The infection is restricted to the epithelium of the nasal mucosa and external genitalia, without affecting the basal membrane or the cells of the immune system. The clinical signs are consequence of the lytic effect of the virus and the host's local inflammatory response, which can be complicated by secondary bacterial infections of the lesions.

Clinical signs

The lesions develop within a week and consist of circular red nodules in the vulva, vaginal vestibule, clitoral fossa and perineum in the mare and on the surface of the penis and prepuce in the stallions. The size of the lesions increases up to 10-15mm giving rise to vesicles that can break resulting in ulcers. These are very painful lesions that can cause discomfort during erection and loss of libido in stallions.

Diagnosis

The clinical diagnosis is made by inspection and detection of the lesions described in the external genitalia. Laboratory diagnosis can be made by viral isolation and virus DNA detection by conventional PCR or real time PCR.
Recently, a new method of virus detection has been described by isolated isothermal PCR, which allows detection of the virus in field conditions. The sampling can be done by scraping the lesions or using swabs applied on the active edge of the lesions being transported in 2-3ml of transport medium and under refrigeration conditions.

Treatment

The treatment consists of sexual rest until the lesions disappear. Cleaning and disinfection with antiseptics and local or systemic antibiotics in case of secondary bacterial infections. Some cases have been successfully treated topically with the antiviral acyclovir. An in vitro comparative study of three antivirals: acyclovir, ganciclovir and cidofovir, concluded that ganciclovir is the most effective of the three and could be used topically for the treatment of this disease.

Prevention and control

The prevention consists in performing a clinical examination of the animals to detect the characteristic lesions of the disease, before being used for reproduction. If compatible lesions are found, confirmation by laboratory tests is recommended. Affected animals will be isolated and treated, and special care should be taken with the use of instruments, ultrasound probes, etc., between animals and using disposable material.

Public Health Considerations

It is ahighly specific virus with respect to its host, affecting only the equids, soit is not considered zoonotic.