Page 644 - The Veterinary Care of the Horse

Horses with EHV-3 develop fluid-filled vesicles, pustules or ulcers on the vulva, penis or

prepuce. Affected stallions may be sore and unwilling to mate.
VetBooks.ir With EHV-4, young animals may develop a secondary pneumonia. Abortion occasionally

occurs in a single mare.

Transmission

Infection with EHV-1 and EHV-4 occurs by inhalation of the virus released into the
atmosphere as an aerosol from the respiratory tract of infected horses. This occurs when a

horse coughs or snorts. EHV-1 infection can be also acquired by ingestion of material
released onto the pasture from the foetus, foetal membranes and fluids when a mare aborts.

The mare will be infectious for a month after the abortion occurs. Sick foals with EHV-1 are
also a source of infection. EHV-3 is spread by direct genital contact or indirect contact by
handlers, e.g. the use of shared sponges for cleaning the genitalia.

It is possible for a horse to carry and spread the virus without showing any symptoms.

The virus may be shed at times of stress, such as weaning, following transportation or when
new animals are introduced into an established group.

When to call the vet

Call your vet as soon as symptoms are observed. Measures to prevent the spread of the
disease can then be implemented straight away. The owners of any ‘in-contact’ horses should

also be notified immediately.

Diagnosis

Diagnostic tests include the following.

• Isolation of the virus from naso-pharyngeal swabs taken early in the course of the

disease. Swabs taken from other horses in the group that have a temperature can be
helpful in making a diagnosis.

• Isolation of the virus from fresh tissues of the aborted foetus, dead foal or paralysed
horse (following euthanasia).

• Isolation of the virus from swabs taken from the external genitalia of horses with EHV-3.

• Laboratory examination of tissues from the dead foal, aborted foetus and membranes.

• Measurement of antibody levels in the blood. As soon as a horse is challenged by a virus,
antibody levels begin to rise. Blood is taken when the symptoms first appear and again 3