EHV-3 is highly infectious between susceptible horses and may be transmitted by direct or indirect genital contact. The virus may be transmitted from subclinically infected animals that have no recognisable signs of skin lesions.
Horses that have recovered from infection and those that showed no recognisable signs of typical skin lesions may become latent carriers of EHV-3. It is believed that the most common source of infection for ECE is the periodic recrudescence of virus (resumption of viral shedding) from a latently infected carrier mare or stallion that does not have clinical signs.
Nasogenital transmission of EHV-3 between mares at pasture and at teasing, with demonstrable nasal, lip and nostril lesions, has been reported. The role of stable flies for potential vulval to vulval transmission is proposed but unproven.