The killer virus
Four horses died in the recent outbreak of equine herpes virus. Vet Geri Long explains what it is and how to identify the symptoms, as well as discussing treatment and prevention
PHOTOS: BAUER LIBRARY
ALMOST EVERY HORSE throughout the entire world will have been infected with the DNA virus, equine herpes virus (EHV). Almost every one of those that has been infected, however, will suffer minimal side effects. But, like all herpes viruses, equine herpes viruses have the ability to establish a dormant infection localised in neurons and lymphoid tissue that may be reactivated at a later stage. This reactivation may be linked to stress, coexisting infections, or being transported over long distances. Reactivation of the virus can lead to the shedding of the infectious virus without clinical signs. This makes it particularly difficult to know where it started.
Infection can be transmitted between horses in any of the following ways:
Respiratory route.
Contact with aborted foetuses, foetal membranes and fluids.
Indirect transmission via objects, such as tack, equipment and feed bowls, all of which can lead to the spread of the virus. The virus may remain infective in the environment for less than two weeks, but it can survive for up to six weeks on suitable objects. The incubation period for EHV is between two and 10 days.
There are many different types of EHV, but EHV-1 and EHV-4 are the most significant. EHV-1 can manifest itself in four ways in horses — a neurological form, respiratory disease, abortion and neonatal death. EHV-4 mostly causes non-fatal upper respiratory tract disease in youngstock and is occasionally associated with abortion. On rare occasions it is associated with neurological disease.