Look but don’t touch - A timely reminder to wash and disinfect when moving between properties.

As we move into a busy period of horse activity remember New Zealand still has some nasty infectious diseases that we need to ensure we don’t spread through casual management.

Equine herpes Virus 4 (EHV 4) has reared its head across the North Island as a bug to be suspected in sick young horses.  Earlier this spring a 10-month-old Thoroughbred colt from Manawatū- Whanganui region died as a result of infection with EHV4. The colt was underweight and had never really thrived. He presented dull and lethargic with raspy lung sounds and was found dead 3 days later. A necropsy was performed, which revealed thickened small intestines but no other gross abnormalities. Sections of small intestine and kidney submitted to a regional commercial laboratory were examined and tests were completed to rule out exotic diseases.

However, the tissues and bloods were positive for equine herpesvirus type 4 (EHV-4). Involvement of EHV-4 was confirmed in the development of pathological lesions by demonstration of strong labelling on immunohistochemistry staining at Cornell University Animal Health Diagnostic Centre, USA. This confirmed a rare case of enteritis caused by EHV-4. EHV 4 was also cultured in a group of young horses in the Waikato.  Three sick yearlings had sustained high (40 C plus) temperatures for over three days with runny noses.  The observant owners local equine veterinarian carried out nasopharyngeal swabs and the laboratory returned a result that was positive for EHV4.

EHV4 is one of the several herpes virus strains that cause acute respiratory disease of horses around the world including Australia and new Zealand. Foals are often infected in the first few weeks of life and the virus circulates, often sub clinically, amongst the mare and foal population. Acute respiratory disease due to EHV4 occurs most commonly in foals over 2 months old, as passive immune protection derived from their mothers wanes. Weanlings and yearlings typically become infected and display clinical signs of respiratory disease caused by equid herpesvirus 4 as they are mixed into new social groups following weaning, or during preparation for yearling sales. There is fever, anorexia, and a profuse serous nasal discharge that later becomes mucopurulent. Recrudescence of latent virus may lead to disease episodes in later life. Vaccines are available, including combined products that include both equid herpesviruses 1 and 4. It has been reported that live-attenuated equid herpesvirus 1 vaccines provide some protection against equid herpesvirus 4 infections.

In New Zealand it is less common for owners to see the clinical signs as in these cases.  Certainly the cold wet spring and early summer have added a bit more stress into the lives of all this year. Cases that are complicated by secondary bacterial infections usually require antibiotic treatment hence a veterinary consultation is necessary. To minimise the chances of re-infection, good stable hygiene is important. Equipment used on infected horses should be disinfected before being used on other horse with an effective virus-killing disinfectant. Consider how you might reduce the stresses impacting on these young horses. If this is done, complications will be fewer, recovery quicker and the cost of treatment less.

NZEHA recommends that all properties should ensure visiting or new  horses are segregated for the first weeks after they arrive, and if you have guests or workers from other horse properties ensure you provide good washing facilities so they do not become a vehicle for transmission of viruses and bacteria such as EHV and strangles between properties.  For horses with respiratory symptoms, call a vet and get a diagnosis.

Vaccination is available in NZ but will not completely prevent individual horses from infection, however it may reduce the severity of clinical infection in individual horses. In this scenario there will be less virus shed from an infected vaccinated horse which can lead to reduction of risk of infectious spread to other horses.  Always supplement the protection from vaccines with good animal management and biosecurity.