January Pet of the Month

Harry is a mature dressage and jumping Thoroughbred gelding who is a regular patient of the Bullsbrook Veterinary Large Animal Practice. These recent photos find him in fine form and excellent health after a worrying period of disability and prolonged recovery lasting nearly 6 months.

Last year, Harry was diagnosed with encephalitis (brain and nervous system disease) caused by Kunjin Virus. Kunjin virus is a mosquito borne virus that can (but rarely) causes neurological disease in horses. Only a very small number of horses develop signs after infection with Kunjin virus. For the first time in Perth, there were 4 diagnosed cases of Kunjin virus infection in horses, one of these being Harry.

Heavy 2011 summer rainfall in areas of Australia had increased mosquito activity and increased the prevalence of the diseases with neurological signs in horses have been linked to mosquito-borne diseases known as ‘arboviruses’. These viruses include Ross River virus, Murray Valley encephalitis (MVE) and Kunjin virus. Kunjin virus is transmitted by mosquito vectors, especially the Culex annulirostris. They pass the virus to water bird reservoir hosts, a major example is the Nankeen Night Heron.  It is also passed to horses and humans. It has been found all over Australia and is particularly prevalent in areas near wetlands and rivers.[

Early signs of infection include depression or mild colic. These initial signs are followed by nervous signs including lack of coordination, high stepping in front limbs, weakness in the hind quarters, muscle twitching and increased responsiveness to touch and sound. In some cases there has been facial paralysis or twitching, especially of the lips. Severely affected horses may fall repeatedly and in rare cases develop convulsions. Harry had many of these symptoms bar the severe convulsions and falling over.

In Harry’s case he was attended to by Drs. Warwick Vale, Deryck Tan and Paula Bell Cross. Despite this being a new viral disease in Perth horses, the veterinarians were still able to provide Harry with special supportive medications to help with his fevers, inappetence and lethargy. Because this is a viral disease, there is no specific treatment. Supportive care, nursing and treatment with pain relief, broad spectrum antibiotics and anti-inflammatory drugs are used to keep the horses comfortable

Fortunately Harry did not get the very severe neurological debility that some horses get and he remained able to stand and walk, all be it with some difficultly. Most horses with clinical signs recover over several weeks with good husbandry and veterinary care. Some of the more severely affected horses have been euthanased on animal welfare grounds.

Horses are a "dead-end" host for mosquito-borne arbovirus infections, which means a horse is not a source of new infection for people or other horses. However, in a small percentage of cases bites from mosquitoes carrying these viruses may cause serious infection in people. Appropriate protection against mosquito bites is highly recommended for both people and horses. Registered repellents, rugs, fly veils, reduced exposure at dawn and dusk are recommended for horses as prevention against mosquito borne diseases.