Recently the West Nile virus has been in the news. This year has provided excellent conditions for the virus to be seen. Thirty-two states have reported human cases. Most of the cases are occurring through Texas, Mississippi and Louisiana. Missouri has had 2 cases occurring in horses.
West Nile is transmitted by mosquitos and the virus itself is found in wild birds. It was first reported in North America in 1999. The life cycle of the virus is very complex. However, it is basically accepted that the mosquitos become infected by biting an infected bird. The mosquito then bites the horse, dog, cat or man and transmits the virus to them, thereby infecting the recipient of the bite.
Clinical signs of West Nile usually are seen 5-15 days after the mosquito bites. Signs are consistent with encephalitis. Horses may be uncoordinated, stumble, have muscle twitches and even partial paralysis. Depression is also common. Head pressing and circling can also be seen. Fevers occur in less than 25 percent of the cases. Convulsions can also occur, followed with collapse.
Treatment is essential, however; there is no specific treatment. Supportive therapy may allow for recovery. Therapy is focused on reducing the inflammation of the brain. Many drugs can be used. Fluids are needed if the patient is unable to drink. If the patient cannot stand, putting the patient in a sling is needed. Therapy may be required for up to four weeks. Most will show improvement within a week of starting therapy.
Data supports that 50 percent will recover, and 33 percent will die. The remaining 17 percent will have lasting effects of the virus. Prevention is the best approach. A vaccine is available for horses and is usually recommended in the yearly vaccination program. Also reducing the population of mosquitos is helpful. Minimizing standing water in the environment will reduce your horses’ exposure to mosquitos.
Remember, it takes 7 to 12 weeks for maximum immunity to develop from the vaccinations. As of August 14, 2012, there have been 77 cases reported of the West Nile Virus. Twenty-one of those were in Louisiana. Missouri has also reported cases. If you are traveling with your horses, check the area of your destination and make sure your vaccinations are up to date. The Missouri State Veterinarian’s Office is recommending West Nile vaccinations.
Frankie Bowers, DVM, MS practices at Animal Clinic of the Ozarks in Ozark, Mo.