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We all should be pretty grateful for all the rain this year, breaking the drought in much of the affected areas, however with all the rain Texas and other western states have had this year so far, Mosquitos are a larger potential problem than in the recent past. And with Mosquitos come the threat of West Nile Virus, a viral disease transmitted from mosquitos to horses, and from mosquitos to people as well. Horses are pretty susceptible to West Nile, more so than people. Humans who are at risk are usually those who are already immunological weakened. There are still some misperceptions on West Nile such as "an infected horse can infect another horse", and no this is not the case. Only infected mosquitos can infect a horse.
West Nile attacks the nervous system and can cause brain and spinal infection or inflammation. A horse will appear to be drunk - lack of coordination in movement and loss of balance. Other symptoms can be: extreme lethargy; lack of appetite; and, dullness in the eye and other signs of depression such as head pressing on a stall wall or post.
There are other diseases, such as Encephalitis (Venezuelan, Eastern or Western) whose symptoms can mimic West Nile. Only with a blood test can you be sure, and then only supportive care for the symptoms can be done.
A few years ago, when I was running a large horse stables, a boarder brought in a horse and while in quarantine the horse started showing signs of lethargy, dullness, loss of appetite and severe loss of coordination and balance in movement - staggering when trying to turn around. A blood test confirmed West Nile. A week later the horse was pretty sound and was absent all symptoms, although the owner decided to sell the horse anyway. I found a buyer for him and transported the horse to a good home with several young boys who were even able to rope off of this horse.
There are several things a horse owner in a mosquito area can do to minimize risk to his horses. Even though I live in an area without mosquitos, I often trailer 15 miles away, close to the Rio Grande, where mosquitos are present, so the West Nile vaccination is part of my routine April or spring series of immunizations for my horses. In the first few years of the West Nile outbreak it was common for horses to receive an initial shot with a booster a few weeks later.
Taking care to drain or remove sources of stagnant water will help reduce breeding grounds for mosquitos. On most properties you would be amazed at the number of items capable of holding water that would attract mosquitos. Store empty buckets upside down. Open trash cans or dumpsters (without lids) could use a couple drain holes at the bottom to reduce collecting water. At the stables I managed years ago, I would spray insect killer on the manure pit, in-between dumpings, to help reduce chances of mosquitos. Fly spray, not insect killer, can help keep a horse protected as well, although I try to limit my use of fly spray on horses to a minimum. It seems that whenever I use fly spray I can't help but spray myself and go on about the day with the taste in my mouth. I guess that just goes along with me never being accused of having acute coordination.
Anyway, If you have any questions on whether you should vaccinate your horses against West Nile, talk to your Vet. Most Vet's would approach it from the side of caution and urge a West Nile vaccination, but it gives you peace of mind to inoculate your horses, even though the immunization won't keep your horse from getting West Nile, it just give him a better chance of making through the disease if he becomes symptomatic.
The Texas Animal Health Commission (TAHC) has reported West Nile present in Harris County (Houston) and Tarrant County (Dallas) and even El Paso County (El Paso) had a human death from West Nile, so it is not necessarily only the really humid areas, or areas close to water sources that are primarily the WNV threat areas.
The United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA- APHIS) keeps track of animal diseases. The map below is the nationwide cases of West Nile Virus from last year. A complete list of counties in the U.S. where West Nile has been confirmed can be accessed here:
