West Nile Virus
That first hard frost in the fall means something different for different people. It could mean the beginning of nice, brisk and chilly mornings as you slowly sip your coffee. You could be sighing thinking of the past summer gone and the soon to be blustery months of winter. Or pleasant thoughts of the holiday season may be in the back of your mind as you look out on the beautiful, crisp, white landscape. Or you could be a horse owner. That first hard frost means something entirely different for horse owners. No mild regrets of the summer past, no serene thoughts of soon to be holiday season nope our thoughts are on those pesky mosquitoes carrying the West Nile Virus and we will soon be laughing in delight thinking of all those "poor" little mosquitoes slowly freezing to death and taking that horrible virus along with them.
Hopefully you and your entire stock of horses have survived this West Nile warfare that we have been fighting over the past few months. But sadly I know for certain some of your beloved companions have not pulled through the fight. I have had the unfortunate opportunity of diagnosing West Nile Virus in approximately sixteen horses over the past 1-2 months. Thankfully, we have had several pull through and our percentages mimic what most are reporting-that approximately 1/3 of the horses succumb to the disease. The clinical signs I have witnessed out in the field vary greatly from horse to horse. I have seen horses with just mild muscle tremors through the head and neck, weakness in the rear limbs, one sided rear weakness or even where the first clinical sign an owner notices is a completely down horse that cannot stand up anymore. I have had horses respond remarkably well to treatment and others with no response to any type of treatment whatsoever. Each horse presents, reacts and responds differently to the disease process.
If a horse tests positive and survives through the disease, there is no reason to feel the horse needs to be isolated from other horses. Horses (and humans) are incidental hosts, which mean we are not an important part of their life cycle and the virus does not multiply in high numbers within our bodies. Therefore, it is highly unlikely that mosquitoes feeding on an infected horse could ingest enough of the virus to transmit it to other animals. Also, if the horse does contract the virus do not believe that he now has a lifelong immunity to the disease. There is not enough research on the disease to know the length of immunity that may be obtained after an infection; therefore, vaccines are still recommended for the next mosquito season. The vaccine itself is also a cause of controversy. Some people, veterinarians included, are professing that it has not been tested and it is not proven. It is true that the vaccine was released on a conditional release. It was released this way because of the epidemic problems the United States was going to face. As a conditional release it has proven it can mount an immune response to the virus, it just has not had enough time to prove how effective the immune response is once exposed to the virus itself. However, Fort Dodge has recently completed their efficacy study for the West Nile Vaccine. Their study is showing a 94% efficacy when exposed to the virus as many as 12 months after the second vaccine. Although the study still hasn't been completely approved, these results are promising. Currently, Fort Dodge has three cases they have considered vaccination failures, which is a low number since they have sold approximately 1.1 million doses. In my opinion, the horse population in this area was completely naïve to West Nile Virus with no previous exposure. Therefore, any immune response to the virus is better than nothing. I would rather my horse have some antibodies circulating around in his blood stream that recognizes West Nile Virus and can call for reinforcements if the time ever comes, than have my horse's immune system having no idea what West Nile Virus is and having to start from scratch with antibody production AFTER he's been exposed to the potentially fatal virus.
According to the USDA as of October 13th there were 559 confirmed cases of West Nile Virus in horses in the State of Indiana. Of the 38 states that had reported confirmed cases, there were only 8 states (from highest to lowest: Nebraska, Iowa, Minnesota, South Dakota, Texas, Illinois, Missouri, and North Dakota) that had more cases than the state of Indiana. The total number of West Nile Virus cases through the 38 states was 10,172. (To keep track of this information you can check it out on their website at http://www.aphis.usda.gov/oa/wnv/wnvstats.html.) The worst of the threat should be curbed when the frosts hit and the mosquito population dies off; however, it will take the first hard freeze to verify all the larvae will die. In the Southern states, the virus will live over winter and West Nile will be back next year as well. There have been discussions that state the vaccine may have the strongest immune response to the virus the 6-7 months after the vaccine. Therefore, it would be ideal to vaccinate your horses during the spring of next year to have the next 6-7 months be during the peak periods of mosquito populations. (However, with the recent release of the Fort Dodge study, it appears the vaccine may show a higher protection even longer.)
There is no specific treatment for West Nile Virus; therefore, therapy is limited to supportive care only. Anti-inflammatories are used to help calm down inflammation in the brain and spinal cord while the body attempts to fight off the virus. Tranquilizers are sometimes warranted in horses that are down and injuring themselves as they struggle to stand. Other measures you can take to help prevent your horse from contracting West Nile Virus generally revolve around controlling the mosquito population. Eliminate standing water, spraying the horses with mosquito/fly repellant during peak times of the day, keeping a fan on low during the evening hours to keep a small amount of air circulation to affect the mosquito's flight, etc
I hope this answers a few of your questions on West Nile Virus you may have had regarding your horse. I've tried to touch base on several topics I get asked frequently. Here's hoping that you and your horses get through the remainder of this mosquito season safely. Don't forget to raise your coffee with me that first hard frost morning to cheer the demise of our pesky virus carrying mosquitoes.
Emergency Kit and Consent Forms
We at Greener Pastures Veterinary Clinic, Inc. have compiled an emergency kit for the continuing care of your horse. Enclosed in the kit you will find a compilation of medication and products that will enable you to help your horse in an emergency situation until veterinary care arrives. The kit is in no way promoting you to treat your horse in an emergency situation without medical supervision. You are always free to call us if there are any questions or if you need advice or further medical attention for your horse. You may also need to consider what to do with medical emergencies when you are out of town. Greener Pastures Veterinary Clinic, Inc. has created an emergency consent form that you can fill out to help assist the people remaining to watch and care for your horses. The form will help you and your care givers to decide how to handle emergency situations. Contact us for more information.
Greener Pastures Veterinary Clinic, Inc. has designed an Equine Wellness Package to provide our clients with the peace of mind that comes with knowing that their horses are receiving the best preventative health care on a regular and timely basis. One annual fee will cover the cost of physical examinations, routine dental work and routine vaccinations. This is a convenient way for both owner and veterinarian to keep track of your horse's care. We have finalized the guidelines for the Wellness Packages which will be available starting in the Spring of 2003. Please contact us for more information.
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