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More About the West Nile Virus

16 August 2011 No Comment

More About the West Nile Virus
By: Dr. Jessica Jahiel

Dear Jessica,
We are beginning to get very worried about this West Nile Virus that we hear and read about all the time. We’ve heard all kinds of things about it, that it is spread by mosquitoes and birds and that infected horses should be destroyed, because they will quickly infect other horses and humans. Our vet says that he doesn’t think it’s that serious, but he is basically a cattle vet, not a horse vet, and I don’t think that horses are a very big part of his practice.
I guess this is more than one question, but I hope you’ll answer them. They are all related, anyway. I want to know how horses get the virus, if one infected horse will infect the other horses, if my wife and I can get the virus from the horses, what we should do if a horse gets the virus, etc. We have our horses vaccinated every year against just about everything there is. I know that they get a lot of vaccines: here is the list from this spring: Tetanus, Rabies, PHF, EEE, WEE, and VEE. I’m not sure what all of those letters stand for, but will any of those vaccines help protect our horses from West Nile Virus? Also, is it true that there is a new vaccine that will keep horses from getting West Nile Virus? I’ve heard from two friends who also have horses, one of them is getting this vaccine, the other says it’s pointless. Which one is right and what should we do? My wife doesn’t believe in giving too many vaccines, and our horses are the only ones on our property, so we usually don’t vaccinate for flu or strangles. She’s willing to use this new vaccination if it’s necessary.

Also, we have a small pond on our property and I hear that it is a bad idea to have water because of the mosquitoes and West Nile Virus, but I hope we don’t need to fill in the pond. Is there anything we could put in it that wouldn’t be poisonous but would get rid of the mosquitoes?

Thank you very much,

Hi Carlos!
I’ll do my best to answer all the questions, and at least give you some topics to discuss with your vet.

Birds aren’t a problem directly – horses and humans are both infected by the bite of infectious mosquitoes. The current thought is that biting infected birds has infected the mosquitoes.

West Nile Virus causes a form of encephalitis – the brain becomes inflamed, and the horse’s central nervous system doesn’t function, as it should.

I don’t believe that there is a single documented instance of a horse getting West Nile Virus from another horse, or of a human getting West Nile Virus from handling or treating an infected horse. Obviously you’ll want to be careful when handling any horse with any virus, but beyond those basic precautions, I don’t think you need to get too agitated.

The initials in your list of vaccinations stand for Potomac Horse Fever
(PHF), Eastern Equine Encephalitis (EEE), Western Equine Encephalitis
(WEE), and Venezuelan Equine Encephalitis (VEE). Because they have received those vaccines, your horses will be protected against those forms of encephalitis, but NOT against West Nile Virus, which is a completely different virus.

As for the West Nile Virus vaccination, this is all I know: The vaccine has been approved, but is not PROVEN, which means that it is unlikely to harm your horse, but may have little or no effect against West Nile Virus. Given that, it may be more sensible to wait – at least until the vaccine is proven effective, or until a better vaccine is developed. But that’s something that you and your vet will need to discuss. The status of the currently available vaccine is “conditional approval” by the FDA. According to the information available right now, the vaccine MAY (or may not) reduce some of the effects of the infection, and has NOT been proven to prevent infection. On the plus side, though, it doesn’t appear to have many side effects. So it’s really going to be up to you and your vet and the conditions in your area – for some people, it may make sense to vaccinate their horses; for others, it may not.
When it comes to medical information, don’t pay too much attention to rumors, or even to other horse-owners, even if they are close friends of yours. They may not be completely accurate in their reports of what they think they remember that their vet may have said to them.

Remember that I’m not a vet. I can give you some general information and some suggestions, but you need to get real medical information, and get it as directly as possible. Talk to your vet, talk to an equine specialist vet, call your county extension agent, or get in touch with the United States Department of Agriculture (USDA) for the most up-to-date information. The department you want is APHIS, the Animal and Plant Health Inspection Service.

I can make a suggestion about what to do with your pond, though. Don’t fill it in with dirt – stock it! If you have a pond full of hungry fish, the mosquitoes won’t have much of a chance. They are far more likely to multiply in areas where there’s just a little bit of standing water – in a puddle of water inside an old tire on the rubbish heap, for instance, or in the inch or two of water inside an old jam jar on that same rubbish heap.

Get the best information you can, and do the best you can – that’s all any of us can do. And remember that not all horses get infected, and that most infected horses DO seem to recover.

Good luck!
To find out more about Dr. Jessica Jahiel, click here.

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