West Nile Virus

We’re firmly entrenched in the last week of August, and with the weather running warm to hot for the foreseeable future, I want to take some time to discuss a zoonotic disease that’s making headlines locally and nationally. This is something that -everyone- should pay attention to, whether you’re an outdoorsy or indoorsy person. Dog and Cat owners don’t have much to be concerned about with their pets, but horse owners should be concerned.

West Nile Virus (WNV) is closely related to a small set of viruses known as flaviviruses. It’s found throughout the majority of the US. While it generally infects birds, animals and people are potential hosts for the virus. Interestingly, WNV in the US hasn’t changed much since about 1999. In contrast, many types of virus can change their makeup more frequently.

WNV is primarily found in birds. Birds can survive the infection and become immune, but some of them will die after being infected. Mosquitos transfer the virus from bird to bird when they bite to drink a blood meal. These same mosquitos can bite other animals or people, which can lead to infection of those other animals. The main difference in the infections is that birds develop very high levels of virus in the bloodstream. Humans and other animals generally do NOT develop high levels of virus in the bloodstream. Animals other than birds and humans are called “dead-end hosts” because they don’t serve as a means for the virus to reproduce.

WNV 21August 2012 a

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Spending time outdoors is the primary risk factor for contracting WNV. Anywhere that you can get bitten by a mosquito puts you at risk for contracting WNV. One of the mosquito species that transmits WNV can survive the winter by hibernating in places like barns, underground, or in root cellars. The presence of mosquitos indoors means that people and indoor pets are at risk of being infected.

As I mentioned, dogs and cats are quite resistant to this virus. The CDC reports that a 1999 study (in New York) showed many dogs are infected by WNV but do not develop any symptoms. Horses, on the other hand, seem to be more susceptible. Not every horse that is infected will get sick, but those that do have a 40% chance of dying from the infection. A vaccine exists, but no one is certain how much it’s helping protect horses.

For people that are infected by WNV, about 80% will have no signs or symptoms at all. People over 50 years of age, or those with diabetes or other immune suppression, are more susceptible. About 20% of the people infected will develop flu-like symptoms 3-14 days after being bitten by a mosquito: fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. People can feel sick for a few days to a few weeks. About 1 in 150 of the people who are infected will get severely sick. High fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis can occur. These symptoms may last several weeks, and neurological effects may be permanent. If you think you may have WNV, you should contact your physician for further instructions.

There is no vaccine for people. Preventing mosquito bites is the best way to avoid contracting WNV. According to the CDC, these methods can be used to lessen your risk:

Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellent with an EPA-registered insect repellant. Wear long sleeves and pants at these times or consider staying indoors during these hours. Make sure you have good screens on your windows and doors to keep mosquitoes out. Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they aren’t being used.

Here’s the CDC webpage about WNV.

Here is the wikipedia page about WNV.


1 Comment

Filed under infectious diseases, wildlife, zoonotic

One response to “West Nile Virus

  1. All good advice. My horse started getting the West Nile vaccine as soon as it was developed. Prevention is always better than damage control.

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