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The Informed Parent

West Nile Virus Revisited

by Louis P. Theriot, M.D., F.A.A.P.
Published on Jul. 26, 2004

Mrs. James came to the office with her 14-month-old son, all in a panic. “We were at the park last night. When Alex got up this morning I noticed that he had a number of mosquito bites on his legs. Please tell me that I don’t have to worry about West Nile Virus!”

Last weekend I did physicals for incoming athletes at a local high school. One of the student trainers came running into the room where I was doing my exams. He looked very worried but politely did not want to interrupt me. I sensed that this might be something serious, so I excused myself from the area where I was doing my physicals. “What’s the matter?” I asked him as we moved to the side of the room. He said in a concerned voice, “I was over by the soccer field where there are a bunch of trees, and I saw a dead crow. Do we have to worry about West Nile Virus?”

I recently saw a two-year-old in the office with a classic case of Hand Foot and Mouth disease. When I explained my diagnosis to the mom, she sheepishly said, “I figured that is what she had. And you’re probably gonna think I’m crazy, but I just wanted to be sure that it wasn’t West Nile Virus.”

West Nile Virus, WNV, is most definitely here, and probably here to least for the foreseeable future. A few months ago the Health Department in Southern California started to report finding the virus in surveillance tests done on crows. There have recently been reports of humans infected with WNV in California. The media has given a tremendous amount of coverage about this. Although it is important to keep the public informed, it has worried and scared many people. In this article I would like to put WNV in the proper perspective.

In 1999 WNV first entered the United States in New York. Shortly thereafter much coverage followed. I wrote an article addressing the virus for The Informed Parent (see our archives). From 1999-to-2001 there were 149 confirmed cases in the United States with 18 deaths reported, due to WNV. Most of the deaths were in elderly patients. 2002 was a big year for WNV as it had moved across the country and had reached the West Coast, Canada and parts of Mexico. A large outbreak hit in the United States in 2002 with over 4000 cases being reported and 284 deaths. It has now reached Southern California. What is WNV, and who should be afraid?

WNV is a virus that is transmitted to humans, birds and other animals through the bite of an infected mosquito. The mosquito obtains the virus by taking a blood meal from an infected bird. Ten-to-fourteen days later the virus has replicated in the mosquito in sufficient numbers to be transmitted to the next host that the mosquito bites. These can be humans, birds, horses or other animals.Studies have shown that humans and horses are not capable of being a reservoir for spreading the virus. They simply do not get sufficient numbers in their system. However, they are known as “dead-end hosts”, meaning that if they get the virus from a mosquito bite they cannot spread it to another mosquito that would subsequently bite them. Many species of birds can become infected with WNV but crows and jays are particularly susceptible. Essentially all such birds die from the virus.

Eighty percent of humans that get the virus from infected mosquitoes DO NOT get any symptoms whatsoever. The remaining twenty percent have a moderate fever, headache, nausea, vomiting, swollen lymph nodes and a mild rash. It is a mild, self-limiting disease that requires very conservative treatment of the symptoms. Of the twenty percent who have symptoms a very small number, 1/150, go on to develop a more serious disease that includes encephalitis and/or meningitis. In these 1/150 that develop severe disease, the mortality rate is ten percent. The likelihood of one going on to develop a serious case of WNV is very rare under the age of 50 years. The vast majority of deaths from WNV have been in older patients. Fifty percent of these older patients who developed encephalitis or meningitis did not achieve a full and total recovery. There was some neurological deficit or sequelae that was permanent.

Other areas of concern regarding WNV and the transmission through blood are the implications in transfusions and blood banking, organ transplantation, pregnancy and breast-feeding. The Center for Disease Control and the Red Cross are currently studying these valid concerns. In regard to pregnancy, only one case has been reported where a pregnant mother passed the virus to the fetus. The baby was born healthy, showing no signs of illness. While the virus can be passed into the breast milk, there have been no reported cases of a baby getting sick with WNV from tainted breast milk. The CDC and other agencies are monitoring this very closely.

There is no treatment for WNV but one can try to minimize their chances of being bitten by a mosquito. It is important to remember that the peak time for mosquito bites is from dusk to dawn. Mosquitoes lay their eggs in still or stagnant water. It would be wise to check your backyard for discrete areas where water accumulates: in old tires, wheel barrels, empty flower pots, inflatable wading pools for children, etc.

Insect repellent is very effective in keeping the mosquitoes away. A very potent ingredient is DEET. The higher concentration of DEET the longer it will be effective. However, this result is only true in a concentration of fifty percent. Beyond that concentration the effectiveness is no greater. Children two years and above can safely use this product but one should always read the instructions on the can first. When applying a repellent to a child, the parent should never spray it directly on the child; rather, first spray it on their own hands, and then rub it into the child’s skin. Parents should also remember never to apply it on the child’s hands, as they tend to constantly put hands and fingers in mouths. DEET has also been shown to be safe and effective for pregnant women.

West Nile Virus is definitely here, and seemingly here to stay. Fortunately, it does not cause any symptoms in the vast majority of cases. Only a small percentage of patients go on to develop a severe form of the disease. It is fatal in a very small number of these patients, almost all who are over fifty years of age. It is important for the public to be aware and informed, but things must be kept in proper perspective. There is certainly no need to panic or be fearful. There are a number of things that one can do to minimize risk of getting bitten by mosquitoes. Health care workers must be vigilant and on the lookout for WNV. The CDC and numerous agencies across the country are doing research every day to help combat and eventually eradicate WNV.

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