West Nile Virus Alert | Carson Tahoe Health

Doris Dimmitt, Hospital Epidemiologist Carson Tahoe Health


I can’t help it. It’s just the way my mind works. When I think about mosquito bites, I think about disease transmission. We don’t have to worry about most mosquito transmitted diseases here in our little corner of the world, but we do have to worry about West Nile Virus. There hasn’t been much in the media so far this season, a couple of cases in Washoe County and a few mosquitoes testing positive, but that doesn’t mean it is no longer a problem. We can expect a few cases every season from now on. Not near as many as the 2004 and 2005 seasons when the epidemic was raging, (I hope) but a few cases none the less.

The truth is most of us have been bitten by infected mosquitoes already. Since most people don’t experience any symptoms at all the infection goes undetected. Our bodies however, recognize the threat and develop antibodies to protect us from getting the infection in the future. But some unprotected people still come down with the illness which can be very serious. Since we don’t have any way of knowing which group we are in, we must protect ourselves and prevent West Nile Virus. Let’s review the facts:

Fact #1. West Nile is transmitted by a bite from an infected mosquito. The only human to human transmission documented is by blood transfusion, organ donation, and from a mom to her unborn baby.

Fact#2. Only 20% of those infected will develop the disease, and only 1 out of 150 patients with disease symptoms will develop full blown encephalitis. Most of the cases present as minor flu like symptoms that last 3-6 days. The incubation period is 3-14 days after being bitten. Those most susceptible to the infection are people over the age of 50, pregnant women, and anyone who is immune-suppressed.

Fact#3. The primary means of protection from West Nile infection is to avoid mosquito bites. This is especially important for pregnant women. The CDC recommends the use of a mosquito repellant containing DEET, ( consult with your physician before using DEET if you are pregnant) wearing long sleeved shirts, long pants, and avoiding infested areas at dawn and at dusk when mosquitoes are most active.

Fact #4. There is currently no vaccine for West Nile, but vaccination against other arboviral infections such as yellow fever may provide some protection.

Fact #5. The symptoms for mild disease are malaise, anorexia, nausea, vomiting, headache, eye pain, myalgias, rash, and swollen lymph nodes. In severe disease, fever, weakness, gastrointestinal symptoms, flaccid paralysis and changes in mental status are seen which may progress to the neurological symptoms of encephalitis with or without seizures.

Fact #6. The treatment for West Nile infection is supportive, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections. Some antiviral drugs such as ribavirin in high doses have been shown to help.

The best thing that can be done at this time is to get rid of any sources of standing water, or treat water sources to kill the mosquito larvae. Mosquito fish, work very well, and are environmentally friendly, so you might want to consider that as an alternative. For more information including the CDC’s “Fight the Bite” program, go on line to cdc.gov. As always if you have any questions, feel free to email me at [email protected]. Remember that infection control is about making it difficult for the little buggers to get in. Understanding the epidemiology of how germs work is the best way to stay healthy. Don’t make it easy for them. Don’t let them bite.