Epidemiology Corner

May 7, 2004

Mosquito-borne disease in Houston

What are mosquito-borne viruses?

Viruses that are carried by mosquitoes are called arboviruses. In the United States, arboviral illness may be due to St. Louis encephalitis (SLE) virus, Eastern equine encephalomyelitis (EEE) virus, Western equine encephalitis virus, LaCrosse virus or West Nile encephalomyelitis (WNV) virus. Currently the most common mosquito-borne viruses circulating in the Houston and Harris County area are WNV and SLE.

How are mosquito-borne viruses spread?

West Nile virus and SLE are spread to humans by the bite of an infected mosquito. A mosquito becomes infected by biting a bird that carries the virus. These viruses are not spread by person-to-person contact such as touching, kissing or caring for someone who is infected.

What are the symptoms of mosquito-borne illness?

Many people may not even know they are infected with an arbovirus. When symptoms do occur (2-15 days after the bite of an infected mosquito), they may include fever, headache, fatigue, dizziness, weakness and confusion. WNV may also cause a rash or muscle weakness. People 50 or older tend to be more severely affected by SLE or WNV. The most severe cases can lead to coma and death.

What to do to reduce the risk of becoming infected with mosquito-borne illness?

Mosquitoes lay their eggs in standing or slow-moving water, like ditches or storm water basins that do not drain. Unattended weeds, tall grass and bushes provide adult mosquitoes with hiding places during the day. They can enter homes through unscreened windows and doors or broken screens.

Protect your home from mosquitoes:

• Make sure that doors and windows have tight-fitting screens. Repair or replace all screens that have tears or holes.
• Remove any open containers or tires that can potentially hold water.
• Make sure roof gutters drain properly. Clean closed gutters.
• Clean and chlorinate swimming pools, outdoor saunas and hot tubs. If not in use, keep empty and covered.
• Change the water in stock tanks and birdbaths at least once a week.
• If outside from dusk to dawn when mosquitoes are most active, or during the day in an area where there are weeds, tall grass, or bushes, people should wear protective clothing, such as long pants, loose-fitting, long-sleeved shirts and socks, and consider the use of an insect repellent containing DEET (N,N-diethyl-m-toluamide).

The American Academy of Pediatrics recommends that repellents used on children should not contain more than 10 percent DEET. For additional information on mosquito-borne illnesses view the CDC website at: http://www.cdc.gov/ncidod/diseases/list_mosquitoborne.htm
For additional information on WNV in Houston view the HDHHS website at:
http://www.ci.houston.tx.us/departme/health/westnile.html