West Nile encephalitis activity has already picked up in Louisiana with the virus reportedly being found in birds throughout the state and in the mosquito population around Baton Rouge, said Jim Olson, entomologist with the Texas Agricultural Experiment Station.
"With that being an indication, we could be in for another year of West Nile virus activity," in Texas, Olson said.
"This is probably one of the earliest records of a mosquito-borne virus (becoming active) in the South." Normally, activity begins in May or June, he said.
In 2002 – the first year West Nile was reported in Texas – 202 laboratory-positive human cases and 13 deaths in the state were attributed to the virus, according to the Centers for Disease Control and Prevention.
According to the CDC, West Nile virus is commonly found in Africa, West Asia and the Middle East. It is closely related to the St. Louis encephalitis virus, and it can infect humans, birds, mosquitoes, horses and some other mammals.
West Nile fever is usually a mild disease in people and is characterized by flu-like symptoms – it typically lasts only a few days and does not appear to cause any long-term health effects, the CDC said.
Olson said West Nile virus is bird-borne; to date, more than 110 species of birds have been found to be infected with and have the ability to serve as the source of the virus.
"Mosquitoes feeding on infected birds become infected themselves and then pass that on to other birds," he said. "Or if, by chance, if they feed on horses and humans, they could infect those."
State health officials are still encouraging horse and mule owners to vaccinate their animals. If the animals were vaccinated last year, a booster is recommended, Olson said.
"Consult your veterinarian and get them vaccinated now," he said. "There is a delay time from when the vaccination starts and when the horses will build a high enough immunity to be considered protected. That delay time can be up to six weeks."
For people to avoid mosquitoes and the possibility of disease, the entomologist recommended the three P's:
- Protection of self, using protective clothing and a repellent of choice and avoiding being outside during the times of day when mosquitoes are active.
Olson suggested wearing clothing that is loose-fitting. "With tight-fitting clothing, mosquitoes can drill right through the fabric," he said.
Long-sleeved and long-legged clothing provides protection for skin. Clothing should be light-colored because mosquitoes are attracted to darker hues, he said.
- Prevent mosquito breeding around the house by removing all sources of standing water, dumping artificial containers and removing those containers.
- Prevent mosquitoes from getting into homes with the proper screening and sealing frames doors and windows. Olson said he suspected most human infections of West Nile and other encephalitis viruses are caused by bites either in the home or places close by, such as yards and patios.
Citronella candles offer some protection outside if they are used in areas with little wind movement, but Olson urged people to practice safety when burning those.
Insect-killing devices, such as the "bug zappers" should be placed at a distance – about 50 feet – from the area you're trying to protect. "They do tend to attract more mosquitoes than they kill," he said.
Community-wide spraying can be effective if done properly, he said.
Proper surveillance by health authorities can determine those two factors.
"Indiscriminate spraying of mosquitoes that is not out of a sense of need is not recommended. There has to be an actual need. Otherwise, other measures are sufficient," he said.
Further information is available from http://www.cdc.gov/ncidod/dvbid/westnile/
Edith A. Chenault is a writer for the Texas Agricultural Experiment Station. e-mail: [email protected]