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Experts detail West Nile virus transmit process, surveillance |
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By LYNN MONTGOMERY | East Texas Edition |
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August 22, 2002 -- As the number of West Nile virus (WNV) cases climb, so does public concern. The Texas Department of Health (TDH) held a meeting Aug. 14 in Tyler to inform people, like city and county animal control officers, how they can help control mosquito populations; therefore helping control the spread of West Nile. By now, most people are very aware of WNV. This virus lives in the bird population. A mosquito will bite an infected bird and become a carrier. The mosquito, requiring a blood meal, will then bite a horse or human. At this point, the horse or the human may or may not become infected, according to Dr. James Wright, a veterinarian with the TDH's Tyler Regional Office Zoonosis Control Division. Wright explained the reason infection may or may not occur is the virus has to have time to incubate. This incubation period is between 10 days and 14 days. So, if a mosquito bites a bird today, and then bites a horse or human tomorrow, the virus has not had time to incubate. There are risk factors with WNV, with people over 50 having the highest risk. The best thing, according to Wright, is not to get bitten by a mosquito. "Wear long sleeve shirts and pants. Wear insect repellent with DEET if possible," Wright stressed. Wright expressed concern about the number of calls his office is receiving regarding dead birds. "We are receiving more calls from individuals saying they have a dead bird. If the bird is not a blue jay, crow or hawk, we can not send it to the lab in Wisconsin," Wright said. "West Nile has the ability to kill only these three birds, for some reason. Typically, encephalitis doesn't kill birds. This virus has killed these three birds. Also, if someone says they have a dead crow, the crow must have a black eye. If it has a golden eye, it is consider a grackle and we don't want grackles. The birds must also have died within the last 24 hours." The bird cannot be decomposed in any way and void of fluids, maggots and ants. It also can not have any trauma due to a car or other animals. The Texas Department of Health is asking people if they find a dead bird to contact their nearest TDH office. There are areas in East Texas under mosquito surveillance. Smith County and the City of Longview are using traps to catch mosquitoes. The mosquitoes are sent to Austin where they are monitored for the virus. If the virus in detected, "then we know that the virus is in the area where the mosquitoes were caught," according to Wright. Hoyt Henry, a vector control entomologist, told the animal control officers there were three different types of mosquitoes under investigation: the Culex quiquefasciatus Say (southern house mosquito), Culex salinarius, and the Aedes albopictus (Asian tiger mosquito). Comparing the three, the Culexs lay their eggs in rafts of stagnant water; complete cycle is 8 to 12 days depending on temperature and food availability; feed dusk to dawn; prefer birds. The flight range for the quiquefasciatus is 1/2 mile to 2.5 miles. Flight range for the salinarius is 1/4 mile to 5 miles. The Aedes albopictus lays its eggs above the water line, which makes their cycle from 8 days to whenever because the water must come up to the eggs. A good example of a prime egg laying area is tires. "They love tires," Henry said. The Aedes' life cycle depends upon temperature, availability of food and availability of water. The are day-time feeders and will feed readily on humans, according to the entomologist. Their flight range is less than 1/2 mile. Henry stressed the importance of integrated mosquito control. Steps are surveillance, source reduction, public education, larvicidial treatment and adulticidial treatment. It was also noted there is a case of Saint Louis encephalitis, another mosquito-transmitted virus, in a bird in Harris County. |
