Cool spring weather in the eastern half of Texas may have slowed the buildup of West Nile virus in mosquitoes and birds.

Dr. Jim Olson says the southern house mosquito, the primary vector of the disease, has not been able to reproduce as readily as in previous years.

"Its numbers are considerably lower this year than at this time last year," he says. "Now, we're going into bird-nesting time, which is the prime build-up period for the bird and mosquito populations." Since fewer mosquitoes are feeding on nesting birds, Olson hopes that will translate into a lower infection rate of West Nile in birds.

The virus cycles from mosquitoes to birds to more mosquitoes and perhaps humans.

"So we're hoping for the best and planning for the worst," Olson says.

West Nile is a potentially serious illness in humans, according to the Centers for Disease Control and Prevention. Most people will show no symptoms at all, but up to "20 percent of those who become infected have symptoms such as fever, headache and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back," the CDC says.

These symptoms can last for several days to a couple of week. About one in 150 people will develop even more severe symptoms.

To date, no virus has been isolated from birds or mosquitoes, but possible human cases in the Dallas-Fort Worth and Houston area raise the possibility that the virus is active.

"That indicates to us and the people we protect that we can't let our guard down," Olson says. "Even though infection rates are smaller in number we would hate for anyone to be one of those infections.

"So, we ask people take care of themselves, do what they're supposed to do. That means cover up, use repellents, get rid of mosquito breeding sites, and mosquito-proof their houses. No amount of spraying, no amount of work by the city and county health departments or mosquito control districts can do as much as the individuals themselves."

The flooding rains in some areas have received lately also will deter the buildup of the virus, Olson says.

"The mosquitoes primarily involved in the transmission are being flushed out and becoming fish food in the streams and rivers. On the downside, the rains are hatching floodwater species." While these are not vectors, they are a major annoyance, and people living in coastal areas especially need to take precautions.

"In the next 10 days or so, the mosquitoes will be coming to town looking for blood meals," Olson says. "They're going to come hungry, and there's not much you can do about it except stay inside and watch TV for the next 10 days to two weeks."

The West Nile virus has been found in mosquitoes and birds in all 48 contiguous states. Texas-where West Nile has been found virtually all of the state-ranked third in the nation in the number of human cases last year. Idaho ranked first and South Dakota, second.

"Most of the infections occur when mosquitoes are in houses," Olson says.

Given the choice, the southern house mosquito would rather feed on birds.

"It's when they are trapped inside, they're more apt to feed on humans," he says.