LANSING, Mich. — The mild winter, early spring and continuing hot, dry conditions have encouraged early development of the mosquito that carries West Nile Virus (WNV), and health officials are urging people to take precautions.

The virus can be transmitted to humans and horses by an infected female Culex mosquito – also called the house mosquito – although this species typically gets its blood meal from birds and is considered less of a threat to humans and animals.

House mosquitoes breed in stagnant water, live 10-14 days and are weak fliers, so they don’t go more than a mile or so from their breeding ground. They pick up WNV by biting an infected bird.

“Hot and dry conditions favor development of the virus and the mosquitoes that transmit it,” said Erik Foster, Michigan Department of Public Health (MDPH) medical entomologist. “These mosquitoes may breed near people’s homes in storm drains, shallow ditches, retention ponds and unused pools.

“When these areas are not flushed out by rains, (water) becomes stagnant and highly organic, which is appealing to mosquitoes that can transmit the disease.”

In mid-June mosquito pools collected in two Michigan counties tested positive for WNV, but there have been no human cases, according to Angela Minicuci, MDPH public information officer.

“With the hot, dry weather, there’s an increased risk because the type of mosquito that carries West Nile Virus breeds in stagnant water,” said Melaney Arnold, spokesperson for the Illinois Department of Public Health, adding that anything that must hold water should be refreshed every couple days to avoid becoming stagnant.

She said many people don’t think about mosquitoes being a problem unless weather is rainy and the environment stays wet. But house mosquitoes breed in stagnant water, which may be found in flowerpots, old tires, buckets and other containers left sitting outside – especially in the shade.

Arnold reported as of last week there were about 20 Illinois counties that had positive mosquito pools or bird cases; the first were reported in mid-May. According to Centers for Disease Control and Prevention (CDC) maps, nine counties had bird cases and 13 counties had positive mosquito pools.

Indiana State Department of Health Media Relations Coordinator Ken Severson reported 13 counties with mosquito pools testing positive for WNV. His office has a website about mosquito-borne diseases at www.in.gov/isdh/23592.htm that has a fact sheet on WNV and a map showing where current cases have been reported.

“There are no cases in humans, no bird infestations and no equine cases,” he said.

At the Kentucky Department of Public Health, public information officer Beth Fisher said there’s been one confirmed human case so far this year. She said that was in Henry County. Because of budget cuts, Fisher said, the department no longer tests mosquito pools, so there are no data on mosquito or bird cases.

Woody McMillin, director of communication for the Tennessee Department of Health, said there have been no human or equine WNV cases reported in his state. There have been positive mosquito pools, however, in three counties. McMillin said the first confirmed mosquito case was in May, no earlier than usual.

The CDC maps at http://diseasemaps.

usgs.gov/index.html last weekend showed eight Ohio counties with positive mosquito cases, but no bird or human cases. There were no cases of any type reported in Iowa as of last week.

About four out of five humans contracting WNV won’t show symptoms. Up to 20 percent of people who get it may have fever, headache, body aches, nausea or vomiting, and sometimes swollen lymph glands or a rash. Symptoms may last a few days to several weeks.

About one in 150 people will develop serious symptoms, which may include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Neurological effects may be permanent.

To prevent WNV, use an insect repellent containing DEET, wear long sleeves and pants, consider staying indoors during dawn and dusk hours when mosquitoes are most active, make sure window screens are free of holes and tears and eliminate mosquito breeding sites.

Unvaccinated horses may exhibit staggering, stumbling or a wobbly gait; become uncoordinated or circle; develop hind limb weakness or multi-limb paralysis and fall; and develop blindness, lip droop or teeth grinding. Other clinical signs include colic, anorexia, fever and lameness.

Behavioral changes, such as listlessness or excitability, also may occur. There may be residual effects from the disease in surviving equine.

Vaccinating horses annually before the onset of mosquito breeding will protect them. Controlling the environment by eliminating mosquito habitat, having adequate screens in shelters and using fans and insect repellents also can help protect horses.

Dead birds, a sign infected mosquitoes may be in the area, should be reported to the local health department, which also can provide information on proper disposal.