Hot, dry weather perfect for West Nile virus spread

In this photo provided by the Northwest Mosquito Abatement District, lab assistant Carter Sharp sorts mosquitoes in Wheeling, Ill., that were collected from Chicago’s northwest suburbs for West Nile virus testing. Illinois already has seen at least two human West Nile virus infections this year, more than a month earlier than usual. The rate of infected mosquitoes in the state is the highest in a decade and higher than in 2002, when 67 people died. Health officials say the hot, dry weather is a factor.

CHICAGO — Life’s a picnic this year for the small, sneaky mosquitoes that carry the West Nile virus and pose a deadly risk to humans. Hot, dry weather in the Midwest has created the perfect conditions in still-damp ditches and underground storm water basins where the Culex mosquito breeds.

Where there’s water in the drought-plagued Midwest, it’s stagnant water, the Culex mosquito’s favorite breeding habitat. The heat also speeds up the mosquito’s life cycle, which means more breeding and more mosquitoes, and accelerates the West Nile virus replication process.

Illinois, Indiana, Ohio and Texas are reporting higher rates of infected mosquitoes compared with past years. More infected mosquitoes mean a higher risk for humans. Minnesota, Illinois, Oklahoma and Texas are reporting earlier-than-usual cases of human infection.

“I am quite concerned we may be facing one of our most severe seasons for West Nile virus since it arrived in our state in 2002,” said Kristy Bradley, state epidemiologist in Oklahoma, which has had eight confirmed human cases of West Nile infection, with seven of those being the serious, neuroinvasive form of the disease. “I’m somewhat bracing myself for a rocky road ahead.”

West Nile virus is a cyclical disease in humans, appearing in the summer and disappearing in the winter as carrier mosquitoes die off and hibernate.

Illinois, which usually sees its first human cases in August, already has two confirmed cases this year. Both are women in their 60s from the Chicago suburbs. Both were hospitalized and are receiving further care in rehabilitation centers.

“The risk is high and people need to listen,” said Linn Haramis, an entomologist with the Illinois Department of Public Health. “This thing could put you in a wheelchair at age 60 for the rest of your life.”

Most people infected with West Nile virus won’t get sick, but approximately one in 150 people will develop the severe form of the illness. Symptoms include headache, high fever, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.

The best advice? Wear insect repellent containing DEET, picaridin or oil of lemon eucalyptus. Avoid being outdoors between dusk and dawn, when mosquitoes are biting. Install or repair screens to keep mosquitoes outside. Drain standing water to eliminate breeding habitat.

Haramis noted that in Illinois the rate of infected mosquitoes is the highest in a decade, and higher than in 2002 when 67 people died. But he won’t make predictions because a streak of cool weather or heavy rain could “knock the legs out of this thing.”

Minnesota’s first human case came in late May, much earlier than in previous years. The Minnesota man got sick with West Nile encephalitis and meningitis after traveling in the south-central part of the state. He is recovering after being hospitalized.