West Nile Fades in Some Areas of the US

by Medindia Content Team on Jul 31 2007 2:55 PM

Summer rains create ideal breeding conditions for mosquitoes; they present an ominous health hazard carrying different diseases like west Nile, chikugunya etc. But it seems that the presence of the pest has decreased in some areas in the US resulting in less in less number of West Nile cases.

The top mosquito tracker is detecting some unusual signs this year, with fewer pests than normal showing up in many places while other sites are hot spots.

West Nile activity in the Washington region has been minimal this year, with just one human case reported in Virginia this summer. Last week, Arlington County officials reported their first West Nile-positive mosquitoes of the year. The District and Maryland have had no West Nile activity in 2007, even in mosquitoes.

"We've kind of steadily gone down both in human cases and infections in animals," said Kimberly Mitchell, Maryland's chief of rabies and vector-borne diseases.

This is also due to the effective preventive measures adopted by the Mosquito Control and Wetlands Management teams in different parts of the country. Truck-based spraying to knock out the unusually large pockets of virus-prone bugs was done in places like Hamilton, Lynn, Merrimac, Revere and Winthrop. They raised raising public awareness about prevention and applying larvicide to storm drains and other target areas. Public was enlisted in eradicating breeding grounds. Mosquitoes’ trapper known as resting boxes were also set up in different places to trap them. The long spell of dry summer also helped the situation.

In some parts of the country there has been an increased activity of the mosquitoes but no human case has been reported as yet.

West Nile is spread to people by infected mosquitoes that get the virus by biting infected birds. Symptoms range from mild, flu like discomfort to encephalitis and meningitis. In extreme cases, it can be fatal.

Predicting the risk of bug-borne viruses is tricky in any year, according to disease specialists, because part of the equation depends on precipitation. Some mosquitoes thrive in soggy conditions; others flourish in times of drought. Both Culex pipiens, a primary carrier of West Nile virus, and Culiseta melanura, known for bearing EEE, thrive in drought conditions, specialists said.

The Culex breed in catch basins, which often have stagnant water even during droughts. They also feed on the organic material left behind when wetlands dry up. And Culiseta are known to hang out in fresh-water, woodsy swamps, where their favorite breeding spots are in crevices of uprooted tree stumps that often are exposed during dry spells.

The health authorities have warned the public to protect themselves against the mosquito bites. As soon as a virus is tracked the public in the neighborhood is alerted by Web site postings or news releases.