PENNSYLVANIA Several conditions lead to decline in West Nile cases

One reason for the decline is better mosquito control, officials say.
HARRISBURG (AP) -- A year after Pennsylvania experienced a surge in West Nile cases, the number of people infected with the mosquito-borne virus appears to be headed back down.
State agencies have received reports of only four Pennsylvanians contracting the virus so far this year, compared with 63 at this time a year ago.
Officials say cooler weather, more rain, a more careful public and better mosquito control efforts are probably responsible for the decline.
"The fact that we've had a lot of rain makes you think mosquitoes would be breeding more," Department of Health spokeswoman Jessica Seiders told The Morning Call of Allentown. "But we think the continual rainfall actually helped flush out stagnant water."
Frequent rains can flush out pools of standing water that serve as breeding grounds for mosquitos, which are also less active in the cool than in the heat.
The state also has used chemical sprays to kill the bugs in areas where they were a problem last year.
Last year, Pennsylvania had about 240 human cases of the West Nile virus. Eight people died.
Spread of the disease
West Nile is carried by birds and livestock and can be transmitted to people by mosquitos. Most people who get the illness recover, but it can be fatal for people who are frail or have compromised immune systems.
A longtime fixture in Africa, Europe and Asia, the virus first appeared in the United States in New York in 1999.
It has since spread throughout the country. Some states, such as Arizona and California, have experienced more severe outbreaks this year than in years past, authorities said.
Cases have been reported this year in Lancaster, Bucks, York and Erie counties. None of the cases was fatal.
It's unclear whether this year's numbers will remain low. Mosquito season generally ends with the first frost, but last year the state continued to receive reports of cases through December.