West Nile virus threat diminished by heavy rains in 2003

INDIANAPOLIS -- Standing water is a mosquito's friend and flood water an enemy -- a reality that helped Indiana avoid a threatened increase in West Nile virus cases last year.\nAs for this year, state health officials Tuesday said it was too early to forecast either a second consecutive year of conditions unfavorable to the virus or a repeat of 2002, when Indiana ranked among the top five states in human West Nile cases.\nBut officials said last year's data made it clear heavy rains and floods that caused property damage across much of Indiana carried a silver lining. The water flushed away mosquito eggs in septic ponds, roadside catch basins and other breeding sites.\nIn 2002, the year after the virus emerged in animals in Indiana, the state recorded 293 confirmed human cases of West Nile and 11 deaths after summer drought and hotter-than-usual temperatures accelerated young mosquitoes' development cycle.\nAccording to historic patterns among East Coast states, where the virus is more established, Indiana should have seen an increase last year. But there were just 47 cases and four deaths, thanks in part to the flooding from heavy rainfall, including the nine inches that fell on some Indiana counties over Labor Day weekend.\n"We saw the best of situations and the worst of situations the last two years," Michael Sinsko, a state Department of Health entomologist, said in a presentation of research findings.\nThis year's mosquitoes are too early in their developmental cycles to serve as a predictor of the 2004 season, he said.\nWhile Indiana experienced a decline in West Nile cases among humans last year, the virus continued spreading nationally, with nearly 10,000 cases confirmed -- more than double the previous year -- in 45 states.\nThe initial U.S. outbreak in New York in 1999 followed a three-month drought and a three-week heat wave. Researchers reported last fall that the worst outbreaks seem to follow summer droughts preceded by mild winters, a pattern researchers are studying as a possible way to predict where the virus might hit hardest.\nIn Indiana last year, scientists got confirmation that mosquito breeding areas with standing water "will wash out very efficiently during heavy rainstorms," Sinsko said. "If there's not much rain, they will hold water for a much longer time and produce more mosquitoes."\nHumans can become infected by the bite of a mosquito that has been infected after feeding on infected birds.\nThe virus, which can present severe complications that include brain swelling, affects mostly the young, elderly and those with weaker immune systems. Less severe and more common symptoms include fever, headaches, muscle aches and joint pain.\nThere is no treatment or human vaccine for the West Nile virus, but it is preventable by avoiding bites from infected mosquitoes. Public health officials urge people to take precautions including emptying standing water from containers or clogged gutters that could become breeding sites for mosquitoes.