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West nile threat lower this year { August 23 2003 } Original Source Link: (May no longer be active)
http://www.tcpalm.com/tcp/the_news_local_news/article/0,1651,TCP_1028_2203659,00.htmlhttp://www.tcpalm.com/tcp/the_news_local_news/article/0,1651,TCP_1028_2203659,00.html
West Nile threat lower this year, scientists say
By James Kirley staff writer
August 23, 2003
VERO BEACH — Florida will not be stricken hard this year with mosquito-borne West Nile virus, said several scientists, who nonetheless warned people to avoid becoming an isolated case.
"I don't think there is anybody in Florida who thinks we will see what we would call the 'big event' of 1,000 people who require medical attention due to West Nile," said Walter Tabachnick, director of the University of Florida's Medical Entomology Laboratory in Vero Beach.
"Nevertheless, there are going to be cases and you don't want to play this lottery. Put on (mosquito repellent)."
"We will see that big year (someday)," predicted Jon Day, professor of medical entomology at the laboratory, which is part of UF's Institute of Food and Agricultural Sciences.
How to forecast a coming epidemic was among the topics Friday morning during breakfast at a Vero Beach restaurant.
Tabachnick, Day and Roxanne Rutledge, the lab's extension medical entomologist, met informally and compared notes with Alan Curtis, Doug Carlson and Don Shroyer, scientists from the Indian River Mosquito Control District.
They reported a lot of mosquitoes were buzzing the Treasure Coast — Day recently baited a trap near 27th Avenue at the St. Lucie-Indian River County line with a live chicken and caught between 12,000 and 14,000 mosquitoes in one night.
Such samples are part of attempts to gauge how many mosquitoes are infected with West Nile or other viruses and can sicken humans.
Those numbers currently appear low on the Treasure Coast.
"It looks like the focus of (West Nile) transmission is to the south, in Lee and Collier counties," Day said.
But the scientists warned that danger can increase two to three days after a heavy rain. That is when older mosquitoes, already infected with virus, lay their eggs and go hunting for blood to produce more eggs.
There are about 75 different mosquito species on the Treasure Coast and one, Culex nigripalpus, is suspected of transmitting illness to humans.
Day said there have been 13 human cases of West Nile virus reported in Florida so far this summer, four of which were found in blood samples of people who had not become ill enough to seek medical treatment.
That number increased to 14 by Friday afternoon, with another human case reported in Broward County, Shroyer said.
Fever and flu-like symptoms are the most common result of exposure to West Nile, which has a mortality rate of about 5 percent. Illness can strike all ages, but death or permanent nerve damage happens more frequently in people 50 years and older.
Dangerous to gamble
Tabachnick's references to West Nile as a lottery are deliberate. He said that, for reasons still unclear, not all mosquitoes infected with West Nile virus are capable of transmitting it. Scientists also know that only about one out of 100 people infected with the virus will become physically ill.
"So, if you've got 100,000 people in a stadium and each one gets bitten once, and one in 1,000 mosquitoes are capable of transmitting the virus, 100 people that night are infected with West Nile," Tabachnick said. "That will translate into one case."
Even with these long odds it's wise to wear repellent, Tabachnick said, because of the severe damage West Nile can inflict.
"It's not pretty," he said.
There have been no human cases reported so far this year in Indian River, Martin or St. Lucie counties.
Jim David, director of St. Lucie County mosquito control, said his agency recently sprayed from the air to kill mosquitoes in a 20-mile long by two-mile wide swath between west county citrus groves and homes to the east.
"In the transitional areas between agriculture and residential neighborhoods, we got a 90 percent reduction (in mosquitoes)," David said in a phone interview Friday. "We still have a lot of them near the North Fork of the St. Lucie River. That's an environmentally sensitive area and we can't spray there unless it's a medical emergency."
Mosquito-borne diseases have long been a part of natural Florida. Malaria was a problem through the early decades of the 20th century and three cases recently were reported in Palm Beach County.
But malaria today is an isolated disease, Curtis said, almost always brought into Florida by somebody traveling aboard. Unlike West Nile and other viral illnesses, malaria is a protozoan disease that can be spread from infected to uninfected people by mosquito bites. Curtis said it can be controlled by isolating outbreaks.
West Nile, which arrived in Florida in 2001, is less well understood. It appears similar to St. Louis encephalitis, which last reached epidemic proportions in Florida during the summer and fall of 1990.
Florida's last evidence of St. Louis encephalitis virus was found in Lee County in 2001, the same year West Nile arrived in the state.
jim.kirley@scripps.com
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