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Surging Threat of West Nile Virus Can be Controlled, say Experts - 2003-08-13

The U.S. Centers for Disease Control and Prevention reported in early August that the number of West Nile Virus cases tripled in a week. The virus has infected more than 4,000 people, and killed nearly 300 since it first appeared in the United States four years ago. Public health officials say West Nile Virus and other mosquito-borne diseases can be largely controlled if people take simple steps, such as eliminating sources of stagnant water.

Joe Humkey's insecticide sprayer is a powerful machine. It has to be. Mr. Humkey, a Mosquito Control Inspector for Miami Dade County, is hunting for mosquito larvae, and lately, his job has a sense of added urgency.

The reason: West Nile Virus, a deadly mosquito-borne disease that has killed nearly 300 people since it was first detected in the United States in 1999.

Mr. Humkey is a constant presence in the West Miami suburbs that crowd the edges of the Everglades swamp, an area infested with mosquitoes. "They look sort of like a little worm wiggling," explained Mr. Humkey as he hunts for mosquito larvae. "There are other things that look similar, but you can tell the mosquito larvae. These here are swimming, like in a figure eight. That is aedis aegypti, which is the yellow fever mosquito. Fortunately, we do not have a problem with yellow fever, but they do bite and they are very annoying. These are ones that go after your ankles and your elbows. They are one of the biggest pest mosquitoes around."

So far, Joe Humkey has not encountered any mosquito larvae of the type believed to cause West Nile Virus. However, alarms were raised recently when the virus was detected in the carcasses of two birds found in the southern part of Miami-Dade county.

The virus mainly affects birds, and researchers believe it has been spread by migrating birds. Other animals, such as horses and even alligators have been infected by the virus, too. It is believed it is passed to humans from bites by mosquitoes carrying the virus they picked up from infected birds.

The virus gets its name from the West Nile District of Uganda, where it was first reported in the 1930s. With increased world travel, West Nile is another of a number of diseases that have spread around the world in recent years, causing alarm among public health officials.

Most of those who do get sick experience only flu-like symptoms. Experts say less than one percent of infected people will develop the potentially deadly West Nile encephalitis or meningitis. The elderly are most at risk.

But so far, Florida has been spared any West Nile outbreak, says entomologist Marlon Nelms, who runs the Miami-Dade Mosquito Control Division. "The mosquito that we believe transmits it is called the Aeschylus mosquito," said Mr. Nelms. "We do not have large numbers of these mosquitoes, but we do have enough to transmit the disease. It is a brown mosquito, relatively innocuous, and actually prefers to feed on birds, more so than it does on people. We think this is one of the reasons why there are not very many people infected with it."

Even so, Mr. Nelms said, people can take steps to avoid being bitten. "You can either do this by staying away from them, which means staying indoors, although at some point you have to go out of doors. If you do [go outdoors], wear repellent, wear long-sleeved clothes, and inspect your property on a routine basis for anything that can hold water, because all it takes to have a mosquito problem is to have standing water for about a week, and you will very likely have mosquitoes."

Mary Jo Trepka, who directs Miami-Dade County's Office of Epidemiology and Disease Control, says good communication among health care professionals is the key to fighting a public health threat like the West Nile Virus outbreak, or the anthrax scare that followed the 2001 September 11th terrorist attacks.

"I think the best way to deal with potentially new illnesses is to have a very good surveillance system," stressed Ms. Trepka. "That is, to have a very good communication between healthcare providers and public health agencies. So if a health care provider sees something unusual, the person knows whom to call. That is crucial. And it is also crucial that our ongoing system for regular disease reporting is strong. I think a good example of that was our anthrax attack. The first case was in Florida, and it was identified by an infectious disease physician in Florida, who called the head of the Palm Beach County Health Department, and said, 'look, I think I have something going on here.' That led to the rapid identification and response to that outbreak."

Florida public health officials also say the public can and does help. They are advised to get rid of standing sources of water where mosquitoes breed. And they are encouraged to participate in programs like the dead bird surveillance system, which asks community residents to report any bird carcasses they see lying around.

Public health officials say that system has helped them catch early cases of West Nile Virus, before they spread to humans and create a public health emergency.

This is part of VOA's series of reports on World Health