New bugs of summer bring exotic infections

By Anita Manning, USA TODAY

The bugs of summer are on their way back, but this time with a difference. Their bites and stings are capable of delivering more menace than ever before.

Here's the buzz so far:

	Researchers have already determined that last summer's most unwelcome immigrant, the West Nile Virus, survived the cold New York winter. An outbreak last year killed seven people in the Big Apple.
	Texas is on the lookout for mosquito-borne dengue fever. An outbreak last year caused 60 illnesses and the death of a little girl.
	In New England, the upper Midwest and Pacific West Coast, residents are checking for ticks that carry Lyme disease and two newer infections, babesiosis and ehrlichiosis. They all have similar symptoms, and if left untreated might lead to persistent health problems. Lyme disease alone has been reported in 48 states, and the ticks that carry it are expanding their presence in parts of the country.

The increasing threats from summer pests have public health officials undertaking preparations with a new sense of urgency.

"We live in an era of emerging infections," says Steve Ostroff of the National Center for Infectious Diseases, part of the Centers for Disease Control and Prevention in Atlanta (CDC).

"Our task is to assure that the public health system is as well prepared as possible to deal with them."

In states up and down the East Coast, public health teams are mobilizing. From Massachusetts to Florida, mosquito control specialists are out looking for larvae in storm drains, construction sites, rain barrels or anywhere standing water makes for a nice breeding spot. They're dumping larvicides and stocking water sources with mosquitofish, a kind of living pesticide, to reduce the mosquito population. They're taking samples to test for the presence of West Nile Virus, a form of encephalitis never seen in the Western Hemisphere until last year.

On the tick front, the news is not much better. Nobody is counting how many cases of babesiosis or ehrlichiosis occur each year, but they're believed to be far fewer than the 15,000 cases of Lyme disease reported annually. Lyme disease is the most common tick-borne illness and "the trend of incidence is still upward," says David Dennis of the CDC's Division of Vector-Borne Infectious Diseases . "That's a concern."

Despite much greater awareness, only 15%-20% of cases are reported, he says. That could be because most are caught and treated early on, while it's still a mild illness, and health-care workers don't feel the need to "go through the process of reporting, which requires paperwork.

"This is a disease that if not detected early or treated appropriately can go on to serious complications," he says. "We've had a pretty big effort on Lyme disease, a lot of research, a lot of surveillance, and yet the incidence of disease continues to climb."

That's probably due to "increasing density of ticks wherever (the infection) has become established," Dennis says. "We do not have good means to control or eradicate ticks."

Research is focusing on preventing the animals that carry deer ticks -- mainly deer and mice -- from becoming infested, and on developing public education strategies to arm residents of endemic areas with knowledge on how to protect themselves.

Public education is a large part, too, of West Nile Virus prevention in New York, says Sandra Mullin of the city's Department of Health.

Residents asked to help

The nation's most-populous city had no mosquito control program at all when the outbreak emerged and is scrambling to get up to speed. Using $7 million in state and federal funds, health officials are starting surveillance and testing of mosquitoes and birds. This month, they are placing throughout the city crates of sentinel chickens whose blood will be tested over the summer.

Residents are being asked to eliminate stagnant water from their yards, keep screens repaired, clear gutters and other spots where untreated water can accumulate. " New Yorkers are going to have to adapt to a new way of life for the time being, while this threat looms over the city," Mullin says.

First discovered in Uganda in 1937, the virus in its American debut may have infected thousands in the city. No one knows for sure. "In New York last year, we detected 62 cases of serious clinical disease," says Roger Nasci of the CDC.

But blood tests in Queens, where most of the cases occurred, indicated "many more were infected but most did not produce symptoms." Those most seriously affected were elderly people, he says.

The virus also killed "probably thousands of birds," mostly crows, says Robert McLean of the National Wildlife Health Center in Madison, Wisc. He has tested blood samples from hundreds of birds sent to the center from 10 states.

Last month, a dead hawk infected with West Nile Virus was found in New York, and tests on hibernating Culex pipiens, or Northern house mosquitoes, confirmed that the virus survived the winter.

West Nile Virus is the newest, but not the only, mosquito-borne virus that circulates in the USA. Other forms of encephalitis, including St. Louis, Eastern Equine, Western Equine and La Crosse occur almost every year, though in small numbers.

Last year, Texas suffered the worst outbreak of dengue fever in about 20 years. The tropical menace flew across the border from Mexico. Health officials say they're beefing up mosquito control and surveillance and initiating cross-border talks in efforts to get mobilized against "Dengue 2000."

Dengue fever and its more deadly variant, Dengue Hemorrhagic Fever, are carried by the Aedes aegypti mosquito found in the southern United States and Central and South America. Massive mosquito-eradication programs kept it under control, but after a half-century hiatus in the Western Hemisphere, it has come roaring back, causing outbreaks from Mexico to Brazil.

Tropical dangers

"Most of the worst mosquito-borne diseases are tropical -- malaria, filariasis, dengue, yellow fever," says entomologist Wayne J. Crans of Rutgers University. But that doesn't mean Americans are immune.

Public health experts have been warning for years that as global commerce and travel have increased and funding for mosquito control programs has declined, it was only a matter of time before new bugs and new health menaces emerged in the USA.

The fact that West Nile Virus made it through the winter doesn't necessarily mean there will be another outbreak of disease. The virus must be passed back and forth between infected mosquitoes and birds many times to build a large enough population of infected mosquitoes to pose a serious threat to humans, the CDC's Nasci says.

"It's a big numbers game, a big probability game," Nasci says. "It's difficult to predict when humans are at risk." By reducing the mosquito population now, before the bugs reach adulthood, health officials hope to avoid having to spray pesticides later in the year.

To push these efforts forward, the CDC has awarded $2.7 million to 18 states from Massachusetts to Texas, and the District of Columbia, for development of better surveillance and response programs that focus on West Nile Virus.

States are forking over their own money for the effort, too. Pennsylvania will spend nearly $10 million on an intensive effort to track and combat the virus.

Because the odds of humans being infected rise with the number of infected mosquitoes, says Crans, if anyone gets sick with West Nile Virus, "it won't be until late August, and shame on us if there are enough mosquitoes to do that."

In New Jersey, Crans says, "We didn't have any cases (in 1999) when we didn't know it was coming," thanks to ongoing mosquito control programs throughout the state. "I don't think there's any chance there will be cases this year, when everybody's got their antennae out and are looking for it."

Still, some health experts fear there could be human cases this year, in part because New York City has to build its mosquito-control program from scratch.

"For them to go from nothing to something that is going to have an impact on West Nile Virus this summer, that would be a challenge for the best existing mosquito control system," says entomologist Durland Fish of Yale University School of Medicine.

With the exception of a few states, including Connecticut and New Jersey, which have had ongoing mosquito control programs, he says, "we had better mosquito virus surveillance 20 years ago than we do now. "

That is changing now in response to the new flying threats, says Julie Rawlings of the Texas Department of Health. In Texas, a test to detect the West Nile Virus will be added to the battery of mosquito-borne diseases for which state labs already test.

Wary out West

Even California is watching for West Nile Virus, says entomologist Vicki Kramer, chief of the state health department's Vector-Borne Disease Section. "We conduct ongoing surveillance for Western Equine encephalitis and St. Louis encephalitis," she says. "Anything that turns up positive for St. Louis will also be tested for West Nile."

There's no hint that the virus has moved West, she says, but "our conditions here are just as suitable as New York. We have the appropriate vector (mosquito), the appropriate climate. People travel. Birds can fly. I'm not saying it's likely, but it's important to expand the surveillance network."