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Reports of West Nile virus, expected to peak during Labor Day weekend, have nearly tripled compared to this time last year.
But that may not mean the country is suffering from a surge in the disease, health officials say. The increase could stem from wider testing for the virus, not a heightened threat from the mosquitoes that carry it.
``The more you look, the more you'll find,'' said Dr. Lyle Petersen of the Centers for Disease Control and Prevention's insect-borne disease lab in Colorado.
As of the end of last week, 34 states had reported 1,602 cases of West Nile, according to the CDC. That is up from 555 cases in 26 states at the same point last year. In both years, there had been 28 deaths reported as of Aug. 29.
But last year, about three-fourths of patients had the life-threatening complications of encephalitis or meningitis. This year, less than half do.
``If you just look at serious disease, we're closer to the same (as last year),'' Petersen said.
More aware, diagnosed
Increased awareness of West Nile and the availability of new tests have resulted in the detection of more mild cases, he said. That is especially true in Colorado - the source of nearly half of this year's cases - where almost 80 percent of patients have the less-severe form of the disease.
People with mild cases usually have fever, fatigue, nausea, headache and a rash. More serious symptoms include a stiff neck, seizures and a sensitivity to light.
But the vast majority of people who get the virus never become ill. The CDC estimates that about half a million Americans were infected last summer, when the official count as tallied at year's end was 4,156 cases and 284 deaths. Another half a million are expected to be affected this year.
Last summer's hot spots as of Labor Day were Louisiana and Mississippi. This year, they have been Colorado, South Dakota and Nebraska, and the first human cases have been reported in Arizona and New Mexico.
Climate boosts insects
A wet spring and a dry, hot summer in the Midwest and Rocky Mountains could be boosting mosquito populations in those regions, Petersen said. Also, people in states with several years of West Nile activity may be more mindful of wearing mosquito repellent and removing stagnant pools of water.
But it's too early to sum up or fully understand this year's trends, said Katherine Bryant, an epidemiologist with the Georgia Division of Public Health. More than half of last year's cases nationwide came in September and October.
Georgia has had three West Nile cases this year, compared with six, including two deaths, at this point last year. A study looking for mild cases at Grady Memorial Hospital in Atlanta hasn't found any in more than 100 patients with fevers who have been tested.
That picture could soon change. The Southern house mosquito, the state's main West Nile culprit, was all but absent in June and July, when heavy rains washed away the dirty ponds the species favors. In recent weeks, the critters have returned with a vengeance.
``It could be that the heavy rains only delayed the onset of the season this year in Georgia,'' Bryant said.
Meanwhile, the science of combatting West Nile continues to progress, with human trials of two vaccines possibly beginning soon.
One study by Acambis - a British company with a plant near Boston - will start by October, spokeswoman Lyndsay Wright said. Another, by researchers at the National Institute of Allergy and Infectious Diseases, could be launched by December, said Dr. James Meegan, a virologist with the agency.
At least two other experimental human vaccines are in lab or animal studies, and another vaccine in development for birds could be used to protect endangered species.
A West Nile treatment, using antibodies from people who have had the virus, could be offered to patients in a study by next month.
A test that has been screening the country's blood supply for West Nile for six weeks has detected 163 donors with the virus, including 11 who have become cases of the disease.
Repellent key weapon
While technological advances may have a great impact on the epidemic eventually, the simple measure of wearing mosquito repellent can have a profound effect today, said Petersen of the CDC.
He should know. One evening in mid-July, he walked to the mailbox outside of his Fort Collins home, figuring the quick jaunt didn't require protection. But he ended up talking to a neighbor for a while. Somewhere along the way, he suffered a mosquito bite.
Three days later, he was knocked flat in bed by the virus he has studied more than almost any other person.
Even a mild case is a pretty miserable thing to have,'' Petersen said.You just can't be too vigilant.''
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c.2003 Cox News Service
