Early West Nile case may bode ill for western U.S.
"Since West Nile virus was [first] detected in 1999, we've seen a lengthening period of transmission," said Ned Hayes, M.D, of the Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases in Fort Collins, Colo.
As the virus has spread south and west across the United States, new "ecological dynamics" have influenced transmission patterns, he explained.
A wetter than normal winter in California and the Southwest may suit mosquitoes well, meaning physicians will need to be especially alert to possible cases of the now reportable disease.
The Los Angeles County Department of Health Services announced an infection in an older man in east Los Angeles County on Feb. 8.
As of mid-February, state and federal health officials had not completed confirmatory tests on the case.
Symptoms of the infection include fever, headache, fatigue, body aches, skin rash, and swollen lymph nodes.
More serious manifestations of West Nile encephalitis or meningitis also include neck stiffness, stupor, disorientation, coma, tremors, convulsions, and muscle weakness, as well as a paralysis that can resemble polio.
"It doesn't matter whether we've had one case or five: if you see encephalitis or meningitis, you look for West Nile virus," said Laurene Mascola, M.D., chief of the acute communicable disease control unit of Los Angeles County.
The first bird carrying the virus was found in mid-January, whereas no bird evidence was confirmed in California until the end of March in 2004. Twelve birds in eight counties had been found to have the virus by mid-February.
Birds are a key player in the transmission cycle of West Nile virus and are carefully tracked, although mosquitoes are the direct vectors infecting humans.
California and the Southwest, where the disease struck hardest in 2004, have warmer climates than the northeastern states, where the virus first took hold in the United States. Mosquito vectors also differ, with Culex pipiens most common in the Northeast and C. tarsalis and C. quinquefasciatus more often the culprits in the West.
C. tarsalis was a common vector in Colorado, where West Nile virus infected 3,000 people in 2003, killing 63.
"It's a very efficient vector. It avidly bites humans and also bites birds, and it seems to transmit the virus very well."
Dr. Hayes urged physicians to test for West Nile virus and report any cases to their state health departments, which, in turn, notify the CDC.
West Nile virus infected 2,470 people in 40 states in 2004, resulting in 88 deaths.
BY BETSY BATES
Los Angeles Bureau