Centers for Disease Control and Prevention/Reuters - West Nile virus, spread by mosquitoes, can lead to inflammation of the brain, damaging its speech, language and thinking centers.
Last month, Leis asked a Food and Drug Administration scientist who studies the genetics of the virus whether a new, more virulent strain was circulating.
“You are absolutely right . . . that new genetic variants of WNV might have appeared this year,” the scientist replied in an Oct. 23 e-mail obtained by The Washington Post. The scientist continued that “it is not easy to correlate” the new mutations with any specific type of brain damage.
Eight years ago, a West Nile-infected mosquito bit him. Today he’s still feeling the effects.
Since the virus reached the U.S. in 1999, it has spread widely. Texas has been hardest hit this year.
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Thirty minutes after Leis received the message, another e-mail from the same scientist arrived. It said the previous message had been “recalled.”
When contacted by phone, the FDA scientist, who works at the agency’s Center for Biologics Evaluation and Research, declined to discuss the messages, saying that his superiors had instructed him not to talk to reporters.
In an e-mail, FDA spokeswoman Heidi Rebello said that the agency is studying the genetics of West Nile viruses collected from 270 blood donors this year but that “it is premature for us to draw any conclusions about new genetic variants . . . or of any possible association of new genetic variants with increased virulence.”
West Nile virus, made of error-prone RNA instead of the hardier DNA found in human cells, can evolve rapidly. In 2002, a new strain appeared that quickly churns out copies of itself inside mosquitoes. This fast-replicating version swiftly replaced the earlier dominant variety.
In 2003, another genetic variant, now dubbed the Southwestern strain, appeared in New Mexico and Arizona.
The West Nile virus, first described in Uganda in 1937, arrived in New York City in 1999, killing eight in the city. Infected birds transmit the virus to mosquitoes, which then infect people, who cannot infect one another. By 2003, the virus had crossed the country.
So far this year, health authorities have reported more than 5,000 cases of West Nile illness and 228 deaths in 48 states, with Texas, California, Illinois and Michigan having the most cases. The CDC has classified about half of the illnesses as “neuroinvasive” — meaning the virus has gotten into the spinal cord or brain, causing encephalitis or other brain ailments. That’s the most dangerous type of illness caused by West Nile virus. In the other cases, patients come down with fevers or other flulike symptoms.
As of Nov. 6, there had been eight cases reported in the District this year, 45 in Maryland and 25 in Virginia, with new cases expected to plummet with the temperature.
In Texas, the state hit hardest by the epidemic, virologist Alan Barrett said samples of the virus taken from mosquitoes and birds in the Houston area show signs of genetic changes.
“This year’s virus looks more like the virus from 2002 and 2003” than the virus seen more recently, said Barrett, of the University of Texas Medical Branch in Galveston. Given that the Houston-Galveston area is a major flyway for birds, Barrett speculated that a different virus arrived in the area this year.
But it is too early to say whether this possible new strain is more virulent than those seen in years past, Barrett said. It will also take a while to study the genetics of viruses from other parts of the country. His laboratory, one of the few studying West Nile genetics, is backlogged with samples. “We’re overwhelmed,” he said.
North Texas suffered the worst of this year’s epidemic, with 388 cases and 18 deaths in Dallas County alone. Authorities declared a public health emergency and sprayed insecticide from airplanes and helicopters for the first time since 1966.
The spraying worked, said Christopher Perkins, the county health department’s medical director. “We’re getting one or two new cases a week,” down from 20 to 30 in July and August, he said.
Neurologists in Dallas also witnessed devastating encephalitis this year, but in different areas of the brain than Leis described. Steven Vernino, a neurologist at the University of Texas Southwestern Medical Center in Dallas, said he saw damage to the lower brain stem in several patients but not to the higher language and thinking centers.
Barrett will look at the genetics of viruses from North Texas as soon he gets samples, which he expects any day. “Everybody wants to know what’s going on in Dallas,” he said.
Leis said it’s crucial to know whether the virus is mutating. “Otherwise,” he said, “we might be unprepared to deal with it in the future.”
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