Clues, she went on, may be found in a 1983 study by Soviet scientists, who deliberately infected rhesus monkeys with several different strains of West Nile virus from Uganda, the Soviet Union and India. In many animals, viral infection persisted for nearly six months in the brain. Whether the infected animals developed encephalitis, or merely fevers, or no evident disease at all, autopsies found that the animal brains had undergone an “inflammatory degenerative process.” The findings are “really quite disconcerting,” said psychiatrist Mady Hornig of ColumbiaUniversity. She noted that the limbic region of the brains in these animals, which is associated with emotion and memory in humans, showed extensive damage, including atrophy and scarring. The implication is that people with West Nile infection who show no outward signs of illness could still harbor lingering brain infections that might ultimately produce neurodegenerative disease, an outcome previously reported with Japanese encephalitis, according to Robert Tesh, a virologist and epidemiologist at the University of Texas Medical Branch at Galveston. The number of people suffering from the long-term neurological effects of West Nile infection could be substantially larger than has been assumed. “We haven’t seen that yet in humans,” said Tesh, who has documented a similarly chronic, persistent West Nile brain infection in hamsters, “but it’s a possibility, and it should be studied.”
To be sure, medical researchers point out that the inflammation seen in animals could be medically irrelevant, like a scar that looks bad but doesn’t impair function at all. But researchers are only beginning to study the possible longterm health effects of viral infection. James Sejvar, a CDC physician, has studied 16 people in Louisiana infected by the West Nile virus. The most severely affected were three who developed a polio-like form of paralysis and had not improved after eight months. “It’s likely to be a persistent syndrome, so that’s kind of worrisome,” said Sejvar, who also said that some of the patients with meningitis and milder forms of encephalitis felt that they’d returned to normal after four months.
At a conference on West Nile virus sponsored by the CDC this past February in New Orleans, McNamara, who has a history of describing aspects of West Nile that people don’t necessarily want to hear, mentioned the long-term neurological damage she’d seen in infected birds that had never been obviously sick. “The room got very silent,” she recalled. As one health official later put it, “People are scared enough already.”
As the 2003 West Nile season draws near and I look out over all the water-friendly nooks and crannies in our backyard garden, each a potential incubator of mosquitoes, I realize that we know much more about West Nile now than in the fall of 1999, when the pesticide-spraying helicopters first flew overhead. I’m still reasonably persuaded that West Nile viral disease represents minimal risk to my family, but that risk is not totally in focus, and throughout the virus’s short sojourn in North America, birds and other animals have repeatedly tried to tell us something about the disease, and we haven’t always been particularly good listeners. While the scientists sort out the messages from the rhinos and monkeys and cranes, I’m going to be listening for the buzz of mosquitoes, and keep out of the line of fire.