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On the Trail of the West Nile Virus

Some scientists race to develop vaccines against the scourge while others probe the possible lingering effects of the mosquito-borne infection.

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What they were seeing was an encephalitis epidemic caused by the West Nile virus, an insect-borne, or arboviral, pathogen that was first found in humans decades ago in Africa and reached the United States in 1999. And 2002 turned out to be by far the worst year yet, with the Centers for Disease Control and Prevention (CDC) reporting 4,156 cases of illness and 284 fatalities caused by West Nile virus infection, compared with just 149 cases for the previous three years combined. Illinois led the nation in 2002 with 884 confirmed illnesses and 64 fatalities; some 600 of those cases occurred in CookCounty, which includes Chicago and many suburbs. Dr. William Paul, a deputy commissioner with Chicago’s Department of Public Health, watched the infection break out in the suburbs and then creep into the city, which recorded 227 cases of West Nile disease. “We knew the ingredients were there for a huge arboviral outbreak,” he said. “But I don’t think anybody predicted it would be this big in this part of the country.” Christ Medical Center, which had 56 cases, along with Evanston Northwestern Healthcare, which had 80, turned out to be two of the hottest spots in what would quietly become the largest epidemic of mosquito-borne encephalitis ever recorded in the Western Hemisphere.


Doctors told Yvonne O’Neill that Bennie wasn’t expected to recover. In early September, after Bennie had been hospitalized and essentially mute for three weeks, Yvonne pinned a copy of their wedding picture over his hospital bed. The next day, he opened his eyes, smiled and began talking again. He remained in the hospital another two weeks, and required extensive physical therapy and cognitive reconditioning after his release. He’s home now, but still struggling to regain his normal strength, and not yet able to get back on the golf course. “It’s hard to believe that this was caused by a little mosquito,” Bennie said while standing in his yard. “But all it takes is one, I guess.”


The West Nile virus was first detected in the United States in New York City in September 1999. I remember the autumn night that helicopters began spraying pesticides near our Brooklyn neighborhood. Like many New Yorkers, we tried to figure out how much of a threat this pathogen posed to ourselves, our children, our way of life. We tried to follow the city’s recommendations to use mosquito repellent. We dutifully removed receptacles of standing water in the backyard; it turns out that innocuous children’s toys, such as beach buckets or overturned plastic cars, hold enough water after it rains to breed mosquitoes. We also tried to avoid being outdoors after dusk, when the local arthropod air force was likeliest to bite, although we didn’t always resist the temptation to have dinner in the garden. I had read enough about the West Nile virus to know that the infection rate was quite low, and that the rate of serious neurological illness was extremely small. But I had a more visceral reaction the morning I went to fetch my 1-year-old son from his crib and was horrified to see that mosquitoes had gnawed on his legs. It’s a struggle to balance those reactions, intellectual and emotional, especially as new and disturbing information continues to pour in about a virus that has repeatedly surprised the experts.


By the spring of 2003, the virus had colonized 44 states and the District of Columbia. Last August, a woman in the Los Angeles area was hospitalized with West Nile virus infection, which she apparently acquired there, and California health officials expect the virus to make much more than a cameo appearance this year. The virus’s West Coast arrival was confirmed last fall, when a horse northwest of Seattle developed fever, anorexia and an unsteady gait because of West Nile infection. Researchers aren’t sure exactly how the virus spread across the nation, though migratory birds have likely contributed. The only states that haven’t reported an animal or human case of West Nile virus infection are Alaska, Hawaii, Oregon, Nevada, Utah and Arizona. But Grant (Roy) Campbell, a medical epidemiologist at the CDC’s Division of Vector-Borne Infectious Diseases in Fort Collins, Colorado, predicts that in 2003 “the map is likely to fill out in terms of the Western states.”


Researchers say the virus is astonishingly nimble. In the past year, health officials have documented that West Nile virus can be spread to the recipient of an organ transplant from an infected donor, from a pregnant mother to a fetus, by a blood transfusion from an infected person and possibly through breast milk. The blood-banking industry is working with the CDC, the Food and Drug Administration and the American Red Cross to begin screening the blood supply for West Nile as early as this year.



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