Once Ominous, West Nile Wanes As Area Threat

By Raymond McCaffrey
Washington Post Staff Writer
Monday, July 30, 2007

Five years ago, West Nile virus seemed like a major public health threat to the Washington region, with nearly 100 human cases and 11 deaths. But the disease has receded rapidly here since then, even as it remains a problem elsewhere in the United States.

West Nile activity in the Washington region has been minimal this year, with just one human case reported in Virginia this summer. Last week, Arlington County officials reported their first West Nile-positive mosquitoes of the year. The District and Maryland have had no West Nile activity in 2007, even in mosquitoes.

"We've kind of steadily gone down both in human cases and infections in animals," said Kimberly Mitchell, Maryland's chief of rabies and vector-borne diseases.

West Nile is spread to people by infected mosquitoes that get the virus by biting infected birds. Symptoms range from mild, flulike discomfort to encephalitis and meningitis. In extreme cases, it can be fatal.

The number of West Nile-related human deaths in the region has dropped sharply in recent years after peaking in 2002, the year the virus spread from population centers in the Baltimore and Washington suburbs to Maryland's Eastern Shore and other rural areas.

Health experts credit the region's relatively low toll since then to a well-coordinated response from local agencies that included raising public awareness about prevention and applying larvicide to storm drains and other target areas.

As soon as the first trace of the virus arrived in the area, they say, health officials assiduously tracked its progress: first in crows, then mosquitoes and eventually in horses and humans. Those results were passed on to the public by Web site postings or news releases.

The effort spread to county and city health agencies, which alerted residents to West Nile cases in their neighborhoods and enlisted their help in eradicating mosquito breeding grounds -- whether by emptying a water basin on their property or reporting a neighbor or business that wasn't doing so.

Agencies also warned residents to protect themselves against mosquitoes with insect repellent and proper clothing.

Another factor in the decline this year is the dryness, which has kept down the mosquito population.

"Always with less rain, you have less standing water, which translates into less mosquito-breeding habitat," said Peggy Keller, chief of the District health department's Bureau of Community Hygiene. "So certainly it helps that there is less rain this year."

By contrast, South Dakota has reported 28 people infected with the virus, the most in the nation, followed closely by California, with 27 human cases, according to the federal Centers for Disease Control and Prevention's Web site. Overall, 122 human cases, with three deaths, have been reported nationally, according to the CDC.

The majority of West Nile patients do not become severely sick, experts say, and the population at risk for getting ill from the infection is small, mainly the elderly. Many who contract the virus are unaware of it, and reported cases typically involve people who contract meningitis or encephalitis.

Regional health officials warn that it is too soon to tell whether West Nile activity will remain relatively light or become more serious as the summer progresses.

"We know that the mosquitoes are there," said Aftab Hussain, a supervisor at the Arlington County Environmental Health Bureau. "We know that the virus is endemic in the area. With human cases, we've been lucky."

Maryland reported the only West Nile fatality last year, after the region went without a single human death tied to the virus in 2005, and one West Nile-related human death in Virginia in 2004.

In 2003, Maryland had eight West Nile-related human deaths, while Virginia had one and the District none. In 2002, West Nile virus was tied to 11 deaths in the region: seven in Maryland, and two each in Virginia and the District.

The overall number of West Nile cases involving people in the region has dropped. Maryland reached its peak in 2003 with 73 cases. Virginia had its high with 29 cases in 2002, and the District peaked with 34 human cases that same year. Last year, there were 18 human cases in the region, according to the CDC. West Nile in horses and mosquitoes also has dropped significantly over the past couple of years.

But the virus, first detected in the United States in 1999, has continued to spread across the country. In 2002, there were 284 human deaths tied to West Nile in the nation, the most since the outbreak. The number of human cases nationally peaked in 2003 at 9,862, more than double the 2002 total of 4,156. Last year, there were 4,269 West Nile human cases, with 177 related deaths, according to the CDC Web site.

Officials in the Washington region say they plan to continue the public education campaign. They ask residents to continue to take the traditional precautions: Wear insect repellent when outside and remove standing water from around homes.

Although "the virus seems to be stabilized," Keller said, "it is endemic in our area."

"Our mantra is always protection and prevention," she said, "because we know the virus is here."