West Nile Virus Infection Cases Reach Highest Level Since '99

Cases of West Nile virus (WNV) infection are being seen in the largest numbers since the disease first was detected in the United States in 1999, according to an Aug. 14 update from the CDC.

So far this year, 43 states have reported WNV infections in people, birds or mosquitoes, the agency notes.

"A total of 693 cases of West Nile virus disease in people, including 26 deaths, have been reported," says the CDC. "Of these, 406 (59 percent) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 287 (41 percent) were classified as non-neuroinvasive disease."

It's worth noting that not only is that case total the highest reported to the CDC since 1999, 80 percent of those cases come from only six states: Texas, Mississippi, Louisiana, Oklahoma, South Dakota and California. Moreover, almost half of all cases -- including nine deaths -- were reported from Texas, prompting one judge to declare a state of emergency in Dallas. In response, the state recently began spraying insecticide from crop-dusting planes in certain areas to kill WNV-infected mosquitoes.

Because the signs and symptoms of WNV infection are similar to those of other viral infections, physical examination may not yield any specific findings. However, says the CDC, as many as half of patients with the infection may have a rash.

The most efficient diagnostic method is detection of IgM antibody to WNV in serum collected within eight to 14 days of illness onset or cerebrospinal fluid collected within eight days of illness onset. One caveat, however, is that serological tests for WNV cross-react with other closely related flaviviruses (e.g., Japanese encephalitis, St. Louis encephalitis, dengue).

CT is not useful in the diagnosis of severe WNV infection but can help exclude other etiologies of acute meningoencephalitis. Brain MRI is often normal but will sometimes display leptomeningeal enhancement or parenchymal signal changes. The CDC website offers more information about diagnostic testing, including instructions for submitting specimens for lab analysis.

Generally, mild WNV infections have good patient outcomes, but severe disease cases (i.e., West Nile encephalitis or meningitis) can be fatal. Roughly one in 150 people infected with WNV develop serious illness, with potential symptoms, including

According to the CDC, these symptoms may last several weeks, and neurological effects may be permanent.

Unfortunately, no specific treatment is available for WNV infection. In severe cases, management consists of supportive care that often involves hospitalization, intravenous fluids, respiratory support and prevention of secondary infections.

Although most patients with milder symptoms of WNV infection can be reassured that they do not need medical attention -- many, in fact never know they are infected -- pregnant women and nursing mothers are encouraged to talk with their physicians if they develop symptoms that could indicate WNV infection. Adults older than 50 also are more likely to develop serious symptoms if infected.

Mona Bomgaars, M.D., M.P.H., of Honolulu, past chair of the AAFP's Disaster Preparedness Member Advisory Panel, said that avoiding mosquitoes by using DEET-infused spray, covering arms and legs, and emptying standing water containers goes a long way toward preventing WNV infection.

"Prevention is the best, only way to avoid the disease," she said. "Also, people are advised not to touch dead birds. FPs may find it helpful to log into their state or local health departments to get specific information."

The CDC offers the following tips to prevent mosquito bites: