As West Nile Virus Cases Rise, Vaccine Still Far Off

Nancy A. Melville

September 17, 2012

In This Article

Concerning Patterns

The West Nile virus does not appear to be changing or becoming more virulent, but some concerning patterns are emerging in its manifestation, Dr. Schaffner said.

Encephalitis cases, for instance, appear to have symptoms that linger over time, and some data have shown the virus to be detected molecularly in urine possibly for years after infection, he said.

One study of 139 patients with previous diagnosis of West Nile virus found a high prevalence of chronic kidney disease 4 to 9 years after infection.

"That might be a sign of slow but diminishing kidney function and that the body doesn't eliminate the virus completely the way it does, for instance, with measles," Dr. Schaffner said. "It may be more like chicken pox, where it can remain in your body for a long time."

These issues only increase the need for a vaccine, but experts note that the lack of one after 13 years isn't all that unusual.

There is not a vaccine, for instance, for HIV yet, and antiviral treatments are also not available for other diseases in the flavivirus family, to which West Nile belongs, Dr. Hills noted.

"The lack of a treatment is not unique for the West Nile virus. Other flavivirus diseases, like Japanese encephalitis and yellow fever, also have no treatments, and they have a longer history of causing disease than West Nile," she said.

A main challenge in treating each of the flaviviruses is that the viremia is short-lived in humans, meaning the virus itself is typically cleared by the time of clinical presentation, Dr. Hills explained.

"Any treatment would need to target intracellular virus or the inflammatory response."

A West Nile virus vaccine has been available for horses for 10 years and has been highly effective, reducing cases in the United States from more than 15,000 in 2002 to just 87 in 2011 (the number cases were up this year to 181 as of September 4, according to the US Department of Agriculture's Animal and Plant Health Inspection Service).

Veterinary vaccines are a far cry from human vaccines, however, in terms of rigorous research and purity standards required for the latter, Dr. Hills said.