West Nile virus update

For the past seven years, a new threat has made itself home on our shores: West Nile virus.

West Nile virus is transmitted by mosquitoes. It has been a cause of infection in the Middle East, Africa and Southwest Asia for centuries. Some medical historians even believe Alexander the Great suffered from West Nile virus infection.

The virus normally exists in nature as a bird-to-mosquito-to-bird cycle. People are accidentally infected by virus-carrying mosquitoes, although infections have occurred from blood transfusions, organ transplantation and pregnancy from mother to child on rare occasions.

Some birds tolerate the infection whereas others don’t. Corvids, such as ravens, crows and jays, suffer serious infection and often die. The presence of dead crows and ravens in Manhattan was the key clue that led to the discovery that this disease had entered the USA. You don’t have to travel far to get this infection.

This virus made a surprising appearance in New York in 1999 and in just four years completely crossed the country. It now is present in all of the continental United States, including California (since 2003). Last year, there were over 2,800 laboratory-confirmed cases in the USA, with 264 deaths. As of press time, the national cumulative human disease cases number was 2,951. West Nile virus is also now found in Canada, Mexico and the Caribbean.

The risk to Americans is higher domestically than internationally at this time. It can be clinically confusing if a traveler returns from a trip abroad and within a couple of weeks gets ill from an exotic, yet now domestic, disease.

The peak outbreaks tend to occur during summer.

Just one in five of those infected develop clinical signs and symptoms, which is called West Nile Fever. This usually appears about a week after an infective mosquito bite, but the incubation period ranges from three to 14 days.

Symptoms such as fever, muscle ache, nausea, eye pain or rash typically last three to six days. Only one in 150 develop severe infection, primarily of the nervous system. Severe infections can affect one’s strength, sensation, coordination, alertness, behavior, memory or consciousness. It is then called West Nile Encephalitis.

The most vulnerable to severe infection are the elderly (those over 70 years of age) or the immunocompromised (such as AIDS or cancer patients).

It is a difficult infection to diagnose, requiring laboratories to run the necessary tests on blood and cerebrospinal fluid specimens. If your healthcare provider doesn’t think of this infection, it is not likely to be diagnosed.

There is no definitive treatment for this virus. No antiviral medication stops infection and there are no medications to cure it. There is no human vaccine, although work is currently being done to create one. A vaccine does exist for horses, but safety and cost issues for a human version does not bode well that we will see one on the market soon.

Prevention is your best defense. Simple anti-mosquito personal protective measures will significantly reduce your chance of being bitten and, thus, of being infected. Exposed skin should be covered with DEET-based repellents in a 20%-50% concentration, and clothing can be sprayed with Permethrin, which, once applied to fabric, will last from two to six weeks. Unfortunately, the natural and herbal-based repellents do not offer significant protection from mosquito bites.

Let’s be concerned about West Nile but not overreact. Most infections are mild. The risk for travelers within the United States or abroad is low. Internationally, the highest risk will be in East Africa, the eastern Mediterranean basin and Southeast Europe. While the initial outbreak in the New York area was large and intense, now there are few cases there, suggesting that the virus adapts to people.

There is no reason at this time not to travel for fear of this illness. With knowledge and a few sensible precautions, good health is within reach for all of us.

Healthy travels!

—Travel & Health is written by Alan M. Spira, M.D., DTM&H, FRSTM