President's Message

West Nile Fever is Coming

Todd L. Sack, M.D., President

 
Mosquitoes and the lurking specter of viral encephalitis are a way of life in Florida. Each year we hear of a few isolated cases of human illness due to the equine encephalitis viruses. It is therefore somewhat of a surprise that the West Nile Virus, an "Old World" pathogen that has been known to medical doctors in Europe for decades, has only recently come to the United States. Now it is time to become familiar with West Nile because this virus has moved here and is expected to cause the first human illnesses and perhaps deaths this year.

The West Nile Virus was first isolated in the West Nile province of Uganda, East Africa in 1937. It is a member of the flavivirus family of RNA viruses. It has been found commonly in birds, humans, and vertebrates in Africa, the Middle East and in Eastern Europe. Only in 1999 were the first cases of West Nile Fever reported in the State of New York where in 1999 there were perhaps 13,000 infections, including 7 proven deaths.

The life cycle of the West Nile Virus requires the mosquito. The mosquito becomes infected when it feeds on infected birds that migrate through Florida. The virus incubates in the mosquito for 10-14 days, after which the virus is abundant in the mosquito's salivary glands. The virus is injected into an avian or mammalian host with subsequent feedings. While birds are the principal reservoir for West Nile Virus, many other animals can become infected and even die including dogs, horses, and man. Transmission does not occur from man to man, or dog to man.

Fortunately, the chance of becoming ill from any one mosquito bite is extremely small. Even in areas where mosquitoes do carry the virus, very few mosquitoes—much less than 1%—are infected. If the mosquito is infected, severe illness occurs in less than 1% of people who do become ill.

The incubation time for West Nile Fever is usually 3-15 days. Most infections are mild with symptoms including fever, headache, and body aches lasting about 6 days. The onset of symptoms is usually sudden beginning with a sustained high fever. There is occasionally a skin rash on the trunk and swollen lymph glands. Gastrointestinal symptoms may occur but are not prominent. More severe infection may be marked symptoms of encephalitis such as headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death. Among those with severe illness, case-fatality rates range from 3% to 15% and are highest among the elderly.

There is no specific therapy. In cases where encephalitis develops, intensive supportive therapy is indicated, including hospitalization, intravenous fluids, airway management, ventilator support, and treatment of secondary infections such as pneumonia.

Prevention of West Nile virus infections is available and effective. Individuals need to be informed of measures that can be taken. These include staying indoors at dawn, dusk and in the early evening when mosquitoes are most likely to be feeding. Outdoors we should wear long-sleeved clothing whenever possible and we should spray exposed skin and clothing with a mosquito repellent containing 35% DEET ( N,N-diethyl-meta-toluamide) or permethrin. These repellents should be applied to children as well, but in accordance with the manufacturers' recommendations. Methods such as Vitamin B and "ultrasonic" devices are not effective for preventing mosquito bites. A nice review of this is found in "Mosquitoes and mosquito repellents: A clinician's guide" by Mark S. Fradin, Annals of Internal Medicine, 1998; 128: 931-940.

There is no vaccine available for human for West Nile Virus though a vaccine is available for horses and human vaccines are being developed.

Our Department of Health conducts ongoing surveillance of the mosquito and bird populations to track the presence of this virus in Duval County. When viruses for encephalitis are detected, the County conducts campaigns of aerial spraying of pesticides over neighborhoods. These sprayings are helpful for reducing the mosquito population and for preventing human infection.

The first death from West Nile Fever in Florida was reported in July 2001. It is clear that this virus is in Northeast Florida as well, and that it is likely to stay.

October, 2001/ Jacksonville Medicine

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