Student presentation on

West Nile Virus

by William Macey


Life History
West Nile Virus, WNV, was first isolated in 1937 in the West Nile section of Uganda. It was the found in Egypt in the 1950's. It was first found to cause meningitis and encephalitis during an outbreak amongst elderly people in Israel in 1957. It was first found to infect other vertebrates (equine species) in France in the early 1960's. It did not cross over to the US until 1999 and has now spread to 44 states. There have been 8219 cases in the US since then with 182 deaths. Connecticut has had 12 cases without a death.


Microbial Characteristics
WNV belongs to the virus family arboviruses, so called because they are arthropod-borne. The virion is about 40 nm in size. WNV is a +ssRNA virus. It is also an enveloped, icosahedral virus. Incubation period is about 3-14 days.

Transmission
WNV is transmitted by the female mosquito of the Culex species and can be transmitted to many vertebrates including birds, horses, dogs, cats, and humans. WNV has not been found to be transmitted through person-to-person contact or between any of the secondary carriers (i.e. birds to humans, etc.). It can be spread through blood transfusion, but this has only happened twice in the US.
Symptoms
Most people who are infected with West Nile virus either have no symptoms or experience mild illness such as fever, headache and body aches before fully recovering. Some persons may also develop a mild rash or swollen lymph glands. In some individuals, particularly the elderly, West Nile virus can cause serious disease that affects brain and spinal tissue. Severe illness may include encephalitis, meningitis, and acute flaccid paralysis. Symptoms may include: headache, high fever, stiff neck, confusion, coma, tremors, convulsions, and muscle weakness or paralysis. At its most serious, West Nile virus cancause permanent neurological damage or death. The fatality rate is 10-15% of t he only 1% that develop the more severe condition.

Diagnosis

Diagnostic testing is usually only done on patients that acquire the more severe meningitis or encephalitis. A MAC-ELISA test is performed on the CSF to detect any virus specific IgM. A MAC-ELISA can also be done on serum samples to confirm viremia. Like many other new viral diseases, this test is done when all other infections, bacterial or otherwise, are ruled out as the causitive agent. Diagnosis is based highly on clinical suspicion.

Treatment
The only treatment is usually IV fluids, respiratory support, and prevention of secondary diseases. Ribavirin and interferon alpha-2b have been tried, but only small successes have been shown. Although there is no specific treatment given, the CDC recommends many methods of prevention. These include mosquito-proofing your home and generally being aware of the mosquito environment any time we go out doors. There are also community wide measures that can be taken, this includes spraying insecticides as well as educating on mosquito habits such as peek biting times. A vaccine is also in early human trial stages.
References
http://www.cdc.gov/ncidod/dvbid/westnile/index.htm