Mosquitoes

and

West Nile Disease

In Manitoba, mosquitoes have long been regarded as pests although encephalitis has very rarely occurred in the past. Measures to control mosquitoes have been to minimize their nuisance effect but now with the appearance of West Nile disease reported in birds people are wondering what is the best way to avoid West Nile virus disease. As with many issues in medicine this issue remains controversial. This pamphlet is an abbreviation of several medical authorities many of which don, to agree on all points. At our clinic we routinely advise certain behaviours. Chemicals and clothing to prevent mosquito bites in travelers going to exotic foreign countries where mosquitoes carry other diseases like malaria, Japanese encephalitis virus, yellow fever virus and others.

West Nile Virus Disease

This virus was first isolated in 1937 in the West Nile district of Uganda from a woman with fever. This virus and similar strains are found in many countries in the world. West Nile virus encephalitis broke out in Israel in the 1950s and has since been recognized as a source of human disease and has long been recognized as a risk to travelers to exotic destinations. In 1999 an outbreak of encephalitis occurred in New York City with 59 people being affected with encephalitis and 7 of these dying (approximately 10% mortality rate). Once it was discovered to exist in the New York weather heave use of insecticides along with cold winter was hoped to stop the spread of West Nile disease to the continent. The West Nile virus is also spread to birds by mosquitoes and researchers use dead birds as evidence of the West Nile spread.

Since 1999 other US cases of West Nile Virus has appeared in people in the US and recently in birds in Winnipeg. No one knows for sure how the virus was brought to New Your but it is likely that it was an infected mosquito that arrived with an airplane.

Researchers believe that migratory birds could not have brought it to NY. The type of West Nile virus is very similar to a similar strain circulating in Israel. There is no evidence that this was any form of bioterrorism but appears to have been a biological accident, which has been known to happen when a malarious mosquito has infected airport personnel (“airport malaria”). At present there have been no human cases of West Nile Virus in Winnipeg but given the presence the virus in birds the possibility of West Nile virus in humans exists although it is very small. A horse in Grand Forks also has had the disease. It should be noted that New York city is very densely populated and yet only a very small amount of people have gotten sick from West Nile Virus.

Symptoms of West Nile Virus In New York several people in the Queens area were checked to see if they had contact with the West Nile virus. They test 667 people and found that 2.6% were positive for exposure to West Nile virus of these 20% reported having a fever and flu like illnesses in the weeks prior to the study. This study concluded that most of the people who were bitten by a West Nile infected mosquito did not develop any symptoms and those who developed encephalitis were very rare <1%. As of July 25, 2002 there have been 161 cases of West Nile Virus reported to the Centre for Disease Control with 18 fatalities.

Manitoba health is trying to determine the appearance of West Nile Disease in people by looking at people with symptoms of meningitis (inflammation of the layers surrounding the brain) or encephalitis (inflammation of the brain).

These symptoms include:

Headache, a stiff neck, nausea, vomiting, a decreased level of consciousness, confusion, and delirium, which are very general symptoms and can be caused by many diseases. West Nile disease has also been associated with other focal neurological signs and also occurs with a profound weakness.

Doctors have been asked to collect blood work in cases that may be possible West Nile.

Manitoba Guidelines may change as new information is gathered. The Manitoba Health Website will be regularly updated: www.mb.ca/heath/wnv .

Treatment of West Nile

At present there is no vaccine that s effective in man to prevent or lessen the occurrence or incidence of disease (there is a vaccine for horses). No medication is effective in treating this virus yet. Severely affected people (who are also usually either very young or very old) are treated with advanced support.

Preventing West Nile Disease

West Nile virus is transmitted by infected mosquitoes, primarily members of the Culex species.