NEWS & EVENTS

NEWS ARCHIVE | EDUCATIONAL RESOURCES

UPDATE ON WEST NILE VIRUS (WNV)
Abstract

BACKGROUND

• The West Nile Virus (WNV) is one of a number of viruses that can be contracted by mosquito bite in the US.
• Clinically significant WNV infection is actually quite rare in the US (and the world).
• WNV is less common than other similar viral infections, regardless of the media coverage of the recent outbreak.

THE WEST NILE VIRUS

• WNV belongs to a group of viruses termed arboviruses.
• Arboviruses usually live in an animal (commonly birds) and only occasionally get transferred to another animal or human by a mosquito that first bites an infected bird.
• The WNV has been responsible for multiple outbreaks of illness around the world since 1937.

WNV IN THE US

• In the summer of 1999, 50 cases (with 5 deaths) of WNV occurred in the New York area.
• Since then cases have occurred in the Northeast, Southeast and Midwest:

• Increase in numbers is probably partially due to public and health professionals looking for the illness.
• For perspective, there are around 190 cases of a very similar viral illness spread by mosquitoes (St. Louis encephalitis) each year, found in all of the lower 48 states.
• Also even if you are bitten by a mosquito, the chances that the mosquito is carrying the WNV are very low.

YEAR	# OF CASES	# OF DEATHS
2000	21	2
2001	56	8
YTD 2002	113	5

THE ILLNESS CAUSED BY WNV

• Most people who become infected with the virus show no/mild signs or symptoms of illness.
• At most: mild illness with a little fever, headache, muscle aches and possible rash.
• Less than 1% of those infected with the WNV will develop meningitis or encephalitis.
• Of those that develop meningitis or encephalitis, less than 1 per 1000 will die of the illness, these usually being older patients.

Kenneth C. Cummings, MD
Chief, Clinical Pathology
August, 2002