West Nile Virus
Fact Sheet >PDF
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West Nile virus is a disease
that can be transmitted to humans from mosquitoes.
While it has been
common in Africa, Asia, and the Middle East for decades, it first
appeared in the U.S. in 1999 in New York. It has since traveled westward
across the country and is now in Colorado.
Boulder County experienced significant impact from the virus during the
2003 season.
The virus is carried long distances by infected birds
and then spread locally by mosquitoes that bite these birds.
The mosquitoes can then pass the virus to humans and
animals, primarily birds and horses.
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West Nile Virus Activity: Boulder County 2004
West Nile virus occurs during the summer months, generally from May to
the first hard freeze in October.
During these months, as the weather becomes warmer, mosquitoes are most
active and switch from feeding on nectar to blood.
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