The Colorado Department of Public Health and Environment today reported the state’s first human case of West Nile virus. Surveillance shows the West Nile virus is circulating in mosquitoes around the state.
With the long holiday weekend approaching, the department is reminding people to take precautions to avoid mosquito bites between dusk and dawn when infected mosquitoes typically feed.
“It’s time to pack the mosquito repellent when heading out for fireworks, camping or any outdoor activities during evening hours,” recommended John Pape, state epidemiologist in charge of West Nile virus surveillance. “The threat of West Nile virus doesn’t mean you have to avoid activities you enjoy, but it is important to take a few simple steps to avoid mosquito bites”.
The human case occurred in a Delta County resident who became ill 11 days after reporting numerous mosquito bites while attending an outdoor, early evening event. The patient, who developed West Nile virus fever, a less severe form of the disease, recovered following a brief hospitalization. A West Nile virus-related death also occurred recently from a 2012 case. Investigation revealed the patient had been infected in August 2012 and developed a severe complication of the disease known as acute flaccid paralysis. He never recovered this illness, which eventually contributed to his death this June.
“We know that, for most people, infection with West Nile virus usually results in a mild illness from which patients recover,” said Pape, “But for some people, it is a life-altering or life-threatening illness. Since there is no way to predict how sick any one person will become if infected, the best medicine is to prevent illness by avoiding mosquito bites.”
In addition to the human case, 21 mosquito pools (groups of mosquitoes batched together for testing) have tested positive from Adams (1), Boulder (2), Larimer (6), Mesa (8), Pueblo (2) and Weld (2) counties. A sick llama was confirmed with West Nile virus infection from Mesa county.
The state health department, local health departments and mosquito control companies have conducted surveillance for West Nile virus since 2001. The virus was first detected in Colorado in 2002. West Nile Virus is carried by certain birds and transmitted to people by bites from mosquitoes that have fed on infected birds. Female Culex mosquitoes, the species that transmits the virus, usually start emerging in late April or early May and continue transmitting the virus until the first frost, which usually is in late September along the Front Range. The highest risk period for human exposure is generally from late June through early September, when mosquito populations and infection rates peak.
In 2012, Colorado had an active West Nile virus year with 131 reported cases and five deaths. Forty-six percent of these patients developed more severe, neuroinvasive forms of the disease in which the virus invades the spinal cord or brain. In contrast, 2011 was a very quiet year with just seven cases reported. Colorado’s peak year occurred in 2003 when 2,847 cases and 63 deaths were reported. Although the severity of any given year cannot be accurately predicted, surveillance and weather patterns thus far suggest the possibility of another active transmission season in 2013.
Pape reminds people of the “Four D” precautions to take against West Nile virus:
• Drain standing water around the house weekly since that’s where mosquitoes lay eggs. Be sure to empty old tires, cans, flowerpots, clogged rain gutters, rain barrels and toys where puddles can occur.
• Dusk and dawn are when mosquitoes that carry the virus are most active, so limit outdoor activities or take precautions to prevent mosquito bites.
• DEET is an effective ingredient to look for in insect repellents. Always follow label instructions carefully.
• Dress in light-weight long sleeves and pants during dawn and dusk or in areas where mosquitoes are active.