Spray it on! More time left in West Nile season

So far, so good.

Six years ago, a disease carried by mosquitoes called the West Nile Virus erupted in Colorado, with nearly 3,000 people across the state reporting infections and 63 dying from them.

The summer of 2003 was the year of the deadly mosquito bite, with public health professionals and local officials scrambling to figure out what to do as the death toll rose.

Since then, spraying and public education programs have succeeded in dramatically reducing those numbers. And so far this year, fewer than a handful of infections have been reported and no deaths have occurred.

But whether this will be a low-infection or high-infection year for West Nile remains to be seen. Public health officials in both Larimer and Weld counties are reporting trapping mosquitoes that have tested positive for West Nile, and Weld County recently reported its second human case of West Nile Virus infection, out of three so far documented in the state.

There have been no human infections yet reported in Larimer County.

But the season is still young. The West Nile Virus infection season typically runs from late July into October, when cool temperatures send the insects into hibernation. By the end of August last year there had been 37 confirmed cases of human infection, but the state ended the 2008 West Nile season with 71 cases.

It might seem that a wet summer like this year’s could be producing a bumper crop of potentially lethal mosquitoes. Well, maybe – but not necessarily, say local public health officials.

“There are probably more mosquitoes (this summer) but it’s not a direct correlation,´ said Sara Evans with the Weld County Department of Public Health and Environment. “It has to do with standing water and temperature and other factors. It’s very, very difficult to tell if it’s going to be a bad year.”

The worst year for WNV in Colorado – 2003 – was smack in the middle of an ongoing statewide drought.

Evans said mid-August is prime time for people to become infected but it takes up to two weeks after being bitten by a West Nile-carrying mosquito to get the first symptoms of the disease. Those symptoms can include fever, headache, muscle aches, vomiting, weakness or a rash.

About 1 in 150 people infected develop a severe reaction to the virus, which can cause long-term neurological damage and even death. People over 50 are most likely to have a severe reaction to the WNV infection.

Jane Viste with the Larimer County Department of Public Health and Environment said she thinks the numbers of WNV cases have dropped since 2003 because of a heightened awareness of the disease, which first appeared in Colorado in 2002.

“People became very vigilant after that year,” she said. “I can’t say for sure why the (infection rates) dropped, but education has to be one of the reasons.”

But Viste worries that Coloradans may be relaxing and letting their guard down this year after several summers – with the exception of a spike in 2007 – of lowered infection and death rates.

“People are dropping off in their use of repellants and starting to become complacent,” she said. Viste recommends liberal use of repellants – especially those with DEET -and wearing long-sleeve shirts and long pants if the temperature permits when spending time outdoors.

She also offers a simple solution for keeping the mosquitoes away while relaxing on an open-air deck.

“Just use a fan,” she said.

West Nile by the numbers

West Nile Virus was first identified in Colorado in 2002.

2002 – 14 reported infections, 0 deaths attributed

2003 – 2,947 infections, 63 deaths

2004 – 291 infections, 4 deaths

2005 – 106 infections, 2 deaths

2006 – 345 infections, 7 deaths

2007 – 576 infections, 7 deaths

2008 – 71 infections, 1 death

2009 – 3 infections, 0 deaths (As of Aug. 4)

Source: U.S. CENTERS FOR DISEASE CONTROL

Steve Porter covers health care for the Northern Colorado Business Report. He can be reached at 970-221-5400, ext. 225, or at sporter@ncbr.com.

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