Colorado West Nile mosquitoes take a holiday

With the Summer of 2008 fading into memory, one bit of good news is that Colorado got a break from the sometimes fatal West Nile virus.

The state recorded only 75 cases – and no deaths from the mosquito-borne disease – in 2008, which made it the lowest-case year since before the major outbreak in Colorado in 2003.

But it wasn’t just Colorado that got a reprieve from the pesky killer insects.

“West Nile activity, both nationally and in Colorado, is at its lowest level ever recorded,´ said John Pape, state epidemiologist. “We’ve seen very low activity, very low human cases.”

West Nile virus leaped onto the national scene in 1999 but didn’t show up in Colorado until August 2002. That year 14 cases were recorded in the state with no deaths.

But the worst was to come the next year when nearly 3,000 cases were confirmed and 63 people died of West Nile virus infection.

After aggressive spraying and educational programs were put in place the following year, the number of cases dropped to 291 with only four deaths. Since then, the numbers of cases dipped in 2005 before rising again in 2006 and 2007.

Pape said 2007 was the worst year for West Nile since 2003, with 576 cases confirmed and seven deaths. He said he could not explain how 2008 produced such a low number of cases and no fatalities.

Weather plays role

West Nile is a virus that’s carried by birds and transmitted to humans by Culex mosquitoes. This summer being fairly dry, the lack of mosquito breeding grounds could have played a part, Pape said.

“Clearly, weather is a big, big player in this cycle,” he said. “Precipitation, heat, bird populations – all have an effect on the mosquito population. I’m not convinced there’s one single factor. I think it’s a complex interaction of a variety of things.”

Larimer, Boulder and Weld counties had the highest number of West Nile cases in the state in 2008, with Weld leading with 21, Boulder recording 16 and Larimer reporting10.

The West Nile virus produces a variety of symptoms that appear three to 14 days after infection, including fever, headache, nausea and vomiting, muscle aches, weakness and rash. More serious cases include inflammation of the brain and spinal cord, and death can occur among those with weak immune systems – typically those over 50.

Since its appearance in the United States a decade ago, researchers have been trying to develop an effective vaccine to prevent or treat West Nile infection. A vaccine for horses – which were found to be particularly susceptible to West Nile – has been developed and is widely used with good effect.

But a human vaccine remains elusive, says Richard Bowen, a professor in Colorado State University’s Biomedical Services Department. While CSU has done and continues to do research into West Nile virus through its Infectious Disease Supercluster, Bowen said funding for research on a human vaccine has been limited.

“There’s concern over whether a human vaccine is justified,” he said. “Will a (drug-manufacturing) company spend that kind of money to develop it and who would get it? It’s tragic for individual people but is this a reasonable thing to be doing when there are so many other diseases that need treatments?”

Horses’ best friend

Bowen said CSU has helped make some significant contributions to the development of an equine vaccine. “We’ve done a ton of work on the equine front,” he said. “There’s now three vaccines for horses and we’ve done all the testing for those.”

Bowen said that’s in part due to the fact that CSU also has a large veterinary hospital and other facilities that cater to horse treatment and research. “There’s no other place in the country where you can test 20 horses at a time.”

Bowen said research into a vaccine for horses may ultimately prove to be the breakthrough needed for a human vaccine. “One of the vaccines we’ve been involved with and that’s currently on the market for horses is furthest along for a human vaccine,” he said.

But when that may come to fruition – especially with the more stringent standards required by the Federal Drug Administration in approving drugs for human consumption – remains an open question.

And the ultimate irony is that it may take more outbreaks with more human deaths to get drug companies to pony up the money to fund the painstaking research needed to find that vaccine breakthrough.

“Unfortunately, it takes a lot of money to get these things going,” he said.

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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