Mosquitoes with West Nile found in Yuma County

A mosquito sample collected near the front gate to Yuma Proving Ground is the first this year to test positive for the West Nile virus, according to the Yuma County Pest Abatement District.

The mosquito sample was collected April 28. Testing on Friday confirmed the presence of the virus, the district said in a news release Monday.

Using an in-house diagnostic system that provides same-day results, the district found samples were positive, but it was also confirmed by a more reliable test by the Arizona Department of Health Services laboratory, said Chris Sumner, pest abatement district manager.

He noted that he wasn't certain if the virus was from mosquitoes surviving from last winter or if it was caused by a new infection of birds. Mosquitoes do not hatch with West Nile virus and can only contract it by feeding on birds who already have the virus.

But once mosquitoes become infected, they remain so for life and can spread it to whomever they bite. The virus can only be spread by mosquito bites.

Each spring the infection cycle may begin with mosquitos that were infected from the previous season and survived the winter. Bird nestlings are especially susceptible because their immune systems are weak and do not have much feather covering to guard against mosquitoes, Sumner said.

As a precaution, people are advised to avoid the Colorado and Gila rivers at sundown when it is peak feeding time for the Culex mosquitoes, the species carrying the virus. But for anyone who is on the river at sunset, long sleeves and trousers are recommended, Sumner said.

Sumner also advised people wear an effective repellent. There are basically three types. The "gold standard" is any of the various formulations containing the chemical DEET. It is very effective but for some people it has a greasy feel and a chemical smell, he noted.

A product with Picaridan can be equally effective but does not have the oily texture or odor of DEET, Sumner said. Yet for anyone who prefers an organic repellent, oil of lemon eucalyptus is an all-natural product and any repellents could be found at a camping supplies store, he said.

Only one in 150 people exposed to West Nile will become ill. Of those who do experience symptoms, the majority will notice high fever, headaches, a sore neck, a body rash and intense fatigue, similar to the flu.

Most recover within a few days to a couple of weeks. Some may transition into a more severe form and experience tremors and loss of mobility of a limb, but this rarely occurs, Sumner said.

Beginning Tuesday, pest abatement district workers will spray the swampy areas of the Colorado River just below Prison Hill with Vectobac Granules. It contains a natural bacterium that is specifically toxic to mosquitoes and should kill the larvae before they hatch, Sumner said. Vectobac is not harmful to wildlife or humans, he stressed.

Increasingly, abandoned or poorly maintained swimming pools have become a problem, Sumner noted. Anyone with a swimming pool is advised to keep it chlorinated. Untreated, "green pools" can attract mosquitoes. If a pool is not going to be used for a length of time, it is advised to drain it, he said.

Also vulnerable to mosquitoes are above-ground pools, even those with covers. It is best to keep a chlorine floater in these pools as well. And pet water bowls should be emptied and filled with fresh water once a week.

Anyone who would like to report a green pool is asked to contact the Yuma County Health Department at 317-4584.

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William Roller can be reached at wroller@yumasun.com or 539-6858.