SIERRA VISTA — Arizona’s West Nile virus season is just starting to peak, and state health officials are warning residents to take precautions against biting mosquitoes.

“We’re actually getting into the high risk season right now,” said Craig Levy, program manager of the vector borne disease program for Arizona Department of Health Services. “West Nile virus is a disease people should take seriously. For those who become sick with this disease, it can be life altering.”

As summer rains begin to taper off, Levy says Arizona residents tend to relax when it comes to protecting themselves against mosquito bites. But for the past three years, the number of human cases in Arizona climbed in late August and September, tapering off in October.

Statewide, there have been nine human cases of West Nile reported this summer. Most of those are from Maricopa County. There have been 88 positive mosquito samples from five counties, and Levy expects that number will climb dramatically in the next few weeks. So far this year, no cases of the virus have been reported in Cochise County, nor have there been positive mosquito samples.

“Again, we’re just approaching the peak season for Arizona,” Levy warned. “Our numbers are lower this year than this time last year, but people should not be lulled into complacency. This is a serious public health problem.”

It only takes one infected mosquito bite to get seriously ill, Levy said.

Since mosquitoes are most active during dusk and dawn, it’s best to remain indoors during those times. However, for those who must be outdoors during prime mosquito times, wear clothing that covers the arms and legs, along with an insect repellent on exposed skin. Look for repellents containing DEET or other EPA-registered active ingredients effective against mosquitoes and follow the package instructions carefully. For the best protection, spray clothing with repellent, as well.

Keep mosquitoes out of the home by closing windows and doors. Check screens for holes and keep them in good repair. 

Get rid of mosquito breeding sites by emptying standing water from such containers as flower pots, buckets and barrels. Change the water in pet dishes and bird baths at least once weekly. Get rid of old tires, as they hold water. Children’s wading pools should be emptied and stored on their sides when not in use.

Horses can become extremely sick with encephalitis if infected with West Nile virus. There is a vaccination that protects horses against the disease. Levy advises horse owners to contact their veterinarians and take advantage of the vaccination.

From 1999 through 2007, the Centers for Disease Control and Prevention reported more than 26,500 human cases of West Nile in this country, Levy said. Of those, more than 10,400 were considered serious, affecting the brain, spine and nervous system. There have been 960 human deaths. During that time span, the CDC reports more than 53,000 positive mosquito samples, along with more than 24,000 positive animals. With the introduction of the vaccine for horses, the number of infected animals has dropped off, Levy said.

While more than 58,8000 birds have been reported with the disease, Levy said the bird mortality number is actually much higher. “These are only the birds that were tested,” he said. “All of these are conservative numbers. West Nile has had a widespread, adverse effect on a number of bird species.”

Last year in the U.S. there were 3,630 human cases reported in 42 states, with Arizona ranking 13th of the 42. The current count for 2008 is 236 human cases, of which two were fatal. One of the fatalities is from Arizona. To date, 28 states are reporting human cases. California is leading the count with 78, followed by Mississippi and Colorado.

“West Nile virus is a human public health problem, a veterinary health problem and a wildlife disease problem,” Levy said. “It’s had a tremendous impact on multiple fronts.”

Facts about West Nile virus

The following information is from the Centers for Disease Control and Protection Web site.

What are the symptoms of West Nile virus?

• About one in 150 people infected with West Nile virus will develop severe illness. The severe symptoms can include a high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks and neurological effects can be permanent.

• Up to 20 percent of the people who become infected have symptoms such as fever, headache, body aches, nausea, vomiting and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though some people have become sick for several weeks.

• Approximately 80 percent of people infected with West Nile, or about four out of five, will not show any symptoms at all.

How does West Nile virus spread?

• Most often, West Nile virus is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals when they bite.

• In a very small number of cases, the virus has been spread through blood transfusions, organ transplants, breast feeding and during pregnancy from mother to baby. The risk of contracting the virus through medical procedures, however, is extremely low.

West Nile virus risk factors

• People over the age of 50 and those with compromised immune systems are at a higher risk for developing serious symptoms of West Nile virus, if they get sick once they’re infected.

• Being outdoors during prime mosquito times — dusk and dawn — can increase the risk of getting bitten by an infected mosquito. Wearing protective clothing and insect repellent is important while outdoors during these times.

On the Net

Arizona Dept. of Health Services West Nile site: westnileaz.com

Herald/Review reporter Dana Cole can be reached at 515-4618 or by e-mail at dana.cole@svherald.com.