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SIERRA VISTA — A mosquito sample from Yavapai County tested positive for West Nile virus a state health official said Monday. The positive sample marks West Nile’s first Arizona appearance in 2007.
“We’ve been conducting ongoing surveillance in Maricopa County for some time now,” said Craig Levy, head of the Arizona Department of Health Services Vector-Borne and Zoonotic Diseases section. “But there have been no positive samples found in Maricopa County so far this year.”
With warm summer weather approaching, state and local health officials are urging residents to protect themselves against the disease.
A mosquito-borne illness, West Nile virus is transmitted to humans and animals through the bite of an infected mosquito. Mosquitoes first become exposed to West Nile when they feed on infected birds.
 Humans can get West Nile virus through the bite of a mosquito. (Purdue University) |
Since its arrival in Arizona in 2003, the Arizona Department of Health Services is reporting that more than 650 residents have been infected with the disease. Thirty-five of those people have died. Last year, there were 150 cases in Arizona, with 11 deaths attributed to West Nile virus.
“I want to emphasize there are two things you can do to help combat West Nile virus,” said Vaira Harik, director of Cochise County Health Department.
“First, to protect yourself, use insect repellent and make sure you have good screens on your windows and doors.”
In addition, wear lightweight clothing that covers the arms and legs when going outdoors during dawn and dusk, or when you are in areas where mosquitoes are active.
“Secondly, what you can do for your community is get rid of places where mosquitoes can breed,” Harik said. “Eliminate as many sources of standing water as possible.”
Harik suggested checking for items outside the home that collect water, such as old tires, cans, bottles, jars, buckets, drums and other containers.
“Be aware of your surroundings,” she advised. “If you must have containers outside, turn them over so they can’t collect water. The best possible prevention is for everyone to be proactive and work together.”
As in past years, county health officials will be conducting survellience for positive mosquitoes.
“Mosquitoes are breeding earlier this year because of warm weather and recent rains,” Levy said. “While we can’t predict how severe the West Nile season will be this year, Arizonans should be taking steps to protect themselves against mosquito bites.”
Symptoms of West Nile virus
Most people who become infected with West Nile Virus — about four out of five cases — will not develop any type of illness, which is called an asymptomatic infection.
It is estimated that about 20 percent of the people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, lethargy and body aches. Occasionally, the person will have a deep skin rash and swollen lymph glands. The illness can run from a few days to several weeks.
In severe cases of the disease, the person can suffer from West Nile encephalitis or meningitis, infection of the brain and spinal cord or their protective covering. Symptoms include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. It is estimated that approximately one in 150 persons infected with West Nile virus will develop a more severe form of the disease. While serious illness can occur in people of any age, those over 50 and some immunocompromised persons are at the highest risk for getting severely ill when infected. In severe cases, the person often requires hospitalization and the neurologic effects can be permanent.
Once infected, incubation period for the disease is from two to 15 days. Most of those infected will typically have one of three outcomes: No symptoms, which is most common; West Nile fever, about 20 percent of the population; or severe West Nile disease, which occurs in less than 1 percent of the population.
Anyone who develops a high fever with a severe headache should consult his or her health care provider.
— Centers for Disease Control and Prevention
West Nile virus in horses
Horses are prone to severe West Nile virus infection. Just as with people, horses become infected after being bitten by an infected mosquito. There is no evidence that horses can transmit the disease to other horses, birds or people.
In cases where horses become critically ill, the virus infects the central nervous system and causes symptoms of encephalitis. Clinical signs of encephalitis in horses include loss of appetite and depression. In addition, there can be any combination of the following signs: fever, weakness, paralysis of hind limbs, muscle twitching, impaired vision, head pressing, aimless wandering, circling and inability to swallow.
There is no specific treatment for West Nile encephalitis in horses. Supportive veterinary care is recommended.
Currently, there are four vaccines available for horses to prevent West Nile virus. At least a one yearly booster is recommended after the initial series is administered. Horse owners need to know that horses vaccinated against Eastern, Western and Venezuelan equine encephalitis are not protected against West Nile virus. It is a separate vaccine.
Veterinarians are recommending that horses be vaccinated against the disease now. It’s best not to wait until mosquito season is here.
Along with the annual vaccination, veterinarians recommend using topical preparations containing mosquito repellents. If possible, change water every four days in watering troughs to prevent mosquito breeding grounds. Mosquitoes are capable of breeding in any pool of water or puddle that lasts more than four days.
The usual breeding period for a West Nile virus infection is usually between five to 15 days.
— Ohio State University
Herald/Review reporter Dana Cole can be reached at 515-4618 or by e-mail at dana.cole@svherald.com.
