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Human West Nile Virus Case Found In Tuolumne County

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Sonora, CA — Environmental and public health officials are alerting residents that a human case of West Nile virus has been confirmed in Tuolumne County.

Environmental Health Director Rob Kostlivy shares that last Friday he received notification of what he is describing as an isolated case. The news has triggered an investigation into where the patient might have been exposed as well as examining the family members to determine whether or not they, too, may have exposure risk.

Eight in ten people who are exposed to West Nile virus (WNV) show no sign of illness upon being infected, according to Kostlivy. He adds that the other 20 percent may experience a range of flu-like symptoms such as fever, headache, body aches, nausea, vomiting, and/or swollen lymph glands. Officials stress that about one percent of the population do develop serious neurological symptoms relating to encephalitis or meningitis, which are illnesses caused by inflammation of the brain, membranes surrounding the brain and/or spinal cord. Signs are high fever, serious headache and neck stiffness; other symptoms may include stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. However, Kostlivy stresses that these instances are very rare and only occur in about one in 150 people who have the active WNV in their body.

It should be noted that those with compromised immune systems and/or certain medical conditions (cancer, diabetes, hypertension, kidney disease, organ transplant recipients) are also at greater risk for developing severe symptoms and illness with those over age 60 being the most susceptible.

Use ‘Three D’ Protection

Humans can prevent exposure to mosquito bites and West Nile virus by practicing what Kostlivy refers to as “the Three Ds.” Below are the basic directions:

1. DEET — Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus, or IR3535 according to label instructions. Repellents keep the mosquitoes from biting. DEET can be used safely on infants and children two months of age and older.

2. DAWN AND DUSK — The mosquitoes that transmit WNV bite in the early morning and evening, so it is important to wear proper clothing and repellent if outside during these times. Make sure doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

3. DRAIN — Mosquitoes lay their eggs on standing water. Eliminate or drain all sources of standing water around homes and properties, including buckets, old car tires, rain gutters, birdbaths, and pet bowls. If a swimming pool is not being properly maintained, please contact environmental health to report green pools.

What Spreads The Virus

The main species of mosquitoes responsible for spreading WNV are Culex mosquitoes. Widespread in California, they feed on birds — mosquitoes’ main host — as well as other animals, and humans. Kostlivy says mosquitoes get the virus by feeding on an infected bird, and may transmit the virus to humans the next time they bite. Culex mosquitoes tend to bite in the morning and evening and are not known to spread Zika, dengue, or chikungunya viruses.

“In my other jurisdiction, I inspected a pond that had infected waterfowl [mallards],” he recounts. “The waterfowl behaved in an odd way; they would swim in a three-foot wide circle — only to one side. Some bird species when infected produce high quantities of the virus, which can then be passed on to other mosquitoes that bite them, maintaining a bird-mosquito cycle. WNV infection has been reported in more than 225 bird species. Not all infected will appear ill, but the infection can cause serious illness and death in some. Signs in birds may include lethargy, uncoordinated movement, and difficulty breathing. “The most severe illness and rapid death is seen among corvid birds, which include crows, jays, ravens, and magpies — and tree squirrels with WNV can develop neurological symptoms such as uncoordinated movement, paralysis, shaking, or circling and may die,” he points out.

“The public should be aware of birds that are lethargic, uncoordinated, or behaving oddly,” Kostlivy emphasizes. Too, he warns, “Horses can become ill from WNV through the bite of an infected mosquito. Clinical signs of WNV illness in horses may include stumbling, circling, hind leg weakness, inability to stand, drooping lips and lip smacking, hypersensitivity to touch or sound, muscle tremors, and death.”

He states that the American Association of Equine Practitioners (AAEP) recommends incorporation of a WNV vaccine as an annual core vaccine in equine vaccination protocols, advising horse owners to consult with a veterinarian about the WNV vaccine and other vaccines against mosquito-borne viruses, such as western equine encephalitis.  “A few months ago, we had an equine test positive for the WNV in the Don Pedro/La Grange area.  You can call our office to report these animals for possible testing,” Kostlivy directs.