Testing has confirmed that a dead California scrub jay found on Sept. 4 in Sonora was infected with West Nile virus, according to the Tuolumne County Public Health Department.

This comes nearly two months after a human in the county tested positive for the sometimes deadly mosquito-borne illness for the first time in more than 10 years, prompting health officials to urge people to take precautions.

“The detection of WNV in a dead bird provides an early signal that mosquitoes carrying WNV are present in our environment, and an early warning that it is important to take protection against mosquito bites,” the county Public Health Department stated in a news release this week.

According to the release, the bird was found in Sonora on Sept. 4 and was confirmed for WNV infection on Sept. 21. A person tested positive for the virus in late July.

The release included a statement for Dr. Karen Smith, director of the California Public Health Department, that said West Nile activity throughout the state was on the rise.

The department has confirmed a total of 100 human cases of West Nile virus in 25 counties since the beginning of the year, up from less than 20 cases in six counties at the beginning of August.

Eight horses, 445 birds, 1,802 mosquitoes and 122 chickens have also been infected statewide since the beginning of the year.

Two people in California have died from the virus this year, one from Glenn County and one from Yuba County.

About 2,000 people in the United States have died of West Nile since the virus was first detected in New York City in 1999, representing roughly 4 percent of all confirmed cases.

Although the virus can lead to death in some rare instances, about 80 percent of people won’t experience any symptoms if infected. The most common symptoms can include fever, vomiting, head and body aches, nausea, skin rash and swollen lymph glands.

Health officials stated that less than 1 percent of people infected will develop more serious neurologic illnesses, such as encephalitis or meningitis.

People 50 years or older and those with diabetes or hypertension have the higher chance of getting sick and developing complications after being infected with the virus, according to health officials.

At least one person in Tuolumne County was infected, but did not die, during an outbreak of the virus in 2005 that also infected at least 59 birds and three horses in the county. Calaveras County also experienced a peak in confirmed cases that year with two people, 10 birds and six horses infected.

Culex tarsalis, a breed of mosquito that becomes most prominent in the Sierra foothills in July, is the most common carrier of the virus because it feeds on both humans and birds.

Mosquitoes can also pass the virus to other animals, including horses, chickens and squirrels.

While the Calaveras County Public Health Department maintains and regularly tests a flock of sentinel chickens to detect West Nile virus in the area, Tuolumne County does not provide the resources for an early-detection program and relies on the public for prevention and reporting animals that might be infected.

Common signs that an animal is infected with West Nile can include weakness, stumbling, trembling, head tremors, an inability to fly or walk, and lack of awareness that allows them to be easily approached or handled, according to the U.S. Geological Survey.

For protection from the virus, the state health officials recommended people follow what it calls the “Three Ds” of prevention — DEET, dawn and dusk, and drain.

• DEET: Apply insect repellent containing DEET, picaradin, oil of lemon, eucalyptus, or IR3535 when going outside, though they should be used on children under two months old.

• Dawn and dusk: Mosquitos are typically most active in the early morning and evening during dawn and dusk, so wear proper clothing and repellent if going outside during those times.

• Drain: Eliminate all sources of standing water on your property because it can provide a breeding ground for mosquitoes.

Contact Alex MacLean at amaclean@uniondemocrat.com or (209) 588-4530.