Stanislaus County’s mosquito abatement districts watch for Zika virus signs

Following a winter with El Niño storms, mosquito control districts expect to have a tougher time this year with mosquitoes that spread West Nile virus, and they are watching for any sign of Zika.

The Zika virus is now on the radar of local health officials after the carrier mosquitoes, Aedes aegypti, were found in Madera and near Fresno in 2013.

Experts have debated whether Zika is likely to become a public health threat in the Northern San Joaquin Valley, but mosquito control personnel are keeping a close watch on their traps.

So far, the carrier mosquitoes have not not been detected in Stanislaus County.

“There are no locally mosquito-transmitted cases of Zika, Dengue or Chikungunya virus in California,” said Lloyd Douglass, manager of East Side Mosquito Abatement District, who referenced to two other viruses that could become a problem. “We are actively trapping for the invasive species of mosquitoes that carry these diseases.”

The outbreaks of Zika in Central and South America are a concern for health officials in the United States. The Zika virus results in a minor illness for some of those infected, but infected pregnant women may give birth to babies with microcephaly. The birth defect is characterized by small skulls and underdeveloped brains.

David Heft, general manager of the Turlock Mosquito Abatement District, said the conditions for spreading Zika don’t exist in the county today. It’s believed the virus is spread when a mosquito bites an infected person and then the infected mosquito bites another person.

“To start the transmission cycle, first you would need to have the vector, Aedes aegypti, and, second, you would need to have someone who traveled to one of those countries bring the virus into the county,” Heft said. One study has suggested that other native California mosquitoes could transmit Zika, but it’s inconclusive, Heft said.

Local cases of Zika could surface in a county that hosts migrant farmworkers from Central America and has residents who frequently travel to countries with outbreaks.

Heft said the district has put out special traps designed in the Caribbean for mosquitoes that carry Zika.

“It is on our radar,” he said. “We are paying attention to any cases that are reported to county public health.”

The illness caused by Zika lasts for several days, with symptoms including a fever, rash, joint pain, headache and conjunctivitis, or red eyes. Many of those infected don’t notice it.

Pregnant women with symptoms are urged to see their doctor because of the risk of birth defects.

In March, the state Department of Public Health confirmed a Southern California case of Zika transmitted through sexual contact. A woman was infected by a Zika-infected partner who had traveled to South America.

Stanislaus County officials are still mostly concerned about West Nile illness, a neurological disease that is devastating, or even fatal, for a number of county residents every year. The county had 13 cases of West Nile last year, down from 38 cases and two deaths in 2014. The virus sickened almost 800 people in California last year with 58 fatalities.

About 20 percent of people infected with West Nile have a fever, headache and body aches lasting for weeks. A more rare, life-threatening neurological disease can result in tremors, convulsions, paralysis and long-term disabilities.

The warm temperatures this spring, along with standing water and humidity, are perfect conditions for mosquitoes that spread West Nile, Heft said. Residents should pay attention to the black mosquitoes near their homes, which typically bite in the morning and evening.

Those Culex pipiens mosquitoes are the most common West Nile carriers, but the conditions also favor Culex tarsalis mosquitoes that are able to spread West Nile even faster, Heft said. The latter mosquitoes breed in rural areas in the spring and then creep into residential neighborhoods.

“I am expecting West Nile to creep up a little faster this year, with the rains and amount of standing water we are seeing,” Heft said.

The general manager, who previously worked in Southern California, said West Nile is more prevalent in the San Joaquin Valley, owing to the Valley’s hot summer temperatures.

The latest challenge in the battle against West Nile is resistance to the insecticide pyrethrin. With a large percentage of mosquitoes showing resistance to the insecticide, the Turlock district last year switched to a second chemical, Naled, for three aerial spray applications on the edge of cities and towns.

The aerial spaying timed in July, August and September could be necessary again this year, Heft said. The newer chemical is considered safe and is used in small volumes – a half-ounce per acre – to kill mosquitoes by contact in the air, he said.

Officials are hoping that careful use of Naled, in combination with ground spraying with pyrethrin, will continue to give abatement districts a weapon against mosquitoes. There are no other chemicals approved for the West Nile program, Heft said.

Residents are urged to take part in the “fight the bite” program by draining standing water around homes, using insect repellent and limiting their time outdoors near dawn and dusk.

The Turlock and East Side abatement districts also focus attention on neglected swimming pools that harbor mosquito larvae.

Agencies track the presence of West Nile virus by testing dead birds. People can report dead birds to a state hotline at 877-968-2473 or at www.westnile.ca.gov.

To report mosquito problems, residents in Modesto or other communities north of the Tuolumne River may call the East Side Mosquito Abatement District at 209-522-4098. The Turlock Mosquito Abatement District covers the remainder of the county; call 209-634-1234 or go to www.turlockmosquito.org.

This story was originally published May 4, 2016 at 5:53 PM with the headline "Stanislaus County’s mosquito abatement districts watch for Zika virus signs."