With Zika virus spreading internationally, local vector control districts brace for upcoming mosquito season

The Zika virus causing worldwide alarm gives central San Joaquin Valley mosquito-abatement leaders new reason to fret about efforts to control the pests.

Zika can be spread by the same black and white mosquitoes, known as Aedes aegypti, that are aggressive day-biters and can be carriers for yellow fever and chikungunya.

Aedes aegypti were first discovered in Madera and Clovis during the summer of 2013 and have been widening their range ever since.

“The way it’s spreading – it’s like wildfire,” said Tim Phillips, district manager of the Fresno Mosquito and Vector Control District. “Short of Mother Nature taking a stand, I don’t think we’ll be able to control it – it will change the way we live in California.”

A recent and ongoing outbreak of Zika virus in Central and South America, where it’s suspected to be causing birth defects in newborns, has concerned public health officials in the United States and beyond.

The symptoms of the disease, which are only felt by a small portion of people infected, are flulike and relatively mild, said Dr. Kenneth Bird, a Fresno County health officer.

The primary cause of international alarm has been the more than 10-fold increase of cases of microcephaly, which causes small skulls and brains in infants, in countries where the virus has infected many people.

“There are a very few number of viruses that can be found in the amniotic fluid prior to birth,” said Jared Rutledge, senior epidemiologist at the Fresno County Department of Public Health. “The public health community in Brazil has observed Zika virus in the amniotic fluid prior to birth of children with this disease.

“So what they saw is an exponential increase in microcephaly cases with the appearance of Zika virus,” Rutledge said.

As of Feb. 4, health officials in Brazil are investigating nearly 4,800 suspected cases of microcephaly and have confirmed more than 400 – up from around 150 cases reported in a normal year.

“This is a very rare birth defect and it requires, generally, hospitalization or some elevated level of care,” Rutledge said. “So it’s unlikely that any cases would go undetected.”

On Feb. 1, the World Health Organization declared Zika virus a global health emergency, putting the virus in the same category of concern as Ebola.

With Aedes aegypti – a Zika virus carrier – in the Fresno area, local mosquito control officials hope to reduce their numbers before the insect can ever serve as a vector for Zika, or any other disease, said Steve Mulligan, manager of Consolidated Mosquito Abatement District. His district serves an area that includes Selma, Parlier, Sanger and Clovis.

Aedes aegypti, along with another mosquito species, Aedes albopictus, have been discovered in 12 of California’s 58 counties.

In preparation for the upcoming mosquito season, vector control districts have focused their attention on trying to get rid of the preferred living spots of Aedes aegypti.

“During the spring or summertime, you’re going to have Aedes aegypti breeding,” said Leonard Irby, manager of Madera County Mosquito and Vector Control District. Because the adult mosquitoes are not easily killed with pesticides, the districts are focusing on removing breeding habitats.

The mosquito likes small containers of water, whether inside or outside. The females lay their eggs in the water, where they develop over several days.

Just an ounce or two of water is enough for the insect. “It survived in this area even during the drought,” Mulligan said.

In the event an Aedes aegypti bites a disease-infected person in the central San Joaquin Valley, Mulligan said, “our initial focus will be to impact the disease transmission cycle, and we will be aggressive in increasing our efforts to reduce the numbers of adult and immature mosquitoes around the immediate area using approved public health insecticides.”

Because mosquito control districts can’t remove all the buckets, empty bottles, ceramic pots and other small water receptacles from properties across the Central Valley, officials are asking the public to participate in the control effort.

Aedes aegypti can take root inside homes, and mosquito abatement districts ask that residents get rid of open containers of water there, if possible. For pet water bowls, the districts ask that they be emptied, washed out and refilled a couple times a week so mosquitoes do not have time to develop.

Experimental mosquito control techniques that the Consolidated, Madera County and Fresno districts are considering include releasing sterile male mosquitoes into the population – only the females bite – to reduce Aedes aegypti offspring.

At the same time, districts have accepted that, for the foreseeable future, these mosquitoes are here to stay, Mulligan said.

For anyone traveling to Brazil, Colombia, El Salvador, Honduras, Bolivia or other countries where Zika outbreaks are occurring, public health officials recommend being vigilant both during and after travel.

“Only 20 percent of the people exposed (to the Zika virus) get symptoms,” Rutledge said. “If you’re coming back from these countries, just assume that you have it – for the next 14 days, continue to apply mosquito repellent here, because the virus will burn out of the system, you’ll be recovered and less capable of infecting the local mosquito species if you prevent the mosquito species from biting you once you return.

“It’s twofold – protect yourself while you’re over there, and protect yourself when you return,” Rutledge said.

This story was originally published February 6, 2016 at 2:07 PM with the headline "With Zika virus spreading internationally, local vector control districts brace for upcoming mosquito season."