San Francisco health officials monitor for invasive mosquitoes

SAN FRANCISCO (KRON) — Mosquito season is underway, and San Francisco health officials are stepping up surveillance efforts to detect invasive mosquito species before they can become a public health threat.

On Tuesday, the San Francisco Department of Public Health partnered with the San Francisco Recreation and Parks Department at the San Francisco Botanical Garden to demonstrate how crews monitor for invasive mosquitoes and treat breeding areas throughout the city.

“One thing about the invasive mosquitoes is they’re not like the local mosquitoes that lay their eggs in the water,” said Nader Shatara, a senior environmental health inspector with the San Francisco Department of Public Health. “They lay their eggs on a surface right above the water.”

According to Shatara, invasive mosquitoes can carry diseases that are uncommon in the United States but pose serious health risks, including yellow fever, Zika virus, Chikungunya fever and dengue fever.

Throughout the botanical garden, inspectors have placed monitoring buckets designed to attract egg-laying mosquitoes. The buckets are routinely inspected for invasive mosquito eggs, allowing officials to identify new populations before they spread.

During Tuesday’s inspection, Shatara found no invasive mosquito eggs.

“That’s good news,” he said, explaining that no invasive mosquito activity was detected at that location.

While inspectors found no invasive species in the monitoring buckets, they did observe mosquito activity in nearby storm drains.

“The males are there to mate with the females, and then they go off looking for a blood meal,” Shatara said.

Shatara said his team conducts mosquito surveillance and treatment from April through October, when mosquito activity is at its highest.

To reduce mosquito populations in storm drains, Dylan Hayes, integrated pest management and acting wildlife biologist with the San Francisco Recreation and Parks Department, applied a surface treatment called Agnique.

“So what this does, in essence, put a film over the surface of the water so they cannot transpirate or breathe through the surface of the water and therefore then turn into adults,” Hayes said. “This is a preventive measure.”

Because the treatment only remains effective for a few days before evaporating, crews also use a longer-lasting product called FourStar.

The solid briquette contains naturally occurring microbial spores that produce proteins toxic to mosquito larvae. When larvae feed on the proteins, their development is interrupted before they can mature into adult mosquitoes.

Although inspectors did not find invasive mosquito eggs Tuesday, officials say continued monitoring is essential.

“I’m most worried about dengue fever and also Zika,” Shatara said. “Those seem to be the main ones coming in from abroad.”

Health officials are encouraging residents to help reduce mosquito breeding by eliminating standing water around their homes.

Shatara said residents should routinely inspect their properties for places where water collects, including decorative ponds, fish tanks, storm drains, catch basins, air conditioner drain pans, buckets and other containers. Removing standing water can interrupt the mosquito life cycle and help prevent invasive species from becoming established in San Francisco.

For the latest news, weather, sports, and streaming video, head to KRON4.