Wet weather breeds mosquitoes 

All the April showers — followed by May and June showers — we’ve had this year have been great for aquifers, river ecosystems and farmers.

Unfortunately, they’ve also been great for mosquitoes.

Mosquito abatement teams in San Francisco and the Peninsula are reporting more of the pests in marshes, pools and other standing bodies of water thanks to heavy rains that came late in the season and were often followed by warm fronts.

The insects are a concern not only for their infernal annoyance at barbecues, but because they can transmit West Nile virus between birds and humans. The virus can kill birds and can cause symptoms in humans ranging from prolonged fatigue to, in extreme cases, paralysis and coma.

The drought of recent years resulted in fewer cases of West Nile virus in birds and humans; last year, a single bird in San Francisco and another in San Mateo County were discovered with the virus, but no humans were affected. In 2008, San Mateo County had two West Nile-infected birds and San Francisco had none.

Though none have been found yet this year in either county, some 13 birds have been found dead of the virus in Santa Clara County — just one shy of the number found all of last year, according to Russ Parman, acting district manager for Santa Clara County’s Vector Control District.

Public health officials in San Mateo County are worried the virus could migrate north.

“There’s been late rains this year so we’re expecting the standing water to last a lot longer than it has in the last couple years,” said Chindi Peavey, laboratory director for the San Mateo County Mosquito Abatement District.

Brian Weber, who has been a technician for the district for five years, said his workload has increased this year. For example, he said he normally treats marshes along the Bay with hormones to discourage mosquitoes two to four times a season. But this year, he had to treat them five or six times because the repeated rains resulted in more mosquito larvae.

The San Francisco Department of Public Health has seen an uptick in complaints about mosquitoes, said Erin West, supervisor of the Mosquito Abatement Courier Team. The team, operated by pest control company Pestec, has been hired by The City to bike around town and treat standing bodies of water on public properties.

“We’re definitely anticipating a big year,” she said. “Last year, West Nile virus was at a pretty low number, but with all this rain, they’re actually anticipating a lot this year.”

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Katie Worth

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