Drought conditions could raise risk of West Nile virus


Add increased potential for mosquito-borne illnesses to the list of concerns raised by the prospect of a drought.

"Drought conditions can turn a once healthy and flowing creek into a limited water source for mosquitoes and birds. The high concentration of the two allows for greater virus transmission between them and eventually to people," Contra Costa Mosquito and Vector Control District spokeswoman Deborah Bass said.

In drought years, dried up creeks and rivers can lead to the presence of scattered and still water puddles, which act as ideal spots for female mosquitoes to lay their fragile eggs, Bass explained in the district's January newsletter.

These leftover puddles become important sources of water for birds and other creatures, resulting in many birds (which can carry West Nile virus) and mosquitoes (which can transmit the virus to humans) being placed in close proximity, she said.

Last year, two people reported contracting West Nile virus in Contra Costa County while 13 mosquito samples and 68 dead birds -- including four from Danville -- tested positive for the virus in the county, according to district officials. Most of those instances occurred during the summer months.

Another drought factor would be the reduction of mosquito-eating fish, whose habitats could dry up, Bass said. And should rain eventually come, the water would collect in areas that no longer contain those fish, she added.

As a result, district technicians are prepared to increase mosquitofish stocking to re-establish fish populations in those water sources, according to Bass.

"Without these predators, mosquito activity can flourish. More mosquitoes may mean more virus," she said.

District officials ask county residents to be even more cognizant of standing water and mosquito activity in light of predicted drought conditions.

"From large flowing streams to scattered water puddles, the landscape may be a challenge for us this year," general manager Craig Downs said. "Every year is different, and we're used to and good at adapting, but the real challenge will be for homeowners who might not know the significance a water puddle can make. Think exponential."

Mosquitoes able to transmit West Nile virus in the county can lay as many as 400 eggs in as little as two tablespoons of water, according to district officials.

The district recommends people regularly check their yards for mosquitoes and avoid over-watering to compensate for drought conditions because doing so could create puddles and fill underground catch-basins where mosquitoes could flourish undetected.

People who discover mosquito activity should contact the district at 771-6196. More information can be found on the district website.


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