A new season of West Nile virus – a potentially deadly disease spread by mosquitoes – is underway in Orange County.
Orange County Mosquito and Vector Control District officials say they collected mosquitoes Friday in La Habra and Seal Beach that tested positive for the virus, meaning that the insects are capable of spreading it to humans.
West Nile virus season typically runs from May to October, when the weather is warm and dry.
“It’s strikingly on time,” said Jared Dever, a vector control spokesman.
West Nile virus infection rates have intensified in Orange County the past couple of years, with back-to-back epidemics in 2014 and 2015 that struck 377 people and killed 17.
Many people infected with West Nile never show symptoms, but among those who do, many develop neurological complications, such as meningitis or encephalitis, which can lead to lifelong disabilities. Of last year’s 97 reported cases, 71 were neuro-invasive and five asymptomatic, according to OC Health Care Agency data.
Dever said it’s difficult to forecast how this season will unfold. But if there’s a high number of infected mosquitoes and birds, the district could launch an aerial attack, spraying low doses of the pesticide Duet from an airplane over targeted neighborhoods to kill adult mosquitoes.
Hundreds of parents have protested that proposal. Though Duet – which is highly toxic to bees – is registered with the Environmental Protection Agency, Dr. Dean Baker, director of UC Irvine’s Center for Occupational and Environmental Health, has said the EPA does not go far enough in testing the pesticide’s health effects on children.
District trustees are expected to talk about who has the authority to pull the trigger on aerial spraying at their Thursday meeting. Last month, trustees voted not to give the district’s manager unilateral power to make that decision.
“That’s definitely something the district manager wants to discuss at the board meeting, the alternative to ‘adulticiding,’ bolstering outreach and education, and the authority to do the aerial application, that was left largely unresolved,” Dever said.
West Nile virus seasons weren’t always so unpredictable.
Scientists once knew that every fourth year – most recently 2004, 2008 and 2012 – would bring a high number of human infections. The four-year waves coincide with the life cycle of birds, an important part of the West Nile virus transmission cycle.
Mosquitoes pick up the virus after biting an infected bird, then pass it on to more birds. Once a bird has the disease, it becomes immune for its short life, but its offspring will be susceptible.
The years 2014 and 2015, however, “didn’t play by the rules,” Dever said, and officials do not know why.
Contact the writer: jchandler@ocregister.com and @jennakchandler on Twitter
