Yellow Fever Mosquito Found in Castro Valley

For the first time, the yellow fever mosquito, scientifically known as Aedes aegypti, has been spotted in Castro Valley. This particular mosquito has been showing up in various parts of California since arriving in 2013, and its increasing presence is raising alarms. It’s known to transmit serious diseases like dengue, Zika, and yellow fever, which is concerning for public health.

On July 20, several Aedes aegypti mosquitoes were identified in traps set up in Castro Valley, according to the Alameda County Mosquito Abatement District. In response, officials have begun applying an insecticide to target mosquito larvae in the area where the mosquitoes were found.

Erika Castillo, who oversees regulatory and public affairs for the abatement district, noted that the recent humid conditions, influenced by monsoonal moisture and remnants of a tropical storm, have created an environment favorable for these mosquitoes, which are originally from Africa.

Castillo elaborated that these insects typically thrive in tropical climates, so the current humid weather is quite suitable for them.

Aedes aegypti generally inhabit Southern and Central California. Although they’ve caused rare local outbreaks of dengue fever in recent years, these occurrences haven’t taken place in the Bay Area thus far.

With an El Niño developing in the Pacific Ocean, local officials are closely monitoring the situation to see if Aedes aegypti continue their spread across the Bay Area. El Niño conditions can lead to warmer ocean waters along the equator, potentially resulting in more hot, humid weather that is ideal for mosquito proliferation.

Taylor Kelly, who manages scientific and technical services for the Santa Clara County Mosquito and Vector Control District, explained that humidity is crucial for Aedes aegypti, which can easily dry out in arid conditions.

“They thrive in hot temperatures,” she pointed out, adding that warmer weather can accelerate their reproduction. “This humidity can really enhance their survival rates,” she said.

Kelly mentioned that while Santa Clara has seen a slight increase in Aedes aegypti activity this year, significant peaks are expected later in the summer.

“We’re just starting to see their numbers rise,” she stated. Unfortunately, a hot climate might also lead to more frequent mosquito bites.

Additionally, Kelly noted that Santa Clara is experiencing a notable increase in native mosquito species. While these won’t transmit dengue, they can carry the West Nile virus. The California Department of Public Health has reported heightened West Nile virus activity in both mosquitoes and birds, which raises the risk for human infection.

Dr. Peter Chin-Hong, an infectious disease expert and professor at UC San Francisco, explained that as hot weather reduces water availability, birds and mosquitoes congregate in the same areas. Mosquitoes then feed on infected birds, which are primary carriers of the virus, and can transmit it to humans.

Furthermore, he mentioned that elevated temperatures can shorten the incubation period for West Nile virus in mosquitoes. “So when a mosquito gets infected from the bird, it means it has less time before it bites a human, increasing the risk of virus transmission,” he concluded.