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Wednesday, October 27, 2021

Foreclosure blight may breed West Nile Virus

California’s housing market slump may be breeding stress and discontent, but a new study shows that the ongoing foreclosure crisis may also breed disease.

According to researchers at UC Davis and the Kern Mosquito and Vector Control District, a rise in the number of neglected pools associated with abandoned homes in Bakersfield coincided with the city’s first West Nile Virus epidemic, which was also the largest outbreak of the disease in California last year.

Human cases of WNV in the Bakersfield area of Kern County rose nearly fourfold from previous years to 140 in 2007.

This was unexpected based on surveillance factors that pointed toward a mild risk for an epidemic, said William Reisen, a professor in the department of pathology, microbiology and immunology at UC Davis and research entomologist with the Center for Vectorborne Diseases, who led the study.

Hot and dry conditions in the area that year stunted the growth of rural populations of mosquitoes that transmit WNV to humans and birds, which is usually an indicator of a low risk for a WNV epidemic.

What I hadn’t counted on was [the mosquitoes‘] concentration into urban areas, as well as swimming pools replacing the normal ground pools where the mosquitoes breed,he said.

Researchers tested mosquitoes collected from traps in Bakersfield for the presence of WNV DNA, which is an indicator for infection. They found that the infection rate in these mosquitoes had increased much earlier in 2007 than in previous years.

The researchers also found that a growing population of house sparrows had low immunity to the virus and comprised a significant percentage of WNV-positive dead birds.

This indicates that more mosquitoes were feeding on susceptible bird species in Bakersfield where there is water and food for the birds, Reisen said.

The increased risk of infection in birds was closely followed by the human outbreak, which spurred the Governor’s Office to provide emergency funds for mosquito surveillance and control.

Subsequent aerial surveys and examination of service requests for mosquito control showed a large number of unmaintained swimming pools, many of which had turned green with algae and become fertile breeding grounds for mosquitoes.

Bakersfield had been hit hard by the housing crisis, as indicated by a fourfold increase in notices of payment delinquency in 2007 compared to 2006. The researchers speculate that this situation led to an expansion in neglected swimming pools.

It just seems like everything came together as sort of a perfect storm [for WNV] in Kern County last summer,Reisen said.

According to the California Department of Public Health website, there have been no reported human cases of WNV in the county this year.

I think the extra attention to the swimming pool problem really made a huge difference,Reisen said.

Early season surveillance to identify and treat neglected pools, as well as timely extermination of mosquito populations harboring WNV helped prevent further spread of the virus this year, he said.

Similar programs to address the problem of neglected pools have been enacted across the state.

In terms of areas where there were the most foreclosures, we saw an icrease in unmaintained swimming pools [last year],said Joel Buettner, ecological management specialist for the Sacramento-Yolo County Mosquito Control District.

The success of our program comes from the district working with neighbors, real estate agents and various county agencies to identify and treat problem pools, as well as media outreach for public awarenesssaid Luz Rodriguez, the district’s public information officer.

We do think that we were able to alleviate a significant mosquito source [pools] in our districtthat has made a positive impact on reducing public health concerns,Buettner said.

Cases of WNV dropped from 27 in 2007 to 14 this year in Sacramento and Yolo counties.

Yet the number of neglected pools in Kern and Sacramento counties is increasing.

With less money from property tax revenue to support the district’s program as home values decrease and foreclosures increase in Kern County, resources could be stretched thin if there is a wet year, Reisen said.

And there could be a new danger in town.

Culex tarsalis, a mosquito typically found in rural areas, is moving in and exploiting neglected pools not only in Kern County, but all over the state this year, Reisen said.

This species is more efficient at spreading WNV than the Culex pipiens mosquito commonly found in urban areas.

It’s a very complex ecosystem that we’re trying to manage,Buettner said.So it’s difficult to actually put our finger on whether reducing the swimming pool problem had a positive outcome.

WNV arrived in California in 2003. The potentially lethal virus can cause fever, headache, coma, paralysis and other symptoms, according to the state Department of Public Health.

ELAINE HSIA can be reached at adbonde@ucdavis.edu.

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