Monday, October 27, 2008 at 5:41 pm
Subprime mortgages have ruined banks and insurance companies and brought the global economy to its knees. Now it looks like they’re also causing the spread of deadly West Nile disease.
In a weird new wrinkle in the story of the exploding mortgage crisis, the housing market in Bakersfield, Calif., was tied to a 276 percent increase in the number of West Nile virus cases, according to the November issue of the scientific journal, Emerging Infectious Diseases.
It’s easy to find correlations between seemingly unrelated events; epidemiological journals are full of stuff like this which doesn’t mean a thing. For example, as ice cream consumption increases, so do drownings. But it’s not because ice cream causes drowning.
In this case, though, the cause-and-effect link is pretty clear. Delinquent mortgages in Bakersfield and the surrounding community caused people to abandon their houses, and mosquitoes carrying West Nile virus bred in their untended swimming pools. The resulting outbreak is a epidemiologists’ textbook case of the unintended consequences of economic turmoil. It’s not the first such example, and undoubtedly won’t be the last before the crisis ends.
“We’ve had problems with West Nile in California since 2004, but in 2007 the housing market really went south and it resulted in a lot of neglected swimming pools,” said lead author William K. Reisen, an entomologist at the University of California, Davis. “They’ve always had problems with homeowner neglect of pools. But all of a sudden, it went through the roof.”
There were 140 confirmed human cases of West Nile virus in the Bakersfield area in 2007, the largest outbreak in California, and the worst mosquito-born encephalitis virus outbreak in Kern County since 1952. At least two patients — one, a 96-year-old woman — died of the disease, which can also cause brain damage.
The outbreak spread to several other counties and led Gov. Arnold Schwarzenegger to hold a news conference and release $6.2 million in emergency mosquito abatement funds.
Insect-borne microorganisms thrive in times of economic crisis and dislocation. For example, mosquito-borne dengue fever has surged in the growing cities of Asia and Latin America in the past decade; as people move into urban areas that lack running water, they store water in tanks that are perfect breeding grounds for mosquitoes like Aedes aegypti, the leading dengue vector.
Count the Kern County West Nile outbreak in that category. “What’s worrisome is that most U.S. mosquito abatement districts are funded by property taxes,” said Reisen. “As their revenue falls, it’s going to be harder to keep up with the abandoned swimming pools.”
West Nile has spread gradually across the United States since the first cases were reported in 1999 in New York City. It’s carried by several different species of mosquitoes and can infect many birds and mammals — from crows and chickens to cats and horses. In different areas of the country, the epidemic has generally slowed after the virus kills off a large enough number of the birds that carry it from place to place. Only about one in 100 people exposed to the virus become ill; about three percent of those it sickens die from this disease.
No one in Kern County had anticipated the 2007 outbreak. Winter and spring rains were light, and the Kern River, which flows through Bakersfield and sometimes leaves pools of water where mosquitoes can breed, was dry. In fact, water was so short that it changed the bird ecology of the region, resulting in an expansion of house sparrow flocks. Unlike other bird populations in the area, most of the sparrows lacked protective immunity to West Nile virus.
The county Mosquito and Vector Control District conducted an aerial survey of the town that showed an extensive number of green or neglected pools, “most of which were producing mosquitoes,” according to the article in Emerging Infectious Diseases.
“The likely reasons for neglected pools,” reported the journal, which is published by the Centers for Disease Control, “are the adjustable rate mortgage and associated housing crises in Kern County and throughout California, which have led to increased house sales and abandonments.” Kern County suffered a 300 percent increase in delinquencies in the spring quarter of 2007 compared with the same period in 2006.
As chlorine-based chemicals deteriorated in the abandoned pools, “invasive algal blooms created green swimming pools that were exploited rapidly by urban mosquitoes, thereby establishing a myriad of larval habitats within suburban neighborhoods.”
By California law, properties with swimming pools must be surrounded by six-foot-high fences, and so it has been difficult for mosquito control agents to enter foreclosed properties. “They can’t just go breaking the doors down,” said Reisen. “It’s kind of a mystery how to get access to these properties.”
The major carrier of West Nile during the 2007 outbreak was the common mosquito Culex pipiens. But by this year, Culex tarsalis, a more efficient West Nile carrier that typically colonizes rural areas, had moved into some of them.
That said, no human cases had been reported in 2008 as of Oct. 23, though the disease continued to infect mosquitoes and kill birds and horses. Kern County officials have been vigilant in spraying the abandoned pools or stocking them with larva-eating fish.
Then too, West Nile outbreaks are sporadic, and seem to depend on complex factors in the virus’ hosts. High temperatures, raising the viral load of mosquitoes, are one such factor; a die-off of the crow population, causing the virus to run out of hosts, can also play a role.
The Bakersfield story presents another such factor: the crashing of American dreams.
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