Environment | Daily Report

bogdog Dan/FlickrCalifornia researchers suggest mosquitoes may be behind cancer cluster in Nevada.

Something happened to the children of Fallon, Nev., between 1997 and 2003.

Fourteen children were diagnosed with childhood leukemia, a rate for that population size that should only occur, by chance, once every 22,000 years, according to epidemiologists. The Fallon rate was 12 times higher than typically expected.

A new study by California researchers examines the geographic and seasonal occurrences of the diagnoses, and concludes that mosquitoes may have been behind the outbreak.

“The rural location of most cases suggests mosquitoes as a possible vector,” Joe Wiemels, an epidemiologist at UC San Francisco, told New Scientist Magazine.

In 2006, the Centers for Disease Control and Prevention released a study examining possible causes of childhood leukemia.

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The authors showed the disease:

• tends to occur in children between the ages of 2 and 5, when their immune systems are still “naive.”
• may be caused by viruses, as viruses have been shown to cause leukemia in animals, as well as other cancers in people. (The Epstein-Barr virus has been linked to Burkitt lymphoma, a cancer of the lymph system.)
• occurs predominantly in rural areas, where children’s immune systems have been challenged less than those living in urban areas
• may have a seasonal occurrence, showing up during warm and wet periods.

Wiemels and his co-authors took this all a step further by suggesting that because the town is home to a military community, and therefore has a high turnover of residents, a virus may have come into the town with military personnel. Once there, mosquitoes carried the vector and infected young children in the rural area who may already have had a genetic predisposition to leukemia.

"The temporality and seasonality of the epidemic curve is consistent with a point source exposure or an infectious agent acting out a classic 'outbreak' pattern," Wiemels said. And taken together with everything the epidemiological community and the CDC know about childhood leukemia, as well as the high population turnover in the town, it "suggests a possible infectious cause," he said.

Wiemels said there "was a spike in childhood leukemia rates across all military branches at the same time as the Fallon cluster," further supporting the notion that an infectious agent was at the root of the outbreak.

The CDC did not respond to requests for comment on the study.