PSR/Sacramento Position with Regard to

August 20, 2005

West Nile Virus, one of many viruses which can be spread to humans by the bites of infected mosquitoes, was first reported to cause human infection in the U.S. in 1999 and in California in 2002. In 2004, 830 human West Nile Virus infections were identified in California. Although there was an increase in reported West Nile Virus cases in California from 2003 to 2004, nationwide, the number of reported cases went down from over 10,000 cases in 2003 to fewer than 3,000 cases in 2004.

The incidence of mosquito-borne viral infections typically increases in the summer and declines in the late fall and winter. During the past few weeks, a sharp increase in the number of reported human West Nile Virus infections has been noted in Sacramento County. In most cases, human infection with West Nile Virus causes no symptoms. In some cases, infection causes a flu-like syndrome with fever, muscle aches, headache, and a rash. In rare cases (less than one per cent), infection with West Nile Virus causes a serious brain infection, called encephalitis, which can be fatal. Most cases of fatal West Nile Virus infection occur in the elderly, though fatal cases have also been reported in teenagers and young adults. In the entire United States in 2004, there were 84 reported deaths due to West Nile Virus.

The Sacramento-Yolo Mosquito and Vector Control District recently decided to begin widespread truck and aerial spraying of Sacramento County with an insecticide combination called Evergreen EC 60-6 to in an attempt to reduce the mosquito population and the risk of human West Nile Virus infection. Evergreen EC 60-6 contains a combination of pyrethrins and piperonyl butoxide as active ingredients. Both ingredients are toxic to other insects besides mosquitoes, as well as to fish and other aquatic species. Direct exposure to humans can cause immediate eye, skin, and respiratory irritation, as well as gastrointestinal and neurologic symptoms. Significant immediate toxic effects are unlikely to occur, though, with the low concentrations used in the current truck and aerial spraying, in the absence of an accident or misuse of the insecticide.

Of potentially greater concern is that both pyrethrins and piperonyl butoxide have been shown to cause mutations in laboratory studies, and exposure to these agents has been reported to be associated with an increased risk of cancer either in humans or in laboratory animals. The U.S. Environmental Protection Agency has classified pyrethrins as "likely to be carcinogenic to humans" and piperonyl butoxide as a "possible human carcinogen." Although the dose and duration of exposure in the studies linking these agents to cancer are greater than one would expect than with the current truck and aerial spraying, it is possible that smaller doses to a larger number of people could also lead to an increased incidence of certain forms of cancer, and that these cancers would not be detected until many years after the exposure.

Though the risk of acquiring cancer or other toxicity from the current widespread pesticide spraying is probably very low, the risk of acquiring serious West Nile Virus infection in people who take reasonable precautions to avoid being bitten by mosquitoes is also probably very low. There is currently very limited scientific data available regarding the long-term risks versus benefits of widespread pesticide spraying for the control of West Nile Virus. In the practice of medicine, when the risk to benefit ratio of a treatment is unknown, the general rule is to "First, do no harm," and to get the informed consent of the patient before initiating any such treatment. PSR/Sacramento believes that these same general principles should apply to widespread spraying of pesticides for control of mosquito-borne viruses. On the other hand, given the recent sharp increase in reported West Nile Virus cases in the Sacramento region, PSR/Sacramento believes that it was reasonable for public health officials to recommend short-term, low dose truck and aerial spraying with the least toxic pesticides currently available.

PSR/Sacramento believes that more research needs to be done on the long-term risks versus benefits of widespread pesticide spraying for control of mosquito-borne viruses, and that further research is also needed on the risks versus benefits of other more common uses of pesticides, including the household use of over the counter products.

PSR/Sacramento endorses the following recommendations from the Association of State and Territorial Health Officials report on mosquito control:

Finally, PSR/Sacramento believes that all parties involved in discussions regarding pesticide spraying for the control of mosquito-borne illnesses should address each another in a mutually respectful manner, and that such discussions should be founded on best available science and principles of public health.

References

California Department of Health Services. West Nile Basics. Available at http://westnile.ca.gov/West Nile Virus_basics.htm

California Department of Health Services. West Nile Virus Home. Available at http://westnile.ca.gov/

Pogoda JM, Preston-Martin S. Household pesticides and risk of pediatric brain tumors. Environmental Health Perspectives; 1997:105:1214-1220.

Laborda HA. Mutagenic activity in synthetic pyrethroids in Salmonella typhimurium. Mutagenesis 1988;3:509-14.

Suzuki H, Suxuki N. Piperonyl butoxide mutagenicity in human Rsa cells. Mutation Research 1995; 344:27-30.

Takahashi O, Iishi S, Fujinati T, et al. Chronic toxicity studies of piperonyl butoxide in F344 rats: induction of hepatocellular carcinoma. Fundamentals of Applied Toxicology 1994;22:293-303.

Brown LM, Blair A, Gibson R, et al. Pesticide exposures and other agricultural risk factors for leukemia among men in Iowa and Minnesota. Cancer Research 1990;50:6585-91.

Public Health Confronts the Mosquito: Developing Sustainable State and Local Mosquito Control Programs. Recommendations of the Mosquito Control Collaborative - A Project of the Association of State and Territorial Health Officials. Supported by the U.S. Centers for Disease Control and Prevention. February, 2005

Chemicals evaluated for carcinogenic potential. Science Information Management Branch, Health Effects Division, Office of Pesticide Programs. U.S. Environmental Protection Agency. Available at: http://www.epi.uci.edu/valleycenter/epalistcarcinogenicchemicals.pdf