Department of Land Resources & Environmental Sciences
Montana State University
Bozeman, MT 

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A human-health risk assessment for West Nile virus and insecticides used in mosquito management

Robert K. D. Peterson, Paula A. Macedo, and Ryan S. Davis

ABSTRACT

West Nile Virus (WNV) has become a major public health concern in North America since 1999 when the first outbreak in the Western Hemisphere occurred in New York City. As a result of this ongoing disease outbreak, management of mosquitoes which vector WNV throughout the U.S. and Canada has necessitated using insecticides in areas where they traditionally have not been used, or have been used less.  This has resulted in concerns by the public about the risks from insecticide use. The objective of this study was to use reasonable worst-case risk assessment methodologies to evaluate human-health risks for WNV and the insecticides most commonly used to control adult mosquitoes.
We evaluated documented health effects from WNV infection and determined potential population risks based on reported frequencies. We determined potential acute (1 day) and subchronic (90 day) multi-route residential exposures from each insecticide for several human subgroups. We then compared potential insecticide exposures to toxicological and regulatory effect levels. Risk quotients (RQ’s, the ratio of exposure to toxicological effect) were less than 1.0 for all subgroups. Acute RQ’s ranged from 0.0004 to 0.4726. Subchronic RQ’s ranged from 0.00014 to 0.2074. Results from our risk assessment and the current weight of scientific evidence suggest that human-health risks from residential exposure to mosquito insecticides are low and are not likely to exceed levels of concern. Further, our results suggest that, based on human-health criteria, the risks from WNV exceed the risks from exposure to mosquito insecticides.      

Peterson, R.K.D., Macedo, P.A., and Davis, R.S. 2006. A human health risk assessment of West Nile Virus and insecticides used in mosquito management. Environmental Health Perspectives 114 (3): 366-372. (PDF)     

Paula A. Macedo, Robert K. D. Peterson, and Ryan S. Davis

ABSTRACT

Infectious diseases are problematic for deployed military forces throughout the world, and, historically, more military service days have been lost to insect-vectored diseases than to combat.  Because of the limitations in efficacy and availability of both vaccines and therapeutic drugs, vector management often is the best tool that military personnel have against most vector-borne pathogens. However, the use of insecticides may raise concerns about the safety of their effects on the health of the military personnel exposed to them. Therefore, our objective was to use risk assessment methodologies to evaluate health risks to deployed U.S. military personnel from vector management tactics. Our conservative tier-1, quantitative risk assessment focused on acute, subchronic, and chronic exposures and cancer risks to military personnel after insecticide application and use of personal protective measures in different scenarios. Exposures were estimated for every scenario, chemical, and pathway. Acute, subchronic, and chronic risks were assessed using a margin of exposure (MOE) approach. Our MOE was the ratio of a no-observed-adverse-effect-level (NOAEL) to an estimated exposure. MOEs were greater than the levels of concern (LOCs) for all surface residual and indoor space spraying exposures, except acute dermal exposure to lambda-cyhalothrin. MOEs were greater than the LOCs for all chemicals in the truck-mounted ultra-low-volume (ULV) exposure scenario. The aggregate cancer risk for permethrin exceeded 1 x 10^-6, but more realistic exposure refinements would reduce the cancer risk below that value. Overall, results indicate that health risks from exposures to insecticides and personal protective measures used by military personnel are low.

Macedo, P.A., R.K.D. Peterson, and R.S. Davis. 2007. Risk assessments for exposure of deployed military personnel to insecticides and personal protective measures used for disease-vector management. Journal of Toxicology and Environmental Health, Part A 70: 1758–1771. (PDF)

Risk assessments for the insect repellents DEET and picaridin

Frank B. Antwi, Leslie M. Shama, and Robert K. D. Peterson

ABSTRACT

For the use of topical insect repellents, DEET and picaridin, human health risk assessments were conducted for various population subgroups.  Acute, subchronic, and chronic dermal exposures were examined.  No-observed-effect-levels (NOELs) of 200, 300, and 100 mg/kg body weight (BW) were used as endpoints for DEET for acute, subchronic, and chronic exposures, respectively. For picaridin, a NOEL of 2000 mg/kg BW/day for acute exposure and a NOEL of 200 mg/kg BW/day for subchronic and chronic exposures were used. Daily exposures to several population subgroups were estimated. Risks were characterized using the Margin of Exposure (MOE) method (NOEL divided by the estimated exposure), whereby estimated MOEs were compared to an MOE of 100. Estimates of daily exposures ranged from 2 to 59 mg/kg BW/day for DEET and 2 to 22 mg/kg BW/day for picaridin. Children had the lowest MOEs. However, none of the estimated exposures exceeded NOELs for either repellent. At 40% DEET for acute exposure, children 612 years had MOEs below 100. For subchronic and chronic exposures children at 25% DEET and at 15% picaridin had MOEs below 100. Therefore, we found no significant toxicological risks from typical usage of these topical insect repellents.

Antwi, F.B., L.M. Shama, and R.K.D. Peterson. 2008. Risk assessments for the insect repellents DEET and picaridin. Regul. Toxicol. Pharmacol. doi:10.1016/j.yrtph.2008.03.002.
 

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 Other Reports and Articles dealing with Human Health:
Karpati, A.M., Perrin, M.C., Matte, T., Leighton, J., Schwartz, J., & Barr, R.G. 2004. Pesticide spraying for West Nile virus control and emergency department asthma visits in New York City, 2000. Environmental Health Perspectives 112:1183-1187.

Currier, M., McNeill, M., Campbell, D., Newton, N., Marr, J.S., Perry, E., Berg, S.W., Barr, D.B., Luber, G.E., Kieszak, S.M., Rogers, H.S., Backer, S.C., Belson, M.G., Rubin, C., Azziz-Baumgartner, E., & Duprey, Z.H. 2005. Human Exposure to Mosquito-Control Pesticides---Mississippi, North Carolina, and Virginia, 2002 and 2003. MMWR Morbidity and Mortality Weekly Report 54:529-532.

Carr, W.C., Iyer, P., & Gammon, D.W. 2006. A dietary risk assessment of the pyrethoid insecticide resmethrin associated with its use for West Nile virus mosquito vector control in California. The Scientific World Journal 6:279-290.