A Tale of Two Colorado Cities and WNv Disease Control
(Beyond Pesticides, May 4, 2007) Recently published research comparing two adjacent Colorado cities shows an unexpected correlation between West Nile virus (WNv), mosquito control programs and human behavior factors.
Northern Colorado experienced major outbreaks of human WNv disease in 2003. However, the neuroinvasive disease rates recorded were higher in Loveland (38.6 vs. 15.9 per 100,000), which had a more extensive mosquito control program and fewer mosquitoes, than adjacent Fort Collins.
The study, entitled â€œBehavioral Risks for West Nile Virus Disease, Northern Colorado, 2003” (Gujral et al., Emerging Infectious Diseases, Vol. 13, No. 3), calls into question the ability of spray programs to actually reduce the risk and transmission of the virus. Additionally, it shows spray programs may be giving communities a false sense of security, and re-emphasizes the importance of personal preventative measures in lowering disease rates.
During the height of the outbreak, from July 26 to September 5, 2003, the number of mosquitoes (Cx. tarsalis and Cx. pipiens) collected per trap night was higher in Fort Collins than in Loveland, and the WNv infection rates of the mosquitoes were approximately equivalent in the two cities during that period. In other words, more WNv-infected mosquitoes were present in Fort Collins than in Loveland.
Loveland had an integrated mosquito control program in place since 1986. In contrast, Fort Collins reacted to the outbreak by implementing an emergency mosquito control program later in the outbreak (mid-August through early September).
After a full analysis of public perception and behavior, the authors were left with this question, â€œDid Loveland residents choose to rely on the cityâ€™s control program instead of practicing individual preventive measures?” They concluded that Loveland residents may have been less likely to have applied personal preventive measures given their reliance on the long-standing community mosquito control program.
In an effort to explain the findings, a telephone survey was conducted to assess differences in personal protection and risk practices by each cityâ€™s residents. In Larimer County, which encompasses both Fort Collins and Loveland, health officials encourage residents to â€œFight the Bite,” with the typically recommended four Ds of prevention: (1) DEET (Beyond Pesticides recommends using less toxic repellents, such as oil of lemon eucalyptus or picaridin (KBR 3023) products) – wear an insect repellent containing DEET (N,N-diethyl-m-toluamide); 2) Dress – wear long sleeves and long pants; 3) Drain – drain standing water around the home; and 4) Dusk to dawn – limit time outdoors during this time.
The study concluded that personal protective practices may directly influence rates of WNv infection and remain important even when comprehensive community mosquito control measures are implemented.
- Loveland residents were 39% more likely to report seldom or never using DEET, and 30% were more likely to report being outdoors during prime mosquito-biting hours than Fort Collins residents.
- No statistically significant difference was observed between Fort Collins and Loveland residents who reported seldom or never wearing long clothes to protect against mosquitoes.
- According to the authors, the drain model was omitted after careful review of the survey question deemed it too vague for a meaningful interpretation. This was unfortunate because draining water from around a residence may reduce exposure to mosquito breeding sites.
- Compared with the Fort Collins residents, Loveland survey participants were 35% more likely to report spending greater than five hours outdoors during the week, and 30% more likely to report spending greater than two hours outdoors on weekends from dusk to dawn.
The authors conclude WNv neuroinvasive disease rates may be due, in part, to lower use of repellents containing DEET (they did not discuss other repellents) and greater dusk to dawn outdoor exposure among Loveland residents. They also note that persons with lower incomes reported practicing fewer preventive behavioral measures. They emphasize that these findings support the benefit of promoting personal prevention approaches, particularly by using effective insect repellents and reducing exposure to mosquitoes during prime-biting hours.
Beyond Pesticides believes the ideal mosquito management strategy emphasizes education, aggressive removal of standing water sources, larval control, monitoring and surveillance for both mosquito-borne illness and pesticide-related illness. The decision to use pesticides meant for adult mosquito control should be open to public discussion and only made after carefully evaluating all the contributing factors to human epidemics. Citizens should also be given the right to opt-out of spray programs and notice in advance so they can protect themselves.
TAKE ACTION: Find out about safer mosquito repellents, smart community mosquito management, and public service annoucements you can request to be played on your local radio station at https://www.beyondpesticides.org/mosquito.