26
Apr
CDC Study: Pesticide Use Does Not Reduce Risk of Lyme, Other Tick-Borne Disease
(Beyond Pesticides, April 26, 2022) Using pesticides to reduce the number of ticks in residential areas does not translate to lower rates of tick-borne disease in humans. This finding is the culmination of research overseen by scientists at the U.S. Centers for Disease Control and Prevention (CDC), which have been studying the effectiveness of pesticides to manage tick bites and tick borne-diseases for over a decade. While earlier research focused on direct pesticide applications to individual household lawns, the most recent publication, under early release in the Journal of Emerging Infectious Diseases, represented a broader, neighborhood-wide implementation of control measures. Yet in both instances, pesticide use did not play a role in reducing tick-borne disease. The studies are a stark warning for states and communities considering vector disease spray campaign for ticks in a similar manner to mosquito spraying. “The bottom line is that toxic pesticide use is not the answer to tick bites or tick-borne disease,” said Beyond Pesticides executive director Jay Feldman. “To manage ticks, we must embrace ecological solutions that work with natural processes and education campaigns emphasizing personal protection.”
Researchers set out to test two methods of broad area tick control in 24 residential neighborhoods in Dutchess County, NY. The first method, called the tick control system (TCS), includes the use of bait boxes that attract rodents. Exiting the bait box, rodents encounter brushes that coat them with the insecticide fipronil in attempts to kill any ticks present and prevent future ticks from latching. This system aims to stop ticks from feeding on a white footed mice, the primary disease vector for Lyme disease. The other method employed a biological insecticide called Met52, a spray utilizing a fungus that claims to kill ticks in the environment.
Although fipronil represents a highly toxic pesticide that can cause environmental harm even at very small amounts, this study design is an improvement on the hazards to study subjects in previous studies supported by the Centers for Disease Control and Prevention (CDC). Prior research on tick disease from individual household lawns employed sprays of the synthetic pyrethroid bifenthrin, which is a possible carcinogen, and has been linked to neurotoxicity and a range of developmental problems. Families enrolled in the study did not know whether bifenthrin was applied to their lawns, and Beyond Pesticides expressed concerns that they were not provided full information about the hazards associated with the chemical.
The present study, while well-designed, likewise kept certain residents in the dark regarding whether the application to their property was real or a placebo. The questionable ethics of the study notwithstanding, four treatments were established, as the authors indicate, “[i] placebo TCS boxes and placebo Met52, [ii] placebo TCS boxes and active Met52, [iii]active TCS boxes and placebo Met52,[iv] and active TCS boxes and active Met52.” All neighborhoods active in the study had high incidence of Lyme disease and moderate density of one- or two-family homes.
Bait boxes were placed in areas frequented by small mammals, and Met52 was applied via truck-mounted high-pressure sprayers (placebo groups received water for this application) twice per year during peak nymphal tick activity. Introductory and bi-weekly surveys were provided to participating households, and researchers recorded information on general tick abundance, tick burden on rodents, pet tick encounters and disease, and human tick encounters and disease.
The number of ticks collected in neighborhoods was reduced by 53% after using TCS, but reductions from Met52 were not found to be statistically significant. The number of ticks reported on white-footed mice was also reduced by roughly half due to TCS boxes, but Met52 again showed no statistical reduction. The number of ticks found on pets was not reduced to a statistically significant level, but incidence of disease was half of what it was in prior years for both TCS and Met52 applied neighborhoods. For humans, however, no statistical reduction in tick encounters was experienced, nor was there any reduction in the number of reported tick-borne diseases during the study period.
Researchers indicate that the differences seen between humans and pets could relate to the way they act when outside, with pets potentially spending more time in areas where ticks frequent. They also note, “The observed effect of the active interventions on TBDs [tick-borne diseases] in outdoor pets should be interpreted cautiously.” Authors did not confirm the presence of tick- borne disease in pets through veterinarians, but instead relied on survey results from participants.
With years of data now available showing no evidence that pesticide use will reduce the rate of tick-borne illnesses in people, individuals must re-double personal preventive methods. Ticks can move about one’s body for a long period of time before finding a spot they want to bite – often around the head, ears, and other creases or warm areas of the body. It takes between 24 to 48 hours for a tick to transmit Lyme disease after a bite.** This makes regular tick checks and tick removal of paramount importance. In areas that are potential tick habitats, wear light-colored clothing that covers the body (especially your legs) because it makes it easier to spot ticks so they can be removed before they bite. Although many folks balk at the idea of wearing long-sleeved clothing in the warmer months of the year, consider the range of materials available, such as sun-protective shirts and pants that can provide a thin but effective barrier. Use unscented deodorant, soap and shampoo, save for pine tar soap, which has a natural pine scent which can keep ticks from biting once they have been picked up. Similarly, you can try using least-toxic herbal repellents such as oil of lemon eucalyptus and essential oils. Most importantly, after you have walked through high grass in a tick infested area, check the entire body for ticks and shower to wash off any ticks that have not yet become embedded. This practice is essential for hikes and in residential areas of high tick activity. Treat it like any other personal care routine, like brushing and flossing – and make it a regular part of your outdoor activities.
Much like bed bugs, which are notoriously difficult to control with pesticides, ticks can find cracks, nooks, crannies and a myriad of other hiding spots that pesticides cannot reach. And merely killing ticks that may latch onto mice does not appear to make enough of an impact to lower disease rates. Future research by CDC should study the impact of more focused ecological interventions on tick populations, which may include surveys of tick-eating insects, birds, and mammals, and their impact on tick populations, the efficacy of installing possum houses, or surveys of mouse-eating reptiles, birds, and mammals and how they impact the mouse population vector of Lyme disease.
As tick populations rise, there is increasing pressure on Homeowner Associations (HOAs), cities, counties and other local jurisdictions to spray pesticides to manage ticks populations. Pesticide companies likewise will often use mailers or go door to door selling pesticide sprays with a promise of a safer yard. Yet with two strong studies from CDC showing these practices to be ineffective, residents across the country are encouraged to push back strongly against pesticide use suggestions for ticks. Those receiving a spray are less likely to take personal protective measures, thinking that the pesticide will do its job. Harming one’s self, neighbors, wildlife and local ecology with toxic sprays for a false peace of mind is not acceptable.
For more information on managing tick-borne disease, see Beyond Pesticides daily news article on the previous CDC study, as well our ManageSafe entry on ticks.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Emerging Infectious Diseases (early release)
**A 2015 review found that there is no minimum tick attachment time for Lyme transmission. CDC indicates that the risk under 24 hours is “extremely small,” but caution should be made to remove a tick as soon as possible after attachment. Lymedisease.org provides resources for what do to after a tick bite. Apart from Lyme, some tick-borne diseases are transmitted rapidly after attachment.
