Model suggests cattle insecticide could reduce sand fly population, leishmaniasis risk
Cattle treated with the long-lasting insecticide fipronil significantly would reduce visceral leishmaniasis via phlebotomine sand fly bites in environments where humans live closely among the livestock, according to recent study findings.
“This protozoan parasite results in an estimated 500,000 human infections and 50,000 human fatalities annually, making it the second most prevalent parasitic killer on Earth, behind only malaria,” researcher William E. Grant, PhD, of the department of wildlife and fisheries sciences at Texas A&M University, and colleagues wrote. “The highest global rate of occurrence is on the Indian subcontinent with approximately 67% of all human instances occurring in India, Bangladesh and Nepal. Bihar is the most impoverished, most densely populated and most [visceral leishmaniasis (VL)]-endemic state in India, with 90% of the Indian VL cases reported there.”
To determine fipronil’s effect on sand flies, Grant and colleagues executed a mathematical stochastic simulation model that described the insecticide-based drug’s mortality effects on a dense sand fly population in a Bihari village. The researchers wrote that cows supplied orally with safe, low concentrations of fipronil would result in reductions in blood-feeding sand flies and their larvae that feed on cattle feces. They then used the model to simulate fipronil control with different timing and frequency and compared scenarios on sand fly population reductions during peak exposure in June, July and August.
Single annual treatments applied in March, May, June or July effectively reduced the sand fly population in peak season within 30 to 60 days after treatment. The population, however, recovered quickly, the researchers wrote. The simulation also included treatments applied three times annually at 2-month intervals and determined that sand fly populations were reduced by about 90% during April and August when the insecticide was supplied in March vs. nontreatment. Treatments started in January and applied every 2 months reduced population peaks between June and August by 95%, and monthly treatments would result in sand fly extermination within 2 years, according to the model’s results.
Grant and colleagues recommended that a field trial to treat cattle with fipronil would offer a cost-effective solution for Bihari villagers.
“While more frequent applications obviously are more efficacious, they also are more expensive and more difficult logistically,” the researchers wrote. “Thus, the ability to assess not only efficacy of treatment schemes per se but also their cost-effectiveness and their logistical feasibility is of paramount importance.” – by Kate Sherrer
Disclosure: This study was funded by the Bill and Melinda Gates Foundation in effort by Genesis Laboratories. The researchers report no relevant financial disclosures.