Ivermectin halts spread of river blindness, could interrupt West Nile virus transmission
Although not recommended to treat COVID-19, ivermectin has shown the potential to stop the spread of some infectious diseases, according to several studies presented at the American Society of Tropical Medicine and Hygiene Annual Meeting.
One study assessed the use of ivermectin for interrupting the spread and transmission of West Nile virus.
“This study came about as an investigation of a novel West Nile virus control strategy,” Karen Holcomb, PhD, a recent graduate from the University of California, Davis, told Healio.
She noted that West Nile virus is still the leading cause of mosquito-borne disease in the U.S., and unfortunately, current mosquito control strategies are limited in reducing viral transmission.
“The mosquitocidal properties of ivermectin, which involve a different mode of action than that of currently utilized insecticides, and well-documented history of safe use in mammals and birds, make ivermectin a promising alternative control strategy,” Holcomb said.
Treating birds to kill mosquitoes
Holcomb and colleagues hypothesized that treating birds that are commonly fed upon by mosquitoes could reduce West Nile virus transmission by killing mosquitoes before they take another bloodmeal, preventing future infections. Ivermectin is deadly for mosquitoes but not birds.
To assess the efficacy and feasibility of this strategy, Holcomb and colleagues first placed 48 chickens into four treated and four untreated control flocks in backyard coops across Davis, California, administering ivermectin daily in feed to treated flocks between July and September 2019. According to the study, they monitored serum ivermectin levels and tested for West Nile virus antibodies in all of the chickens.
Overall, the study showed that West Nile virus seroconversions were reduced in treated flocks compared with untreated flocks, indicating reduced transmission intensity at treated coops. Holcomb said subsequent modeling suggested that deploying ivermectin-treated bird feeders could result in a reduction of more than 60% in biting of West Nile virus-infected mosquitoes within a neighborhood. The results also indicated that treating birds that are frequently fed upon by mosquitoes resulted in the largest reductions, regardless of the species' ability to transmit West Nile virus to feeding mosquitoes, she said.
“While still in development, ivermectin-treatment of backyard birds using specialized bird feed has the potential to substantially reduce local West Nile virus transmission in the future,” Holcomb said. “Large reductions will require high spatial coverage of a neighborhood with ivermectin-treated bird feeders and high rates of mosquito mortality following a bite on a bird that has self-medicated at a treated feeder.”
Elimination of river blindness
Additional data presented at the meeting showed that mass treatment with ivermectin has eliminated river blindness transmission in two states in Nigeria, marking the first Nigerian states to achieve this distinction in a country that has the world’s highest burden of the disease.
According to the study, Plateau and Nasarawa States were designated as the first Nigerian countries to interrupt transmission and stop mass drug administration for onchocerciasis, or river blindness, after between 8 and 26 years of mass administration with ivermectin. Researchers completed a 3-year post-treatment entomological evaluation, which is necessary to declare transmission elimination, during the 2019-2020 transmission season.
For the evaluation, the researchers collected and tested blackflies for the presence of the L3 infective state of Onchocerca volvulus by O-150 PCR.
The evaluation yielded 93 pools in Nasarawa State comprised of 7,925 flies found and zero positive pools (95% CI, 0%-0.024%). Similar results were seen in Plateau State, where 89 pools composed of 7,368 flies resulted in 0 positive pools (95% CI, 0%-0.026%).
According to the study, the results meet the 2016 WHO entomological criteria for elimination of transmission infectivity threshold of less than 0.05%.
“It’s taken 25 years of hard work by community volunteers to distribute the medicine, and particularly strong commitments from Nigeria’s Federal Ministry of Health, Merck’s ongoing donation of ivermectin, and many donors and partners,” Abel Eigege, a program director for The Carter Center in Nigeria, said in a press release. “But we are hoping this success can accelerate elimination efforts elsewhere in Nigeria and throughout Africa.”
Kahansim B, et al. Abstract 0432. Presented at: American Society of Tropical Medicine & Hygiene Annual Meeting; Nov. 17-21, 2021;virtual.
Nguyen C, et al. Abstract 1351. Presented at: American Society of Tropical Medicine & Hygiene Annual Meeting; Nov. 17-21, 2021;virtual.