Millions still die from malaria every year. Researchers are thrilled by a new treatment that kills mosquitoes. Amazingly, this is possible with the widely-used drug ivermectin. It's used to control parasite infections like onchocerciasis and lymphatic filariasis. This is an important new control measure, as some mosquitoes are now resistant to insecticides in treated bed nets.
Dr Rebecca Thomas of LSTM and Dr Joseph Okebe from the Noguchi Memorial Institute for Medical Research(link is external), University of Ghana) first looked at the experimental evidence that the drug kills mosquitoes by giving it to people.
All the included studies demonstrated large effects of Ivermectin upon mosquito mortality. The researchers then sought studies to determine if this had an effect on malaria transmission or the number of people in areas with malaria. Only one study was published so far. Based on the original trial report, there was a lot of media coverage about ivermectin's ability to reduce malaria in children when it was published in 2019.
Despite the fact that this paper was published in Lancet, the statistical methods used for the analysis were not consistent and did not adequately adjust for clustering. Therefore, it is possible that the effect was overestimated.
After the original researchers provided the data, Dr Clmence Leyrat of London School of Hygiene and Tropical Medicine, an expert in small samples and noncompliance in clusterrandomized trials, and Dr John Bradley of the London School of Hygiene and Tropical Medicine, reanalyzed the data and became part of the Cochrane review authors team.
Dr Leyrat, Dr Bradley stated that there had been one pilot study of ivermectin. The original publication was too optimistic about the evidence provided by the trial. This reanalysis shows that there was no strong evidence that mass ivermectin administration is effective in preventing malaria. It leaves the question of its effectiveness open. There are other larger trials that will provide additional evidence.
Eight villages from Burkina Faso were included in the one-included study. They were randomly assigned to either ivermectin, or a control. As part of the planned control of lymphatic filariasis, all villages received ivermectin. The treatment villages also received five additional doses of Ivermectin every three weeks. Children under five years old were not tested for the effects of ivermectin. These children did not experience any significant differences in malaria prevalence between the treatment and the control groups. The team reviewed the data and concluded that it was not clear whether community administration of Ivermectin had affected malaria transmission.
Dr de Souza, NMIMR, said that there may be many reasons for the lack of evidence. The mosquito behavior, incubation time of malaria parasites and the length of the mosquito reproductive cycle are all possible challenges to ivermectin's use. Although laboratory experiments are controlled carefully, natural variations may cause some variation. Although ivermectin administration may reduce the risk of malaria transmission, it may not have a lasting impact on the mosquito population. Due to the half-life of ivermectin in blood, it is important to maintain a sufficient ivermectin level over several days and even weeks in order to kill any mosquito feeding on blood.
Dr Joseph Okebe, senior author, agreed that it was not yet possible to determine if treatment of an entire community with Ivermectin decreases malaria. We anticipate that there will be more information on this important question as a result of several ongoing research studies.
De Souza DK. Thomas R. Bradley J. Leyrat C. Boakye D. Okebe J. Ivermectin treatment for humans to reduce malaria transmission. (link is external). Cochrane Database of Systematic Reviews 2021 Issue 6. Art. Art. No. DOI: 10.1002/14651858.CD013117.