Differential susceptibilities of Anopheles albimanus and Anopheles stephensi mosquitoes to ivermectin

• Published in: Malaria Journal
• Main Authors: Staci M. Dreyer, Kelsey J. Morin, Jefferson A. Vaughan
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2018
• Subjects: Anopheles albimanus; Anopheles stephensi; Endectocide; Ivermectin; Vector control; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-018-2296-3; https://doaj.org/article/11ed5ff89e1a4f838987f22c5910bb70

Abstract Background Vector control is a crucial element of anti-malaria campaigns and works best when there is a thorough knowledge of the biology and behaviour of the Anopheles vector species responsible for transmitting malaria within a given locale. With the push to eradicate malaria stronger than ever, there is a growing need to develop and deploy control strategies that exploit the behavioural attributes of local vector species. This is especially true in regions where the vectors are exophagic (i.e., prefer to bite outdoors), exophilic (i.e., prefer to remain outdoors), and zoophagic (i.e., as likely to feed on non-humans as humans). One promising strategy targeting vectors with these behavioural traits is the administration of avermectin-based endectocides, such as ivermectin, to humans and livestock. When ingested in a blood meal, ivermectin has been shown to reduce mosquito survivorship and fecundity in a number of Anopheles species. In this study, the relative toxicity of ivermectin was compared between two zoophagic, exophilic malaria vectors—Anopheles albimanus and Anopheles stephensi. Results Toxicity of ivermectin was assessed using membrane feedings, intrathoracic injections, and mosquito feedings on treated mice. When ingested in a blood meal, ivermectin was much less toxic to An. albimanus (4-day oral LC50 = 1468 ng/ml) than to An. stephensi (4-day oral LC50 = 7 ng/ml). However when injected into the haemocoel of An. albimanus, ivermectin was much more toxic (3-day parenteral LC50 = 188 ng/ml). Because the molecular targets of ivermectin (i.e., glutamate-gated chloride channels) reside outside the midgut in nerves and muscles, this suggests that ingested ivermectin was not readily absorbed across the midgut of An. albimanus. In contrast, ivermectin was considerably more toxic to An. stephensi when ingested (4-day oral LC50 = 7 ng/ml) than when injected (3-day parenteral LC50 = 49 ng/ml). This suggests that metabolic by-products from the digestion of ivermectin may play a role in the oral ...