Background: The STECLA strain of Anopheles albimanus Wiedemann has been in continuous colony for many years and is the reference strain on which genomic studies for the species are based. Recently, the STECLA strain was demonstrated to be much less susceptible to ivermectin ingested in a blood meal (LC 50 of 1468 ng/ml) than all other Anopheles species tested to-date (LC 50 values range from 7 – 56 ng/ml). The ability of A. albimanus to survive ingestion of ivermectin at concentrations far beyond that typically found in the blood of ivermectin-treated people or livestock ( i.e ., 30 – 70 ng/ml) could invalidate the use of ivermectin as a malaria vector control strategy in areas where A. albimanus is a primary vector.
Methods: To investigate this, we captured host-seeking A. albimanus in northern Belize and conducted membrane feeding bioassays of ivermectin, using the same methods as described earlier with the STECLA strain.
Results: Field-collected A. albimanus in Belize were 55 times more susceptible to ingested ivermectin than were the STECLA reference strain. Oral susceptible to ivermectin in wild A. albimanus from Belize (LC 50 of 26 ng/ml) was equivalent to that of other Anopheles species tested.
Conclusion: Contrary to our initial assessment using a highly inbred laboratory strain of mosquito, we show that ivermectin treatment of livestock could reduce A. albimanus populations in areas of Central America and the Caribbean where malaria transmission may occur. Future toxicity screening of ivermectin and other systemic parasiticides for malaria control should consider examining wild populations of the vector species being targeted.