Location: Livestock Arthropod Pests ResearchTitle: Acetylcholinesterase mutations and organophosphate resistance in sand flies and mosquitoes Author
|Tong, Fan - University Of Florida|
|Bloomquist, Jeffrey - University Of Florida|
|Carlier, Paul - Virginia Tech|
|Totrov, Maxim - Molsoft, Llc|
|Perez De Leon, Adalberto - Beto|
Submitted to: Texas Mosquito Control Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/28/2015
Publication Date: N/A
Interpretive Summary: Blood feeding insects may transmit diseases. Mosquitoes are well-known agents transmitting malaria and many other diseases. Sand flies transmit leishmaniasis. Both mosquitoes and sand flies can severely impact military operations, requiring development of effective control strategies. Acetylcholinesterase is a key enzyme of the central nervous system of sand flies and mosquitoes targeted by organophosphate pesticides. Insects can develop resistance to pesticides as a result of mutations. Scientists utilized recombinant DNA techniques to clone and express sand fly acetylcholinesterase and discovered that it was extremely similar to acetylcholinesterase of mosquitoes. By producing mutations in the sand fly acetylcholinesterase that were known to be responsible for mosquito pesticide resistance, scientists were able to synthesize and screen new chemicals that were effective against the mutant acetylcholinesterase. It is believed that these studies will result in production of new pesticide chemistries that are effective in controlling sand flies and mosquitoes that have become resistant to conventional pesticides.
Technical Abstract: The sand fly, Phlebotomus papatasi (Scopoli) is a major vector of Leishamnia major, the principle causative agent of human cutaneous leishmaniasis in the Middle East, southern Europe, northern Africa, and Southern Asia. Sand fly bites and leishmaniasis significantly impacted U.S. military operations in Iraq and Afghanistan, as well as up to 0.7 – 1.3 million people in areas where P. papatasi and Lutzomyia longipalpis (Central & South America) are indigenous. Sand fly control is reliant on area-wide pesticide treatment and use of pesticide-treated bed nets and repellents. Although there have been scattered reports of sand fly pesticide resistance, there have been very few studies demonstrating resistance. One study from Sudan, Africa, reported high level resistance to organophosphate (OP) pesticide in bioassays, but did not characterize the resistance mechanism. We identified, cloned, sequenced, and expressed the cDNA encoding acetylcholinesterase 1 of Phlebotomus papatasi. The enzyme had very high amino acid sequence identity to acetylcholinesterase 1 of Lutzomyia longipalpis, Anopheles gambiae, Aedes aegypti, Culex quinquefaciatus, and other mosquito vectors of human pathogens. In addition to biochemical characterization of the wild type (susceptible) recombinant enzyme (PpAChE1), we constructed, expressed and characterized recombinant PpAChE1 incorporating mutations known to produce OP-resistant acetylcholinesterase in mosquitoes. The mutations G119S, F290V, and F331W, each resulted in production of a recombinant PpAChE1 with reduced inhibition by organophosphate inhibitors. Novel synthetic carbamates were produced that exhibited improved inhibition properties for one or more of the various enzyme constructs, including improved mammalian safety profile or improved inhibition of OP-resistant forms of the enzyme, and molecular docking models of inhibitors successfully mimicked biochemical inhibition results. Further, we developed DNA-based molecular assays to survey P. papatasi flies for the presence of the G119S mutation or the codon (GGC) that can produce the G119S mutation by a single nucleotide transversion. Use of these assays demonstrated presence of the GGC codon, but not the G119S mutation, in our laboratory colony sand flies, as well as wild sand flies collected from Marigat in Kenya, Africa, strongly suggesting that natural sand fly populations may rapidly develop OP-resistance via the G119S mutation when subjected to selection pressure, such as the malaria eradication program. Anopheles mosquitoes in West Africa exhibit G119S-based resistance to OP pesticides. Several novel synthetic carbamates were identified in our studies that were effective inhibitors of recombinant PpAChE1(G119S) constructs, suggesting that these compounds may effectively prevent or remediate G119S-based pesticide resistance.