Trends of insecticide resistance monitoring in mainland Tanzania, 2004–2020

• Published in: Malaria Journal
• Main Authors: Patrick Tungu, Bilali Kabula, Theresia Nkya, Pendael Machafuko, Edward Sambu, Bernard Batengana, Wema Sudi, Yahaya A. Derua, Victor Mwingira, Denis Masue, Robert Malima, Chonge Kitojo, Naomi Serbantez, Erik J. Reaves, Charles Mwalimu, Samwel L. Nhiga, Mohamed Ally, Humphrey R. Mkali, Joseph J. Joseph, Adeline Chan, Jeremiah Ngondi, Shabbir Lalji, Ssanyu Nyinondi, Erin Eckert, Richard Reithinger, Stephen Magesa, William N. Kisinza
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2023
• Subjects: Insecticide resistance; Malaria vectors; Resistance trends; Tanzania; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-023-04508-3; https://doaj.org/article/48c3b9cfbdb3417d8883427f951e8907

Abstract Background Insecticide resistance is a serious threat to the continued effectiveness of insecticide-based malaria vector control measures, such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). This paper describes trends and dynamics of insecticide resistance and its underlying mechanisms from annual resistance monitoring surveys on Anopheles gambiae sensu lato (s.l.) populations conducted across mainland Tanzania from 2004 to 2020. Methods The World Health Organization (WHO) standard protocols were used to assess susceptibility of the wild female An. gambiae s.l. mosquitoes to insecticides, with mosquitoes exposed to diagnostic concentrations of permethrin, deltamethrin, lambdacyhalothrin, bendiocarb, and pirimiphos-methyl. WHO test papers at 5× and 10× the diagnostic concentrations were used to assess the intensity of resistance to pyrethroids; synergist tests using piperonyl butoxide (PBO) were carried out in sites where mosquitoes were found to be resistant to pyrethroids. To estimate insecticide resistance trends from 2004 to 2020, percentage mortalities from each site and time point were aggregated and regression analysis of mortality versus the Julian dates of bioassays was performed. Results Percentage of sites with pyrethroid resistance increased from 0% in 2004 to more than 80% in the 2020, suggesting resistance has been spreading geographically. Results indicate a strong negative association (p = 0.0001) between pyrethroids susceptibility status and survey year. The regression model shows that by 2020 over 40% of An. gambiae mosquitoes survived exposure to pyrethroids at their respective diagnostic doses. A decreasing trend of An. gambiae susceptibility to bendiocarb was observed over time, but this was not statistically significant (p = 0.8413). Anopheles gambiae exhibited high level of susceptibility to the pirimiphos-methyl in sampled sites. Conclusions Anopheles gambiae Tanzania’s major malaria vector, is now resistant to pyrethroids across the country with ...