Researchers have discovered that mosquitoes have become resistant to chemicals applied during the indoor residual spray exercise by the Ministry of Health in northern Uganda.
The research was conducted by scientists at Gulu University with support from Training Researchers into Vocational Excellence in East Africa (THRIVE), a consortium that operates across East Africa.
The scientists say mosquitoes in the northern region have over time developed special adaptation to shield themselves from the effect of the chemicals that kill them.
The revelation was made on Monday during the dissemination of research findings at Gulu University campus.
"We found that the effectiveness of chemical vector control measures using pyrethroid in the north is currently being challenged by the development of insecticide-resistance by all major malaria vector species. If left unchecked, it could lead to a substantial increase in malaria incidence and mortality," Dr Richard Echodu, one of the investigators, said.
Using samples collected from Gulu, Kitgum, Agago and Oyam districts as well as Moroto and Abim districts of Karamoja Sub-region that had the highest prevalence of malaria, the study aimed at identifying anopheles sibling species and its susceptibility to carbamate (bendiocarb), pirimiphos-methyl and pyrethroid insecticides.
According to the findings, mosquito mortality ranged from 98 to 100 per cent for bendiocarb, and 100 per cent for pirimiphos-methyl insecticide in 24 hours of post-exposure. However, mortality was lower in mosquito samples exposed to pyrethroid insecticide, which is commonly used in the north.
During the study, adult anopheles mosquitoes were identified morphologically and by Polymerase Chain Reaction (PCR) techniques. Their susceptibility status was then assessed using the standard World Health Organisation (WHO) tube test method during September and October 2019.
In an interview, Prof Elizabeth Opiyo, the principal investigator, said a total of 500 (two-five days old) adult female anopheles reared from larval/pupal collections from various breeding sites were exposed to tests to establish their susceptibility.
"In areas where we have seen resistance, definitely we need to rotate and use other different classes of insecticides than the one in use now because the mosquitoes have developed resistance to pyrethroids, it can be bicarbonates or organophosphates," Prof Opiyo said.