Study flags a setback in fight against malaria
scientists discover that the malaria-causing mosquito has developed resistance to a long-used insecticide in the eastern and southern Africa region.
Scientists have found that a mosquito species blamed for malaria transmission in eastern and southern Africa has developed resistance to a long-used insecticide in the region.
Anopheles funestus is one of the main malaria vectors in the region, including Kenya, and scientists warn the discovery raises concerns about the effectiveness of insecticides in malaria control.
Researchers discovered that the insect is genetically mutating to develop resistance to dichlorodiphenyltrichloroethane (DDT) -- a banned insecticide whose stockpiles continue to affect the environment.
The results of the new peer-reviewed study are published in the journal Molecular Ecology.
The study was led by the University of Glasgow and the Ifakara Health Institute in Tanzania.
The discovery of 'knock-down resistance' (kdr) -- an important insecticide resistance mechanism in insect pests -- is the first time such a mutation has been documented in this species.
The 'kdr' mutation was discovered when researchers carried out whole-genome sequencing of several mosquito populations in Tanzania to better understand genetic variation in the mosquito species.
The new resistance mutation in the mosquito species has been attributed to widespread contamination and historic stockpiles of DDT.
DDT was developed in the 1940s as the first of the modern synthetic insecticides.
It was initially used with great success to control malaria, typhus and other insect-borne human diseases in military and civilian populations.
The insecticide was banned by the Kenyan government, first for use on livestock in 1976 and then as an agricultural spray in 1986. Its use is restricted to the control of disease vectors.
"Our discovery raises concerns on the effectiveness of current malaria control methods, which rely heavily on insecticides. Understanding the development of insecticide resistance is key to combating malaria, a disease that kills hundreds of thousands of people annually, mostly in Africa,” said Joel Odero, the lead author and a PhD student at the University of Glasgow School of Biodiversity, One Health and Veterinary Medicine. Odero is also a researcher at Ifakara Health Institute.
“The research highlights how environmental legacies such as DDT pollution can shape modern public health challenges. The emergence of new resistance mechanisms could threaten decades of progress made in reducing malaria transmission and mortality,” he added. Odero noted that the Anopheles funestus was recently blamed for persistent malaria transmission in countries such as Kenya.
Fredros Okumu, a Kenyan parasitologist and entomologist who works as director of science at the Ifakara Health Institute, told the Nation that a follow-up study is needed.
“An urgent follow-up study is required to monitor the evolution of vector DDT resistance and determine whether this type of resistance could occur in other insecticide families that are currently being rolled out in products across the African continent,” said Okumu.
The researchers also noted that when they observed the unexpected resistance to DDT within one population, further analysis revealed that the resistance is linked to novel kdr mutations.
“After identifying the resistant population, the researchers made the discovery that the collection of this species had been from a region near a large, historical DDT stockpile. This finding suggests that prolonged environmental contamination may have exerted selective pressure on the mosquitoes, driving the emergence of this resistance,” the study highlights.
Today, chemical insecticides are central to the control of agricultural pests and disease vectors such as mosquitoes.
The control of Anopheles mosquitoes through the distribution of over 2.9 billion insecticide-treated bed nets has helped avert an estimated 633 million cases of malaria, a disease that still kills 600,000 people each year.
However, the widespread use of insecticides to control agricultural pests and disease vectors also has negative consequences, including direct lethal and sub-lethal effects on human and animal health.
A major obstacle to sustainable malaria control is the evolutionary arms race between mosquitoes and insecticide-based mosquito control, the researchers said.
"Our discovery sheds light on the far-reaching and unintended consequences of historical insecticide use, highlighting how past environmental contamination can shape the evolution of vector populations and impact current public health interventions," Francesco Baldini of the University of Glasgow School of Biodiversity, One Health and Veterinary Medicine told the Nation.
In an interview with the Nation, Mary Muthoni, the Principal Secretary for Public Health and Professional Standards, said 22 counties received 15.3 million bed nets to fight malaria in July this year. This comes after Kenya recorded 5,447,220 malaria cases in the last 12 months with Busia County topping the list with 231,307 cases.
The Ministry of Health, while citing Budalang’i, noted that cross-border transmission along the Busia border, drug-resistant malaria parasites and climate change leading to unpredictable rainfall and flooding are the key factors fuelling the surge in malaria infections in the country.
According to the ministry, insecticide resistance in mosquitoes and changes in biting behaviour are other headaches the country is grappling with.
“The ministry has an elaborate surveillance system that conducts both routine epidemiological and periodic entomological surveillance. Integrated Disease Surveillance System (IDSR) is crucial in detecting malaria upsurges and epidemics for prompt response,” the PS said.
“Busia has a malaria prevalence of 38.5 percent against a national prevalence of 6 percent, which is why we embarked on high impact indoor residual spraying (IRS) was introduced and this saw 95 percent of target structures sprayed in March this year,” she added.
“The distribution of mosquito nets has concluded in 13 counties namely Homa Bay, Kisii, Nyamira, Kisumu, Siaya, Migori, Mombasa, Kwale, Tana River, Lamu, Taita Taveta, Kakamega, Vihiga and Bungoma,” PS Muthoni told the Nation.
