A concerning new study reveals widespread insecticide resistance in mosquitoes across Cameroon, threatening to reverse decades of progress in malaria control. Published in Malaria Journal, the research underscores a growing global challenge as mosquitoes adapt and evade the protective effects of commonly used insecticide-treated bed nets. With Africa accounting for the vast majority of malaria cases and deaths worldwide – nearly 250 million infections and over 565,000 fatalities in 2023 alone – maintaining effective prevention strategies is critical to safeguarding public health and achieving global eradication goals. This report highlights the urgent need for innovative vector control methods to combat this evolving resistance.
A new study reveals a “strong” resistance to insecticide-treated bed nets among mosquitoes in Cameroon, raising concerns about the future of malaria control efforts in Africa. Published in Malaria Journal in September 2025, the findings highlight a growing threat to public health on the continent.
Malaria remains a significant health challenge globally, with Africa bearing the brunt of the disease. According to the World Health Organization (WHO), the region accounted for approximately 94% of malaria cases and 95% of deaths worldwide in 2023, totaling 246 million cases and 569,000 fatalities. Bed nets are a cornerstone of malaria prevention, but their effectiveness is now being compromised.
Researchers at the Centre for Research on Infectious Diseases (CRID) in Yaoundé, Cameroon, and the University of Yaoundé 1 investigated the extent of insecticide resistance in the country, which experiences high rates of malaria infection and mortality. The WHO’s World Malaria Report documented 7.3 million cases and 11,600 deaths in Cameroon in 2023.
The study, conducted from 2020 to 2021, demonstrated that many mosquitoes are now surviving exposure to pyrethroid pesticides, which are used to treat the nets. Researchers assessed mosquito populations across Cameroon, finding that mortality rates ranged from 0% to 17% when insects were exposed to nets treated solely with pyrethroids.
“If we do not replace these bed nets in a timely manner, we will undoubtedly face a resurgence of malaria in the coming years, leading to millions of new cases and an increase in deaths.”
Charles Wondji, Liverpool School of Tropical Medicine (England)
“We used the WHO’s insecticide susceptibility bioassay protocol to assess and quantify the level of mosquito resistance,” explained Charles Wondji, lead author of the study and a professor of genetics and vector biology at the Liverpool School of Tropical Medicine in England. “We first used the standard diagnostic dose of insecticide, called 1x, which is supposed to kill 100% of a susceptible mosquito population. However, we found that this dose killed less than 20% of mosquitoes at some study sites.”
Further testing with a much higher dose of the chemical yielded even more alarming results. “Barely 10% of the mosquitoes died at this dose,” said Wondji, who is also the executive director of CRID. The WHO considers this “high-intensity resistance.”
A Warning Sign
Wilfred Mbacham, a professor of public health biotechnology in Cameroon who was not involved in the study, warned that these findings are a critical warning for malaria control efforts across Africa. He suggested the resistance could “spread throughout the region in a few years and more widely across the continent in a few decades.”
A rapid loss of effectiveness in pyrethroid-only treated nets “translates to increased survival of vectors that bite people sleeping under these nets,” Mbacham added. This diminished protection could lead to “increased malaria risk hotspots” and place significant operational pressure on national control programs, which will need to urgently explore alternative interventions to avert a continental crisis.
Wondji and co-author Hervé Tazokong echoed these concerns, noting that increased resistance could lead to a rise in malaria cases, with direct and indirect consequences for economic growth, workforce attendance, worker productivity, and medical costs.
“If we do not replace these bed nets in a timely manner, we will undoubtedly face a resurgence of malaria in the coming years, leading to millions of new cases and an increase in deaths,” Wondji cautioned.
Researchers have not yet established a direct link between mosquito resistance to insecticide-treated nets and the spread of malaria. However, Mbacham cautioned against complacency, stating that “the risk of control failure is independent of the immediately observed infection rate.” The fundamental danger, he explained, lies in the loss of the nets’ primary function: killing mosquitoes.
“If bed nets stop killing mosquitoes, epidemiological consequences often follow, sometimes with a delay, sometimes in the form of localized outbreaks,” he said.
Epidemiological Implications
The researchers recommend that public health officials in Africa move away from conventional bed nets and adopt new tools, such as nets incorporating piperonyl butoxide (PBO), to stay ahead of resistance. However, Wondji noted that increasing evidence suggests mosquitoes are also developing resistance to PBO-treated nets. This was observed in Uganda, where mosquitoes developed resistance just three years after their introduction.
In Cameroon, the National Malaria Control Program (NMCP) has already taken steps to slow the spread of mosquito resistance to insecticide-treated nets. “Mosquitoes react differently to various classes of insecticides: some can kill them, while others are ineffective due to the resistance they develop,” explained Raymond Tabue, a medical entomologist and senior official with the NMCP.
He recalled that nets treated only with pyrethroids were used during mass distribution campaigns in 2011 and 2015 and, while initially effective, resistance eventually emerged.
New Chemical Combinations
In 2019, nets treated with different chemicals were introduced in some areas, but Tabue lamented that “we found that mosquito populations continued to develop resistance, even to these new chemicals.”
According to Tabue, in 2022, three types of nets were deployed nationwide, including next-generation nets like the Interceptor G2. Another national campaign is planned later this year to distribute new-generation nets combining pyrethroid insecticides and chlorfenapyr.
The WHO reports that clinical trials and pilot studies have shown that dual-insecticide nets improve malaria control by 20% to 50% compared to standard pyrethroid-only nets. This finding offers a potential pathway to regaining ground in the fight against the disease.
“The strategy we are currently applying is to avoid using only one type of insecticide,” Tabue concluded.
