Invasive Mosquito Spreading Malaria in Africa

A new strain of mosquito, known as Anopheles stephensi, has been advancing across Africa at a rate that has alarmed public health experts. This insect, which is resistant to common insecticides and traditionally found in urban areas, has moved into regions where malaria has not previously posed a significant threat. Many health specialists now believe that efforts to eliminate or even control it may be too late.

Recent genomic analysis of this mosquito, collected from ten different countries, indicates that the African populations show resistance to all insecticides currently in use for mosquito control. This resistance renders these traditional methods ineffective.

The mosquito is rapidly spreading through the continent, particularly in flat and open landscapes, moving westward toward Ghana and southward through Kenya since its introduction in Djibouti over a decade ago.

“In recent years, there’s been less discussion about containing this invasion. It’s become clear to experts that the situation has gone beyond control,” stated Tristan Dennis, a researcher at the University of Queensland in Australia and lead author of the study published in the journal Science.

This mosquito raises significant concerns because it thrives in both urban and rural settings, making it especially dangerous for megacities like Lagos and Kinshasa, each hosting around 20 million people. “Historically, we didn’t have to worry about malaria in urban locations,” noted Dr. Eric Ochomo, head of entomology at the Kenya Medical Research Institute.

Urban populations often lack immunity to malaria, which can lead to severe illness. Furthermore, once a stable population of stephensi is established, it poses a year-round transmission risk rather than being restricted to seasonal outbreaks, complicating existing malaria management strategies.

Currently, in many countries, stephensi has not yet established a high enough population to assess its impact on malaria rates. However, in Djibouti and Ethiopia—countries that were among the first to experience its presence—the dangers are already visible.

Before the arrival of stephensi in 2013, Djibouti was on the verge of declaring malaria eradicated, with only 27 reported cases in 2012. However, within a year of the mosquito’s detection, cases surged to nearly 1,700. By 2020, the number exploded to over 70,000 cases.

In Ethiopia’s Dire Dawa, stephensi was responsible for a surge in malaria cases in 2022, which initially perplexed healthcare workers unfamiliar with treating the disease.

The emergence of stephensi represents yet another hurdle in Africa’s ongoing struggle against malaria. Data suggests that there were nine million more malaria cases in 2024 compared to the previous year, signaling a worrying trend. With cuts to health program funding, the full extent of the 2025 data remains unclear.

Amid armed conflicts and climate-related displacements, scientists are combining their limited surveillance efforts to gauge the scale of the threat posed by stephensi.

In Niger, Mahaman Lamine, a parasitologist, had students collect mosquito samples for a biodiversity survey. To his astonishment, they identified stephensi within their samples, a species previously unreported in the country. “I couldn’t believe it at first,” Dr. Lamine recounted.

The genomic analysis confirmed that after entering Djibouti, the stephensi population diverged into three groups, with one extending into Ethiopia and Kenya, another crossing the Red Sea into Yemen, and a third traveling through Sudan to West Africa.

Some scientists suspect that stephensi may have been introduced from South Asia through West African ports, but the new analysis illustrates the remarkably fast spread of this mosquito across the mainland, expanding its range by nearly 300 miles each year.

Dr. Ochomo remarked on this unprecedented spread, admitting he had initially believed stephensi would only impact northern Kenya. Instead, it continues to spread into various habitats across the country.

Stephensi is believed to have arrived in Africa around 2013 via shipping routes from Pakistan or India, coinciding with a significant increase in malaria cases in Djibouti, where efforts to eradicate the disease were underway.

The mosquito’s spread coincides poorly with shrinking resources for malaria-control programs. The United States, which was the largest funder of anti-malaria initiatives, significantly reduced funding during the Trump administration, leading to budget cuts of a third or more across many malaria-affected countries.

“Surveillance is often the first thing to go,” Dr. Ochomo pointed out. When there’s insufficient data on mosquito distributions, determining effective resource allocations becomes increasingly difficult.

In Niger, Dr. Lamine faces funding challenges and limited lab equipment. “We strive to continue our work despite the setbacks because we are passionate about science,” he said.

Dr. Dennis indicated that human interactions with the environment have facilitated stephensi’s spread. “This is occurring amid significant instability, lots of displaced populations, and insufficient state control on a rapidly urbanizing continent,” he explained.

There are concerns that stephensi has also reached additional countries, such as Chad and South Sudan, where resources for vector surveillance are scarce. “There’s no monitoring happening in those regions,” Dr. Dennis observed.

Researchers from various nations, including Afghanistan, Pakistan, and several African countries, collaborated on the genomic study. They faced various challenges, as many regions involved were experiencing conflict during the research period.

Hmooda Toto Kafy, a medical entomologist in Sudan, collected samples just weeks before the outbreak of civil war, aiming to monitor stephensi’s contribution to malaria transmission. “But conducting research amidst conflict is challenging,” he lamented.

Regions once targeted for monitoring have become inaccessible due to ongoing violence, straining resources even further. In Yemen, Dr. Tarek Sultan Bin Hawail found stephensi in camps around Aden, where displaced populations live. Larvae were discovered in water containers inside homes. Health care providers, overwhelmed with fever patients, misdiagnosed some malaria cases as dengue fever simply because malaria wasn’t previously known to exist there.

Africa is home to nearly half of the world’s displaced population. The situation has created a perfect storm for the spread of diseases like malaria.

Dr. Dennis’s genomic analysis revealed that the resistance genes found in the invasive stephensi population confer resistance to essentially all insecticides employed in mosquito control. This discovery appears to worsen the already dire situation.

Despite the growing concerns surrounding stephensi, there are few indications that resources are being redirected to address the issue. “Data may point to certain problems, but without the necessary infrastructure to respond, it doesn’t make much difference,” Dr. Dennis noted.

Still, those studying stephensi speak of the mosquito with a degree of respect. Typically, invasive species struggle to adapt and remain small and genetically limited. “It’s remarkable that this mosquito has maintained its genetic diversity and conquered such vast territories across Africa,” Dr. Dennis concluded.