>> Writes: Bilal Mpembamoto

It's a cool evening. You’re sitting on your porch, sipping tea as the sun dips below the horizon. A faint buzz interrupts the evening calm—a mosquito, small but persistent, hovering nearby. You swat it away, but in that fleeting moment, you’ve brushed up against one of nature’s most dangerous creatures.

In Tanzania’s coastal neighbourhoods, where evenings like this are common, a team of scientists has just uncovered a new player in this age-old battle: a mosquito unlike any other, hiding in plain sight along the shores of East Africa - Tanzania in particular!

This isn’t just another insect. It’s a discovery that could reshape how we fight malaria, a disease that claims hundreds of thousands of lives each year. Led by a young Tanzanian scientist, Sophia Mwinyi, and her mentor, Dr. Fredros Okumu, researchers from the Ifakara Health Institute, alongside partners from the University of Glasgow and the Wellcome Sanger Institute, have found a new mosquito group within the anopheles gambiae complex. They call it the pwani molecular form, and its story is one of resilience, mystery, and hope.

A mosquito that defies the rules

Think about the last time you tried to solve a puzzle, only to find a piece that didn’t quite fit. That’s what the pwani mosquito is—a puzzle piece that challenges everything we thought we knew about malaria-carrying mosquitoes.

The team analyzed whole-genome sequences of 300 mosquitoes collected between 2012 and 2015 across four northern Tanzanian districts: Muleba, Muheza, Moshi, and Handeni. Using advanced genomic tools, they identified three taxa: Anopheles gambiae s.s., anopheles arabiensis, and the newly discovered pwani form, which is genetically distinct and restricted to coastal areas like Muheza and Handeni.

What makes pwani special?

Unlike its cousins, this lacks common insecticide resistance markers, such as target-site mutations in genes like vgsc (associated with pyrethroid and DDT resistance) and rdl (linked to dieldrin resistance), as well as copy number variations in metabolic genes like Cyp6aa1 and Gste2. These absences make pwani uniquely susceptible to insecticides, a rarity in a region where resistance is widespread.

The study found that while anopheles gambiae s.s. and anopheles arabiensis showed evidence of selection for resistance, pwani’s genome suggested little to no selective pressure, possibly due to its coastal ecology or behavioral traits like outdoor biting.

A young scientist’s breakthrough

At the heart of this discovery is Sophia Mwinyi, an early-career researcher whose curiosity and grit brought pwani to light. Picture a young woman poring over genetic data late into the night, determined to uncover secrets hidden in mosquito DNA.

Under the guidance of Dr. Fredros Okumu, a seasoned mosquito ecology expert and Vector Biology professor at the University of Glasgow, Sophia led a team that included global experts like Dr. Alistair Miles from the Wellcome Sanger Institute, alongside collaborators from the Liverpool School of Tropical Medicine, Tanzania’s National Institute for Medical Research (NIMR), and Kilimanjaro Christian Medical University College (KCMUCo).

Their work, published on April 16, 2025, in Molecular Ecology, is a testament to what happens when local knowledge meets global collaboration.

Sophia’s passion resonates with anyone who’s ever chased a dream against the odds. “The discovery of the pwani molecular form reveals gaps in our understanding of mosquito diversity,” she says. She hypothesizes that pwani may sustain malaria transmission during the dry season, when other mosquitoes are scarce, due to its potential to breed in brackish coastal waters or bite outdoors, evading indoor-focused interventions like bed nets.

This could explain persistent malaria cases in coastal areas despite control efforts, much like how a single overlooked detail can unravel a carefully laid plan in our own lives.

A tale of two mosquitoes

The study revealed striking geographical structuring in anopheles gambiae s.s. populations. Mosquitoes from Muleba in northwest Tanzania formed a distinct genetic cluster, separate from those in Muheza, Moshi, and Handeni, suggesting limited gene flow due to ecological or geographical barriers.

Muleba’s gambiae s.s. showed higher frequencies of resistance mutations, like the vgsc-L995F allele (present in 80% of samples), and elevated copy number variations in detoxification genes, indicating strong selection for pyrethroid resistance. In contrast, Muheza’s gambiae s.s. had lower resistance markers, with vgsc-L995F at just 20%, reflecting weaker insecticide pressure or different control practices.

Meanwhile, anopheles arabiensis showed no such divisions. Its genetic uniformity across all four regions, with consistent resistance profiles (e.g., vgsc-L995F at moderate levels), suggests unrestricted gene flow, possibly due to its adaptability to diverse habitats. The pwani form, however, stood out for its coastal exclusivity and lack of resistance, with no detected vgsc or rdl mutations and minimal copy number variations.

This contrast—pwani’s isolation, gambiae’s regional quirks, and arabiensis’s uniformity—paints a complex picture of mosquito evolution, like a neighborhood where each family has its own quirks but shares the same street.

Why this matters to you?

Malaria isn’t just a distant problem; it’s a global challenge that touches millions, from rural farmers to urban families. In Tanzania, where malaria accounts for 3.2% of global cases, it drives 26% of outpatient visits and countless lost days of work or school.

The discovery of pwani could change how we tackle this disease. As Dr. Okumu puts it, “Understanding the DNA of mosquito populations helps scientists and public health officials design better interventions.” The study’s findings suggest that pwani’s susceptibility to insecticides could be exploited with targeted coastal interventions, like outdoor spraying or larvicides, to curb dry-season transmission.

Dr. Alistair Miles adds urgency: “This cryptic taxon calls for urgent entomological and epidemiological investigations to determine its behavior, ecology, and vector potential.” The study notes that pwani’s genetic divergence (Fst values of 0.15–0.20 compared to other taxa) and low nucleotide diversity indicate a distinct evolutionary history, possibly adapted to coastal microhabitats like brackish pools.

If pwani is a less efficient malaria vector or bites outdoors, it might explain lower coastal malaria prevalence (e.g., 8% in Pwani region in 2022 versus 38% in Kagera). But its role in sustaining transmission during dry seasons, when inland vectors wane, means current indoor-focused tools may miss it, like trying to catch a fish with a net full of holes.

A collaborative triumph

This breakthrough didn’t happen in isolation. Funded by the Wellcome Trust, the Bill & Melinda Gates Foundation, and the UK Medical Research Council, the study united Tanzanian institutions with global partners.

The team used cutting-edge genomic techniques, including principal component analysis and admixture modeling, to uncover pwani’s distinct lineage and confirm its absence in non-coastal sites like Muleba. It’s a shining example of what happens when diverse minds rally for a common goal, much like a community coming together to solve a shared problem.

A new chapter in the malaria fight

The discovery of the pwani molecular form is more than a scientific milestone; it’s a beacon of hope in the fight against malaria. The study concludes that pwani’s unique profile and coastal restriction demand tailored surveillance and control strategies. Its lack of resistance suggests current insecticides remain effective against it, but its potential outdoor biting and dry-season activity highlight gaps in indoor-focused interventions. The researchers call for urgent studies to assess pwani’s vector competence, biting behavior, and ecological niche to confirm its role in malaria transmission.

For Sophia Mwinyi and her team, this is just the beginning. Their findings challenge us to rethink malaria control, emphasizing genomic surveillance to track evolving mosquito populations. As the study warns, failing to adapt to cryptic taxa like pwani could undermine control efforts, especially in coastal hotspots where malaria persists at low but stubborn levels. It’s a reminder that even in the smallest creatures, there are secrets waiting to be uncovered—secrets that could save lives.

Next time you hear that familiar buzz, pause for a moment. Somewhere along Tanzania’s coast, a tiny mosquito named pwani is rewriting the rules. Thanks to a team of relentless scientists, we’re one step closer to outsmarting it. Let’s keep their discovery in mind—a testament that in the smallest details, we can find the biggest answers.

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Bilal Mpembamoto heads the Communications Office at the Ifakara Health Institute. He’s an experienced science writer and media editor, having worked for reputable and top-notch media outlets in Tanzania, including The Guardian and Mwananchi Communications.