The Changing Battlefront In the Fight Against Malaria in Africa

By Grey Frandsen

In 2012, malaria was regarded as a relatively minor and declining threat to the people of Djibouti, a small country of 900,000 people in the Horn of Africa suffering only a few hundred cases each year. Then something changed. The following six years saw year-on-year increases in reported malaria cases and a devastating 74-fold increase in suspected cases over that period.[1] In 2018, more than 10% of the entire population of Djibouti were estimated to have been infected.
The culprit for this dramatic change – a single, invasive mosquito species. Sometime around 2012, the Asian malaria vector Anopheles stephensi arrived in Djibouti – most likely as an accidental passenger on one of the many ships that stop in this important trade hub connecting Africa and the Middle East. Unlike the native malaria-spreading Anopheles species already resident in Djibouti and across Africa, Anopheles stephensi is highly adaptable and readily colonizes towns and cities: it can breed in water tanks, wells and any other artificial water containers that are common hallmarks of urban settings. In Djibouti, where 70% of people live in the capital city, this urban invasion has exposed most of the country’s population to a very new and deadly threat.

It turns out that was just the beginning of a new chapter in the fight against malaria in Africa.

Anopheles stephensi has now moved beyond Djibouti, reaching Ethiopia, Somalia and Sudan so far.[2] Models of the future distribution of this invader project that 126 million people in cities across Africa could be at risk.[3] A 2019 letter written by two eminent malaria experts warned that “urgent action is needed to prevent urban malaria epidemics from emerging and causing a public health disaster”.[4] Countries to the south of Ethiopia and Somalia may be the next stop for Anopheles stephensi: in neighboring Kenya alone, the cities of Nairobi and Mombasa are regarded as ideal habitat for the vector, and are home to 6 million and 1.2 million people, respectively. The World Health Organization recognizes the Anopheles stephensi threat, warning of “a major potential threat to malaria control and elimination in Africa”[5] and calling for targeted vector control efforts to fight it.
Unfortunately, our existing toolset for combating this new malaria vector is limited.

Current management options include insecticide-treated bednets and indoor residual spraying, common-place approaches to the long-standing malaria control efforts in rural Africa. Their effectiveness is likely to be compromised by insecticide resistance: in Ethiopia, Anopheles stephensi shows widespread resistance to pyrethroids, the most used class of chemistries.[6] When the mosquitoes bite and where they rest may also impact effectiveness of these tools. In their native range, Anopheles stephensi are typically characterized as biting around dawn and dusk and resting outside of peoples’ homes. If that holds true for invasive Anopheles stephensi in Africa, the utility of bednets and indoor residual spraying may be limited. New tools are urgently needed to slow the march of Anopheles stephensi across Africa and protect large urban populations from the predicted explosion of urban malaria cases.

This is why we are throwing ourselves into the fight against this invasive pest. With a global team of scientists, public health experts, local governments and community leaders, civil society leaders, engineers, software developers, and others to develop a new, targeted solution for controlling Anopheles stephensi powered by our self-limiting genetic platform. With the support of world-class partners, we are working with urgency to deliver a new, biological and sustainable solution for controlling this vector, with a particular focus on the growing threat in Africa. The technology relies on the natural mating instincts of our self-limiting, non-biting Anopheles stephensi males to find and mate with pest females in complex urban environments. In doing so, they will pass on a copy of the self-limiting gene to reduce biting females in the next generation. As a non-toxic and highly targeted way of controlling mosquitoes, ours promises to be precisely the type of tool needed to combat this urban malaria vector – extremely effective, scalable, species-specific, and harmless to humans and biodiversity.

To deliver this, we’re building on more than a decade in developing self-limiting mosquito technologies. Most pertinent to our Anopheles stephensi effort is the fact that we’ve proven our self-limiting technology against another dangerous urban mosquito. In large-scale deployments targeting the dengue-spreading Aedes aegypti mosquito in Brazil, a similar self-limiting strain has suppressed populations of the vector by up to 98%, even in densely populated urban communities. In total, over 10 years, we have released more than 1 billion self-limiting male Aedes aegypti with excellent results, and we have just heralded a major step forward in Brazil.
Having spent a good portion of my career working on challenges across the African continent, often in the most remote locations, I’ve seen first-hand just how difficult malaria control is in rural settings. I’ve also spent time in Africa’s major urban centers where I’ve witnessed just how vulnerable certain communities are to new public health challenges. With so few tools or methods to effectively control this city-dwelling Anopheles stephensi, low-cost, highly effective, easily deployable, environmentally sustainable solutions will be increasingly important in this new battlefield in the fight against malaria.

The race is on to protect threatened communities.
Accordingly, we are working around the clock in multiple time zones to ready our technology for deployment in partnership with governments and impacted communities before Anopheles stephensi gains a strong foothold. Doing so, we believe, will have the potential to save many, many lives and slow or prevent its spread into vulnerable communities.
New solutions can’t come fast enough to combat this spreading vector and we look forward to joining with others in the fight against this growing threat to millions of people.

Grey Frandsen is the CEO of Oxitec, an Oxford-based biotechnology company.


[1] https://wwwnc.cdc.gov/eid/article/27/6/20-4557_article

[2] WHO Malaria Threats Map

[3] https://www.pnas.org/content/117/40/24900

[4] https://wwwnc.cdc.gov/eid/article/25/7/19-0301_article#r7

[5] https://www.who.int/news/item/26-08-2019-vector-alert-anopheles-stephensi-invasion-and-spread

[6] https://malariajournal.biomedcentral.com/articles/10.1186/s12936-021-03801-3

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