A small insect, a global impact
Every year on 20 August, World Mosquito Day marks the extraordinary role of one tiny insect in shaping human health. Mosquitoes are responsible for transmitting some of the world’s most devastating diseases, including malaria, dengue, Zika, and yellow fever.
Malaria alone causes more than 260 million cases and nearly 600,000 deaths annually. Around 95% of this burden is borne by people in Sub-Saharan Africa. Despite investments of over USD 4 billion in malaria control efforts in 2023, global funding still falls short of what is needed to meet the World Health Organization’s Global Technical Strategy.
The relationship between humans and malaria is ancient. Evidence suggests the disease afflicted populations from the time of the Egyptians and may even have been described by Hippocrates.
From discovery to mathematics
World Mosquito Day commemorates the discovery by Sir Ronald Ross, on 20 August 1897, that female Anopheles mosquitoes transmit malaria. Ross also pioneered the first mathematical model of vector-borne disease, showing how infected mosquitoes create infected people and vice versa.
His insights laid the foundation for malaria control strategies: if mosquito numbers are reduced, the opportunities for transmission fall. George Macdonald later refined this work, introducing the concept of the ‘reproduction number’ or ‘R number’ — a measure familiar today from its use during the COVID-19 pandemic.
An Anopheles mosquito with macaques, which can host the malaria parasite Plasmodium knowlesi. Pigs are hosts of Japanese encephalitis virus, another disease studied by Dr Harrison.
Fighting back
Mosquito-borne diseases can be tackled by controlling mosquito populations, reducing human exposure, and treating infections. Approaches include removing stagnant water, spraying insecticides, releasing genetically modified mosquitoes that reduce reproduction, using repellents and bed nets, and deploying effective medicines.
Several key malaria drugs come from natural sources. Quinine, derived from the bark of the cinchona tree, was used for centuries and even gave rise to tonic water. More recently, artemisinin, discovered in 1972 from sweet wormwood (Artemisia annua), revolutionised malaria treatment. Its discovery earned Chinese pharmacologist, Tu Youyou, the Nobel Prize in Physiology or Medicine in 2015.
But widespread drug use also fuels drug resistance. Artemisinin-resistant parasites were first documented in 2008, and are linked to specific mutations in the parasite’s genes. To preserve treatment effectiveness, the WHO now recommends combining artemisinin with a partner drug to slow the evolution of resistance.
Mapping resistance
At Oxford, my work focuses on mapping the spread of genetic mutations in malaria parasites across Sub-Saharan Africa. These mutations are linked to resistance against frontline drugs such as artemisinin.
With the power of modelling, my maps use the data that is available to predict what proportion of malaria parasites may have mutations linked to drug resistance in locations where we don’t have any data.
In many regions where malaria transmission is most intense, there is little or no genetic data. Running clinical trials to test drug effectiveness is costly and resource-intensive. To overcome this, we use geospatial models that can predict the likely distribution of resistance even in areas without data.
These models combine available genetic data with information on the distance and time between data collections, and environmental conditions such as malaria prevalence. By doing so, we can predict the prevalence of resistant parasites in areas where we don’t have any data.
The maps produced at the University of Oxford will be made freely available through the Infectious Diseases Data Observatory’s Artemisinin Molecular Surveyor. The Surveyor is a living systematic review which can be used by researchers and policy-makers to visualise the current state of global drug resistance in the malaria parasite.
A screenshot of the Infectious Disease Data Observatory’s Artemisinin Molecular Surveyor, which visualises published genetic data of the malaria parasite.
Looking ahead
This World Mosquito Day reminds us that mosquitoes remain one of humanity’s most persistent threats. At Oxford, researchers are combining field data, genetics, and advanced modelling to provide the evidence needed to guide global health decisions, helping to ensure that life-saving drugs remain effective for the communities that need them most.
Thank you Lucy Harrison
The full story is available on the University of Oxford website