Research from the Epidemiology and Modelling group in collaboration with colleagues in 17 African countries predicts the spread of cassava brown streak virus (CBSV) across sub-Saharan Africa.
The Cambridge team has built the first continental-scale model to predict CBSV spread across all 32 major cassava-growing countries in the region using surveillance data and local knowledge from partners. The tool aims to inform policy and support subsistence farmers and smallholders who rely on cassava as a vital food security crop.
Cassava is a staple crop for 500 million people in sub-Saharan Africa, particularly in Nigeria, the world's largest producer. CBSV causes devastating crop losses, leaving smallholder farmers particularly vulnerable due to limited access to resources like pesticides for vector control.
The current outbreak was discovered in Uganda in 2004, and now CBSV is spreading from East and Central Africa westwards, putting West African cassava under threat. Predicting its arrival is essential for governments and organisations to prepare early-warning monitoring and responses to protect farmers against the epidemic.
The research, published in Scientific Reports, combines epidemiological modelling from Cambridge with disease surveillance data from African collaborators to predict arrival times and spread rates across the continent.
The model predicts that key production regions such as Nigeria are likely to be infected by 2050, with the remainder of West Africa within a decade following that. There is also the risk of direct introductions on infected planting material.
Dr Richard Stutt, co-lead author from Cambridge’s Epidemiology and Modelling group, said: “This is the first study of the disease at this scale and detail. In collaboration with our co-authors across sub-Saharan Africa, we used real-world reports of CBSV spread in East, Central and Southern Africa to improve the accuracy of predictions and produce a model capable of capturing the key features of the disease.”
Professor Justin Pita, Executive Director of WAVE RESEARCH, a key collaborator on this project, said: “This work epitomises the true spirit of international partnership to tackle field and food security realities in Africa in order to deliver real-world impact.”
Two routes of introduction – regional spread versus direct introduction
The team used the model to look at two likely entry routes for the disease to West Africa.
The first was to map progressive cross-continental spread – what would happen if it travelled across the continent from East Africa across Central Africa and the Democratic Republic of Congo (DRC).
CBSV is spread at the local level by whitefly (Bemisia tabaci) and the transport of infected cuttings, which is a risk because cassava is propagated with stem cuttings from plants in one season used as planting materials in the next.
The study found that spread across sub-Saharan Africa is highly variable due to sparsely populated and loosely connected areas in Central Africa. “At the same time, if it gets a few lucky jumps, then it could very rapidly cross large areas,” said Dr Stutt.
A critical gateway is Yaoundé, the capital of Cameroon. Once CBSV reaches Yaoundé, it can quickly enter Nigeria. The research shows that due to Nigeria's high population density and intense cassava cultivation, the disease could spread across all remaining West African countries within 10 years of entering Nigeria.
"The scale and density in Nigeria puts things on another level... Proactive measures in southern Cameroon are key to stopping it before it becomes established in Nigeria," Dr Stutt explained.
The second scenario models direct introduction – the risk of infected stem cuttings being transported directly over long distances by air, sea or road. Movements of cuttings by private companies or NGOs could introduce CBSV to West Africa at any time without advance warning, bypassing neighbouring countries entirely.
While direct introductions may be rare, a single instance could trigger a severe, isolated outbreak, spreading the infection far faster than previously seen in East Africa.
Priorities for prevention and action
The study highlights the urgent need for forward planning to safeguard the livelihoods of millions of smallholders and curb CBSV transmission.
To mitigate disease spread, the authors identify three core priorities: enforcing strict quarantine measures at borders and ports to prevent long-range entry, establishing early-warning surveillance for rapid detection, and developing clean seed systems.
Professor Chris Gilligan, Head of Epidemiology and Modelling at the University of Cambridge, said: “Preparedness is crucial. This includes having surveillance programmes in place so that you can find the disease as soon as it arrives, so the epidemic hasn't taken off before anyone knows about it.”
To respond effectively when CBSV arrives, countries need to set up certified seed multiplication farms and formal certification networks, ensuring smallholders can access guaranteed virus-free planting material. Although establishing these seed systems requires long-term effort, deploying them prior to an outbreak is essential for protecting rural communities against CBSV and other endemic plant threats.
Ultimately, the new model provides a blueprint for decision makers to test, refine, and improve how they monitor and control crop disease across the region.
About WAVE RESEARCH
WAVE RESEARCH is a non-profit organisation dedicated to protecting crops and strengthening food security across West and Central Africa. Governed by its member countries, it operates a network of plant health innovation laboratories based at universities and national research centres. Headquartered in Côte d'Ivoire, WAVE RESEARCH works across 10 countries: Côte d'Ivoire, Benin, Burkina Faso, Cameroon, Gabon, Ghana, Nigeria, Togo, DRC, and Sierra Leone.
Funding
The Epidemiology and Modelling group at Cambridge gratefully acknowledges support for the modelling work from the Gates Foundation jointly with the UK Foreign, Commonwealth and Development Office, and the UK Biotechnology and Biological Sciences Research Council (BBSRC).
Reference: Godding, D., Stutt, R.O.J.H., Savi, M.K. et al. ‘Predicting the cross-continental spread of the cassava brown streak disease epidemic in sub-Saharan Africa.’ Scientific Reports, DOI: 10.1038/s41598-026-59438-2.
Image: Mohamed Gbewca from the Maomaheh Farmer's Association in Sierra Leone collects cassava roots. Credit: Karen Kasmauski / Getty Images.