Palm leaves and mountain

Hannah Karuri

Theme: Global challenges

​CIRCLE alumnus Dr Hannah Karuri, a senior lecturer and nematologist at the University of Embu, is on a quest to help farmers combat the microscopic parasitic worms wreaking havoc on vital crops.

What comes to mind when you think of climate change? Perhaps it’s melting ice shelves and droughts or raging wildfires and floods. To see the large-scale manifestations of a warming planet, we need not look far.

On a microscopic level, however, climate change paints a very different picture. For Dr Hannah Karuri, a nematologist and senior lecturer at Kenya’s University of Embu, the most harmful impacts of climate change are those that we cannot see nor feel – the invisible worms.

What is Nematology?

Nematology is a complex discipline concerning the study of microscopic worms, known as nematodes, which can be either beneficial or parasitic. Hannah explains that the latter types are wreaking havoc on vital crops for Kenyan smallholder farmers, such as sweet potatoes and maize, and that rising temperatures are causing plant-parasitic nematodes (PPN) populations to swell below the ground.

“This problem is very widespread in Kenya. In a small handful of soil, you often get millions of these nematodes,” says Hannah. “It’s getting worse over time, but the challenge is that you can’t see them with your eyes, so people don’t know they exist. Farmers will just see their crops wilting or take on a strange colour, and they assume it’s some nutrient deficiency when in fact it’s due to the nematodes.”

“Just try telling people that an invisible worm is killing your crops!” she adds with a chuckle.

Steadily growing populations of parasitic nematodes have severe implications for food security and rural livelihoods. Controlling the PPN has become an urgent battle which finds Hannah at the front lines.

Using science to empower farmers

At the University of Embu, Hannah currently lectures and mentors young researchers while simultaneously advancing her research in nematology and climate change. For the time being, she is the only nematologist at her institution, but she is hopeful this will change as she now trains postgraduate students in the lab and field skills they need to take up the discipline.

“My interest in this area began while I was doing my master’s course and studying sweet potato, where I got to see how nematodes actually affected a crop that was so important to smallholder farmers. Once I got into the nematodes, I stuck on until now,” Hannah recalls.

When Hannah connected nematology with climate variables, she knew she had to do more research on how climate change was causing PPN populations to grow. It led her to apply for the CIRCLE Fellowship programme, which she successfully completed at the University of Nairobi.

CIRCLE enabled Hannah to travel around Kenya on the search for sweet potato varieties that demonstrated resistance to PPN. Based on the attributes of these varieties, she then developed innovative, low-cost parasite management techniques and acquired CIRCLE’s dedicated Research Uptake funding to begin translating her research into practice.

To date, Hannah has trained farmers in ten different localities across the fertile regions of Embu and Mwea to apply the new PPN management techniques she developed for maize, rice, and sweet potato. She garnered a great deal of positive engagement from regional officers in the Kenya Agricultural & Livestock Research Organisation and the Ministry of Agriculture, Livestock & Fisheries, who were supportive of her work.

Hannah recalls overcoming major challenges in her work, as many farmers were initially unconvinced that invisible worms were responsible for the death of their crops. In response, she developed and distributed factsheets in local languages which clearly communicated the urgent need to address the problem.

“Farmers are very good at what they do, but they often don’t know the scientific causes behind things they see,” Hannah explains. “With climate change for example, they can tell if the rain doesn’t come as often as before or if the sun is too hot. So, for researchers like us, it’s important to integrate farmers’ knowledge and our scientific knowledge, then try to make them understand how the two are linked. That way, farmers can understand why something is happening, and they can be more receptive to what they need to do to deal with climate impacts.”

It didn’t take long for the farmers to grasp the gravity of the problem. In fact, the individuals Hannah trained have also been passing the knowledge onto new farmers in their community – over eight hundred farmers have benefitted from Hannah’s research.

Despite the challenge of attracting researchers and funding to an understudied field, Hannah is optimistic that the field of nematology will grow. She envisions a future where the science of the invisible worms will be de-mystified, where people will understand its connection to climate change, and where farmers can access a variety of resilient crops.

“The most fulfilling thing for me when I do this research is when I talk to a farmer and tell them about PPN management techniques that are low-cost and readily available. Then, you just see the joy the farmer has on their face. The joy that they don’t have to incur heavy costs to control these pests…the joy of knowing they can continue their work and maintain their livelihoods.”

For a moment, Hannah pauses to reflect on her journey. “It is my hope that no farmer will go hungry again.” 


The CIRCLE Programme was funded by the UK Foreign, Commonwealth and Development Office (FCDO), led by the Association of Commonwealth Universities and delivered in partnership with the African Academy of Sciences (AAS), Vitae UK and the Natural Resources Institute (NRI) of the University of Greenwich.

The CIRCLE programme works to strengthen climate change research within sub-Saharan Africa through an innovative dual approach. The CIRCLE Visiting Fellowships Programme supported 97 outstanding African researchers to undertake research into local climate impacts, while the CIRCLE Institutional Strengthening Programme worked with 31 universities across 10 countries to improve institutional capacity to support and promote quality research.


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Theme: Global challenges