Tomas Leon
Looking for signs of the snails and fish that have the parasite in a river near villages with high rates of human infection.

It’s monsoon season, and another deluge opens on us as we quickly wrap up collecting water samples from the murky ponds and race back to the pickup truck. I’m in northeast Thailand, in Khon Kaen Province, where I’ve spent large portions of my summers since I first came to Berkeley for graduate school in 2012. My research and the work of my Thai collaborators has been focused on the role of the environment in transmission of the Southeast Asian liver fluke, a parasitic worm that villagers get by eating raw and fermented fish salad, a popular dish in the region. Infection with this worm is linked with a highly fatal liver cancer that claims thousands of lives every year, so we are working towards control and elimination of the liver fluke in the region. Its movement in the environment is sustained and exacerbated by the seasonal floods, and 2017 was one of the worst for flooding in a while; by July, roads were already under water. In an average year, this wouldn’t happen until September.

To study the ecological aspects of how the disease is spread, we collect snails, fish, water, and animal feces to test them for presence of the parasite and make other relevant environmental measurements. My colleagues and I tramp across rice paddies, ride along in fishing boats, and track animals in the villages and countryside to obtain these samples. Though we suspect these worms have been with us and inside of us for millennia, in the case of the Southeast Asian liver fluke we have only a century’s worth of science and still cannot answer some very basic questions about how it moves around in the environment, which prevents us from controlling it effectively. Because it is difficult to change eating behaviors, especially involving deeply embedded cultural traditions, I focus on how we can optimize water management (dams, irrigation systems, farming practices) and environmental control strategies to minimize contamination with the parasite and exposure to humans.

Collecting snails from a rice paddy to test for liver flukes. About 1 in 500 snails is infected.
Collecting snails from a rice paddy to test for liver flukes. About 1 in 500 snails is infected.

Amidst all of the sickness and scientific uncertainty, I have an opportunity to do impactful research and make a difference in people’s lives. I return annually to the Tropical Disease Research Center at Khon Kaen University to work with students and professors from all over the world. Whether it’s a French student helping me with lab work or a Thai public health worker conducting interviews in villages, my dissertation project relies upon the contribution and support of many others and their disciplines.

In summer 2017, I spent a large chunk of my time with hydrologists in the engineering school modeling flooding in the past decade and seeing how that makes sense of the liver fluke infection data we have from those years. How does understanding the rainy season and its impacts help us improve timing of treatment and control programs? That is one question I am working to answer. When my piece of the puzzle is put together with the doctors, engineers, farmers, villagers, and everyone else involved with this effort, we make progress towards fewer cases of cancer and parasite infections and improved public health for the people of northeast Thailand.


Tomás León is a PhD Candidate in the Environmental Health Sciences Graduate Group. He previously completed a MS in Global Health and Environment at Berkeley and spent a Fulbright year in Thailand. He will finish his PhD in 2018.


Categories: Headlines, March 2018
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About Tomás León