In the wake of recent Kona Low systems that brought heavy rain and flooding across Hawaiʻi, concerns around leptospirosis have resurfaced.
The bacterial disease, often linked to contaminated water, can spread when floodwaters carrying animal urine enter the body through cuts in the skin or through the eyes, nose or mouth.
Building on these renewed concerns, student-researchers at the Department of Tropical Medicine, Medical Microbiology, JABSOM are examining how the disease spreads and how it can be detected earlier.
One of the most significant developments is expanding understanding of where leptospirosis can live.
“For years, we’ve primarily thought of this as a waterborne disease,” said graduate student Dr. Rodson Zorilla. “Now, we also see the soil as a possible variable. It could serve as another agent that helps transmit the bacteria.”
That finding adds a new layer to how exposure is understood, particularly after flooding events when water can carry contaminants beyond streams and into surrounding areas.
Building on that, Colby Macapagal, a senior undergraduate student who will graduate in May 2026, is studying how leptospirosis moves through Hawaiʻi’s natural and urban environments. In traditional ahupuaʻa systems (where water flows from the mountains to the sea), runoff can pick up contaminants along the way, eventually reaching taro farms and lower-lying communities.
“My research project looks into the environmental factors and things that follow the stream that lead into these urban areas, which causes the spread of leptospirosis as well,” Macapagal said. “The concentration of zoonotic pathogens like Leptospira found in these urban areas and in stagnant water, due to floods, is definitely very concerning for not just the animals but the communities and the people that are living there as well. It's without a doubt something that needs to be studied, not just for the sake of Leptospira, but also for other zoonotic diseases and things that have worked their way downstream…to these urban areas.”
Macapagal’s work also includes monitoring areas like dog parks, where both animals and humans may be exposed to Leptospira.
Dr. Zorilla emphasized that - “Together, these findings highlight what researchers describe as a One Health approach—recognizing the connection between environmental, animal and human health.”
While some JABSOM researchers focus on how leptospirosis spreads, others work to improve its detection. Reyson-Jase Ramos, a recent graduate of UH Manoa and a postbacc, noted that ELISA (Enzyme-Linked Immunosorbent Assay) is commonly used for Leptospirosis screening because it can detect antibodies more quickly, but it may have limitations in specificity and typically targets a single antigen.
Ramos explained that he is assisting the team in conducting PCR assays and purifying the proteins essential for developing a (MIA) microsphere immunoassay; a tool that will enhance sensitivity and specificity during the early phase of the disease, as well as be useful for long-term serosurveillance. Unlike ELISA and (MAT) microscopic agglutination test, MIA can incorporate multiple antigens and differentiate between IgM and IgG antibodies, respectively, allowing researchers to better distinguish between acute and chronic immune responses.
That delay can make early diagnosis difficult, increasing the risk of more severe illness if left untreated.
At the same time, Duy Linh Nguyen Tran, a sophomore undergraduate student, is working on improving screening methods using blood samples, while also uncovering a concerning trend.
Historical data from a statewide leptospirosis screening in 1943 by Dr. Alicata showed a positivity rate of 3.8 percent. More than 80 years later, recent testing data, 2020-2024, reveals persistence of leptospirosis threat at a 2.65% seropositivity rate. This indicates that the pathogen remains a hidden but steady threat to public health in Hawaii.
“There have to be some innovative ideas now in which you can really push for prevention,” Nguyen Tran said. “Those ideas will be important for the community to see what ways we can push for the prevention aspect of it, too.”
As Nguyen Tran sees the devastation on the North Shore, he knows his work is timely and important.
“ELISA is one of the longer types of assays, so each time I run it, it takes about five to six hours,” he said. “But I don’t feel it’s a hassle. The current events in Hawaiʻi really connect with my project. Spending five or six hours feels worthwhile because I contribute to my community and the people who fostered my youth in Hawaiʻi.”
As severe weather events put the spotlight back on leptospirosis, researchers say understanding the disease and improving its tracking and prevention will be critical to protecting public health.
This work is supported in part by the Hawaiʻi Community Foundation grant, awarded to Dr. Vivek R. Nerurkar, whose funding will help advance diagnostic development. Additional support from UH Manoa undergraduate student development programs including INBRE, UROP and MHRT has helped drive student research efforts across these projects.
