A groundbreaking scientific study has uncovered a persistent and dangerous presence of Leptospira bacteria in the waters of Kerala's iconic Vembanad Lake. The research warns that extreme weather events, particularly flooding, significantly elevate the risk of transmission of leptospirosis to humans in surrounding communities.
Key Findings from the Water Column Analysis
The comprehensive study was conducted by a collaborative team from the National Institute of Oceanography (NIO) in Kochi, the Cochin University of Science and Technology, and the Nansen Environment Research Centre (NERC). Over a 12-month period, scientists collected water samples at roughly 20-day intervals from 13 different stations across the lake, which is a designated Ramsar site and the state's largest lake.
Using advanced molecular surveillance via quantitative real-time PCR, the team detected genetic material from Leptospira in the lake's water column. Crucially, these pathogens were found not only during the rainy season but also in the dry months from January to May, indicating a year-round, endemic presence.
The Flood Connection and Urban Expansion
The analysis of disease incidence data revealed a stark pattern. The region is confirmed as endemic for leptospirosis, with a dramatic spike in cases witnessed in September 2018. During that month, which saw catastrophic once-in-a-century floods, nearly 50% of the year's total cases were reported, primarily in areas near Vembanad Lake.
"We were looking at various microbial and bacterial presence in the lake after the 2018 Kerala floods and found that this pathogen is prevalent in the water column," explained Nandini Menon of NERC, a co-author of the study led by NIO-Kochi principal scientist Anas A. The research established a significant positive correlation between rainfall and disease incidence.
Compounding the problem is massive urban change. The study notes that over the past five decades, built-up areas around the lake have expanded by almost 150%. This unchecked development reduces natural water absorption space, increasing flood likelihood and the potential for pathogen spread during such events.
Environmental Drivers and Urgent Call to Action
The distribution and prevalence of Leptospira in Vembanad Lake are not random. Researchers identified that key water quality parameters directly influence the bacteria. These include:
- Temperature of the water
- pH levels
- Specific nutrient composition, particularly phosphate (PO₄) and nitrite (NO₂) concentrations
Published in the August 2025 issue of Springer under the title "Impact of Extreme Weather Events and Land Use on Leptospira Distribution in Vembanad Lake and Associated Disease Outbreaks in Near Shore Areas," the study underscores an urgent need for a multi-pronged strategy. The researchers advocate for:
Enhanced surveillance combining molecular techniques and remote sensing, robust public awareness campaigns, integrated floodwater management plans, incorporation of rodent control measures into urban planning, and other targeted interventions to break the environmental transmission cycle of this dangerous disease.
