Kolkata: A breakthrough study by the diptera division of the Zoological Survey of India (ZSI) identified a hidden public health threat in the North Bengal hills — river blindness, a parasitic disease spread by blood-sucking black flies that thrive along mountain streams.
The research, published in the journal ‘Vector-Borne and Zoonotic Diseases’, presents the first-ever use of DNA barcoding in India to identify the elusive fly species responsible for transmitting Onchocerca volvulus, the parasitic worm behind onchocerciasis, commonly known as river blindness.
According to the World Health Organization, river blindness is among the world’s most neglected tropical diseases and ranks second only to trachoma as the leading cause of infection-related blindness.
The study found that multiple rivers in Darjeeling and Kalimpong serve as fertile breeding grounds for these black flies, known locally as pipsa or potu. These flies belong to the Simuliidae family and are notoriously difficult to identify by appearance alone. “Distinguishing between different species of Simuliidae by external features is often inconclusive. Using DNA barcoding, we can now make precise identifications quickly and accurately — an essential step in breaking the disease transmission chain,” said Dhriti Banerjee, director of ZSI.
The research team, led by senior research fellow Ark Mukherjee, extracted DNA from the legs of black fly specimens and sequenced the mitochondrial cytochrome c oxidase subunit I (COI) gene. This allowed them to distinguish four specific species — Simulium dentatum, Simulium digitatum, Simulium praelargum, and Simulium senile — from samples collected from eight locations in the central Himalayan region. “This molecular approach ensures precision in identifying vectors and will greatly aid targeted vector-control efforts,” said Atanu Naskar, officer in charge of the diptera division.
What heightens the concern is the potential exposure for tourists. “Darjeeling and Kalimpong attract thousands of visitors year-round. These black flies are minuscule — people don’t even realise they’ve been bitten until it’s too late. Once inside the human body, the worm forms nodules beneath the skin and eventually migrates to the eyes, leading to irreversible blindness,” Banerjee said.
While no case of active transmission was recorded in the region recently, scientists say the study raises a red flag. With increasing ecological vulnerability in Himalayan ecosystems and growing human movement, the findings are a timely call for proactive vector surveillance and control. “This research isn’t just academic — it has immediate real-world implications. Accurate species identification is the first and most vital step towards protecting public health,” Banerjee said.
As the study draws international attention, researchers hope their work will inform broader vector-control strategies and serve as a model for other endemic regions.
