ZSI study finds human blindness-causing blackfly in rivers flowing through Darjeeling, Kalimpong

Indian Express

26-04-2025

The Zoological Survey of India (ZSI) has recently spotted blackflies, which serve as carriers of a worm causing human blindness, in many rivers flowing through the northern parts of West Bengal.
Locally called 'pipsa' or 'potu', the blood-sucking flies were found in rivers in areas such as Darjeeling and Kalimpong that serve as the insect's breeding grounds. The finding raises concern as the areas draw many tourists throughout the year.
'Whether Darjeeling or Kalimpong, both places are favourites among Bengalis on the tourism map, making them socio-economically significant. People visit these places throughout the year. Visitors may unknowingly get bitten by these blood-sucking flies while enjoying themselves. Although local people are more vulnerable to these flies, the risk of blindness remains a concern,' Dr Dhriti Banerjee, Director of the Zoological Survey of India.
ZSI scientists have, however, confirmed that no individual has so far been diagnosed with the infection called 'river blindness' in the region.
According to the World Health Organization (WHO), the blindness caused by the worm called Onchocerca volvulus is among the most neglected tropical diseases.
'When these blood-sucking blackflies bite humans, the worms enter the human body from the fly. Initially, the worms form nodules under the skin. As they grow, they travel through the bloodstream to the eyes, ultimately resulting in blindness,' explained a scientist.
The first step towards protecting people from the infection is to identify and control the vector – the black fly, and therefore, better identification of the disease carrier is essential for improved treatment, said the scientists at the Diptera division of the ZSI in a statement.
'These black flies of the Simuliidae family are extremely small. They are barely noticeable to the naked eye. Before one realises it, the fly has already sucked blood and departed. Many species in this family look almost identical externally. In scientific terms, distinguishing between two different species of Simuliidae flies based on external characteristics is quite difficult and time-consuming. Sometimes accurate species identification is not even possible,' said Dr Banerjee.
Amid rising health concerns posed by the presence of the blackfly, researchers from the Diptera division have used DNA from these flies as a means of identification. The method employed for identifying the flies is called DNA barcoding.
Dr Atanu Naskar, scientist at the ZSI's Diptera division, revealed that they conducted their research in eight locations across Darjeeling and Kalimpong districts of West Bengal, which are part of the Central Himalayan region, and collected blackfly samples.
After preliminary segregation based on external characteristics, DNA barcoding methods were used to identify the species.
Ark Mukherjee, a senior research fellow at the Zoological Survey of India and one of the researchers involved in the blackfly study, explained, 'First, DNA was collected from the legs of the blackfly samples, and then that DNA was barcoded.'