The Diptera Section of the Zoological Survey of India (ZSI) has conducted a breakthrough study using DNA barcoding to accurately identify different species of blackflies. This method is expected to improve strategies for disease control and vector management, particularly in ecologically vulnerable regions such as central Himalayas.
The research, published in the international journal Vector-Borne and Zoonotic Diseases, has reported the first use of DNA barcoding in India to identify a hidden public health threat—river blindness (onchocerciasis)—in the North Bengal hills. The disease is caused by the black fly species, which carries Onchocerca volvulus, a parasitic worm. The authors of the study are Arka Mukherjee, Oishik Kar, Koustav Mukherjee, Bindarika Mukherjee, Atanu Naskar, and Dhristi Banerjee.
DNA Barcoding and its Applications
DNA barcoding is a technique used to identify specimens by analysing short, standardised DNA sequences. Each species has a unique DNA barcode like fingerprints. By comparing these barcodes to a reference database, scientists accurately determine the species’ identity.
For barcoding, different genes are used:
- For animals, the commonly used gene used for DNA barcoding is Cytocrome c Oxidase Subunit 1 (CO1).
- For plants, regions like Ribulose-1, 5-bisphosphate carboxylase/oxygenase large subunit (rbcl) and Maturase K (matk) genes are used.
Significance Apart from species identification, this technique is valuable in food authentication, detecting adulteration in herbal or animal products, correct identification of medicinal plants, and identifying illegal wildlife trade items.
About River Blindness
River blindness is a filarial disease, which is transmitted through the bites of infected blackflies. These blackflies breed near fast-flowing rivers. The disease can lead to severe skin conditions, and in some cases, permanent blindness; so, the term ‘river blindness’.
According to the World Health Organization (WHO), river blindness is one of the most neglected tropical diseases. It is the second leading cause of infection-related blindness after trachoma.
Global Burden and Elimination of Onchocerciasis
Over 99 per cent of onchocerciasis cases are concentrated in sub-Saharan Africa, Yemen, and parts of Latin America with the remainder along the Brazil-Venezuela border.
The WHO has verified five countries as free of onchocerciasis following sustained elimination efforts: (i) Colombia (2013), (ii) Ecuador (20214), (iii) Mexico (2015), (iv) Guatemala (2016), and (v) Niger (2025)—the first African country to have achieved this status.
Why DNA Barcoding Matters
Blackflies belong to the Simuliidae family and are extremely small. They often go unnoticed by the naked eye and so are capable of biting and feeding on blood before a person becomes aware of their presence.
The research team extracted the DNA from the legs of blackfly specimens and sequenced the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene from samples collected at eight locations across the central Himalayan region.
This molecular approach provided precise species identification, significantly enhancing targeted vector control efforts. Distinct gene sequences were used to differentiate the blackfly species identified as potential vectors. A global survey has catalogued 2432 species of Simuliidae (2415 living and 17 fossil), with at least 27 species or species complexes identified as vectors for the parasitic worm, Onchocerca volvulus.
Key Findings and Public Health Implications
Several rivers in the Darjeeling and Kalimpong regions serve as ideal breeding sites for blackflies, locally known as pipsa or potu. Scientifically, distinguishing between different species within the Simuliidae family based on external features is both challenging and time-consuming. The researchers employed DNA barcoding to identify four blackfly species: (i) Simulium dentatum, (ii) Simulium digitatum, (iii) Simulium praelargum, and (iv) Simulium senile.
The potential risk to tourists further heightens concerns. Darjeeling and Kalimpong which attract thousands of visits throughout the year, may unknowingly expose travellers to blackflies. Once inside the human body, the parasitic worm forms nodules beneath the skin and can eventually migrate to the eyes, leading to irreversible blindness.
Although no recent cases of active transmission have been reported in the region, scientists view the study as a critical warning. With increasing ecological vulnerability in the Himalayan ecosystems and growing human movement, the findings underscore the urgent need for proactive vector surveillance and control measures.
Treatment
The elimination of onchocerciasis primarily relies on population-based treatment with ivermectin, a strategy known as mass drug administration (MDA). For this approach to be effective, it is essential to achieve a minimum therapeutic coverage of 80 per cent within the target population.
Way forward
As the study draws international attention, the researchers hope their work will contribute to the development of broader vector-control strategies and serve as a model for similar efforts in other endemic regions. The researchers emphasised that accurately identifying and managing the blackfly—the vector of the disease—is a crucial first step in safeguarding people from river blindness. They noted that effective treatment depends on correctly identifying the insect, responsible for transmission.
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