On World Snake Day, call to develop effective antivenom

The antivenom available in India cannot counter the venom of the green pit viper behind most snakebite cases in the northeast

July 16, 2022 01:08 pm | Updated 01:33 pm IST - GUWAHATI

Green Pit Viper. File

Green Pit Viper. File | Photo Credit: Special Arrangement

The green pit viper may not be more lethal than Russell’s viper, the saw-scaled viper, the spectacled cobra or the common krait. But what it injects from its poison glands often renders the polyvalent antivenom derived from the venom of the other four ineffective.

The monocled cobra, the banded krait, the lesser black krait, the great black krait, the mountain pit viper and the redneck keelback are among 15 venomous snakes out of 64 species recorded so far across the northeast. Most of the snakebite cases in the region involve different species of the green pit viper, bringing up the other venomous snakes.

The hemotoxic venom a green pit viper injects prevents the blood in the body of a bitten person from clotting, leading to internal bleeding. “Hardly any of the cases we have been fatal. But we cannot draw an inference as very little data on such snakebites are available,” Guwahati-based herpetologist Jayaditya Purkayastha said.

According to Surajit Giri, one of very doctors dealing with snakebite cases in the northeast, the antivenom derived from the ‘Big Four’ snakes are ineffective on the toxin injected by the green pit viper, or for that matter, most other venomous snakes found in the region.

The doctors referred to a 2019 study titled “Beyond the Big Four” to underline the reason. The study said venoms across these species and subspecies are extremely diverse, citing the example of the monocled cobra from West Bengal whose venom contained mostly neurotoxins while the same species from Arunachal Pradesh had cytotoxins in its venom.

Neurotoxin is a poison that acts on the nervous system. Cytotoxins kill the cells in a body.

“The antivenom we have in India is a case of one size fits all. Apart from depending on four species of snakes, experts have pointed out that about 80% of all polyvalent antivenom are derived from snakes caught in one district of Tamil Nadu,” Mr. Purkayastha said.

There have been cases of doctors administering more than 50 vials of antivenom for each cobra or krait bite in northern India because of low efficacy of the standard antidote, putting patients at risk of developing adverse reactions.

Herpetologists and clinicians in the northeast have thus called for developing a range of antivenoms that can do what the four-snake concoction cannot. They chose World Snake Day – celebrated every July 16 to raise awareness about snakes and their importance in our ecosystem – to make the appeal.

Data deficient

The true global burden of snakebit is not known due to the lack of standardised reporting or underreporting, but available data say there are more than 1.4 million cases resulting in 1,25,000 fatalities annually.

More than 46,000 people – the highest on earth – die and thrice the number are disabled due to snakebites every year with 77% of the victims dying outside healthcare facilities, indicating that people go for alternative treatment.

Most snakebite cases in India are reported between June and September and 58% of the victims are farmers and labourers.

About 1,800 vials of antivenom are sold from Guwahati – supplied to various parts of the northeast – every year. This, experts said, is negligible in a region where snakebite is common and points to limited use of antivenom due to its ineffectiveness.

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