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Anti-venom for big four ineffective in treating other snakebites

By Jayashree Nandi
PUBLISHED ON DEC 06, 2019 12:05 AM IST

New Delhi: Anti-venom used In India to treat snake bites from the so-called big four—the common cobra, common krait, Russell’s viper, and saw-scaled viper, which cause most deaths from snake bites in the country — are ineffective in treating bites of other snakes from the same family or even geographically distinct populations of the same species, a new study has found.

The study published in the journal PLOS Neglected Tropical Diseases on Friday revealed dramatic differences in venom compositions of medically important (which means enough people are bitten by them) yet neglected snakes which are poorly studied.

For example, anti-venom was found to be hardly effective in treating common krait bites—one of the big four, in parts of north India. And anti-venom was found to be ineffective for the two populations of monocled cobra investigated in this study.

About 60 of the 270 snake species found in India are medically important. This includes various types of cobras, kraits, saw-scaled vipers, sea snakes, and pit vipers for which there are no commercially available anti-venom. Usually, when a person is bitten by one of these, a big-four antivenom is used for treatment.

The authors of the study, from the Indian Institute of Science, the Gerry Martin project and the Madras Crocodile Bank Trust found that one population of monocled cobra from West Bengal secretes a venom which is three-times more neurotoxic (toxic to nerve tissue) than the venom of the common cobra, and that the venom of another population from Arunachal Pradesh is extremely cytotoxic (toxic to cells) with more than five times the cytotoxins found in the venom of the common cobra.

They also found that the Sind Krait in western India secretes venom that is 40 times more potent than that of the common cobra. The Sind Krait can be easily classified as one of the most “toxic snakes” in India but there is no effective anti-venom to treat its bite, the study added.

Evolutionary geneticists characterised the venom compositions, biochemical and pharmacological features and toxicity profiles of some major neglected species and their closest big four relatives to arrive at these results. Herpetologists including Romulus Whitaker and Gerard Martin helped collect venom for the experiments.

“The big four snakes are largely distributed across the country but there are many regions where other species dominate. For example, in many states in the Northeast, the big four species are not found. Therefore, given the disturbing deficiency in the big four anti-venoms in treating bites from these, producing region-specific anti-venoms in India is the need of the hour,” said Kartik Sunagar, lead author of the study.

“Yes, there is intra-species variation where venom from the same species, say Russel’s Viper in south India is immunologically different from Russel’s Viper in north India. This is because the venom for developing anti-venom is sourced from a small part of Tamil Nadu. Sri Lanka which uses anti-venom from India has poorer outcomes for their cobra bites. Also, in the northeast and Bangladesh the monocled cobra is more common for which anti-venom may be ineffective. In Kerala, for a long time people misunderstood hump nosed pit viper bites to be saw-scaled viper bites. They needed higher doses of anti-venom to treat,” said Ravikar Ralph, researcher at Christian Medical College and Hospital in Vellore.

About 46,000 people die and 140,000 people are disabled every year in the country because of snakebites.

The only scientifically validated treatment for snakebites is the use of antivenom, for which manufacturing protocols have remained unchanged for over a century, the study said.

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