Public health

Ineffective antivenoms for snakebites

Print edition : January 03, 2020

The monocled cobra (Naja kaouthia) from Arunachal Pradesh. Photo: Gerard Martin

A NEW study the Indian Institute of Science (IISc) carried out in collaboration with the Gerry Martin Project (Survey #1418/1419 Rathnapuri, Hunsur, Karnataka) and the Madras Crocodile Bank Trust and Centre for Herpetology has found that commercially available antivenoms in India can be ineffective in treating bites from certain medically important but neglected snakes. According to a release from the IISc, though the bites of these snakes are harmful to humans, the snakes are poorly studied. The study was published in “PLoS Neglected Tropical Diseases”.

“India is the snakebite capital of the world,” said the senior author of the study, Kartik Sunagar of the IISc’s Centre for Ecological Sciences. Each year in India, says the release, about 46,000 people die and 140,000 people are disabled 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. In India, a polyvalent antivenom is produced against the so-called “big four” snakes: the spectacled cobra, the common krait, the Russell’s viper and the saw-scaled viper.

India is home to 270 species of snakes, about 60 of which are considered medically important. But specific antivenoms are not produced against these species; instead, the big four antivenom is routinely used to treat all snakebites.To better understand the consequences of using the polyvalent antivenom to treat all snakebites, the researchers conducted a twofold study. In the first part, they characterised the venoms of the major neglected snakes—including the Sochurek’s saw-scaled viper, the Sind krait, the banded krait and two populations of monocled cobras, as well as their closest big four relatives (saw-scaled viper, common krait and spectacled cobra)—on the basis of their composition, pharmacological activities and potencies.

The results revealed that the venom compositions of these snakes were significantly different and also differed between geographically separated populations of the same species. “For instance, stark variation was observed in the venoms of two populations of the same monocled cobra species from West Bengal and Arunachal Pradesh. The former was found to be highly neurotoxic (targeting the nervous system) while the latter was rich in cytotoxins (targeting cells and tissues),” Sunagar explained.

In the second part of the study, the researchers evaluated how effective commercially marketed Indian antivenoms were. They found that the antivenoms were highly inefficient in overcoming the effects of the toxins, with one of the antivenoms being completely ineffective against the Arunachal Pradesh monocled cobra in a mouse model. Surprisingly, this widely marketed commercial antivenom even failed to neutralise the venom of the common krait from north India.

The study also found that the venom of the Sind krait from western India is over 40 times more potent than that of the spectacled cobra, making it the most venomous Indian snake. There is, therefore, a pressing need to develop region-specific snakebite therapies for the many neglected species, Sunagar said. The paper provides directions for Indian antivenom manufacturers to improve the pan-India effectiveness of their commercially marketed antivenoms. According to him, the researchers have initiated collaborations with some Indian antivenom manufacturers to produce these regionally effective antivenoms.

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