Snakes considered most important medically; Classification to help develop effective anti-venoms
Snakes like the green mamba have been classified by the study. Photo: Wikimedia Commons The venoms of 26 types of snakes in sub-Saharan Africa, like the black and green mambas and ring-necked spitting cobra, have been classified by a new study to understand their composition and function better. These snakes are considered the most important medically and cause thousands of deaths yearly.
The study was published by the Center for Antibody Technologies, Technical University of Denmark, in the journal GigaScience on December 13, 2022. Professor Andreas Laustsen-Kiel of the university headed the research.
Snakes bite an estimated 5.4 million people each year worldwide. These result in 2.7 million envenomings — a potentially deadly condition due to the toxins in these reptiles — and 81,000-138,000 deaths yearly, as per the World Health Organization (WHO).
Read more: January 30 now ‘World Neglected Tropical Diseases Day’: WHA
An estimated 500,000 people suffer from snake bites in sub-Saharan Africa yearly, leading to 7,000 to 20,000 deaths. However, the disease is severely neglected despite being fatal and causing amputations and permanent disabilities.
Snakebite envenomation is included among neglected tropical diseases — a group of infections that are most common among marginalised communities in the developing regions of Africa, Asia and the Americas.
The research covered two key families of the reptile: Elapids — which include the black and green mambas and Anchieta’s cobra, and vipers such as the West African gaboon viper and the West African carpet viper.
The findings build a basis for a deeper understanding of snake biology and evolution. It may “aid in the development of effective antivenoms through better understanding of the behaviour of snake venoms and their roles as drug targets” as well, the authors noted.
Antivenoms are in low production, as per the WHO. This is partly due to poor demand, resulting in manufacturers ceasing production and a dramatic rise in prices over the past two decades, making it unaffordable for those who need it.
The high prices are also reducing demand. “Many believe that unless strong and decisive action is taken quickly, antivenom supply failure is imminent in Africa and in some countries in Asia,” the global health body noted in a May 2021 factsheet.
A changing environment moulds how snakes behave and evolve, the study found. “This is reflected in their venoms, which are typically highly adapted for their biological niche, including their diet and defence mechanisms for deterring predators,” it detailed.
The study also profiled and compared the 26 venomous snakes to understand the varying clinical manifestations of different toxins. The composition and functions of snake venoms is complex, which dictates how they present themselves in those who have been bitten.
The analysis said:
Elapid venoms contained large amounts of neurotoxic and cytotoxic 3FTxs (a class of proteins called “three finger toxins”) and PLA2s (a class of enzymes), whereas the viper venoms were dominated by cytotoxic PLA2s, (and other enzymes such as) Snake Venom Metalloproteinases and Snake Venom Serine Proteinases.
A neurotoxic snake bite presents as frothy saliva, slurred speech, respiratory failure, and paralysis of the skeletal muscles. It typically attacks the neuromuscular junction.
A cytotoxic snake bite manifests as painful and progressive swelling at the bite site, developing into blistering and bruising, according to the WHO. The most common kind of poisoning is hemotoxicity, which has cardiovascular effects, presenting as organ degeneration, tissue damage and internal bleeding.
The 26 venomous snakes were selected by the authors, given they belong to category 1 or 2 snakes of the highest medical importance as classified by the WHO.
Several factors dictate the medical importance of a venomous snake, like highly venomous and how common and widespread are the snakes. The frequency of biting attacks and mortality, morbidity and disability levels are some other factors.
Read more: Half the global snake bite deaths happen in India. Why are we not prepared?
A 2013 paper published in the Journal of Venomous Animals and Toxins including Tropical Diseases, argued since death from a snakebite is an extreme outcome, other factors must also be considered when classifying snakes based on their medical importance.
“Geographical variations that affect snake venoms, even within the same species, have led to contrastingly different outcomes in patients from different regions bitten by the same snake species,” the paper noted.
Factors other than the lethal nature of the venom must also be taken into account.
“Frequency of medical attention after a bite, local or systemic envenomation provoked by the bite, long term consequences, availability of antivenom therapy as well as the size of the population at risk — that may vary from one region to another” are some of the other factors.
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