Snake bite defense: The Opossum

Drs. Norbert Herzog & David Niesel

Drs. Norbert Herzog & David Niesel

Medical Discovery News

If you live in a rural area, you’ve probably had to deal with snakes. Almost 500,000 people are bitten by snakes and more than 20,000 die from them worldwide each year, although the World Health Organization notes these figures may be closer to 1.8 million incidents and 94,000 deaths. Opossums, on the other hand, never have to worry about that since they are resistant to snake venom. Opossums have a protein in their blood that binds to the toxins in snake venom and neutralizes them. Now scientists are looking into whether this protein could be used to treat human victims of snake bites.

Venomous snakes generally have different combinations of toxins: cytotoxins that kill cells, neurotoxins that affect the nervous system, cardiotoxins that act on the heart, hemotoxins that influence the blood and mycotoxins that are toxic to muscle. Venomous snake bites can cause paralysis that prevents breathing and can cause fatal hemorrhages, irreversible kidney damage and destruction of tissue in and around the bite site, which can lead to amputation.

Currently, poisonous snake bites are treated using antivenins. To make antivenin, poisonous snakes have to be milked for their venom (a dangerous prospect) often thousands of times. Then, small amounts of venom are injected into mammals such as horses, pigs and sheep for about a year. The animals’ immune systems respond to the venom’s proteins by making antibodies against them. When injected into a human victim of a snake bite, these antibodies bind to and neutralize the toxins in the venom. This process is expensive, costing thousands of dollars per vial, and some people require 20-30 vials or more to treat a single snake bite. Some people experience adverse reactions to the antivenins, so a better treatment would be welcome.

More than 20 years ago, researchers discovered that opossums are protected from snake venom thanks to a specific blood protein called Lethal Toxin Neutralizing Factor, or LTNF. When injected into mice, not only did LTNF protect them from poisonous snake bites but it also protected them from other toxins like ricin and botulinum toxin (Botox). Binie Ver Lipps, the virologist who patented this discovery in 1996, then determined that only the first 10 to 15 amino acids of the protein were required for protection against toxins.

Relatively little work was done on this protein until Claire Komives, a professor of chemical engineering at San Jose State University, was looking for research project ideas while she was on a sabbatical in India, Ver Lipps’ native country. After reading old literature about LTNF, she came up with the idea to synthesize the active portion, the first 11 amino acids, in bacteria. Abundant amounts of it were made inexpensively, then isolated and purified. When tested, it protected mice from the venoms of western diamondback rattlesnakes and Russell’s vipers with no ill effects. Further testing will prove whether it is a universal antivenin that could cheaply and effectively replace those currently being used, and most importantly whether it is safe for humans.

Professors Norbert Herzog and David Niesel are biomedical scientists at the University of Texas Medical Branch. Learn more at

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