Tropical snakebite

Published on March 29, 2020   40 min

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Good morning. My name is Professor Rob Harrison at the Center for Snakebite Research and Interventions at the Liverpool School of Tropical Medicine. My HST talk is going to be on tropical snakebite. In particular, I'd like to describe why snakebite is considered a disease of the rural poor and our attempts to improve the treatment of snakebite.
It's important to understand as we start this talk, that there are two main groups of snakes that are responsible for deaths and disability. The first group are the elapids. These consist of mambas, cobras, crates, and so on. They primarily cause a descending neuromuscular paralysis. You see here a victim of a black mamba bite being unable to open their eyes, ptosis, because of the paralysis of the muscles controlling the eyelids. The other main group of medically important snakes are the vipers. These include the true vipers and the pit vipers and rattlesnakes and so on. They primarily cause a hemorrhagic and sometimes coagular perfect syndrome. Here you can see an instance of someone envenomed by a saw-scaled viper showing bleeding from the gums. A classic manifestation of saw-scaled viper envenoming.
The next thing to understand is that antivenom can be an effective treatment for both of those main conditions of snakebite. Antivenom is manufactured using a system that hasn't really changed much in the past 100 years. We are still collecting venom from venomous snakes, and then we're injecting that in subtoxic doses into horses or sometimes sheep in tiny doses so that you generate an antibody response without causing toxicity to the animals. This is repeated sometimes for many, many years. Here you can see that the blood is being drawn from a horse that's been injected with venom to make antivenoms with our collaborators in Costa Rica. The expensive part of the whole process is the next one where you're purifying the immunoglobulin, the IgG, from the whole blood, and that is the drug that is antivenom. Antivenom is the IgG extracted from hyper immunized horses or sheep. It is, as I said, effective against the neurotoxic and the hemotoxic effects of snakebite.