The mathematical solution to snakebites

The mathematical solution to snakebites
The mathematical solution to snakebites

Treating a venomous snake bite is a race against time. The World Health Organization estimates that between 1.8 and 2.7 million people are envenomed by snakes annually and that about 81,000 to 138,000 of them die as a result. Prompt treatment with a high-quality antidote can save both lives and livelihoods.

But snakebites often occur in remote, rural areas, far from large hospitals with modern equipment. All the antidote in the world won’t help someone if health professionals can’t put that medicine into their body.

Brazil is unique among countries with a high number of snakebites in that the country can (and does) produce its own antidote and provide it for free in hospitals. In theory then, access to antidote should not be a problem.

A vial of antivenom can cost anywhere from $18 to $200, and treating a single bite can require 20 or 30 vials

But when João Ricardo Nikenig Visocci, a data scientist at Duke University, and his colleagues in Brazil analyzed data on the time between a snake bite and the start of antivenom treatment in the vast state of Amazonas, they found that it took hours, even days, for people to reach hospitals with antivenom.

These delays in care can lead to more severe outcomes, including loss of limb function, organ failure, and death.

«People just can’t get treatment in time,» Visocci says.

Training workers in small health clinics that served Amazonas could make a big difference, given that the state has 8.7% of Brazil’s population but accounts for 44.6% of the country’s snakebites. To convince politicians to redistribute the antidote away from urban centers and into small health clinics, especially in rural areas like Amazonas, Vissoci needed to show that such an investment would pay off in improved health.

«There is a lack of good epidemiological data on snakebite,» says Julien Pote, neglected tropical disease policy adviser at Doctors Without Borders. «This kind of information would be very useful to optimize distribution and also to ensure that antivenom is available at the right level of care.»

A researcher analyzes samples for a study indicating that a compound found in the fruit can neutralize the venom of the hararaca snake, at the Butantan Institute, in Sao Paulo, Brazil, on May 18, 2022.
REUTERS/Carla Carniel

Math vs snake

Originally from Maringa in southern Brazil, Visocci wanted to use his experience to find out why people continue to die from snakebites in Brazil, given that the country produces enough antidote and that the drug is provided free of charge.

Using his expertise in Big Data, Vissoci found that while Brazil has plenty of anti-venom, it is concentrated in major cities, far from the country’s snakebite hotspots. Redistributing this life-saving drug to rural health clinics would be both cost-effective and life-saving, according to a recent analysis by Vissoci in The lancet.

The team built mathematical models of the health and economic impact of snakebite in Amazonas and studied three scenarios: the status quo, increasing the availability of antivenom only in hospitals, and increasing the availability of antivenom in public health centers.

The second two options showed significant economic savings and improvements in health outcomes. However, the move to community health clinics was a clear winner.

«With a small investment from the health care system to increase antivenom coverage, the burden we would reduce by saving people’s lives is much higher than what we see in areas like HIV treatment,» Visocci says.

The burden we would reduce by saving people’s lives is far greater than what we see in areas such as HIV treatment

Joao Ricardo Nikenig Heights

Humans have been dealing with snakes and their bites since before our species existed. However, the long history of snakebite has not eliminated the problem. Not all snakes are venomous, and not all venomous snakebites inject toxins into the victim, but researchers like David Williams, the World Health Organization’s Antivenom Technical Officer, know that the number of snakebite victims is far too high. Such small animals should not cause such a large medical burden.

The social and financial impact of these bites is harder to measure, but Williams says the poverty of snakebite families is often exacerbated by the double whammy of paying for antivenom and the resulting loss of wages.

Why snakebite antivenom is valuable

The first snakebite antivenoms were developed more than a century ago and were made by injecting a horse with minute amounts of venom, slowly increasing the dose over time. This action prompted the horse to produce antibodies against the venom, which were purified and packaged to be administered to snakebite victims.

A man milks a coastal taipan for its venom in Melbourne, Australia, on November 7, 2008.
REUTERS/Mick Tsikas

The process can be time-consuming, but it’s both well-established and cheap to produce, Potet says. However, many countries remain unable to produce their own antidote, forcing them to import from other countries. If the antivenom is not freeze-dried, it also requires a cold chain and has a limited shelf life.

As a result, when antidote is available, it is often expired, of questionable quality, and prohibitively expensive. A vial of antivenom can cost anywhere from $18 to $200, and treating a single bite can require 20 or 30 vials.

«Victims have to pay out of pocket,» says Potet. «This limits the number of people who can access good quality treatment.»

For Williams, Vissoci’s kind of big data approach is exactly what the snakebite field needs to improve outcomes.

«The more data we can provide, the better,» says Williams. “Snake bites are still very under-reported. It’s really a disease of invisible communities—communities where it’s not necessarily easy to get the data, or ones that always seem to be forgotten when it comes time to collect data.”

A hararaka snake is seen at the Butantan Institute in Sao Paulo, Brazil, May 18, 2022.
REUTERS/Carla Carniel

Carrie Arnold is a public health journalist based in Virginia.

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