FEATURE: The unsung heroes of snake antivenom production
By Jake Chung / Staff writer, with CNA
Taiwan is home to a rich diversity of snake species, and nearly 1,000 people are bitten by snakes each year. In emergency rooms, where every second counts, administering the right antivenom in time can mean the difference between life and death. Behind this lifesaving treatment is an unlikely group of contributors: immunized horses.
The National Immunized Horse Farm at National Pingtung University of Science and Technology covers 2.91 hectares and houses 57 horses in six stables, with four outdoor exercise fields and two horse walkers. Of the horses, 44 are involved in antivenom production, and 13 have retired.
“People often ask us if we get to ride the horses when we travel for work. We always joke, ‘No, the horses outrank us,’” Centers for Disease Control (CDC) Center for Diagnostics and Vaccine Development animal technology specialist Lee Chia-jung (李佳蓉) said with a laugh.
Immunized horses are pictured at the National Immunized Horse Farm in Pingtung in an undated photograph.
Photo: CNA
Unlike horses at recreational riding stables, which are trained for activities such as riding and running, immunized horses have a very different role, Lee said, adding that the horses’ primary job is to stay healthy and undergo immunization, providing the plasma needed to produce antivenom.
Temperament is the top priority when selecting horses. Neither a spirited racehorse, which might bolt at the prick of a needle, nor a massive draft horse weighing more than a tonne, which could be difficult to restrain if something went wrong, would be suitable, deputy director Hsieh Wen-chin (謝文欽) said.
Only horses with a calm, gentle temperament are suited to the work, he said.
Antivenom must be produced using venom from locally occurring snake species, Hsieh said.
The CDC supplies four types covering Taiwan’s six major venomous snake species.
Each horse produces only one type of antivenom during its lifetime, Hsieh said.
Laboratory staff inject it with one type of venom and wait to see whether it develops antibodies. If none appear within a certain period, they try another type, repeating the process until antibodies develop. Horses that fail to respond to any available type must be retired early.
Once sufficient antibodies have developed, researchers collect the horse’s plasma and separate and purify the antibodies to make antivenom, he said.
Immunization must proceed gradually to allow the horse’s immune system to build a response. Early side effects can include wounds, abscesses and granulomas, but improved formulations have reduced these risks. The farm takes precautions to protect the horses’ health, he said.
Sheep and alpacas can also produce antivenom, but horses remain the most widely used animals because of their size, relatively docile temperament and greater plasma yield, Vaccine Manufacturing Division chief Chen Chao-hung (陳昭宏) said.
Taiwan’s immunized horses mainly come from the US and the Netherlands, Hsieh said.
Imports from New Zealand were discontinued after some horses developed anhidrosis, a condition that prevents sweating and can cause their body temperatures to rise in hot weather.
After quarantine and health checks, horses undergo training to familiarize them with their surroundings and working conditions, Hsieh said.
They learn to wear a halter, follow handlers, enter and leave restraint stocks, and tolerate the smell of alcohol, protruding objects, and pressure on their necks and skin, he said, adding that this preparation reduces stress and injury risks during immunization and blood collection.
Horses typically serve for eight to 12 years, giving blood nearly 100 times over their working lives. Each kilogram of plasma can produce about 30 doses of antivenom, meaning one horse can help save thousands of snakebite victims, Hsieh said.
Taiwan began producing antivenom during the Japanese colonial period, when the mortality rate from venomous snakebites exceeded 6 percent. Today, it has fallen to 0.18 percent, and no one has died from an allergic reaction to antivenom.
A total of 195 medical institutions across Taiwan stock antivenom, while the CDC maintains 6,000 doses across four types, enough for at least 18 months.
National Health Insurance data from 2017 to 2021 show that an average of 979 people in Taiwan are bitten by snakes each year.
“Antivenom cannot wait until someone is bitten before production begins,” Hsieh said.
Finished-product stocks cover 1.5 to two years of demand, while reserve plasma typically covers more than three years, providing a double safety net.
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