Invasive snakes brought a parasite that is killing Florida’s native reptiles 

A close-up of a Burmese python.
Burmese pythons have caused severe population declines in the species they prey on, including raccoons, opossums, rabbits, bobcats and foxes. dwi – Adobe Stock


  • Although Burmese pythons are an essential part of their ecosystem in Myanmar, they are an invasive species in Florida’s Everglades and are spreading a deadly parasite to Florida’s native reptiles.
  • The parasite Raillietiella orientalis (R. orientalis) first emerged in Florida around the same time Burmese pythons appeared in the state. Now, it seems to have established itself in Florida’s ecosystems and is spreading in new hosts.
  • When an animal is introduced to a pathogen that it didn’t co-evolve with, the results can be deadly.

For decades, Burmese pythons have been ravaging Florida’s Everglades National Park and other ecosystems in the state. These invasive snakes were likely introduced to Florida from pet reptile importing.

Jim Wellehan holds a hawk in the University of Florida zoo ward.
Wellehan treats a variety of animals including owls, tortoises, hawks and snakes. (Photo courtesy of Jim Wellehan)

The plummeting populations of animals that the Burmese python eats, including rabbits, deer and raccoons, are well documented. But what many people have not seen is how they have also contributed to the spread of disease.

Burmese pythons are one of the largest snake species in the world and can grow to be nearly 20 feet long and weigh up to 200 pounds. Their exact population is unknown, but estimates say it could be anywhere from 30,000 to 300,000.

Experts agree that removing Burmese pythons from the ecosystem is likely no longer possible, especially because the snakes can go up to six months between meals. Burmese pythons have not just survived in southern Florida—they have thrived. The warm, subtropical climate is similar to that of the Burmese python’s original habitat in Myanmar. With no natural predators and plenty of prey, they established a self-sustaining population and are handily outcompeting other snakes.

“Anything that a Burmese python eats is disappearing, and they’re not picky as far as predators go,” said Jim Wellehan, a member of the University of Florida’s Emerging Pathogens Institute. As a tenured professor in the UF College of Veterinary Medicine, Wellehan divides his time between research and working in the zoo medicine ward, where he treats native wildlife species, as well as exotic pets. “We also see an impact in things the Burmese pythons aren’t eating, like other reptiles.”

Around the same time the invasive snake first showed up in Florida, a parasite known to be endemic in wild Burmese pythons also emerged: Raillietiella orientalis. Closely related to crustaceans and resembling a worm, R. orientalis infects the respiratory system, causing lung inflammation and breathing difficulties.

Parasites and host organisms often evolve together, giving hosts a chance to develop mechanisms for resisting the parasite. Burmese pythons went through a selective process with the parasite, which means the parasite isn’t as dangerous for them. But as a new pathogen for Florida’s wildlife, R. orientalis has proven to be deadly.

“When we’re bringing in new and diverse species that our native snakes and other things aren’t adapted for, you get a perturbation of the whole environment,” Wellehan said.

Full body of a dusky pygmy rattlesnake on a packed dirt road.
The Dusky Pygmy Rattlesnake is the smallest species of venomous snake in Florida. It preys on rodents that are often considered pests and its bite, while painful, is not usually life threatening. raptorcaptor – Adobe Stock

From the throat to the lungs, the human respiratory system branches out into increasingly smaller airways—the trachea leads to the smaller bronchi, which lead to the smaller bronchioles, and so on. As a result, when humans have foreign material in their lungs, the obstacle travels from smaller to bigger passageways on its way back out of the body.

But a snake’s respiratory system is constructed differently. Its trachea opens up directly into the lung with a large central chamber, so an object would have to go from a larger space, the lung, through a smaller space, the trachea, to get out. This makes it easy for R. orientalis to establish itself inside a snake’s lung, but tremendously difficult for the parasite to get out.

R. orientalis is especially dangerous for Florida’s reptiles, because they are much smaller than the Burmese pythons that the parasite co-evolved with. R. orientalis easily fits inside the trachea of a 14-foot Burmese python, but causes a lot more damage in species like the pygmy rattlesnake, which is typically only one to two feet long.

One man’s pathogen is another man’s treasure 

Two common marmosets perch on a branch side by side. There is green foliage in the distant background.
In the common marmoset, human herpes viruses can cause severe disease that usually leads to death 2-14 days after symptoms begin. Gatot – Adobe Stock

Wellehan cautions against demonizing a species for the damage it is causing to one particular ecosystem. “Burmese pythons are an essential part of the ecosystem in Myanmar. It’s all about how something fits into the ecological context,” he said. While Burmese pythons continue to wipe out the native flora and fauna in Florida’s Everglades, they too face the threat of invasive species back in their native habitats in Myanmar.

“And a pathogen isn’t necessarily always a bad thing. That also depends on the context for the host,” Wellehan said.

A human herpes virus, which causes cold sores, for example, does not cause disease for most people. In fact, around 90% of adults have been infected and carry a latent form of the virus without incident. But in other mammals, the same microbes can be deadly. In marmosets and gibbons, this human herpes virus can inflame the brain and liver, leading to death.

On the flip side, the rhesus monkey carries a cold sore virus that is not a problem for them, but deadly for humans.

To this end, Wellehan argues that survival of the fittest doesn’t necessarily mean being the smartest, fastest or strongest. A larger factor is having the right genes against a pathogen—especially those that have yet to be introduced to an ecosystem.

“If you have a pathogen that doesn’t impact you in a very large way but impacts your competitors in a very large way, that’s a significant advantage to be running around with. It really is context dependent,” he said.

Tracking the invasive parasite in Florida 

Alarmingly, R. orientalis has been found in snakes further north than the Burmese python’s habitat reaches. This suggests the deadly parasite has established itself in Florida’s ecosystems and no longer needs Burmese pythons to sustain its population.

“We’re seeing it here in Gainesville, which is too cold for the Burmese python in the winter. R. orientalis also seems to have gotten into other species and is being spread in some different hosts than the Burmese python it was introduced in,” Wellehan said.

Scientists are still figuring out what’s most ecologically important in the spread of the parasite. Snakes infected with R. orientalis carry the adult form of the parasite, which passes its eggs through the snake’s digestive system. Researchers suspect that wildlife the snakes prey on—such as small mammals, frogs and lizards—may consume contaminated fecal matter and become hosts for the parasite to develop into larvae, then adults. Once a snake eats an animal carrying R. orientalis, it becomes infected, and the spread of disease continues.

Burmese pythons are also known to carry viruses in the order Nidovirales. Viruses in this group, which includes coronaviruses, are notorious for their ability to jump to new hosts.

An Eastern indigo snake slithers, with its tongue out, across a forest floor with pine needles and fallen leaves.
R. orientalis infection has been associated with the death of an Eastern indigo snake, a non-venomous snake that eats small mammals, toads, frogs, turtles and their eggs, lizards and small alligators. Chase D’Animulls – Adobe Stock

“In the short term future, there’s going to continue being turbulence and upheaval as new species get brought in here. Florida is a big place for importing reptiles into the United States,” said Wellehan. “And that will have very significant consequences for our ecosystems.”

Written by: Jiayu Liang