New Published Research: Monitoring the Spread of an Invasive Snake Parasite

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Close up of a pentastome on black background.
An adult Raillietiella orientalis from Florida. – Jenna Palmisano

The southeastern U.S. is a hotspot for snake diversity. For example, Georgia is home to approximately 47 native snake species, including the imperiled Eastern Indigo Snake (Drymarchon couperi) and charismatic Eastern Diamond-backed Rattlesnake (Crotalus adamanteus). Snakes in this region face many challenges. Habitat destruction and fragmentation (particularly by roads), along with persecution by humans, are common threats throughout this region. The Southeast is also home to a plethora of nonnative species from around the world, which can sometimes have negative effects on native species. Here we examine one of the more unusual nonnative species – the snake lungworm.

 

What is a Pentastome?

Pentastomes (sometimes referred to as lungworms) are crustaceans that parasitize several groups of vertebrates, including snakes and lizards. Made up of approximately 130 species in the subclass Pentastomida, this group has a global distribution. Pentastome infections can have significant negative health impacts on hosts and may lead to death in severe cases.

Pentastomes have a complex life cycle with one or more intermediate hosts (infected by larval stages) and a definitive host (infected by reproductive adults). For example, eggs can pass through the digestive system of the definitive host before being consumed by an intermediate host, where larval pentastomes then develop. Depending on the species, the larval pentastomes may pass through a second intermediate host before finally making their way to the definitive hosts when the intermediate host is consumed.

Graphic showing the life cycle of the Pentastome with arrows indicating the transfer from one host to another.
The life cycle of Raillietiella orientalis involves two intermediate hosts. Eggs are ingested by invertebrates, which are then eaten by small vertebrates (lizards, frogs, or small mammals). Larvae continue to develop in this second intermediate host until a snake eats the infected prey. The larvae then move to the lungs of the snake, where they molt into the adult stage to feed and reproduce. – Paul Evans

A New Threat to Snakes in the Southeast

Raillietiella orientalis is a pentastome that specializes in infecting snakes, although it has also been documented in some lizard species (Fieldsend et al. 2021; Goetz et al. 2021). Raillietiella orientalis is native to parts of Southeast Asia and Africa but is thought to have been introduced to southern Florida alongside the Burmese Python (Python bivittatus). Raillietiella orientalis was first confirmed in Florida in 2012 (Miller et al. 2018) and has now been documented infecting at least 18 native snake species. This includes reports of mortality in Eastern Indigo Snakes associated with Raillietiella orientalis infection (Bogan et al. 2022). Furthermore, there is already some indication that the arrival of Raillietiella orientalis has coincided with declines in Pygmy Rattlesnake (Sistrurus miliarius) populations (Farrell et al. 2019; Palmisano, unpublished data), and researchers are currently working to better understand the effects of infection on susceptible species. Overall, it is clear that Raillietiella orientalis can cause lethal infections in several native snake species, which may ultimately translate into population-level effects.

A Black Racer (snake) found dead on the road with an invasive pentastome crawling out of its mouth.
A Black Racer found dead on the road with an invasive pentastome crawling out of its mouth. – Jenna Palmisano

Snake Lungworm Alliance and Monitoring (SLAM)

Given evidence of snake mortalities and growing concern about the spread of Raillietiella orientalis through native snake populations, the Snake Lungworm Alliance and Monitoring (SLAM) group was formed in 2022. SLAM is composed of over 100 researchers, citizens, students, and organizations that are opportunistically documenting the spread of Raillietiella orientalis by collecting samples from potential host species. The overall goal of this effort is to assess the presence, prevalence, and intensity of Raillietiella orientalis infections in native snake populations and provide critical data to support informed conservation decisions for native herpetofauna.

As part of this effort, The Orianne Society began collecting samples from across southern Georgia in 2022. The majority of samples have been collected from Eastern Indigo Snakes during routine monitoring in Georgia, but we have also collected samples opportunistically from other species. To date, we have contributed over 150 samples for this effort and will continue monitoring Georgia’s native snakes for the arrival of Raillietiella orientalis.

Several contributors to SLAM recently published an update to the distribution of Raillietiella orientalis in the journal BioInvasions Records (Palmisano et al. 2025). As of June 2024, the group had collected and processed 384 snake carcasses and 220 fecal samples from around the Southeast. Across dissected snakes, 66 Raillietiella orientalis infections were documented from 217 Florida snakes, while zero infections were found across 170 Georgia snakes. Positive detections included locations from 14 Florida counties where Raillietiella orientalis had not been previously documented. Furthermore, four snakes from captivity (but assumed to be wild-caught in Florida) were dissected, and all four were found to have Raillietiella orientalis infections.

The known distribution of Raillietiella orientalis in 2022 (left) and the updated distribution of Raillietiella orientalis in 2025 (right). Red counties indicate locations with new detections over the previous three years. – Jenna Palmisano

Conservation Implications

The available data indicate that Raillietiella orientalis has rapidly spread across Florida since its introduction to the state. There are no clear barriers to continued spread, and it is likely only a matter of time before Raillietiella orientalis arrives in states bordering Florida—if it hasn’t already. Several of the intermediate hosts can easily be transported long distances, either intentionally or unintentionally. Furthermore, the presence of Raillietiella orientalis in captive snakes suggests that this invasive parasite could be further spread as snakes and intermediate hosts are sold as commodities, both within the U.S. and internationally.

As Raillietiella orientalis continues to spread, it will present another challenge to the successful conservation of our native snake species. This is particularly true for species like Eastern Indigo Snakes, which already face significant conservation challenges throughout their range. More research is clearly needed to understand its effects on individuals, populations, and communities. Additional data may also offer potential solutions and help practitioners decide when management actions are necessary.

You can read the recent publication in the publications section of our website. The effort to monitor invasive pentastomes and establish SLAM has been led by Jenna Palmisano. Jenna was interviewed by Dr. Jenkins as part of the Snake Talk podcast – listen to Episode 93: Exotic Parasites in Snakes Spreading Across North America. Finally, more information about Raillietiella orientalis is available on the SLAM website, and further questions or potential sightings can be directed to slam.conservation@gmail.com.