Ben StegengaViews:
Becoming Involved in Parasite Monitoring
If asked what The Orianne Society does, most people would immediately think of conservation efforts for one of our focal species, like Eastern Indigo Snakes, Eastern Diamondback Rattlesnakes, Spotted Turtles, or Wood Turtles. Yet others might think of our prescribed fire and habitat restoration efforts. All of which is true, but on the research side of things, we’re involved in a lot of small things that don’t necessarily get much spotlight. You can think of them as side-projects or small collaborations to aid the work of other researchers, and they’ve taken many forms over the years. From collecting Florida Pine Snake genetics to sampling Spotted Turtle claw clips for isotope analysis to documenting leeches on new amphibian host species to searching for new Gopher Frog breeding wetlands. These projects often arise after an unexpected observation in the field, a conversation with peers at a conference, or an email from fellow researchers who think we might be able to contribute to a project. And that’s exactly how we got involved in this current parasite monitoring project.
Back in April of 2022, Jenna Palmisano, a PhD student at the University of Central Florida, reached out to Houston and myself about potentially collaborating on a project to map the spread of an invasive parasite that’s affecting our native snakes. Before this, I had heard rumblings in the snake world of an invasive pentastome, a worm-like parasite, that was turning up in Florida. I didn’t know much else, but Jenna quickly filled us in on everything during our first Zoom meeting.
Understanding the Invasive Pentastome
The pentastome species in question is Raillietiella orientalis, which naturally occurs in Asia and Africa but has now been introduced to Australia and Florida. Although they superficially look like worms and are commonly referred to as snake lungworms, R. orientalis are actually crustaceans. It’s believed that these parasites were introduced with Burmese Pythons (Python bivittatus), however, many other introduced species (Argentine Tegus, Tokay Geckos, Cuban Treefrogs, Brown Anoles, etc.) are suitable hosts and have likely played roles in subsequent introductions. However, the real worry is the effects R. orientalis is having on our native species, but to understand that, one must first understand the basics of its life cycle.
R. orientalis has a complex life cycle with multiple intermediate hosts before infecting a final or definitive host, which is usually a snake. Pentastome eggs are consumed by an invertebrate, such as a cockroach, when feeding on infected feces. After being consumed, the eggs quickly hatch into larvae, infecting the invertebrate. When a small vertebrate predator such as a frog or lizard preys on an infected invertebrate, it consequently becomes infected with the larvae. And finally, when a snake feeds on that infected vertebrate, the larvae travel from the snake’s digestive tract into the snake’s lungs where they become reproductive and spend the rest of their lives. Once adults are established in a snake’s lungs, they’ll feed on the snake’s blood, breed, and lay millions of eggs which are “coughed up” and passed through the snake’s digestive tract, starting the cycle all over again. It’s worth noting that this is the life cycle that has been documented, however, there are many questions regarding their natural history that remain unanswered, and other hosts or infection pathways may exist.
The Impact on Native Snake Species
The consequences of an infection are also poorly understood at this time, and there are many unanswered questions regarding the full impact of pentastomes in our native species. However, there is a growing body of evidence that for at least some species, a pentastome infection can result in severe complications like lung lesions, sepsis, pneumonia, and even death.
The Dusky Pygmy Rattlesnake (Sistrurus miliarius barbouri), which is Jenna’s focal species for her doctoral research, is one of those species that appear to be getting hit hardest. Although regularly considered a common snake in Florida, the Dusky Pygmy Rattlesnake appears to be declining in many of its southernmost populations. And while we can’t definitively say that pentastomes are the cause for this, it’s likely they’ve at least played a role. Pentastome populations also appear most robust in south peninsular Florida, and Jenna has now repeatedly observed newly deceased pygmy rattlesnakes in the field with obvious pentastome infections. However, R. orientalis isn’t the only pathogen present at these sites. Ophidiomyces ophiodiicola, the fungal agent that causes Snake Fungal Disease (SFD) is also a major component of Jenna’s research, and she’s investigating the impacts of both diseases on pygmy rattlesnake populations. Unlike SFD, which seems to be present throughout the Southeast, R. orientalis are currently only known from Florida, but their distribution keeps expanding northward, with the most recent records occurring less than 50 miles from the Georgia state line. Additionally, pentastomes have been recorded in at least 18 species of native snake, including the Eastern Indigo Snake (Drymarchon couperi).
The Threat to Other Species and Expanding Range
Within minutes of talking with Jenna, it became evident that this emerging conservation threat could be looming over not only our focal species, but snakes across the entire Southeast. It was also apparent that The Orianne Society was positioned in a really critical spot to collect samples and be the first line of detection for the state of Georgia. Throughout the year I’m working on several research projects across South Georgia and North Florida, where I’m either already taking data on snakes or could easily take samples off incidental captures. So we immediately agreed to collect as many samples as we could. Testing fecal samples for pentastome eggs is the most reliable way to confirm an infection in live snakes, but not every snake is willing or able to “donate” a sample. To increase sampling effort, we also began taking cloacal swabs to test for eggs, and while swabs aren’t quite as effective as fecal samples, they do allow us to sample every snake we encounter. And finally, we also collect a lot of roadkill snakes. When a snake dies, any R. orientalis in the lungs will often migrate to the mouth and even exit the snake entirely. A visual inspection of the mouth will often detect those, and then a necropsy can be done to thoroughly search the lungs and trachea before the specimen is preserved and placed in a museum collection.
Of course, all infections are of concern, but we were especially worried about the state’s populations of Eastern Indigo Snakes and Southern Hognose Snakes (Heterodon simus), both of which are severely imperiled range-wide, but have some remaining strongholds in Georgia. Since frog, toad, and lizard eaters are disproportionately affected, it’s logical to think that both indigos and hognose snakes are at high risk, and while there’s still no known infections in any hognose species, Southern Toads are a staple in their diets and a known intermediate host for the parasite. Southern Hognose Snakes in particular are also fairly small, so I can’t help but wonder if they’d succumb to infections with the same frequency as Jenna’s pygmies.
The Role of SLAM and the Power of Collaborative Science
I wish I could wrap up this story with a surprise twist and tell you how we’ve figured out how to stop R. orientalis dead in its tracks and it’ll never reach snakes outside of Florida, but unfortunately that’s not the reality of the situation. Pentastomes are steadily spreading northward, likely via both natural means and the human facilitated transport of wild reptiles and amphibians, whether intentional or not. But it’s not all doom and gloom. Back around the time Jenna first reached out to us, she and Dr. Terry Farrell of Stetson University were launching SLAM (Snake Lungworm Alliance & Monitoring), a nexus of researchers, land managers, local government, and citizen scientists that voluntarily monitor for pentastomes and pool data to closely track the invasion. They had the same conversation Jenna had with us probably dozens of times over, and all that hard work and dedication has paid off. The SLAM network has now expanded to almost 100 collaborators, spanning across five states, and its members are discovering both range extensions and new host species. As one of those SLAM participants, I have now collected over 150 samples and can happily report that all Georgia samples have come back negative so far.
We may not be able to prevent the spread of R. orientalis, but knowing where and in what species it occurs is the first step to understanding how it’s going to impact native snakes. And our large long-term datasets for species like Eastern Indigo Snakes will allow us to assess species and site-specific impacts if and when R. orientalis reaches our populations. There may never be a feasible way for us to intervene and prevent infections in any meaningful way, but we can identify where to implement research and boots-on-the-ground conservation to provide our native snakes the time they need to adapt to this new threat. And furthermore, I see the SLAM network as a major success in terms of bringing together a large assortment of natural resource professionals and nature enthusiasts alike to achieve far more than any single lab of researchers could do. Collaborative science is effective science, and it’s these types of partnerships that excite me and give me hope for the future of conservation.
For more information regarding pentastomes, SLAM, Jenna’s research, or how to contribute to this effort, you can listen to Jenna’s episode of the Snake Talk Podcast, “Episode 93 – Exotic Parasites in Snakes Spreading Across North America,” or you can visit https://invasionscience.ufl.edu/slam/.
