New Published Research: A protozoan parasite in indigo snake populations


An indigo snake from southeastern Georgia – Ben Stegenga

There are a host of threats that have contributed to indigo snake population declines, range contractions, and ultimate listing as Threatened on the Endangered Species Act. Among these are a host of diseases and parasites that can reduce individual health and fitness or, in severe cases, lead to death (e.g., Foster et al. 2000; Knafo et al. 2016). For example, our recent work on ophidiomycosis (Snake Fungal Disease) found that the causative fungal pathogen was widespread in Georgia’s indigo snake populations (Chandler et al. 2019), and the invasive pentastome, Raillietiella orientalis, was recently documented in a deceased Florida indigo snake (Bogan et al. 2022).

Another potential health concern for indigo snakes is the protozoan parasite Cryptosporidium serpentis. These single-celled parasites infect the gastrointestinal tract of host snakes and cause a variety of symptoms, including lethargy, regurgitation, or weight loss. Severe infections can ultimately lead to death, but many infected individuals may never develop symptoms of infection. Most of the work on this parasite has come from captive snakes, but it has also been documented in wild snake populations. Cryptosporidium serpentis was brought to the attention of indigo snake conservation partners when it was detected in the captive breeding colony in 2016. Since then, extensive time, effort, and money have been spent on testing and colony management to ensure that snakes released at the two reintroduction sites are repeatedly testing negative prior to release. However, it remains unclear whether this parasite is a natural part of indigo snake communities or whether it is restricted to captive individuals.

Along with partners from the Florida Fish and Wildlife Conservation Commission, the Orianne Center for Indigo Conservation (OCIC), the Alabama Natural Heritage Program, and the Jones Center at Ichauway, we recently published research examining the prevalence of C. serpentis in wild snake populations. We sampled both indigo snakes and other snake species that could pass infection to indigo snakes when consumed as prey items. Sampling efforts focused on the two reintroduction sites, the Jones Center, and sites with extant indigo snake populations in both Georgia and Florida. Snakes were sampled using a combination of methods, including cloacal and stomach swabs, stomach biopsies, and necropsies in the case of dead individuals.

Sampling sites for Cryptosporidium serpentis during this project – Lora Smith

In total, we sampled 155 snakes (representing 18 species) from focal sites, eight snakes incidentally encountered at other sites, and 64 indigo snakes encountered opportunistically during other survey work. Of the 227 snakes tested as part of this study, we documented C. serpentis from a single wild indigo snake from southern Florida. This suggests that this parasite does occur naturally in at least some indigo snake populations in the southeast but that it is either absent or not detectable with intermittent testing in many Georgia populations. To the best of our knowledge, this is the largest sampling effort for C. serpentis in the United States to date, but a single positive result leaves many unanswered questions. Additional survey work will be needed to clarify the prevalence and management implications of C. serpentis occurrence in wild snake populations.

Where do these results leave us with the ongoing indigo snake reintroduction project? A single positive test result may actually be one of the more challenging results to interpret, but we ultimately recommend that C. serpentis–positive animals not be released at reintroduction sites. This will require continued testing of indigo snakes at the OCIC and other captive rearing facilities as has been the standard practice in recent years. Continuing to adequately manage potential infections of C. serpentis and other pathogens in the captive breeding colony will be an important aspect of long-term project success.

You can read the full publication here.

Literature Cited

Bogan, J. E., Jr., D. A. Steen, B. O’Hanlon, M. M. Garner, H. D. S. Walden, and J. F. X. J. Wellehan. 2022. DRYMARCHON COUPERI (Eastern Indigo Snake): Death associated with Raillientiella orientalis. Herpetological Review 53:147.

Chandler, H. C., M. C. Allender, B. S. Stegenga, E. Haynes, E. Ospina, and D. J. Stevenson. 2019. Ophidiomycosis prevalence in Georgia’s Eastern Indigo Snake (Drymarchon couperi) populations. PLoS ONE 14:e0218351.

Foster, G. W., P. E. Moler, J. M. Kinsella, S. P. Terrell, and D. J. Forrester. 2000. Parasites of Eastern Indigo Snakes (Drymarchon corais couperi) from Florida. Comparative Parasitology 67:124–128.

Knafo, S. E., T. M. Norton, M. Mitchell, D. J. Stevenson, N. Hyslop, R. Poppenga, M. Olivia, T. Chen, C. Cray, S. E. J. Gibbs, L. Durden, N. Stedman, S. Divers, and E. Dierenfeld. 2016. Health and nutritional assessment of free-ranging Eastern Indigo Snakes (Drymarchon couperi) in Georgia, United States. Journal of Zoo and Wildlife Medicine 47:1000–1012.