Clinical Significance of Cryptosporidia in Captive and Free-Ranging Chelonians
Cryptosporidium spp. are protozoa known to infect a wide range of vertebrates. Cryptosporidium parvum and C. muris are mammalian species, C. baileyi and C. meleagridis infect avians, and C. nasorum are found in fish. A single species, C. serpentis, has been documented in reptiles, although there is evidence to suggest that there may be multiple species or subspecies.4 C. serpentis in snakes may be clinically inapparent or cause signs ranging from mid-body swelling, regurgitation, and loss of condition, to death. In other reptiles, clinical signs are not as dramatic, if they occur at all, and have seldom been reported. It has been shown that C. parvum is not infective for snakes, fish, or amphibians, and that C. serpentis is not transmissible to laboratory mice.1,3 Transmission of C. serpentis among different groups of reptiles has not been documented.
Diagnosis of Cryptosporidium in feces is best achieved by performing a combined battery of tests consisting of a modified acid-fast stain (MAFS), enzyme immunoassay (EIA), and immunofluorescence antibody test (IFA). As many as 66–100% false-negative results may occur using only MAFS testing, and positive tests may, in fact, reflect the presence of nonpathogenic Cryptosporidia. When all three tests are run, it is possible to differentiate C. serpentis from C. parvum.2
Fecal samples from captive-bred radiated tortoises (Geochelone radiata) located at three different sites, recently imported Indian star tortoises (Geochelone elegans) and Travancore-like tortoises (Indotestudo sp.), and free-ranging gopher tortoises (Gopherus polyphemus) and Russian tortoises (Testudo graeca nikolskii) were collected and stored fresh, in formalin, or in PVA (Polyvinyl alcohol, Transcaddy; Baxter Health Care Corp, West Sacramento, CA) until processed. Samples were examined by MAFS, EIA, and IFA.
Nineteen of 38 radiated tortoises, 8/10 Indian star tortoises, 3/4 Indotestudo, 8/20 gopher tortoises, and 4/29 Russian tortoises were positive for Cryptosporidium sp. by MAFS and IFA, and negative by EIA. None of the tortoises had clinical signs indicative of enteric protozoa infections. Of animals that have been examined postmortem, one had numerous Cryptosporidia-like organisms associated with microvillar borders, without any significant pathology noted, and another had severe necrotizing transmural gastroenteritis with massive numbers of bacterial colonies, sloughed epithelial cells, karyorrhectic cellular debris, and clusters of Cryptosporidia-like organisms admixed within the luminal debris. Prolonged contact between positive and negative animals has not been associated with the onset of clinical signs, or with conversion of all animals to a positive test status. However, since it is not known if the organism found in Chelonia is infective for snakes, it is prudent to maintain test-positive turtles and tortoises separate from Squamata.
The authors thank Dr. Thaddeus Graczyk at the Johns Hopkins University School of Hygiene and Public Health, Department of Molecular Microbiology and Immunology, Baltimore, MD, USA, for performing the laboratory procedures; to Dr. Bill Zovickian for his participation and financial support; to Jeff Spratt for collection of samples; and to John Behler for facilitation of surveys.
1. Fayer R, Graczyk TK, Cranfield MR. Multiple heterogenous isolates of Cryptosporidium serpentis from captive snakes are not transmissible to neonatal BALB/c mice (Mus musculus). J Parasitol. 1995;81(3):482–484.
2. Graczyk TK, Cranfield MR, Fayer R. A comparative assessment of direct fluorescence antibody modified acid-fast stain, and sucrose flotation techniques for detection of Cryptosporidium serpentis oocysts in snake fecal specimens. J Zoo Wildl Med. 1995;26(3):396–402.
3. Graczyk TK, Fayer R, Cranfield MR. Cryptosporidium parvum is not transmissible to fish, amphibia, or reptiles. J Euk Micro. 1996;43(5):15–16.
4. Upton SJ, McAllister CT, Freed PS, Barnard SM. Cryptosporidium spp. in wild and captive reptiles. J Wildl Dis. 1989;25(1):20–30.