Abstract
Five adult male African spurred tortoises (Geochelone sulcata) died over a 10-month period at the Saint Louis Zoo with lymphosarcoma. The tortoises arrived in two groups, in 1997 and 1999. Deaths in the first group (n=3) occurred in February and April, and in the second group (n=2) in August and October 1999. During the summer, they were housed in an outdoor exhibit with Speke’s gazelle (Gazella spekei) and wattled crane (Bugeranus carunculatus). Over the winter, they were housed with other chelonid species at the herpetarium, including Aldabra tortoise (Geochelone gigantea), Florida gopher tortoise (Gopherus polyphemus), red-footed tortoise (Geochelone carbonaria), yellow-footed tortoise (Geochelone denticulata), and elongated tortoise (Indotestudo elongata). Only scant non-specific clinical signs of depression, anorexia, and lethargy were noted in initial cases. Gross necropsy findings in all the animals were similar. Multifocal to coalescing raised white nodules were present in the mucosa throughout the digestive tract with varying degrees of intensity and ulceration. There was an impression of a cellular infiltrate in multiple organs, resulting in a waxy appearance to the spleen and kidneys and a prominent reticulate pattern in the liver. Lack of fat stores suggested that the animals had deteriorated over an extended time period. With experience, cases were identified ante-mortem and confirmed by endoscopy, laparoscopy, and biopsy, though the tortoises died despite supportive therapy. Some of the tortoises were terminally septicemic (2/5), which was attributed to secondary infection associated with the ulceration of the gastrointestinal tract. The histologic appearance of the lesions was consistent with disseminated plasmacytoid lymphosarcoma. In certain viscera, up to 40–60% of the parenchyma was replaced by neoplastic cells. Virus was not isolated from frozen tissue. Sera collected from the African spurred tortoises, and from the other species that had been housed with them over winter, were assessed by ELISA for herpesvirus; the results were negative. Attempts were made to culture retrovirus without success, however, during this procedure the presence of particles suggestive of herpesvirus were noted. Further analysis of tissues by electron microscopy is currently proceeding.
Neoplasia in reptiles is reported relatively infrequently,1 and lymphoma in reptiles is generally reported as sporadic cases2. However, a similar clustering of cases of lymphoma was reported in Galapagos tortoises (Geochelone elephantopus) by the Zoological Society of San Diego.8 Again, changes appeared to be centered on the alimentary tract, and neoplastic lymphoid cells in earlier lesions were felt to be invasive rather than destructive in nature. The authors speculated that the neoplasia was derived from the gastrointestinal lymphoid population with hematologic dissemination. The etiology of the neoplasia was not revealed by additional testing, however, an infectious agent or a possible genetic predisposition were suggested, since a sub-group of the tortoises had the same dam. A high prevalence of a neoplasm in a population is suggestive of the involvement of other factors, such as exposure to an environmental carcinogen or an infectious agent, or the potential for an inherited tendency. Given the history of shared housing with other chelonids, it is tempting to speculate that these may have acted as carriers of infection to the African spurred tortoises, and that an environmental carcinogen is a less likely cause of the lesions.
Many viruses, both RNA and DNA, have proved to be oncogenic, though in this situation, retroviruses and herpesviruses appeared to be the most likely candidates. Herpesvirus involvement in neoplasia is well-recognized in conditions such as Marek’s disease in the domestic chicken and in association with Epstein Barr virus in humans. Infection with herpesvirus has been noted in many species of reptile. Sixteen herpesviruses from tortoises from different countries and species were assessed by serology and restriction enzyme digestion patterns, at least two different sero and genotypes were identified.4 An alphaherpesvirus has been associated with fibropapillomas in green, loggerhead, and olive Ridley turtles. A viral sequence has been detected in cleaner fish endemic to the areas in which affected turtles have been observed, suggesting that they may act as carriers of infection.9,10 Other non-neoplastic conditions have been identified. In green sea turtles (Chelonia mydas), gray patch disease is associated with dermal herpesvirus infection in young animals and a further herpesvirus causes lung-eye-trachea disease.3
Chronic rhinitis with stomatitis and glossitis has been documented in captive Mediterranean tortoises (spur-thighed tortoise [Testudo graeca graeca] and Hermann’s tortoise [Testudo hermanii]) in association with herpesvirus infection. A similar case had been reported in a California desert tortoise (Gopherus agassizii).7 The tortoises had elevated lymphocyte counts, aspartate aminotransferase activity and alpha-globulin levels, and some animals had a normochromic-normocytic anemia and heteropenia. An ELISA was developed to detect antibodies to this herpesvirus in Mediterranean tortoises, which has potential as a diagnostic screening tool.6 Other researchers have used PCR to detect a herpesvirus, suggestive of an alphaherpesvirus, from oral swabs and biopsies taken from the tortoises.11
While initial testing has not confirmed the presence of a viral etiology for the cluster of lymphosarcoma cases seen in these African spurred tortoises, the findings suggest infection should still be considered as a probable cause. Investigation of the cases is ongoing.
Acknowledgments
The authors would like to thank Dr. Mark Kombert for clinical input with the cases, Drs. Origgi and Jacobson for herpesvirus isolation and ELISA testing, and Dr. Lee Ratner for retroviral studies assessment.
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