Abstract

A retrospective review of neoplasia in the reptile collection of the Philadelphia Zoological Park was conducted for the years 1901–2002. Necropsy reports were reviewed, and all incidents of neoplasia were identified. Cases were histologically reviewed by one author (JGT) for confirmation of the original diagnosis. For a small number of cases, neither slide nor tissue blocks could be found. These cases were included in the study using the original diagnosis.

Incidence rates were calculated using the total number of reptile necropsies. The total number of necropsies before 1967 was obtained from a previous review, and manually counted for cases from 1968–2002.³ To reduce the influence of sporadic losses of large clutches of neonates, cases determined to have died from “failure to thrive” (after 1967) were eliminated and the incidence re-calculated (Table 1).

Table 1. Incidence of neoplasia in reptiles at the
Philadelphia Zoo for 1901–2002. Results are reported
as a percentage of neoplasms diagnosed/necropsies performed.

^aTotal incidence rate
^bAdjusted incidence rates, reflecting the removal of failure-to-thrive cases (as defined as an animal less than 1 y old with no postmortem diagnosis other than “inanition” or “starvation”, and with no recorded evidence of feeding)
^cNot calculated

The incidence of neoplasia in this collection varied considerably by taxa and time. No neoplasms were diagnosed in crocodilians. Chelonians had relatively low rates when compared to lizards and snakes. Though the overall incident rates are comparable to other reviews, the rates have gradually increased in both lizards and snakes over the 101-year period.^4-6 The cause for this increase is unclear, though longer life spans, more thorough necropsies, and infectious agents are potential explanations.² A similar upward trend has been reported in snakes by another institution.⁷

A total of 94 neoplasms were found in six chelonians, 19 lizards, and 63 snakes. Two turtles, one lizard, and three snakes had multiple neoplasms. The locations of primary neoplasms are reported on Table 2. Overall, the liver was most often affected (22%), a finding common to previous studies, followed by the integument (15%) and endocrine systems (12%).^4,7 The relative frequency of hematopoietic neoplasia was low (6%) in comparison to reports in other collections.^1,4

Table 2. Location of primary neoplasms (by body system)
at the Philadelphia Zoo for 1901–2002

Continued surveillance and further investigations into the etiology of the various types of neoplasia found in this study is warranted.

Literature Cited

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2.  Chandra, A.M., E.R. Jacobson, and R.J. Munn. 2001. Retroviral particles in neoplasms of Burmese pythons (Python molurus bivittatus). Vet. Pathol. 38: 561–564.

3.  Cowan, D.F. 1968. Diseases of captive reptiles. J. Am. Vet. Med. Assoc. 153: 848–859.

4.  Effron, M., L. Griner, and K. Benirschke. 1977. Nature and rate of neoplasia found in captive wild mammals, birds, and reptiles at necropsy. J. Natl. Cancer Inst. 59: 185–198.

5.  Hubbard, G.B., R.E. Schmidt, and K.C. Fletcher. 1983. Neoplasia in zoo animals. J. Zoo Wildl. Med. 14: 33–40.

6.  Montali, R.J. 1980. An overview of tumors in zoo animals. In: Pathology of Zoo Animals. R. J. Montali and G. Migaki (eds.). 1980. Smithsonian Institution Press, Washington, D.C. Pp. 531–542.

7.  Ramsay, E.C., L. Munson, L. Lowenstine, and M. Fowler. 1996. A retrospective study of neoplasia in a collection of captive snakes. J. Zoo Wildl. Med. 27: 28–34.