Abstract

In 1995, an outbreak of mycoplasmosis resulted in the death or euthanasia of 60 American alligators (Alligator mississippiensis) from a population of 74 captive bulls. Following culture and nucleotide sequence analysis of the organism, a new Mycoplasma sp. (American Type Culture Collection [ATCC] 7006190) was identified as the causative organism. Koch's postulates for an etiologic agent were fulfilled by experimentally transmitting the organism to naive juvenile American alligators. An ELISA to detect antibody to the agent was also developed.

In order to determine whether other crocodilian species were at risk of fatal mycoplasmosis from this organism, three species of crocodilians were experimentally inoculated with 10⁶ CFU of ATCC 700619 instilled through the glottis. Eight broad-nosed caiman, Caiman latirostris, (length: 72-83 cm; weight: 1.4-2.5 kg), eight Siamese crocodiles, Crocodylus siamensis, (length: 120-151 cm; weight: 6-12 kg), and 12 American alligators (length: 116-147 cm, weight: 6-13 kg) were used in the study. The crocodilians were divided into two groups: the control group was comprised of two caiman and two crocodiles, with six alligators acting as negative controls, and the inoculated group was comprised of six caiman and six crocodiles, with six alligators acting as a positive control group. Blood was collected from the supravertebral sinus weekly for 4 wk post-inoculation (PI), and then biweekly until necropsy 12-16 wk PI. Blood was cultured for Mycoplasma and assayed by ELISA. Upon death or following euthanasia at the end of the study 12-16 wk PI, complete necropsies were performed on each crocodilian. Swabs for Mycoplasma culture were collected from the trachea, pericardial sac, liver, lung, coelomic cavity, tonsils, cerebrospinal fluid, both elbows, and both stifles. Fresh tissue samples for Mycoplasma culture were collected from the trachea, heart, lung, liver, spleen, and brain. Heart blood was also collected for culture. Tissue samples were collected from the trachea, pericardial sac, heart, lung, liver, spleen, kidney, brain, and synovia of both elbows and both stifles, and fixed in 10% neutral buffered formalin for histopathologic examination.

The ID50 and LD50 of ATCC 700619 for American alligators and broad-nosed caiman was 10⁶ CFU instilled through the glottis. The Siamese crocodiles did not develop mycoplasmosis. In all of the inoculated crocodilians seroconversion occurred 6-8 wk PI. The findings confirm that mycoplasmosis can be rapidly fatal in American alligators and that susceptibility extends to the relatively closely related broad-nosed caiman.

Acknowledgments

This work was supported by a grant from the Morris Animal Foundation. Funds were leveraged by a concurrent project that had the separate objective of conducting a dose-response trial of ATCC 700619 in American alligators funded by the United States Department of Agriculture (USDA). Animals for the study were provided by the St. Augustine Alligator Farm, St. Augustine, Florida, USA.