A Retrospective Analysis of Amoebiasis in Reptiles in a Zoological Institution
Amoebiasis is a significant protozoal disease of reptiles. It is thought to be caused by Entamoeba invadens carried asymptomatically by chelonians and then transmitted to squamates in whom disease then develops; however, this paradigm is not always seen. Investigating the pathophysiology of amoebiasis has been hampered by the inability to speciate amoeba using conventional techniques. This study reviewed necropsy records from WCS collections from 1998–2017. Amoeba were identified histologically in 54 cases. Of these, amoeba were the cause of death in 32 (18 chelonians, seven lizards, and seven snakes), a significant co-morbidity in 14 (six chelonians, two lizards, and six snakes), and seen incidentally in eight cases (one chelonian, six lizards, and one snake). Sixty-five percent of cases had been moved within 180 days of death (median 46 days). Frozen tissue samples from 19 of these cases were tested via an Entamoeba (genus-specific) PCR assay. PCR products were sequenced and speciated. Six individuals were positive for E. invadens (three chelonians, two snakes, one lizard), two for E. ranarum (both snakes), and one for E. terrapinae (chelonian). Amoebiasis was the cause of death or a co-morbidity in nine of the 10 PCR-negative cases, possibly due to using primers specific to Entamoeba genus. E. ranarum has typically been thought to be a disease of amphibians and has only been reported once to cause disease in a snake. E. terrapinae has only been reported incidentally in chelonians. These results suggest that amoebiasis is a complicated and nuanced disease of reptiles, and warrants additional study.