Epizootic of fatal amebiasis among exhibited snakes: epidemiologic, pathologic, and chemotherapeutic considerations.

An epizootic of reptilian amebiasis seems to have caused the death of 15 to 16 large and valuable captive snakes (boas, pythons, and anacondas) occupying one of 5 large display dioramas in the Steinhart Aquarium of the California Academy of Science, Golden Gate Park, San Francisco. Subsequent review of previous snake deaths in the colony indicated that of 464 snakes that had died since early 1969, 89 snakes had intestinal or hepatic lesions, and 80 of these snakes had pathologic features which involved severe intestinal ulceration, hemorrhage, and massive enteritis, with or without hepatic necrosis and destruction, condition compatible with Entamoeba invadens infection. The present epizootic began in November, 1972, with the death by acute enteritis of a red-tailed boa constrictor (Boa constrictor amarali) and was followed by the loss of 15 other large boids and pythonids. The affected snakes became immobile, refused to feed, and began to die 10 weeks after the death of the red-tailed boa. Seven boa constrictors, 4 pythons, and 4 anacondas from the same diorama died during the ensuing 10 weeks. Entamoeba invadens trophozoites were identified in the stool of the remaining living snake, a 3-m boa constrictor, and in the liver and the intestinal tissue of 1 of the dead boas examined microscopically. The parasite was also found in the stool of a giant Burmese python (Python molurus bivittatus) that died in the adjacent diorama and in the tissues of a blue-tongued skink (Tiliqua scincoides), separately housed, that died of enteritis during this period. Amebic cysts were recovered from turtle and alligator fecal samples taken from a central "swamp," or reservoir, draining the dioramas, water that is returned to the snake display areas after passage through a biological sand-gravel filter and ultraviolet radiation exposure. Cultures from these stools were positive and proved lethal to an experimentally infected boa constrictor. Treatment of the surviving snake in the affected diorama with metronidazole at the dose rate of 275 mg/kg proved rapidly effective; toxicosis was not observed. Other snakes and lizards suspected of having the infection were similarly treated and returned to normal behavior and feeding patterns. Epidemiologic considerations review the probable mode of introduction and spread of this highly lethal snake pathogen and recommendations are made for avoiding infection, prophylactic treatment, and handling of similar epizootics when they do occur among captive reptiles in aquariums, zoos, and research laboratories.