Abstract

The Houston toad (Bufo houstonensis) was the first amphibian granted protection under the U.S. Endangered Species Act. Since 2007, the Houston Zoo has participated in a “head start” program, where high-mortality life stages (such as larval and juvenile stages) are protected and released after they have reached a certain size. In 2009, 6 tadpoles and 60 toads from a group of 3000 individuals developed disseminated granulomatous disease with acid-fast bacteria present. Visible lesions were in the form of raised skin masses or of “melting” skin ulcers and were microscopically diagnosed as pyogranulomatous dermatitis with intralesional acid-fast bacteria. Affected toads also had internal pyogranulomatous inflammation with intralesional acid-fast bacteria in the liver, kidney, or intestines, or less commonly in the spinal column, eye, and brain. Many affected Houston toads had internal lesions without visible skin lesions, making antemortem diagnosis of this condition challenging. Mycobacterium chelonae was identified through culture and molecular assay and was determined to be sensitive to ciprofloxacin. Surviving adults have undergone treatment with enrofloxacin, random disease screening, and isolation from other “head start” toad groups. Clinical lesions associated with mycobacterial infection have sporadically been reported in adult anurans, but additional work is required to elucidate epidemiology and develop treatment options. This is the first reported observation of mycobacterial lesions in tadpoles.