Abstract

Between August 2013 and July 2016, multiple raised, pigmented skin tumors were noted on the feet of 10 Houston toads (Anaxyrus houstonensis) from the same wild source genetic lineage. Identical masses were also noted on the faces of four toads with a different lineage, but similar county of origin.

Toads behaved normally despite having small to large masses on their feet, often having more than one foot affected. Average age of onset of tumors was 3.8 yr in the foot tumors and 6 yr in the face tumors. Tumors were slow growing and recurred within an average of 15 mo after surgical excision.

Masses were submitted for histopathology and followup electron microscopy, and were diagnosed as multiple tumors of peripheral nerve sheath cells (PNST). These PNSTs share features with neurofibromatosis in people and bovine, with neurofibromatosis type 1 (NF-1) in people caused by mutation of the gene on chromosome 17.

This captive assurance colony of approximately 500 toads is bred yearly for release of offspring to wild habitat, a critical need to bolster decimated wild populations. In fact, recent breeding efforts by the Houston Zoo are recognized as having a major part in preventing extinction of this highly endangered toad, with signs of recovery on the horizon. These tumors posed a unique challenge for this colony and on veterinary decisions regarding diagnosis, management and clearance for breeding, with the possibility of viral involvement and genetic mutation causing the most concern. Unique diagnostics and partnership with human NF-1 specialists were developed.