Defining the Specific Pathogen-Free State of Xenopus Using TaqMan Assays

Abstract

Colonies of valuable inbred and transgenic laboratory-reared Xenopus frogs maintained for research constitute naïve populations of animals susceptible to some opportunistic infectious diseases. Therefore, it is prudent to characterize any new animal acquisitions before introduction into an existing colony as a biosecurity measure to preclude the concurrent introduction of an infectious microorganism associated with the new animal(s). In addition, some pathogens of Xenopus, such as Chlamydia and Mycobacterium spp, are zoonotic diseases, placing frog aquarists at risk for acquiring an infection. Because it is not cost effective to test for all diseases of Xenopus frogs, we have defined a subset of prevalent infectious microorganisms and developed TaqMan polymerase chain reaction (PCR) assays to detect these agents. The specific pathogens in our test panel were selected from relatively recent publications where they reportedly caused morbidity and/or mortality in Xenopus laevis and/or X. tropicalis. The assays herein do not constitute a comprehensive list of infectious diseases of Xenopus frogs. Therefore, a frog devoid of the infectious agents in our test panel are characterized as “specific pathogen-free.” Three of the described quantitative polymerase chain reaction (qPCR) assays detect many species within their genus (i.e., qPCRs for ranaviruses, Chlamydia spp, and Cryptosporidia spp).