Knowledge concerning microbial infectious diseases in the current amphibian crisis is rudimentary and largely limited to ranavirosis and chytridiomycosis. The family Chlamydiaceae is gaining attention as a common cause of disease in amphibians and may harbour new and emerging amphibian pathogens. We identified a novel species of Chlamydiales (Candidatus Amphibiichlamydia ranarum) with a prevalence of 71% in exotic invasive bullfrog tadpoles (Lithobates catesbeianus) from an introduced population in the Netherlands. The sequence of a 1474 bp 16S rRNA gene fragment showed that the novel taxon forms a well-defined clade with 'Candidatus Amphibiichlamydia salamandrae' within the Chlamydiaceae family. Although none of the tadpoles examined showed signs of clinical disease, urgent evaluation of its pathogenic potential for native amphibian species is required.

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Exotic invasive bullfrogs (Lithobates catesbeianus) are considered to exert a considerable negative impact on native amphibian communities. This can be due to competition and predation, but they are also a notorious source of the infectious diseases chytridiomycosis and ranavirosis, affecting amphibian populations globally. Little is known regarding their carriage of other microbial agents that might be transferred to humans or other animals. In this study we determined the occurrence of the amphibian pathogens Ranavirus and Batrachochytrium dendrobatidis and of the zoonotic agents Coxiella burnetii, Neospora caninum, Leptospira sp., Toxoplasma gondii, Mycoplasma sp., Campylobacter sp., Salmonella sp. and extended-spectrum beta-lactamase producing Escherichia coli in 164 bullfrogs from three populations in Belgium and The Netherlands. Although B. dendrobatidis was present at a high prevalence of 63%, mean infection loads were low with an average of 10.9 genomic equivalents (SD 35.5), confirming the role of bullfrogs as B. dendrobatidis carriers, but questioning their role as primary reservoirs for B. dendrobatidis transmission to native amphibian communities. All tested samples were negative for the other infectious agents examined. These results suggest a limited role of bullfrogs as carrier of these pathogens.