Still Valid: Clearance of Pseudocapillaroides xenopi from a Xenopus laevis Colony Using the 1997 Levamisole Immersion Protocol

Pseudocapillaroides xenopi is a capillariid nematode of the epidermis of Xenopus spp. and a cause of “flaky” or “gray skin disease” in laboratory colonies. The only published regimen for eradicating it from an entire colony, which is a levamisole immersion, dates from 1997. We report its unmodified application in a colony of approximately 480 adult female X. laevis. An index animal with pale, roughened skin and severe weight loss was diagnosed by PCR. Screening all 42 cohabitants of three tanks each holding one animal with macroscopic skin abnormalities gave a prevalence of 21.4% (9/42), with seven of them clinically inconspicuous. Two four-day levamisole baths (12 mg/L) ten days apart, with tank cleaning and dedicated equipment, were applied colony-wide. Post-treatment skin scrapings were negative in 42/42 animals, gross lesions resolved, body weight was maintained and no further cases have occurred. The 1997 protocol remains fully effective. As the untreated infection is ultimately fatal and the alternative to treatment is depopulation, a regimen that reliably clears a colony is also a refinement.