Pneumocystis Murina Infection in Immunodeficient Mice in a Closed Barrier Unit: a Case Report

Pneumocystis is an important pathogen in immunocompromised individuals. In colonies of immunodeficient  mice, P. murina can cause wasting disease and make the breeding and maintenance of immunodeficient  animals difficult, unless they are continuously treated with sulfadiazin/trimethoprim. At University  of Aarhus immunodeficient and immunocompetent mice were co-housed in a barrier unit. The facility was  closed for entrance of animals (except for embryos for embryo transfer) and the entrance for personnel was  highly restricted. The breeding performance of immunodeficient animals was comparable to that of the  immunocompetent mice for a period of more than 3 years, until wasting disease and decreased litter size  specifically in the breeding colony of immunodeficient mice occurred. Clinical symptoms of affected mice  included laboured breathing, hunched up position, unwillingness to move, and ruffled coat. Pneumocystis  infection was confirmed by histological examination and PCR. The partial sequence of the mitochondrial  large subunit rRNA gene obtained (GenBank accession no AF548626) displayed 99 % identity to that of  Pneumocystis murina (formerly Pneumocystis carinii f.sp.muris) found in laboratory mice. The immunodeficient  animals were removed from the barrier and treated with sulfadiazin/trimethoprim in a separate  unit. After the removal of immunodeficient animals, Pneumocystis could not be detected by PCR in the  remaining animals. Our data add to the growing evidence that immunocompetent animals harboring Pneumocystis  as a subclinical infection may be reservoirs for this organism. Still it remains to be determined  how the infection was introduced and whether a latent infection can persist or the outbreak was caused by  leakage in the barrier.