Nested–polymerase chain reaction detection of Pneumocystis carinii f. sp. canis in a suspected immunocompromised Cavalier King Charles spaniel with multiple infections

Petini, Matteo; Furlanello, Tommaso; Danesi, Patrizia; Zoia, Andrea

This case report, in the authors' opinion, highlights four points about the diagnosis and clinical presentation of dogs with Pneumocystis spp. First, in our laboratory, all reference intervals are calculated using a population of dogs matched for age, breed, and sex to the patient being tested. Dogs with chronic inflammatory disease (such as chronic septic pneumonia as in this case) often present with hypergammaglobulinemia and normal-to-high IgG concentration. 14 The decreased gammaglobulins and IgG concentrations identified in this patient, together with the IgM and IgA in the lower limits of the reference intervals, were highly suspicious of an immunocompromised state, in agreement with previously reported cases of PP in CKCS. 15, 16 Alternatively, the lack of vaccinations in this dog may has contributed to the low serum concentrations of gammaglobulins and IgG concentrations, 17 since reference intervals are derived from vaccinated animals. Second, the detection of the fungal pathogen was achieved through PCR testing of a BAL sample which was negative with microscopic visualization for Pneumocystis spp. It must be considered that all Pneumocystis spp. have two developmental stages: the trophic form (formerly trophozoite) and the cyst form. The imbalance between the different lifecycle forms of Pneumocystis spp. might explain the lower diagnostic yield of cytology in certain instances, as cysts are much easier to distinguish than trophic forms using rapid, modified Romanowsky stains such as Diff-Quik. Such an explanation might account for why some specimens can be PCR-positive, yet no organisms can be detected using conventional light microscopy. 2, 4, 6, 9 Similar to humans, PCR method to achieve a PP diagnosis has been suggested in dogs, 4,18 but it has only recently been used ante-mortem. 8, 9 These recent studies confirm that PCR testing can be a valid diagnostic test for the detection of Pneumocystis spp. In addition, the phylogenetic analysis of the Pneumocystis spp. nucleic acid amplified from BAL fluid in the current study showed that it was a specific canine host-related species.