Pneumocystis infection in a Cavalier King Charles Spaniel

A 1-year-old male CKCS presented for tachypnoea and dyspnoea. Radiographs revealed an interstitial lung pattern. The rectal temperature was normal. A bronchoalveolar lavage (BAL) was performed.

Fig 1. Cytological findings revealed low numbers of neutrophils and macrophages and large numbers of extra- and intracellular 4-5um organisms typical of Pneumocystis spp. The red arrows point to two macrophages which are distended by the small fungal bodies (stained with modified Wrights-Giemsa).

Final Diagnosis

Pneumonia associated with Pneumocystis infection


Pneumocystis is an opportunistic fungal pathogen affecting humans and animals with impaired immunity. The entire life cycle is in the lungs and lesions are usually limited to the lungs. Any breed of dog can potentially be affected however Miniature Dachshunds and Cavalier King Charles Spaniels (CKCSs) are predisposed, suspected to be associated with underlying immunodeficiency. Affected CKCSs have been shown to have decreased levels of IgG compared to control dogs. Diagnosis is usually made on direct visualisation of the organisms in BAL fluid or in a transthoracic lung aspirate. The organism will not culture using conventional techniques.