ABSTRACT. Pneumocystis carinii pneumonia was diagnosed by postmortem examination of a one-year-old Cavalier King Charles Spaniel with four-week history of dyspnea. Cytologic and histologic examination of lung tissues revealed numerous P. carinii trophozoites and cysts, and P. carinii specific DNA was detected by polymerase chain reaction. The dog showed hypogammagloblinemia and extremely low levels of serum IgG. It was considered that P. carinii pneumonia in this case was associated with an immunodeficient condition which has already been reported in Miniature Dachshunds. Pneumocystis carinii (P. carinii) is an organism of uncertain taxonomy. It was thought to be a protozoan but has recently been classified as a fungus. It affects both animals and humans, although infections are usually subclinical. It can cause severe or sometimes fatal pneumonia especially in immunosuppressed hosts such as human patients with acquired immunodeficiency syndrome. In dogs, Pneumocystis pneumonia has been most commonly described in Miniature Dachshunds [3,4,6,7]. Immunological studies have revealed that Pneumocystis pneumonia is associated with immunodeficiency in this breed [7]. This is a first report which describes a case of P.carinii pneumonia in a young Cavalier King Charles Spaniel in Japan.A one-year-old male Cavalier King Charles Spaniel, weighing 7.3 kg, presented at the Veterinary Medical Center of the University of Tokyo with a four-week history of anorexia, coughing and respiratory distress. Treatment with antibiotics and aminophylline by the referring veterinarian had failed. Physical examination revealed tachypnea, dyspnea and cyanosis. Rectal temperature was normal and the submandibular lymph nodes were slightly enlarged. On thoracic auscultation, harsh lung sounds were heard over all lung fields without cardiac murmur. Thoracic radiography showed severe generalized interstitial and alveolar patterns in all lung lobes (Fig. 1). The cardiac silhouette was normal in size and shape. Abnormalities of hematological examinations included mildly increased packed cell volume (51%), high WBC count (31.9 × 10 3 /µl) and neutrophilia (27.0 × 10 3 /µl) with increased nonsegmented neutrophiles. The lymphocyte count was within normal range (2.4 × 10 3 /µl), and total plasma protein concentration was slightly high (9.2 g/dl). Routine plasma biochemical profiles revealed increased activities of alkaline phosphatase (910 IU) and alanine aminotransferase (369 IU). Antibodies against Toxoplasma gondii species were not detected by latex-agglutination assay (Eiken, Tokyo, Japan). Serum protein revealed hypogammaglobulinemia by electrophoresis and the IgG and IgM concentration was determined as 0.72 mg/ml (reference range: 15 ± 5 mg/ml) and 2.3 mg/ml (reference range: 1.5 ± 0.5 mg/ml) [9] by quantitative sandwich enzyme-linked immunosorbent assay (ELISA) kits (Bethyl, Montgomery, TX). Treatment with antibiotics (cefazolin sodium and amikacin sulfate), bronchodilator (aminophylline) and nebulization (gentamicin sulfate with sterile saline...

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