Pneumocystis spp

From Dog
Radiograph of a dog with Pneumocystis infection, showing diffuse symmetrical mixed pulmonary radiodensities and reticulonodular pattern[1]
Bronchoalveolar lavage of above dog showing clusters of P. carinii cysts (arrowheads) and polymorphonuclear leucocytes[1]

Pneumocystis is an extracellular opportunistic ascomycete fungus which rarely causes disease in dogs.

This fungus causes pneumonia in immunocompromised hosts and is best known as a pathogen of human AIDS patients.

The only part of the life cycle of the organism that is known is that involving the mammalian lung, in which two main developmental stages can be identified: the trophozoite and the cyst. Cysts may be found with up to eight intracystic bodies (trophozoites) or be found ruptured and empty[2].

Species which are pathogenic to dogs include:

  • Pneumocystis carinii

Pneumocystis carinii of the dog is thought to be genetically distinct from that found in humans and rats[3].

A breed predisposition has been reported in the Cavalier King Charles Spaniel[4], Miniature Dachshund[5] and Yorkshire Terrier (associated with immunoglobulin deficiency)[6] , but this disease can also occur in dogs with chronic demodicosis[7] and canine distemper[8].

In the dog, most affected patients are young and often present with a febrile cough. The respiratory symptoms usually progress to the point where the dog suffers dyspnea, reduced exercise intolerance and weight loss.

In the Cavalier, IgG concentrations are significantly lower in affected dogs[9].

Diagnosis is difficult as hematological or biochemical parameters are usually nonspecific, although leucocytosis, a mature neutrophilia and monocytosis are common.

Lung auscultation often reveals respiratory crackles and wheezes and thoracic radiographs show diffuse interstitial and peribronchial densities throughout the lungs as well as air bronchograms. Pneumonia is not a common feature of this condition. In severe cases cor pulmonale may be present[10].

Various serological tests have been tested[11] but are not reliable due to the underlying immunodeficiency associated with this disease[12].

A definitive diagnosis requires direct visualization of Pneumocystis obtained from bronchotracheal lavage or biopsy specimens and PCR identification of Pneumocystis DNA[13]. Several histochemical stains are useful, and diagnostic immunohistochemical kits are available[1].

A differential diagnosis would include pulmonary interstitial fibrosis, canine distemper virus, heartworm disease and other causes of pneumonia.

Palliative relief may be obtained with prednisolone but specific therapy is aimed at

As a clinical disease, it often has a fatal outcome[14].


  1. 1.0 1.1 1.2 Sukura A et al (1996) Pneumocystis carinii pneumonia in dogs - a diagnostic challenge. J Vet Diagn Invest 8(1):124-130
  2. Yoshida Y (1989) Ultrastructural studies of Pneumocystis carinii. J Protozool 36:53-60
  3. Cho SR et al (1999) Karyotypes of Pneumocystis carinii derived from several mammals. Korean J Parasitol 37(4):271-275
  4. Ramsey IK et al (1997) Pneumocystis carinii pneumonia in two Cavalier King Charles spaniels. Vet Rec 140(14):372-373
  5. Lobetti R (2000) Common variable immunodeficiency in miniature dachshunds affected with Pneumonocystis carinii pneumonia. J Vet Diagn Invest 12(1):39-45
  6. Cabañes FJ et al (2000) Pneumocystis carinii pneumonia in a Yorkshire terrier dog. Med Mycol 38(6):451-453
  7. Furuta T et al (1994) Spontaneous Pneumocystis carinii infection in the dog with naturally acquired generalised demodicosis. Vet Rec 134:423-424
  8. Sukura A et al (1997) Occurrence of Pneumocystis carinii in canine distemper. Acta Vet Scand 38(2):201-205
  9. Watson PJ et al (2006) Immunoglobulin deficiency in Cavalier King Charles Spaniels with Pneumocystis pneumonia. J Vet Intern Med 20(3):523-527
  10. Kirberger RM & Lobetti RG (1998) Radiographic aspects of Pneumocystis carinii pneumonia in the miniature Dachshund. Vet Radiol Ultrasound 39(4):313-317
  11. Chatterton JM et al (1989) Pneumocystis carinii antibody testing. J Clin Pathol 42:865-868
  12. Elvin K et al (1994) Seroreactivity to Pneumocystis carinii in patients with AIDS versus other immunosuppressed patients. Scand J Infect Dis '26:33-40
  13. Hagiwara Y et al (2001) Pneumocystis carinii pneumonia in a Cavalier King Charles Spaniel. J Vet Med Sci 63(3):349-351
  14. Botha WS & Van Rensburg IB (1979) Pneumocystosis: a chronic respiratory distress syndrome in the dog. J S Afr Vet Assoc 50:173-179