Pit Bull with Distemper

SIGNALMENT: 2-year-old female spayed Pit Bull

HISTORY: No clinical history provided. Platelets reported as decreased. Neutrophils = 8925 cells/uL (2940-12670), bands = 210 cells/uL, monocytes = 1260 cells/uL (130-1150).

SOURCE: Blood smear


LEUKOCYTES: The differential is verified, and although the neutrophil concentration is within the reference interval, many cells contain slight toxic changes, and a left shift is verified, confirming an inflammatory leukogram, further supported by a monocytosis comprising reactive variants. The lymphopenia likely represents a concurrent corticosteroid stress response. Within many of the neutrophils and monocytes are purple/magenta, globular to angular inclusions of varying size and shape, typically ranging from 1 to 5um in length or width. Similar inclusions are seen within red blood cells, and with inclusions within both neutrophils and red blood cells, these findings are highly supportive of Distemper infection, and PCR testing as recommended in the CBC report is recommended.

PLATELETS: Rare platelet aggregates are seen at the feathered edge of the slide, and within the monolayer, an average of 5 platelets is counted per 100x objective field, supportive of a moderate thrombocytopenia. Occasional giant platelets are seen, and may suggest a regenerative response by the bone marrow toward the thrombocytopenia, and serial monitoring of the platelet concentration is recommended. Thrombocytopenia is often associated with Distemper infection, but can also be secondary to consumption of platelets, or immune mediated destruction. Serial monitoring of the platelet concentration is recommended.

ERYTHROCYTES: Red blood cell density appears normal. Many red blood cells contain globular pale to medium purple inclusions, similar to those described in the neutrophils, and most supportive of Distemper inclusions.

100X a
100X b
100X c


Distemper inclusions in neutrophils and erythrocytes


PCR was performed on a nasal swab, and confirmed a high canine distemper viral (CDV) load (7,782 thousand/swab) well above levels seen with vaccine interference, confirming CDV infection in the patient. Distemper viral inclusions may be present in both leukocytes and erythrocytes. These inclusions are viral nucleocapsid aggregates that form in precursor cells in the bone marrow. The inclusions often stain more intensely with rapid stains such as Diff Quik®.


Andrew G. Burton, BVSc

Diplomate, American College of Veterinary Pathologists

*Featured case image Photo by Justin Veenema on Unsplash

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