• Commonly seen in pups 6 to 16 weeks of age.
• In the intestine, dividing crypts cells are primarily affected, as opposed to the cells at the tip of the villus (as seen
in corona virus and rotavirus).
• As the enteric cells move up the villus to be lost at the tip they are not replaced from below resulting in the lesion seen
in CPV-2 infection.
• In severely clinically affected dogs, the crypt cells and lymphoid cells in Peyer's patches are destroyed faster than they
can be replaced.
• Nearly all signs occur because of crypt cell and lymphoid/bone marrow destruction.
• It will take 2 weeks before this damage can be repaired.
Bone Marrow effects
• Of major clinical importance is the effect CPV-2 infection has on bone marrow. CPV-2 infection causes necrolysis of the
myeloid and erythroid stem cells in marrow.
• Because of the long half-life of RBCs, few effects are seen on RBC indices although anemia may be seen from blood loss from
• Leukocyte counts reflect both peripheral consumption and myeloid destruction. In severe disease there is progressive reduction
in leukocyte numbers from day 3 to 5 PI.
• Neutropenia, toxic changes in neutrophils, degenerative left shift and often absolute lymphopenia occurs concurrently with
the onset of clinical signs (6 days PI).
• In recovery, leukocytosis + left shift often predict a successful treatment outcome.
• Recently reported that WBC count > 4.5, lymphocyte count > 1, monocyte count > 0.15, eosinophil count > 0.1 with a left
shit are accurate predictors of a good outcome.
Neutrophils: Survivors develop a left shift (usually degenerative): non-survivors don't.
Lymphocytes: Get marked rise in lymphocyte in 1st 24 hrs post-admission in survivors. [more significant than total WBC count]
Monocytes: Quicker production time (3 days compared to 6 days for PMN). So increases in monocytes usually precede those of PMNs.
Eosinophils: Good prognostic indicator when appear especially after 48hrs post-admit.
• Cerebellar hypoplasia (common in kittens infected with feline panleukopenia virus) occurs in dogs (also due to neonatal
infection) but is very rare.
• Can be extremely variable dependent on age (under 3 months), immunity, co-pathogens (parasites, enteric bacteria, viruses),
and infective dose.
• Crowding, poor sanitation reduces the chances of successful immunization in kennels but do not enhance disease in individuals.
• Signs can vary even within single litters.
• Viral dose and antigenic type can influence intensity of illness. Pups infected with CPV-2a or 2b can die acutely even before
diarrhea has developed.
• Depression, anorexia, vomiting, with or without pyrexia are initial signs.
• Dogs vomit repeatedly, sometimes with roundworms in vomitus.
• Then mucoid to then bloody diarrhea develops. Although many clinicians claim they can "smell" a parvovirus case walk in
the door, the character of the vomitus and diarrhea do not distinguish it from other enteritides.
• Severe lymphopenia even to absolute lymphopenia is common and helps distinguish the disease from other causes of severe
diarrhea (Hemorrhagic Gastroenteritis, Salmonellosis).
• Neutropenia may also be present.