Introduction

Canine circovirus (CaCV-1) has recently been identified in the feces from healthy dogs and those with diarrhea. While CaCV-1 has been associated with vasculitis and histiocytic inflammation, there have been no reports of CaCV-1 causing severe morbidity or mortality. Recently, we observed recurrent outbreaks of sudden death and bloody diarrhea associated with dual infections of canine parvovirus (CPV2) and CaCV-1 in a Papillon breeding colony that caused the death of both adult and juvenile dogs despite up-to-date vaccinations against CPV2.

Objective

The goal of this study was to characterize the role of CaCV-1 in these recurrent outbreaks.

Methods

One puppy from the first outbreak and two puppies from the second outbreak were necropsied. Tissues were examined microscopically and screened for CPV2 and CaCV-1 by PCR as well as immunohistochemistry and in situ hybridization.

Results

Histologically, all three puppies had severe segmental crypt necrosis of the small intestine and marked lymphoid follicle depletion in the spleen and Peyer's patches. Immunohistochemistry detected large amounts of CPV2 antigen in intestinal crypt epithelium and Kupffer cells, but few positive macrophages in lymphoid organs. All puppies had marked sinusoidal histiocytosis and multifocal granulomatous inflammation in mesenteric lymph nodes and spleen. Only rare CaCV-1-positive nuclei were detected in regenerating crypt epithelium, but abundant amounts of CaCV-1 DNA were in the cytoplasm and nuclei of histiocytes in all lymphoid tissues, including granulomatous inflammatory foci and Kupffer cells in the liver.

Conclusions

We hypothesize that CPV2 infection predisposed dogs to CaCV-1 infection, ultimately resulting in more severe clinical disease.