Neutrophilic cholangitis associated with intracholangiocytic Hammondia protozoa confirmed in 2 dogs and suspected in 2 dogs.

Four dogs with neutrophilic cholangitis were identified with intracholangiocytic apicomplexan protozoa. Two cases were biopsies, and both cases had gallbladder involvement. The other two cases were unexpected findings on autopsy. Immunohistochemistry against Toxoplasma gondii on all cases labeled the zoites. Internal transcribed spacer-1 polymerase chain reaction (PCR) performed on formalin-fixed paraffin-embedded samples was successful in the 2 biopsy cases, and subsequent sequencing identified >99% sequence identity to Hammondia sp. Of the biopsied dogs, 1 dog recovered successfully after antiprotozoal treatment while the other dog was euthanized due to poor response. The 2 autopsy cases were given immunosuppressive medication. Hammondia are within the Sarcocystidae family of apicomplexan parasites and are closely related to Neospora caninum. This study and the current literature support that Hammondia, specifically Hammondia heydorni, an organism that was previously considered nonpathogenic or minimally pathogenic, can rarely exhibit tropism to the biliary system and cause neutrophilic cholangitis, cholangiohepatitis, and cholecystitis in dogs.