Study links Hammondia protozoa to neutrophilic cholangitis in dogs

A new Veterinary Pathology report describes four dogs with biliary disease linked to Hammondia protozoa, with infection confirmed in two dogs and suspected in two others. The authors say the organism, long viewed as nonpathogenic or only minimally pathogenic, showed clear tropism for bile ducts and was associated with neutrophilic cholangitis, cholangiohepatitis, and cholecystitis. That matters because neutrophilic cholangitis in dogs is usually tied to ascending bacterial infection, not protozoal disease. Earlier pathology conference data from the same research line described severe neutrophilic cholangiohepatitis and cholecystitis in dogs with intracholangiocytic apicomplexan protozoa, with sequencing in one case showing 99% homology to Heydornia spp., a taxonomic grouping that includes Hammondia heydorni. (acvp.org)

Why it matters: For veterinarians, the paper expands the differential list for canine neutrophilic biliary disease, especially when bile cultures are negative, organisms are seen cytologically or histologically, or the history raises concern for exposure to raw meat or prey species. Prior reports have linked biliary Hammondia heydorni findings in dogs to raw-food exposure, and a separate 2026 case report described pancreatic and biliary duct H. heydorni infection in a dog fed raw elk meat, calling the organism an emerging canine pathogen. Taken together, the literature suggests some cases labeled idiopathic or culture-negative cholangitis may warrant closer protozoal workup, including histopathology, PCR, and careful review for apicomplexan organisms. (pubmed.ncbi.nlm.nih.gov)

What to watch: Watch for follow-up case series clarifying how often Hammondia is a true pathogen in dogs, how best to confirm it diagnostically, and whether diet history or treatment approach changes outcomes. (pubmed.ncbi.nlm.nih.gov)