Study links Hammondia protozoa to neutrophilic cholangitis in dogs: full analysis
A new Veterinary Pathology case report adds evidence that Hammondia protozoa can be more than incidental biliary findings in dogs. In four dogs with neutrophilic cholangitis, the organism was confirmed in two and suspected in two, supporting the authors’ conclusion that a protozoan previously considered nonpathogenic or minimally pathogenic can, in rare cases, target the biliary system and drive clinically meaningful inflammation. (acvp.org)
That’s a notable shift from how canine cholangitis is usually framed. Published case series and reviews have generally emphasized bacterial infection, especially Escherichia coli and Enterococcus spp., as the leading infectious explanation for neutrophilic cholangitis and cholecystitis in dogs. In a 54-case descriptive study, 53 dogs had neutrophilic cholangitis or cholangiohepatitis, concurrent biliary disease and obstruction were common, and bacterial isolates were frequently recovered from bile or liver cultures. (academic.oup.com)
The new report also fits into a small but growing body of literature suggesting biliary sarcocystid organisms deserve more attention. A 2016 report described presumed Hammondia organisms in canine bile from a dog with acute neutrophilic hepatitis and negative biliary culture, calling it the first report of presumed Hammondia in canine bile. A 2022 JVIM case report then identified Hammondia heydorni in bile from a dog with acute cholangiohepatitis fed a raw food diet, although the authors said pathogenicity was still uncertain at the time. (pubmed.ncbi.nlm.nih.gov)
Additional context came this year from another canine case report: a 3-year-old Standard Poodle fed a raw elk-meat diet developed pancreatitis and hepatobiliary disease, and PCR plus sequencing identified H. heydorni in pancreatic and biliary tissues. The authors wrote that increasing reports now associate the organism with gastrointestinal and hepatic disease in dogs and described it as an emerging pathogen, while noting that reported infections have repeatedly been linked to ingestion of raw meat. (pubmed.ncbi.nlm.nih.gov)
The pathology trail behind the new paper appears to extend back several years. In a 2019 ACVP/ASVCP abstract, researchers reported three dogs with severe neutrophilic cholangiohepatitis, two with concurrent neutrophilic cholecystitis, associated with intracholangiocytic apicomplexan protozoa. In that work, the organisms stained with Toxoplasma gondii antibody but not Neospora caninum antibody, and ITS PCR on one affected gallbladder yielded a sequence 99% homologous to Heydornia spp. The authors concluded that these protozoa should be considered a potential cause of neutrophilic biliary tree disease. The newly published Veterinary Pathology article appears to build on that signal with additional confirmed and suspected cases. (acvp.org)
Expert reaction specific to this paper was limited in publicly available sources, but the broader literature points to a practical takeaway: pathologists and clinicians may need to think beyond bacteria when evaluating canine biliary inflammation. That’s especially relevant when cytology or histology shows apicomplexan-like organisms, when cultures are unrewarding, or when the dog has a diet history involving raw meat or likely prey exposure. This is still a rare finding, but the consistency across case reports makes it harder to dismiss as a harmless bystander in every case. That last point is an inference based on the pattern across reports, rather than a direct statement from a consensus guideline. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, this report may change both diagnostic thinking and client communication. In dogs with neutrophilic cholangitis, cholangiohepatitis, or cholecystitis, especially those with negative cultures or atypical histology, adding protozoal infection to the differential could influence sample handling, PCR requests, pathology consultation, and diet-history questions. It also reinforces a broader clinical message around raw feeding: while causation cannot be assumed in every case, multiple reports now connect Hammondia biliary disease to raw-meat exposure in dogs. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step is whether larger retrospective or prospective studies define prevalence, risk factors, and treatment response, and whether diagnostic labs begin offering more standardized molecular testing for biliary Hammondia or Heydornia in dogs with suspected infectious cholangitis. (pubmed.ncbi.nlm.nih.gov)