Tennessee wildlife cases put French heartworm on vets’ radar
Bottom line
A newly highlighted wildlife finding is raising a practical diagnostic question for small-animal teams: could some dogs thought to have “heartworm-type” cardiopulmonary disease actually have something else on the differential. In a 2024 case report, University of Tennessee researchers documented Angiostrongylus vasorum, the French heartworm, in a black bear from Sevier County and a coyote from Campbell County, marking the first reported cases in Tennessee and the first published report in an ursid. The authors said these are only the second and third reported autochthonous A. vasorum infections in the US, adding to prior evidence from West Virginia that the parasite is extending its known North American footprint. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, the immediate takeaway is diagnostic vigilance. A. vasorum lives in the pulmonary arteries and right heart and can mimic or overlap with Dirofilaria immitis-like cardiopulmonary disease, but it brings its own pattern of verminous pneumonia, respiratory signs, coagulopathies, and sometimes neurologic or other atypical presentations in dogs. Reviews of canine angiostrongylosis note that the infection is often underrecognized or misdiagnosed, while CAPC separately warns that true macrocyclic lactone resistance in D. immitis is also a real, if still relatively uncommon, concern, meaning “breakthrough heartworm” cases deserve a careful workup rather than assumptions. (pubmed.ncbi.nlm.nih.gov)
What to watch: Watch for more surveillance data in wildlife and domestic dogs, especially in the Southeast, and for whether Tennessee-linked canine cases begin to appear in the published literature. (pubmed.ncbi.nlm.nih.gov)
Key facts
- Parasite
- Angiostrongylus vasorum, or French heartworm
- Species found in Tennessee
- Black bear and coyote
- Location
- Sevier County and Campbell County, Tennessee
- Firsts
- First reported cases in Tennessee, and first published report in an ursid
- U.S. significance
- Second and third reported autochthonous U.S. infections
- Bear date
- November 2022
- Coyote date
- January 2023
- Pathology
- Verminous pneumonia in both animals
- Molecular finding
- PCR sequencing showed 95% similarity in the bear sample and 96% similarity in the coyote sample to European strains
A Tennessee wildlife case report is sharpening attention on a parasite many US clinicians still consider rare: Angiostrongylus vasorum, or French heartworm. In a paper published in Veterinary Parasitology: Regional Studies and Reports, investigators reported the parasite in a black bear and a coyote from eastern Tennessee, establishing the first report in the state and the first documented case in an ursid. The findings were also featured in the 2024 American Association of Veterinary Parasitologists meeting program, underscoring growing professional interest in the organism’s US range. (pubmed.ncbi.nlm.nih.gov)
The report adds to a slow but notable North American story. A. vasorum has long been considered endemic in Newfoundland, with expansion reported in other parts of Atlantic Canada. In the US, a 2014 PubMed-indexed report identified A. vasorum in a red fox from West Virginia, and the new Tennessee paper states the bear and coyote cases represent only the second and third reported autochthonous US infections. That matters because wildlife detections often precede wider awareness in domestic-animal medicine. (pubmed.ncbi.nlm.nih.gov)
The Tennessee animals were found in different counties and at different times: the black bear was found dead in Sevier County in November 2022, and the coyote was trapped in Campbell County in January 2023 as part of a predator control program. In both animals, lung histology showed verminous pneumonia. The authors extracted DNA from lung tissue and used PCR with NC1 and NC2 primers; sequencing showed 95% similarity in the bear sample and 96% similarity in the coyote sample to European A. vasorum strains. The paper concludes that these cases confirm spread further into North America and support the need for additional surveillance. (pubmed.ncbi.nlm.nih.gov)
For clinicians, the story isn’t that A. vasorum is replacing Dirofilaria immitis. It’s that the differential may be getting broader in some US regions. Reviews of canine angiostrongylosis describe a parasite that occupies the pulmonary arteries and right heart, but can present with respiratory disease, bleeding abnormalities, gastrointestinal signs, ocular disease, or neurologic complications. Frontiers authors have argued the infection may be underestimated or misdiagnosed, particularly when signs are nonspecific. That overlap is exactly why Gerhold’s discussion with dvm360 is relevant to practice: a dog with cardiopulmonary signs, eosinophilia, unexplained coagulopathy, or an apparent “heartworm preventive failure” may need a more nuanced diagnostic pathway. (pmc.ncbi.nlm.nih.gov)
There’s also a second layer to the conversation: resistance in conventional heartworm. CAPC says some D. immitis isolates can develop to adults despite routine prophylaxis with available macrocyclic lactones, and published guidance exists for evaluating potential resistant-heartworm cases. That means veterinarians are now balancing two realities at once: some breakthrough cases may involve resistant or partially resistant D. immitis, while others may call for reconsidering whether the parasite is D. immitis at all. The Tennessee wildlife findings don’t answer that question for dogs, but they make it harder to ignore. (capcvet.org)
Why it matters: For veterinary teams, this is a surveillance story with direct clinical implications. Wildlife reservoirs can signal local transmission risk before companion-animal case counts rise. If A. vasorum is present in Tennessee wildlife, practices in the broader region may want to revisit their approach to dogs with chronic cough, dyspnea, pulmonary hypertension, unexplained hemorrhage, or discordant heartworm test results. It also reinforces the value of parasite-specific diagnostics and careful interpretation of antigen, microfilaria, fecal, imaging, and travel-history data when discussing risk with pet parents. (pubmed.ncbi.nlm.nih.gov)
Expert and industry attention appears to be building. The AAVP 2024 meeting program included Gerhold’s presentation on the Tennessee wildlife cases, alongside sessions on macrocyclic lactone-resistant heartworm, suggesting the profession is increasingly viewing emerging cardiopulmonary parasites and heartworm resistance as connected surveillance problems rather than isolated curiosities. That framing is useful for practices trying to make sense of unusual respiratory or cardiovascular presentations in dogs. (aavp.org)
What to watch: The next key developments will be additional wildlife surveillance, any confirmed canine cases linked to local US transmission in or near Tennessee, and whether diagnostic guidance evolves as awareness of A. vasorum rises alongside ongoing monitoring for macrocyclic lactone resistance in D. immitis. (pubmed.ncbi.nlm.nih.gov)