Tennessee wildlife cases put French heartworm on clinicians’ radar

CURRENT FULL VERSION: A Tennessee wildlife finding is raising a practical question for small animal teams: when a dog presents with heartworm-like cardiopulmonary signs, could it be something else? In a 2024 paper in Veterinary Parasitology: Regional Studies and Reports, researchers reported two Tennessee cases of Angiostrongylus vasorum—one in a black bear and one in a coyote—including what the paper describes as the first case in a black bear. The report adds to concern that French heartworm deserves more attention in U.S. veterinary medicine, particularly in the Southeast. (sciencedirect.com)

The backdrop is a parasite landscape that’s already shifting. A. vasorum is a gastropod-borne cardiopulmonary nematode best known in dogs and wild canids, with snails and slugs serving as intermediate hosts. CAPC says dogs become infected by ingesting infective larvae in gastropods or paratenic hosts, and the parasite ultimately localizes in the pulmonary arteries and right ventricle. While it has long been recognized outside the U.S. as a potentially severe canine pathogen, Tennessee researchers and regional reporting have been drawing attention to its appearance in local wildlife for several years. (capcvet.org)

The Tennessee paper is notable for both host and geography. According to the article abstract, the cases involved a wild black bear and a coyote from Tennessee, with the bear representing a first documented host record and the coyote adding to evidence of wildlife circulation in the state. Separate University of Tennessee research summaries also point to A. vasorum being detected during black bear population health monitoring in the Southeast, suggesting the published cases are part of a broader wildlife surveillance effort rather than an isolated curiosity. In a recent dvm360 Vet Blast podcast, coauthor Richard Gerhold said the cases were actually found “by happenstance” by two graduate students working on different wildlife projects—one on coyotes and one on black bears—and emphasized a simple takeaway for practitioners: just because a parasite has not been found or documented in an area does not mean it is not there. That framing matters because it positions the Tennessee report less as a sudden emergence story and more as a reminder of how incomplete passive detection can be. (sciencedirect.com)

For clinicians, the more immediate issue is diagnostic differentiation. A. vasorum can produce respiratory, cardiovascular, and sometimes bleeding-related signs in dogs, and the literature emphasizes that no single test is perfect. CAPC lists Baermann fecal examination and serum antigen testing among the most effective routine diagnostic approaches, while review articles note that false negatives can occur in prepatent infections, with low larval burdens, or because of intermittent shedding and sample quality issues. In other words, a negative early test may not fully close the case if the clinical picture still fits. (capcvet.org)

Industry and expert commentary around the Tennessee cases has focused on exactly that point: don’t assume every “heartworm” discussion is about Dirofilaria immitis. In regional media coverage, Richard Gerhold said the parasite causes severe lung infection and noted that the Tennessee finding followed the death of a black bear in the Smokies. That reporting also highlighted a coyote case in Campbell County, reinforcing the idea that wildlife may be acting as a local signal for companion animal risk. His later podcast comments added another practical message for veterinarians: these detections emerged outside a formal targeted search, which is a reminder that local absence of evidence may simply reflect limited surveillance rather than true absence. (wuot.org)

Why it matters: For veterinary professionals, this story sits at the intersection of diagnostics, prevention messaging, and regional epidemiology. In practice, teams may need to think more broadly when dogs present with chronic cough, dyspnea, exercise intolerance, pulmonary changes, or unexplained coagulopathy, especially if routine heartworm assumptions don’t fully fit. It also arrives while clinics are navigating a separate but related challenge: documented macrocyclic lactone resistance in D. immitis, which CAPC and the American Heartworm Society have acknowledged, with most recognized cases concentrated in hyperendemic areas of the lower Mississippi River Valley. That means “heartworm prevention failure” and “heartworm-like disease” are both becoming more nuanced conversations with pet parents. (capcvet.org)

The bigger takeaway isn’t that A. vasorum is suddenly replacing D. immitis in U.S. practice. It’s that wildlife detections in Tennessee strengthen the case for awareness, surveillance, and careful test selection in dogs from the Southeast and other overlapping habitats. If additional canine cases are recognized, practices may need clearer protocols for when to add Baermann testing, repeat testing, imaging, or referral diagnostics to a workup that initially looks like routine heartworm disease. The Tennessee report and Gerhold’s comments also support a broader surveillance lesson: incidental wildlife findings can surface clinically relevant parasites before they are widely recognized in companion animals. That’s an inference based on the wildlife findings and current diagnostic guidance, rather than a new formal recommendation from regulators or specialty groups. (sciencedirect.com)

What to watch: The next milestones will be whether Tennessee or neighboring states report more confirmed canine cases, whether surveillance defines a clearer endemic footprint, and whether U.S. guidance groups update clinician-facing recommendations on when to suspect and test for A. vasorum in dogs. It will also be worth watching whether additional “incidental” wildlife detections reshape assumptions about where the parasite is already established but underrecognized. (sciencedirect.com)