Ancient “Spaghetti” in Dogs’ Hearts Reveals a Surprising Evolutionary History for Heartworm
New research is reshaping how veterinarians understand one of the most common and dangerous canine parasites: heartworm (Dirofilaria immitis). A global genome-wide study suggests that heartworm has a far deeper and more complex evolutionary history than previously believed—and that ancient canid hosts may have played a pivotal role in shaping its distribution.
Rethinking Heartworm Origins
Researchers analyzed over 100 heartworm genomes from dogs and wild canids across multiple continents. The results challenge the long-held assumption that heartworm spread primarily through recent, human-mediated movement of domestic dogs. Instead, the data point to ancient interactions with wolves, dingoes, and other wild canids, with heartworm lineages diverging over tens of thousands of years.
One particularly intriguing finding concerns Australia. Genetic signatures suggest that Australian heartworms may share ancestry with Asian parasites, raising the possibility that heartworm arrived with dingoes migrating from Asia thousands of years ago. However, researchers caution that a more recent introduction after European colonization cannot yet be ruled out.
Evidence from the Genomes
By sequencing whole genomes from heartworms in different regions, the team reconstructed population histories and tracked parasite divergence. They found distinct regional heartworm populations shaped by ancient canid migrations and geographic isolation during ice ages and interglacial periods. The findings highlight that heartworm evolution is not simply a story of parasites traveling with modern domestic dogs—the parasite has been co-evolving with its hosts for millennia.
Implications for Veterinary Practice
Understanding the ancient and regional diversity of heartworm populations is increasingly important as drug resistance emerges worldwide. Parasites from different regions may respond differently to treatment, and local evolutionary history can inform prevention and control strategies.
While over 100 genomes were analyzed, the authors note that further sampling—especially from underrepresented regions—is needed to refine timelines and confirm the origins of heartworm in Australia.
The Takeaway
This study emphasizes that heartworm is not a uniform parasite. Its long evolutionary history and deep association with wild canids challenge previous assumptions about transmission, adaptation, and treatment. For veterinarians, recognizing the complexity behind this “spaghetti in the heart” could influence how we think about prevention, diagnostics, and emerging drug resistance in canine populations.
Publication: Power R. et al., Population genomics reveals an ancient origin of heartworms in canids, Communications Biology, 2026. DOI: 10.1038/s42003-025-09250-x
