Population genomics reveals an ancient origin of heartworms in canids

Heartworms ( Dirofilaria immitis ) are parasitic nematodes that cause significant cardiopulmonary-associated morbidity and mortality in canids worldwide. The global dissemination of heartworms is believed to have occurred alongside the dispersal of domesticated dogs. To test this theory, we performed the largest population genetics study of heartworms to date, based on whole-genome sequencing of 127 modern adult individuals collected from mammalian carnivore hosts across four continents. Population structure and demographic analyses of the nuclear genome reveal distinct genetic differences between heartworms from different continents, indicating a deeper ancient origin and dispersal in canid hosts than previously recognised. Using admixture analyses, we find an Asian origin for Australian heartworms consistent with the arrival of dingoes thousands of years ago. Finally, the genetic relatedness between European and Central American heartworms suggests that modern dispersal, likely associated with human colonisation of the Americas by Europeans, occurred with domesticated dogs. Our findings shed light on the global population dynamics and evolutionary history of heartworms, which can aid future surveillance and control efforts for this important veterinary parasite.