Every year, millions of dogs come face-to-face with a life threatening parasite coiled up inside one of their vital organs—heartworm. The spaghetti-looking parasite can be fatal when left untreated.
New research into the widespread canine parasite suggests that heartworm has a deeper and more complex history than scientists previously believed and some may have originated in Australian dingoes. The findings are detailed in a study published today in the journal Communications Biology.
Heartworm disease is caused by the parasite Dirofilaria immitis. It is spread to dogs by mosquitoes and can be fatal. Adult worms live in the blood vessels of the heart and lungs and can grow up to 11.8 inches long (30 centimeters). Dog owners and veterinarians often report that worms can look like a strand of spaghetti in the heart.
In the new study, an international team of researchers looked at over 100 heartworm genomes collected from pet dogs and wild canids from around the world. They used whole-genome sequencing to compare heartworms found in different regions, which helped them reconstruct population histories and track how the parasites diverged over time. They then pinpointed distinct regional heartworm populations that were shaped by the how and when ancient canids moved across the earth during ice ages.
They found that ancient canid hosts such as wolves and dingoes played a pivotal role in shaping how heartworms have been distributed across the globe for thousands of years.
“For decades, we assumed heartworms were spread mainly through recent human activity,” Dr. Rosemonde Power, a study co-author and University of Stockholm paleogeneticist, said in a statement. “What we’re seeing instead is evidence of deep co-evolution between heartworms and their canine hosts, even before humans were part of the picture.”
One of the study’s most interesting findings relates to Australia. Genetic signatures in Australian heartworms suggest that they might share ancestry with parasites found in Asia. According to the team, this raises the possibility that heartworm may have arrived in Australia with the continent’s first dingoes. The wild canids are believed to have migrated from Asia thousands of years ago.
However, the team cautions that the evidence is not conclusive. Heartown also may have been introduced to Australia more recently, following European colonization.
“While our data suggest an ancient link between Australian and Asian heartworms, the sample size means we need to be careful about drawing firm conclusions,” said study co-author and University of Sydney veterinarian Jan Slapeta. “What we can say with confidence is that heartworm evolution is far older and more complex than a simple story of parasites hitchhiking with modern dogs.”
Despite being separated by thousands of years, understanding how these ancient parasites evolved does have implications for animals living today. Like with antibiotics, resistance to common heartworm treatments and prevention methods is growing.
“Understanding where heartworms come from and how different populations are related helps us respond more effectively to disease and drug resistance,” added Slapeta. “Heartworms are not the same everywhere, and local history matters.”
In future studies, more sampling, particularly from regions that are more underrepresented regions could help explain more about the parasite, including that mystery of where Australia’s heartworm first originated.
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