Spaghetti-Shaped Parasite in Ancient Canids Reveals the Unusual Origins of Heartworm
A vital part of owning a dog is protecting your canine companion from various ailments, one of the most grave of which is heartworm disease. If the proper precautions aren’t taken, dogs can end up with parasitic roundworms in the blood vessels of their heart and lungs. And new research suggests that canines have dealt with this disease for thousands of years, even before the global spread of domesticated dogs. Spg
The study, published in Communications Biology, says that heartworm may have spread in dogs long before they began to travel alongside humans. Analysis of more than 100 heartworm genomes collected from dogs worldwide has revealed the ancient evolutionary path of the parasite, which evolved to live in the hearts of canines.
“For decades, we assumed heartworms were spread mainly through recent human activity,” said lead author Rosemonde Power, a postdoctoral researcher at Stockholm University, 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.”
Heartworm: A Spaghetti-Shaped Parasite
Heartworm disease can be found in most parts of the world, but it’s particularly prevalent in areas with temperate or tropical climates — regions that contain an abundance of mosquitoes that carry Dirofilaria immitis, the parasite that causes the disease.
When a heartworm enters a canine host via a mosquito, the parasite matures to its adult form. At this stage, it looks like a strand of spaghetti that stretches up to a foot or longer. The adult parasite can then reside in the heart or lungs, and in advanced cases, for 5 to 7 years. Symptoms typically start as a mild, persistent cough, fatigue, decreased appetite, and weight loss.
Over time, symptoms may escalate into heart failure and blockage of blood flow in the heart (known as caval syndrome), which is paired with the sudden onset of labored breathing, pale gums, and dark bloody urine.
Heartworm can usually be prevented with regular injections during visits to the vet or monthly medications; the American Heartworm Society, however, still recommends that owners get their dogs tested for heartworms annually, even if they’re on preventative care.
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The Ancient History of Heartworm
It’s been commonly believed that heartworms spread globally over the past 200 to 400 years based on human-mediated movement. However, researchers involved with the new study challenge this view, saying it overlooks the long co-evolutionary history of canids and mosquitoes.
Researchers took a closer look at heartworm parasites to determine how they became so widespread over time, examining the whole genomes of 127 adult heartworm specimens taken from mammalian carnivore hosts across Australia, the U.S., Central America, Europe, and Asia.
They found that certain wild canids, like wolves and coyotes, have similar worm burdens to dogs, meaning that they were likely the primary hosts for heartworm during ancient times.
The researchers also found that populations of heartworms in Australia share genetic similarities with populations in Asia. This could indicate that Australia’s first dingoes, which are believed to have migrated from Asia, brought heartworm with them. However, the researchers note that more evidence is needed to confirm this theory; there’s still a possibility that heartworms were introduced to the continent following the arrival of Europeans who brought dogs with them.
Heartworm’s Global Spread
By examining heartworm genomes around the world, the researchers could piece together the links between different populations.
“Understanding where heartworms come from and how different populations are related helps us respond more effectively to disease and drug resistance,” said senior author Jan Slapeta, a professor at the University of Sydney School of Veterinary Science. “Heartworms are not the same everywhere, and local history matters.”
Human influence is now a key factor in shaping heartworm diversity; the use of drugs to treat the disease has led to increased resistance in heartworms. In the coming years, climate change and pet travel may also make the disease more pervasive than it already is.
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