Spaghetti-Shaped Parasite in Ancient Canids Reveals the Unusual Origins of Heartworm
An essential part of dog ownership is protecting your canine companion from various diseases, one of the most serious of which is heartworm disease. If proper precautions are not taken, dogs can end up with parasitic roundworms in the blood vessels of their hearts and lungs. And new research suggests that dogs have been battling this disease for thousands of years, even before the global spread of domestic dogs. GSP
The study, published in Communication biology, says heartworm may have spread to dogs long before they began traveling alongside humans. Analysis of more than 100 heartworm genomes collected from dogs around the world has revealed the ancient evolutionary pathway of the parasite, which evolved to live in the hearts of dogs.
“For decades, we assumed that heartworms spread primarily through recent human activities,” lead author Rosemonde Power, a postdoctoral researcher at Stockholm University, said in a statement. “What we see instead is evidence of deep coevolution 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 is particularly prevalent in areas with temperate or tropical climates – areas that are home to an abundance of mosquitoes carrying the disease. Dirofilaria immitisthe parasite responsible for the disease.
When a heartworm enters a canine host via a mosquito, the parasite matures into its adult form. At this point it looks like a strand of spaghetti that extends to a foot or more. The adult parasite may then reside in the heart or lungs, and in advanced cases, for 5 to 7 years. Symptoms usually begin with a mild, persistent cough, fatigue, decreased appetite, and weight loss.
Over time, symptoms can progress to heart failure and blockage of blood flow to the heart (called caval syndrome), which is accompanied by the sudden onset of difficulty breathing, pale gums, and dark, bloody urine.
Heartworm can usually be prevented with regular injections during vet visits or monthly medications; However, the American Heartworm Society still recommends that owners have their dogs tested for heartworms annually, even if they are on preventive care.
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The ancient history of the heartworm
It is commonly believed that heartworms have spread globally over the past 200 to 400 years due to human-caused movement. However, researchers involved in the new study dispute 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 prevalent over time, examining the entire genome of 127 adult heartworm specimens collected from carnivorous mammalian hosts in Australia, the United States, Central America, Europe and Asia.
They found that some wild canids, like wolves and coyotes, have a similar worm load to dogs, meaning they were likely the primary heartworm hosts in ancient times.
Researchers also found that heartworm populations in Australia share genetic similarities with populations in Asia. This could indicate that Australia’s first dingoes, which may have migrated from Asia, brought the heartworm with them. However, the researchers note that more evidence is needed to confirm this theory; it is still possible that heartworms were introduced to the continent following the arrival of Europeans who brought dogs with them.
Global spread of heartworm
By examining heartworm genomes across the world, researchers were able to piece together the connections between different populations.
“Understanding where heartworms come from and how different populations are linked helps us respond more effectively to disease and drug resistance,” said lead author Jan Slapeta, professor at the University of Sydney’s 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 could also make the disease more widespread than it already is.
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