If you made a list of the parasites that plague dogs in tropical countries, you’d no doubt be very thankful you live in Canada. Our cold climate inhibits the survival of many parasites and although we do see some worms, as well as fleas and ticks, our winter temperatures help us control these parasites with relative ease.

Climate has a huge impact on whether or not your dog is at risk for contracting heartworm. You find this parasite only in southern parts of Canada where temperatures support its life cycle.

Heartworms live in the large blood vessel that leads from the heart to the lungs. Over time, the lining of this pulmonary artery becomes irritated and inflamed, thickening so much that blood flow is significantly impaired. A heavy heartworm infestation can ultimately cause heart failure.

Mosquitoes transmit heartworm between dogs and are an essential host for the heartworm parasite – heartworm larvae can infest a dog only after moulting inside a mosquito. Because mosquitoes are active only during warm weather, heartworm transmission is limited to a few months of the year (primarily late summer).

The intestinal worm seen most often in Canada is the roundworm Toxocara. Known as the “spaghetti” worm, Toxocara lives in the dog’s intestine, feeding on intestinal contents, and laying eggs that are passed with the host dog’s stool.

In adult dogs, roundworms rarely cause clinical disease because worm load is so low. Pups, in contrast, can suffer from heavy infestations and become debilitated from malnutrition as the worms utilize all the nutrients the pup consumes. As well, a writhing mass of worms can block the intestine and ultimately cause death.

Puppies are born infested with roundworms. This is because roundworm larvae lying dormant in the bitch’s tissues wake up during pregnancy and migrate across the placenta into her pups. These worms find their way to the puppies’ intestines, where they mature into egg-laying adults. Regular deworming of bitches can reduce worm transfer to puppies.

Adult dogs acquire roundworms in two ways. Most frequently, they consume larvae that have hatched from eggs shed in the stool of infested dogs. This method of transfer is greatly impacted by weather. Larvae can survive and be infective for a few weeks in warm, humid climates, but live for only a brief period if exposed to freezing temperatures or hot, dry conditions.

The second way dogs are infested with roundworms is unaffected by climate. It starts with a rodent consuming a roundworm larva. Because it’s in the wrong host, the larva goes dormant in the rodent’s tissues. When a dog eats the rodent, he ingests the roundworm larva, which then infests him.

These worms are more serious than roundworms because they attach to the intestinal wall and suck blood. They’re readily passed from one dog to another through eggs in the feces. Thankfully, both of these worms can be put on the “seldom seen in Canada” list.

Tapeworms, which are quite common in Canadian dogs, are transmitted between dogs by intermediate hosts. To be infested, a dog must eat a host that’s carrying the parasite. The common intermediate hosts for tapeworm are rodents and fleas.

Tapeworms steal nutrients from the dog’s intestine, so heavy infestations can lead to weight loss, increased appetite and a scurfy coat. A tapeworm infestation is easy to diagnose – worm segments appear on the dog’s stool or around the anus.

If you are a dog owner who battles fleas every year, it’s hard to imagine life without these pests, yet for many Canadians, fleas are unfathomable. Large parts of our country are flea-free zones because the climate is not conducive to flea reproduction and survival.

Fleas spend their adult lives on their hosts, nourishing themselves by sucking blood. They lay their eggs while on their hosts so the eggs fall off where dogs spend most of their time (the couch, the carpet and the bed).

The larvae, which hatch from eggs, feed on organic debris and flea feces in the environment. They eventually moult to pupae. While sequestered in their cocoons, the pupae develop into adults that are ready to feed and reproduce. Heat, vibration and high amounts of carbon dioxide in the air, all emitted by potential hosts, are the triggers for adult fleas to emerge.

Once fleas start feeding, they cause skin irritation and, for most dogs, that’s all they do. However, in very tiny puppies, they can extract so much blood that the pups become severely anemic.

Dogs are susceptible to two types of mange mites that are unaffected by climate – they can be found in Toronto or Yellowknife.

Demodex mites live in hair follicles and are thought to infest every dog. We believe that dogs pick them up as they nurse on their mothers. Most dogs mount an immune response that keeps the demodex mites at bay. However, a few have a deficient immune system that allows this parasite to reproduce without control.

Under these circumstances, the mites generate inflammation and a severe itch.

Demodex lesions first appear on a dog’s face and feet, but over time, they can spread over his entire body in what is called generalized demodecosis.

Demodex mites are resistant to many insecticides so they are difficult to treat.

The sarcoptes mite lives on or in the skin surface, causing intense irritation, but rarely any skin lesions. It is easily treated with common insecticides.

Lice infestations can occur in any climate. In fact, they may be more common in the winter. Though adult lice are hard to see, the eggs (known as nits) are easily visible attached to the hair shaft. Lice induce only mild irritation so they are more a social stigma than a health hazard. Most lice infestations occur in puppies and can be readily treated with insecticide soaps and powders.

Cheyletiella mites live on the skin surface. In dogs, this mite infestation, commonly called “walking dandruff,” causes just a mild itch. Cheyletiella is readily killed with topical insecticides.

Ticks depend on intermediate hosts for their survival; part of their life cycle must be spent on wildlife. Because of this fact, you’ll find ticks in treed sites or pastures, not in highly developed areas. Ticks start ‘questing’ for a host during spring thaw.

Ticks suck blood but not enough to cause anemia. The primary concern with ticks is that they can transmit infections such as Lyme disease.

The last canine skin parasite is a mite that prefers to live in the ears. Ear mites are transmitted between dogs in close contact, especially between mother and pups. Climate has no bearing on the life cycle of ear mites. These microscopic parasites are much rarer than most dog owners believe. An itchy ear in an adult dog is unlikely to be filled with ear mites. Ear disease is more often due to allergies and infections than parasites.

All the above parasites have one thing in common: they are found in Canadian dogs. Though some are rare (whipworms and hookworms), and a few are common (fleas and roundworms), others are diagnosed only periodically.
Compared to canines that live south of the border, our dogs have to cope with very little parasite-induced stress.