Hookworms In Dogs: Intro & How Do Hookworms Spread

Cuban postage stamp featuring the dog hookwormIn areas that are warm and humid hookworms are frequent parasites of dogs. The common canine hookworm Ancylostoma caninum needs warm humid conditions to be infective. The larvae cannot develop below about 55 °F and will not survive freezing temperatures.

However, Uncinaria stenocephala (Northern canine hookworm) can survive freezing so there are cold areas with significant levels of infection. Do not assume that if you are not in a warm humid climate that your dog cannot get hookworms.

Like roundworms, hookworms are nematodes. The two types of worm have both similarities and differences in the way that they infect dogs. One major difference is that hookworms can penetrate skin and infect a dog, whereas roundworms cannot infect a dog this way.

Hookworms can cause serious health problems in dogs, so a regular de-worming schedule is important. Most heartworm medications are effective against hookworms, so they can provide a monthly de-worming for hookworms.

What are hookworms?

Hookworms are small thin worms usually between a ¼ and ½ inch long. The heads of the worms are bent making them look like a hooks.

In the US there are 3 main species of hookworms that infect dogs. Ancylostoma caninum, also called the dog hookworm is the most common The other two species are Ancylostoma brasiliense and Uincinaria stenocephala, both of which can also infect cats. Both Acylostoma species are only found in warm humid areas; Uncinaria stenocephala can survive in cold temeperatures.

The adult hookworms live in the small intestine, attaching to the intestinal wall. Ancylostoma caninum has 6 sharp teeth, Ancylostoma brasiliense has less teeth probably only two, and Uncinaria stenocephala has cutting plates. Adult hookworms feed by sucking blood from the intestinal wall.

How do hookworms spread and how do dogs get them?

The lifecycle of hookworms is quite complicated and a dog can get infected in a number of different ways, and potentially repeatedly.

  • A hookworm larva is swallowed by a dog
  • A hookworm larva enters through the dog’s skin
  • From pregnant dogs (not Uncinaria stenocephala)
  • From nursing dogs (not Uncinaria stenocephala)
  • If a dog eats another animal that is infected with hookworms

An infected dog sheds eggs from the gut

When a dog has adult 30,000 eggs per day.

The eggs are not infectious. They do not become infectious until hatching and developing through several larval stages. Hatching of the eggs and larval development requires the right temperature and humidity, which varies between species.

The larvae can develop in the soil and are also good at swimming. They can swim along wet grass leaves and other vegetation which helps them spread and get higher off the ground. This makes them more likely to find a host.

The larvae can usually only survive for a few weeks, at most a few months, before they die from drying up, or starve, since they don’t feed.

A hookworm larva is swallowed by a dog

If a dog gets larvae on its coat and then grooms by licking, it is easy for a dog the swallow hookworm larvae. Dogs may also eat grass or food that has become contaminated with hookworm larvae.

Once in the digestive tract of the dog, most of the larvae stay in the small intestine and develop into adult worms, and then the females start releasing eggs.

However, some of the larvae migrate.

Some (but not all) larvae will migrate to the lungs and up into the throat. They are then coughed up and most are swallowed and return to the digestive tract. In the small intestine these larvae, mature into adult worms and attach to the intestine.

The larvae that do not migrate to the lungs can remain embedded in the intestinal wall or enter different tissues such as muscle and liver, and encyst and become dormant. These encysted larvae may reactivate at later times, make their way to the lungs, be coughed up and re-enter the digestive tract.

A hookworm larva enters through the skin

If a dog is stands or lies on hookworm larvae they can directly enter the skin. The most common route of entry is through the bottom of the pads.

The larvae burrow into the skin and then enter the blood stream. The larvae make their way to the lungs. The dog coughs up larvae, most of which are swallowed. As with larvae that are directly swallowed (see above) most remain in the gut and mature, but some larvae leave the gut and either cycle back through the lungs or encyst in tissues and can reactivate at a later time.

From nursing dogs (not Uncinaria stenocephala)

If a dog has encysted hookworm larvae in tissue, when a dog is pregnant the changes in hormone levels trigger some larvae to migrate to the mammary glands of a pregnant dog. When the pups drink the larvae are passed to the pups in the milk. This is thought to be the main route of infection of puppies.

From pregnant dogs (not Uncinaria stenocephala)

The changes in hormone levels during pregnancy also activate some larvae migrate through the wall of the uterus and enter the developing pups within the uterus. When the pups are born. the larvae either develop to mature worms, or leave the gut and recycle through the lungs or encyst as described for A hookworm larva is swallowed by a dog.

If a dog eats another animal that is infected with hookworms

If another animal, usually a rodent has eaten a hookworm larva, then larvae will be encysted in various tissues within the body of that animal. When a dog eats the infected animal, larvae in the tissues will activate and infect the dog.


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See also Worms Of The Digestive System: General Information