Dogs and Worms


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How Dogs Get Worms

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How do dogs get worms? As dog worms are the most common health problems of dogs, this question is one of the most popular questions asked by dog owners. And… one of the canine medical fields least known to people.

According to the University of Georgia College of Veterinary Medicine, the bottom line for how dogs get worms is, “How a dog gets infected by worms depends on the kind of worms the dog has. There are a lot of different kinds of worms that live in dogs.” These worms are called parasites because they feed off the dog’s body. The worm does not live independently on its own. Unlike earthworms, another type of worm, they have to reproduce inside of a dog.

Credit: Nancy Houser


The most common dog worms in dogs are roundworms, hookworms, whipworms, tapeworms, and heartworms. Roundworms and hookworms are found mostly in puppies and sometimes in adult dogs and the mother dog. Whipworms, tapeworms, and heartworms are seen more in older dogs.

How do dogs get Roundworms?

Credit: Wikipedia

Roundworms are difficult to distinguish, with the total number of species estimated to be about 1 million. They look a lot like earthworms but are much more dangerous to dogs. They live freely inside the dog’s intestines, eating partially digested intestinal contents. Ugh!

Toxocara canis and Toxascaris leonina are the primary species of roundworms in dogs, but Toxocara canis can be transmitted to humans and is considered more dangerous to a dog’s health.

How dogs get roundworms

  • Infected dogs shed microscopic roundworm eggs in their feces.
  • Nearby dogs can become infected by sniffing or licking infected feces from infected dogs.
  • Roundworm eggs can be spread by other animals such as rodents, earthworms, roaches and birds.
  • The above species animals transport the roundworms, which do not mature into adults.
  • Once a dog eats the parasitic host, it will complete its maturation process into full-grown roundworms.

The roundworm process inside the dog

  • Roundworm larvae (immature worms) migrate and encyst throughout the host’s body.
  • Encysted larvae start to develop during pregnancy and ultimately cross the placenta into an unborn puppy.
  • Clinical signs in puppies, such as stunted growth, potbelly, and recurrent diarrhea, are a good indication of roundworm infection.
  • Definitive diagnosis is made by microscopic examination of the dog’s feces.
  • The most common consequence of roundworms is growth reduction in young puppies.
  • There is a of the risk of roundworm infection in humans. It is recommended by the Centers for Disease Control (CDC) that all dogs be de-wormed monthly.

How dogs get Hookworms

Credit: University of Georgia

Hookworms occur most often in puppies, but they can also occur in adult dogs. Hookworms in dogs, referred to as Ancylostoma caninum and Ancylostoma braziliense, are intestinal parasites that get their name from the hook-like mouthparts that anchors themselves to the lining of the dog’s intestinal wall.

It is difficult to see hookworms with the naked eye, but they are still capable of ingesting large amounts of blood from the tiny vessels in the dog’s intestinal wall.

A large number of hookworms inside a puppy’s body can cause life-threatening anemia. Overcrowding and poor sanitation in kennels and puppy mills can cause hookworms to infest rapidly, due to a warm and moist environment.

Dogs get hookworms by one or all four main routes

  • Orally
  • Through the skin
  • Through the mother’s placenta before birth (in utero)
  • Through the mother’s milk

The hookworm process inside the dog

  • Female hookworms pass hundreds of microscopic eggs in the feces of infected dogs, where they contaminate the environment.
  • Larvae hatch from the eggs and can remain infective in the soil for weeks or months.
  • A dog may become infected when it inadvertently swallows hookworm larvae, often by grooming its feet, or from sniffing feces or contaminated soil.
  • The larvae may also burrow into the skin if the dog walks or lies on contaminated ground.
  • Once in the host’s body, the larvae migrate to the intestine where they mature and complete their life cycle.
  • Part of the life cycle of the hookworm involves migration through muscle tissues, where they may become dormant.

How do dogs get Whipworms?

Whipworms are one of the most infectious agents in dogs, living in the cecum and large intestine (colon). They cause severe irritation to the lining of those areas. A dog who has whipworms will have infectious results: water, bloody diarrhea, weight loss, and general debilitation. Whipworms are not infectious to people. They are exclusive parasites of the dog.

Credit: Wikipedia

How dogs get whipworms

  • Whipworms pass microscopic eggs in the stool.
  • The eggs are very resistant to drying and heat, so they can remain viable (alive) in the environment for up to 5 years.
  • Once laid, they embryonate (mature to an infective stage) in the environment and are able to re-infect the dog in 10-60 days.
  • The embryonated eggs are swallowed and hatch and mature to adults in the lower intestinal tract, completing their life cycle.

The whipworm process inside the dog

  • Parasites pass small numbers of eggs on an irregular basis, so some samples may be falsely negative.
  • It takes approximately 11-12 weeks after hatching for a female adult to begin to lay eggs.
  • Any dog with chronic large bowel diarrhea should be suspected to have whipworms, even if the stool sample was negative.
  • Any dog with chronic large bowel diarrhea should be suspected to have whipworms, even if the stool sample was negative.

How do dogs get Tapeworms?

Tapeworms are what they call “rice worm,” flat intestinal worms that are small 1/4? segments. Dipylidium caninum is the most common tapeworm of dogs. The tapeworms attach to the wall of the dog’s small intestine with hook-like mouthparts, with each adult tapeworm reaching up to 8 inches long.

Credit: JustAnswer

How dogs get tapeworms

  • Each tapeworm segment develops behind the worm’s head and moves down the tapeworm as the chain gradually matures.
  • The tapeworm segment sheds out of the rectum, at the opposite end of the head.
  • It can shed singly or in short segment chains.
  • These segments, called proglottids, are passed through the feces when an infected dog defecates (poops).
  • Each They are about 1/8? (3 mm) long and look like grains of rice or cucumber seeds. Occasionally they can be seen moving on the hairs around the anus or on the surface of freshly passed feces.

Tapeworm process inside the dog

  • When the infected eggs are released into the environment, they have to be swallowed by immature flea larvae in the environment.
  • Once inside the larval flea, the tapeworm egg continues to develop as the flea matures into an adult flea.
  • During grooming or in response to a flea bite, a dog can ingest the tapeworm infected flea and complete the life cycle.
  • As the tapeworm segment dries, it becomes a golden color and eventually breaks open, releasing the fertilized eggs into the environment.

How do dogs get Heartworm?

By the time clinical signs of heartworm are seen, the disease is well advanced into the heart of the dog. However, it takes several years before the signs of infection are seen – usually in two to eight year-old-dogs. The disease is rare in dogs less than one year of age because the microfilariae take five to seven months to mature into adult heartworms after infection.

Heartworm disease clogs the dog’s heart and major blood vessels that lead from the heart, while interfering with the heart’s valve action. When the major blood vessels are clogged, blood supply to other organs is reduced. Worse of all is the blood flood to the lungs, live and kidneys, which causes the organs to malfunction.

Credit Wikipedia

Heartworm disease depends on a lot of things

  • The number of adult worms present.
  • The location of the worms.
  • The length of time the worms have been in the dog.
  • The degree of damage that has been sustained by the heart, lungs, liver and kidneys.
  • Typical signs of heartworm are a soft, dry cough, a shortness of breath… and loss of stamina.
  • Heartworms can live up to five years.

How dogs get heartworm

  • The parasite requires the mosquito as an intermediate host before it can complete its life cycle in the dog.
  • As many as 30 species of mosquitoes can transmit heartworms.
  • The life cycle of the heartworm begins when a female mosquito bites an infected dog and ingests the microfilariae during a blood meal.
  • During the five year lifetime of the adult heartworms, the female heartworm will produce millions of offspring that is called microfilaria.
  • Heartworm disease or dirofilariasis is a serious and potentially fatal disease.
  • Heartworm is caused by a blood-borne parasite known as Dirofilaria immitis, a parasitic roundworm that spreads for host to host through the bite of mosquitoes.
  • Heartworm is a type of filaria, a small thread-like roundworm that causes filariasis – spread by blood-feeding black flies and mosquitoes.
  • Heartworms, when they are adults, are found in the heart and nearby large blood vessels of dogs who have been infected.

Heartworm process inside the dog

  • During the five year lifetime of the adult heartworms, the female heartworm will produce millions of offspring that is called microfilaria.
  • Microfilaria live primarily in the small vessels of the bloodstream… the parasite requires the mosquito as an intermediate host.
  • The parasite requires the mosquito as an intermediate host before it can complete its life cycle in the dog.
  • As many as 30 species of mosquitoes can transmit heartworms.
  • Rarely, but occasionally, the worms are found in other parts of the dog’s circulatory system.
  • The female worm ranges from 6 to 14 inches long and 1/8 inch wide.
  • he male worm is half that size.
  • By the time a dog with heartworm is diagnosed, it can have as many as 300 worms inside its heart.
  • The microfilariae develop further for 10 – 30 days in the mosquito’s gut and then enter its mouthparts. At this stage, they are infective larvae and can complete their maturation when they enter a dog.
  • The infective larvae enter the dog’s body when the mosquito bites the dog. They migrate into the bloodstream and move to the heart and adjacent blood vessels, maturing to adults, mating and reproducing microfilariae within 6 – 7 months.

A dog owner can prevent his or her dog from getting heartworm by using a heartworm preventive. Once this is successful, they should immediately begin a heartworm preventive program. – Medical facts taken from the University of Georgia College of Veterinary Medicine and VCA Animal Hospitals

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WayCoolDog articles are re-posted with the permission of Nancy Houser of WayCoolDogs © 2009 – 2014