Internal Parasites

Hook worms Round worms Tape worms Whip worms
Common adult canine worms, showing the relative size and appearance of adult worms and eggs. The eggs are magnified 500X.

There are many advantages to owning a dog.  Besides companionship, they offer security, empathy, and unconditional love.  With all they have to offer, it is important to remember the responsibility of pet ownership.  Lots of love, a good diet and regular veterinary care are essential to the well being of your pet.  Routine veterinary check ups that include an examination, immunizations and tests for internal parasites will insure a long, happy life for your pet.  Internal parasites are the most common of problems in dogs.  Statistics show that one in three dogs will be infected at some time with intestinal parasites such as roundworms, hookworms, whipworms and tapeworms.


The hookworm's voracious appetite for blood can quickly cause severe anemia and/or death in a dog. Infestation of 500 worms can cause a five-pound puppy to lose half its total blood volume in one day. As few as 100 hookworms can cause a puppy to die of blood loss.

Hookworms attach themselves to a dog's intestinal lining with hook-like teeth, leaving bleeding internal wounds that are particularly dangerous to puppies. Relatively small (1/4 to 3/4 of an inch long), hookworms are dangerous to all dogs – puppies in particular.

How Hookworms are Transmitted

The most common method of hookworm transmission is through the feces of dogs. Hookworm eggs pass through the feces of infected dogs and hatch into larvae. These larvae can be swallowed by a healthy dog or penetrate through the dog's skin or foot pad. Mother dogs can give hookworms to their puppies through their milk.

Hookworm Eggs

Adult hookworms live in the small intestine of dogs, and they lay up to 50,000 eggs per day. The eggs are released with the dog's feces, where they then dwell.

Hookworm Larvae

Within animal feces, the hookworm eggs hatch and develop into larvae. Dogs can be infected through the ingestion of these larvae or from larvae puncturing the pet's foot pad. Once internalized, the larvae migrate to the small intestine.

Adult Hookworm

It is within the small intestine that the hookworms mature into adults. The eggs can again be released into the dog's feces or immature larvae can be passed directly from the mother dog to its nursing pups.


A severe infestation of larval-phase roundworms can cause liver, lung and brain damage. A heavy accumulation of roundworms in a puppy can lead to death. Symptoms include vomiting, colic, poor growth and a "pot-bellied" appearance.

Almost all puppies are born with roundworms or acquire them through their mother's milk. Though most adult roundworms are expelled by dogs by the age of six months, a large proportion of adult dogs continue to have light infestations. Matters can be further complicated by the larvae which can remain "dormant" in tissues until the mother dog is pregnant.

How Roundworms are Transmitted

The most common method of roundworm transmission is when a puppy nurses from the infected mother dog. In addition, roundworms can be transmitted through the feces of dogs, but dogs can also acquire roundworm infection through contact with soil containing these eggs. Moreover, roundworms can be transmitted when a dog eats an infected rodent.

Roundworm Eggs

Adult roundworms live in the small intestine of dogs, where they lay up to 80,000 eggs per day. The eggs are released with the dog's feces, where they then dwell. The larvae develop inside the eggs while the eggs are located in the expelled feces.

Roundworm Transmission and Growth

As the larvae grow within the eggs, the dogs may ingest the unhatched eggs in the environment or the dog may eat an infected rodent. These eggs hatch within the dog, where the larvae develop in the stomach before moving to the small intestine.

Puppies can become infected before birth by having the larvae migrate from the placenta to the liver, from the liver to the lungs, and from the lungs up the trachea and then down to the stomach.

Adult Roundworm

The larvae mature within the stomach and small intestine into egg-laying adults.


Whipworm infection causes bloody diarrhea, weight loss, anemia and dehydration, but diagnosis is very difficult and may require several exams. Symptoms include diarrhea, abdominal pain and mucus-laden stools streaked with blood. A large number of worms (more than 2,000 in some cases) can cause anemia.

Whipworms, 1.75 to 3 inches long, reside in the large intestine and cecum. Using its mouth as a spear-like sword, the whipworm slashes and punctures the intestine and then feeds on the released blood and tissue fluids.

How Whipworms are Transmitted

The most common method of whipworm transmission is through the feces of dogs, but it is also suspected that they may be transmitted through soil. The eggs that pass through the feces can be swallowed unhatched by a healthy dog, where they will hatch inside.

Whipworm is difficult to control outside the dog. Whipworm eggs pass into the soil, where they can survive for years under the most severe weather conditions. Whipworm eggs are virtually impossible to attack chemically (the ova may be absent from feces in many infected dogs).

Whipworm Eggs

Adult whipworms live in the cecum of dogs, where they lay eggs. The eggs are released with the dog's feces, where they then dwell. The larvae develop inside the eggs.

Whipworm Transmission and Growth As the larvae grow within the eggs, the dogs may ingest the unhatched eggs.

Adult Whipworm

These eggs hatch within the dog, where the larvae mature into adults, which then lay eggs to begin a new the life cycle.


Tapeworms are large worms that live in the gut of dugs. They may migrate about in the area around the dog's anus which can lead to irritating itching and thus bad hygiene by the dog. Tapeworms often have an intermediate host in addition to their final host (the dog). The most important intermediate hosts of canine tapeworms are fleas or certain mammals like sheep and rabbits.

How Tapeworms Are Transmitted

The most common canine tapeworm is transmitted by fleas. Flea larvae become infected by ingesting tapeworm eggs that have been shed in the dog's feces. Dogs become infected if they swallow an infected flea while grooming. The tapeworms grow to maturity in the dog's gut. Tapeworm segments which contain eggs are then shed in the dog's feces. Tapeworms also can be transmitted when dogs eat the raw meat of infected intermediate hosts.

Tapeworm Eggs

Adult tapeworms live in the guts of dogs, where they lay their eggs. The eggs are released with the dog's feces, where they then dwell. Tapeworm Transmission and Growth As the larvae grow within the eggs, the eggs may be ingested by flea larvae that are also present in the dog feces. If a dog ingests an infected flea, the tapeworm larvae may hatch and mature in the gut of the dog.

Adult Tapeworm

The larvae mature within the gut of the dog where they may travel as far down as the anus. They generally lay their eggs in the gut.

Veterinarians typically agree that testing for worms and following a good deworming program is essential for puppies. After your veterinarian has dewormed your puppy or dog, do not be alarmed at the stool immediately following the medication. The worms are expelled over a 24 to 48 hour basis and the stool may be full of worms. Do not be alarmed --this is normal.


Heartworm infestation
Heartworm infestation

Heartworms are exactly what the name implies. They are the most serious and deadly parasite to attack an adult dog. These worms are carried by mosquitoes and transmitted when the dog is bitten. Lodging in the heart, the worms restrict blood flow and cause damage to other internal organs. Without treatment, heartworms will cause a long and often lingering death.

Heartworms are horrible. Anyone who has ever known or had an infected dog knows how slowly but surely the parasites can sap the animal’s strength and vitality. Heartworms can do a great deal of damage to your pet if you do not catch them in time. The good news is that you can prevent it from happening.

Virtually all dogs are at risk, especially during the warm weather season. There are often few signs of heartworms until a serious infestation is underway. The most common symptoms of heartworm infections are coughing, sluggishness, and labored breathing. Heartworms can migrate to vital organs within two to three months. The larva complete their migration in six months, ending in the actual heart chamber. These worms, which can reach a length of 14 inches, live in the heart, restricting blood to the organs, left untreated heartworm can lead to heart and lung failure, kidney and liver damage, and eventual death. And yes, all it takes is the bite of just one infected mosquito.

The smart route to travel is one of prevention. A simple blood test done by your veterinarian will let you know if your dog has heartworms. All dogs must be tested for heartworm infection before they can start a heartworm preventive routine. Your dog should be given a blood test for heartworm every year in the early spring. If the blood test is negative, your pet may be prescribed a preventive medication to be given once a month, which also controls many common intestinal worms. Heartworm prevention is as easy as that but it must be done regularly, every month, to ensure continued protection. With routine testing and once-a month medication, you can offer your animal companion complete protection against heartworm infection.