Dog Diseases: Parasites

Heartworm (Dirofilaria Immitis)

Cycle of Infection Picture

Signs and Symptoms

Class 1:  No symptoms or mild symptoms such as an occasional cough.

Class 2:  Mild to moderate symptoms such as an occasional cough and tiredness after moderate activity.

Class 3:  General loss of body condition, a persistent cough, and tiredness after mild activity.  Trouble breathing and signs of heart failure are common. For class 2 and 3 heartworm disease, heart and lung changes are usually seen on chest x-rays.

Class 4:  Also called caval syndrome.  There is such a heavy worm burden that blood flowing back to the heart is physically blocked by a large mass of worms.  Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option.  The surgery is risky, and even with surgery, most dogs with caval syndrome die. 

Diagnosis

Diagnosis is made by a blood test to detect proteins produced by the worms ("antigen") in your dog's blood. The test may be falsely negative early in an infection or if only a small number of worms are present, so repeating the test after six months may be necessary to detect an infection. An older test method involves checking the blood for circulating larvae, but this test is not as accurate.

In addition to blood testing, radiographs and ultrasound can be used to assess changes in the heart and lungs associated with heartworm disease.

Treatment

The drug that you treat with is called Immiticide. It’s an injectable, arsenic-based product. The dog is given two or three injections that will kill the adult heartworms in the blood vessels of the heart.

• Hookworm (Necator americanus; Ancylostoma duodenale)

Cycle of Infection Picture

Signs and Symptoms

• failure to gain weight, or weight loss
• loss of appetite
• diarrhea
• anemia (pale gums, weakness) sometimes seen, and can be cause of death in puppies
• bloody or tarry stools may be present
• sometimes coughing can occur due to the larval migration through the lungs (with very heavy infections)
• skin irritation, most often on the feet between the toes, due to migrating larvae

Diagnosis

The eggs of hookworms can be detected under the microscope in a routine check of a stool sample (the test process is called fecal flotation). It takes a while for infected puppies to shed eggs, so routine deworming of puppies is recommended.

Treatment

Treatment is the same, regardless of the species. There are a number of medications that can be used to treat hookworms, and your vet can help you pick the one right for your dog. Medications will only affect hookworms in the intestines, not migrating larvae. Treatment should be repeated to deal with larvae as they mature (e.g. at 2 week intervals). The number of treatments necessary will depend on the age of the dog and the situation, and will be recommended by your vet.

• Roundworm (Toxocara canis; toxascara leonina)

Cycle of Infection Picture

Signs and Symptoms

• Pot-belly
• Weakness
• Diarrhea
• Vomiting
• Belly pain
• Dull coat
• Weight loss

Diagnosis

The eggs of roundworms are detected under the microscope in a routine check of a stool sample (the test process is called fecal flotation). It is possible to tell the difference between the species of roundowrm based on the appearance of their eggs. Of course, when roundworms appear in vomit or stool, the diagnosis is pretty clear.

Treatment

There are many safe and effective deworming drugs. They include fenbendazole, milbemycin, moxidectin, nitroscanate, piperazine, and pyrantel. Your vet will give your dog one to three doses at first, which will kill the adult worms. Your dog will get follow-up doses to kill any new worms that weren’t fully developed when the first doses were given.

Because it’s so common in puppies, many vets deworm pups when they’re 2-3 weeks old just to be safe.

Even after your dog is treated, he should get regular fecal exams. For puppies, that’s two to four times a year. For dogs 1 year or older, it’s one to two times a year.

• Whipworm (Trichuris trichiura)

Cycle of Infection Picture

Signs and Symptoms

• weight loss
• diarrhea
• mucous or blood in stool
• anemia (pale gums, weakness) can be seen with chronic, heavy infections

Rarely, whipworm infections cause a syndrome similar to Addison's disease, with periodic episodes of weakness and electrolyte imbalance, though the mechanism of this effect is poorly understood.

Diagnosis

The eggs of whipworms can be detected under the microscope in a check of a stool sample (the test process is called fecal flotation).

However, unlike roundworms and hookworms, female whipworms only produce eggs intermittently, so the eggs can be very difficult to catch on fecal tests. Repeated tests may be necessary, and if a whipworm infection is suspected it is common to treat for whipworms even if eggs aren't found.

Treatment

There are a number of medications that can be used to treat whipworms, and your vet can help you pick the one right for your dog (they are resistant to some common dewormers). Repeated treatments are usually recommended for best results (e.g., after 3 weeks and 3 months).

Because the eggs survive for so long, the potential for re-infections from eggs in the environment is significant. Your vet may recommend a monthly parasite preventative effective for whipworms to prevent whipworm infections on an ongoing basis.

Keeping pet wastes picked up promptly can help prevent infections with whipworms.

• Tapeworm (Cestoda)

Cycle of Infection Picture

Signs and Symptoms

• Anal and perianal itchiness (pruritus at and around the anus)
• Licking at the anal and perianal area
• Scooting
• Weight loss (despite maintaining a good appetite)
• Increased appetite (without weight gain)
• Poor hair coat (dull, dry, unkempt)
• Poor skin condition (dry, flaky)
• Abdominal distension
• Diarrhea
• Lethargy
• Irritability
• Abdominal pain (less common)

Diagnosis

Clinical diagnosis is usually made by observing the white mobile tapeworm segments in the feces or crawling around the anus. They often look like grains of rice.

Tapeworm segments are only passed intermittently and therefore are often not diagnosed on routine fecal examination. If you find any segments, white or golden color, bring them to your veterinarian for a definitive diagnosis.

Treatment

The parasiticide may be given either in the form of tablets or by injection. It causes the parasite to dissolve in the intestines so you normally will not see tapeworms passed in the stool. These drugs are very safe and should not cause any side effects.