Common Dog Parasites

Parasites can be a major concern at some point in the lives of pet dogs. They are one of the top reasons for visits to the veterinarian. Heavy parasite loads can have an impact on the health and comfort of pets. Their presence can cause anything from mild irritation to serious health issues.


Can humans get parasites from dogs?

Some parasites in dogs are zoonotic, meaning they can be transmitted from animals to man. Some are also capable of carrying and transmitting disease.


Every pet owner should know about parasites that can affect their dogs so they can take a proactive approach to safeguard their pets from infestation.


What are parasites?

A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host.

Parasites in dogs are classified into 2 main groups — internal parasites and external parasites.


Internal parasites in dogs

The common internal parasites in dogs include intestinal worms such as roundworms, tapeworms, hookworms, and whipworms. Heartworms are also important internal parasites in dogs.


1. Heartworms

Heartworms (Dirofilaria immitis) inhabit the heart and lungs, as well as the major blood vessels that connect these 2 major organs. Heavy infections can cause heart failure, lung disease, and even death. The parasite is mosquito-borne, which means that the infection is transmitted by mosquitoes that have acquired the heartworm larvae from feeding on the blood of infected dogs. They can then deposit the infective heartworm larvae when they feed on other dogs.


Signs of heartworm disease in dogs

Dogs with heartworms may exhibit the following symptoms:



  • Mild persistent cough
  • Poor exercise tolerance even after moderate activity
  • Decrease in appetite
  • Loss of weight


A dog may not show any symptoms at all during the early stages of heartworm disease. But as the problem progresses, dogs may develop heart failure; the accumulation of excess fluid in their abdomen can give them a pot-bellied appearance. As the number of adult heartworms increases, they can block the flow of blood within the heart that can eventually cause cardiovascular collapse. Affected dogs suddenly exhibit labored breathing, pale gums, and dark-colored urine. Prompt surgical intervention is very important to remove the worms that are causing the obstruction. Unfortunately, only a few dogs survive.


Diagnosis and treatment of heartworm disease in dogs



Blood tests are used to establish the presence of heartworms in dogs. It is recommended to consult your veterinarian for the right time that your dog should be tested for heartworms as regular testing is very important.



Treating heartworms can be very expensive and it’s not without potentially serious side effects. Thus, prevention still remains to be the best way to ensure your pet’s protection. All types of heartworm medications need a veterinarian’s prescription.


2. Roundworms

These spaghetti-like worms are extremely common in dogs, especially in puppies. There are 2 important species of roundworm that affect dogs — Toxocanara canis and Toxocaris leonine. Heavy infestations of Toxocara canis can cause serious disease. They can also be transmitted to humans. Adult worms live in the intestine of dogs and they can reach up to several inches long. The worms compete with the nourishment of their hosts. Heavy infestation is a special concern in puppies because their immune systems are not yet fully developed, making them more vulnerable to roundworms and their effects. Puppies with roundworm infestation can become malnourished and suffer from coughing, vomiting and/or diarrhea. They may also have a pot-bellied appearance and worms may be present in their stool or vomitus.


How dogs get roundworms

There are several ways by which dogs can get roundworms-from their mother, from the environment, and from eating animals that are carrying roundworms.


3. Tapeworms

These flat, segmented worms live in the intestines of dogs. The most common flatworms in dogs are Dipylidium caninum. Some types of tapeworms, like Echinococcus granulosus (hydatid tapeworm), can be transmitted to people and cause serious disease.


How dogs get tapeworms

Fleas are important transmitters of tapeworms, particularly Dipylidium caninum. Dogs become infected when they ingest fleas that are carrying tapeworm larvae during self-grooming. Inside the dog’s gut, the worms attach to the walls and develop into adults. They can grow up to 60 cm long! Tapeworms feed on the intestinal contents of their hosts thus getting valuable nutrients that should have been used by the dog’s body.



As for hydatid tapeworm, dogs become infected when they eat meat from animals that are carrying the parasite, such as sheep or kangaroos.


4. Hookworms

Hookworms are blood-sucking parasites. They can cause serious disease in puppies. Hookworm larvae attach to the intestine of the host and suck blood. Heavy infestations can cause severe anemia which can be life-threatening. When hookworms detach from the intestinal walls, blood continues to seep from the sites where they attached. Without prompt medical intervention, dogs can die.


How dogs become infected with hookworms

Hookworms can be transmitted through the mother’s milk. This is the primary way that puppies are infected. Other routes of infection include ingestion from fecal-contaminated food or water and the active penetration of larvae through the dog’s skin.


5. Whipworms

Whipworms live in the cecum and large intestine of dogs. They cause severe irritation to the lining of these organs. Affected pets suffer from watery or bloody diarrhea, general weakness, and weight loss. A dog suffering from chronic diarrhea is often suspected to have whipworms. The main route of infection is by ingestion of mature eggs by dogs. There are several anti-worm medications that can kill whipworms. These include fenbendazole, oxantel, milbemycin, and moxidectin. It is best to follow the dosage recommendations of your veterinarian to ensure that the worms are eliminated. There are now heartworm medications that contain an active ingredient that kills whipworms.


Giardia, coccidia, and spirochetes

These are non-worm parasites that inhabit the intestinal tract of dogs. A dog can be infected with these parasites without showing any symptoms of infestation until they are exposed to stressful situations or their immunity becomes compromised. These parasites can be acquired from contaminated food, water, feces, and soil. Infected animals are also important sources of infestation.


How do vets test for parasites?

Fecalysis or the microscopic examination of the stool can provide important information in establishing the presence of intestinal worms. It can also show the parasite load levels.




Preventive measures against internal parasites

  • Always observe proper hygiene and sanitation. Thorough cleaning of the dog’s immediate environment should be undertaken. All moist areas should be eliminated to prevent infections and re-infections.
  • Work closely with your veterinarian in creating a deworming program that will protect your pet against internal parasites throughout all the months of the year.
  • Heartworm preventatives should be given regularly to ensure maximum protection.
  • Regular stool examination is necessary. It is usually one of the routine tests that dogs undergo during a wellness check.
  • For heartworm, there is a need to protect your pet from mosquitoes.
  • Flea prevention is also important to protect dogs against tapeworms.



External dog parasites

1. Fleas

Fleas are wingless parasites with powerful legs that make jumping from one host to the next easy and convenient. Some dogs are hypersensitive to an allergen in the flea saliva. For these dogs, even a flea bite or two can cause intense itching and they may scratch and bite themselves raw. Fleas are often suspected when dogs engage in intense scratching. These ubiquitous parasites are also important transmitters of tapeworm.


2. Ticks

Ticks are blood-sucking parasites. They can also transmit serious health issues to pets and humans alike, such as Rocky Mountain spotted fever, Lyme disease, Ehrlichiosis, Babesiosis, and tick paralysis. Dogs get ticks when roaming through grassy areas or in places where deer is present. There are several types of ticks that affect dogs. If you spot a tick on your pet’s body, be sure to remove it properly so the mouthpart of the parasite won’t end up still embedded in the dog’s skin. There is a specially designed tick removal tool that you can ask about from your veterinarian. You can also use petroleum jelly to numb the tick before using tweezers to pull if off. Once you have removed the tick successfully, place it in a container with alcohol and bring it to your veterinarian for identification.



There are now medications that contain active ingredients that can kill both fleas and ticks. These medications are available as oral, topical, or injectable preparations. There are also flea-and-tick collars. A flea and tick preventive program should be followed to ensure your dog’s optimum protection against fleas and ticks.




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