Parasites in Dogs That You Should Know

Fleas, Ticks, Worms and More

Parasites in Dogs That You Should Know
Common Canine Parasites -- An Illustration

Illustration: Hugo Lin. © The Spruce, 2018

At some point in their lives, many pets experience discomfort caused by parasites such as fleas, ticks, or roundworms. While fleas and ticks can sometimes be easy for dog parents to spot and identify, that is not always the case, and internal parasites can be present in your dog without you realizing it. These parasites can be extremely irritating to pets and can cause serious health problems or even carry disease. Modern medicines make treatment, control, and prevention of many parasites much easier than in the past.

Some parasites are also zoonotic, meaning a disease or parasite that can be transmitted from animal to people. Every dog parent needs to know about common parasites and how to prevent them from causing serious health problems for both four- and two-legged family members. 

What Are Parasites in Dogs?

 The center for disease control defines a parasite as “an organism that lives on or in a host organism and gets its food from or at the expense of its host.” 

There are two main categories of parasites in dogs that pet parents should be aware of: internal parasites and external parasites.

Internal parasites, such as hookworms, roundworms, and tapeworms live inside the body of an animal, can be transferred in various ways, and can affect a number of organs. External parasites, such as fleas and ticks, live on the body of the host and produce an infestation. 

Symptoms of Parasites in Dogs

Symptoms of parasites can vary depending on the type of parasite, where it lives and severity of infestation.  Most intestinal parasites do not show symptoms until the infestation has become severe. Parasites can cause symptoms ranging from mild discomfort and intermittent loose stool, to severe issues such as anemia, skin disease, secondary infections, difficulty breathing, and malnutrition which is why it’s so important to prevent infestations, and, if they do occur, to treat your pet quickly. 

Preventive care and regular fecal exams are helpful to catch the infestation in its early stages. A fecal examination allows your veterinarian to diagnose intestinal parasites by looking for microscopic eggs or spores in your pet’s stool.

External Parasite Symptoms

  • Excessive scratching
  • Excessive chewing
  • Red and inflamed skin
  • Hair loss
  • Crusting and discoloration of skin 
  • Dry coat
  • Scaly appearance to fur
  • Large amounts of black debris in ears 
  • Fleas or flea dirt
  • Restless behavior 

Internal Parasite Symptoms

  • Diarrhea, with or without blood or mucous
  • Vomiting
  • Weight loss
  • Loss of appetite 
  • Distended abdomen (pot-bellied appearance) 
  • Decreased activity
  • Scooting 
  • Worms or segments (tapeworms) visible in the feces
  • Coughing
  • Difficulty breathing

How Do Dogs Get Parasites?

There are many ways that dogs can contract parasites. Fleas are generally caught from other infected animals, however they can also jump through doors and windows and be brought into the house on a person's pant legs. Ticks are caught from traveling through bushes and long grass. Intestinal parasites are usually transmitted when an animal ingests the eggs or spores in contaminated soil, water, or food. Puppies can contract a parasite from their mothers, either in utero or from nursing. Tapeworms can be contracted by dogs when they eat an infected flea. Heartworm is contracted through the bite of an infected mosquito.

Diagnosis and Treatment of Parasites in Dogs 

If you suspect that your dog is suffering from an internal parasite, the first step will be to identify the parasite with the help of your veterinarian. There is no single medication that can treat and prevent all GI parasites and once your veterinarian identifies the parasite, they can find the most effective treatment for your dog. Fecal testing can detect GI parasites in most cases, but not always, which is why some veterinarians recommend deworming (administering medication to treat and control infections) even if the fecal test doesn’t confirm the existence of parasites. A blood test is needed to detect heartworm.

In severe cases of internal and external parasites, dehydration, anemia and secondary infections can occur and your veterinarian will treat as needed along with medication to kill the parasites.

  • 01 of 08


    Parasites in Dogs That You Should Know
    Detailed illustration of a flea

    Robert Hooke/Wikimedia Commons

    Fleas can make your pet's life miserable. Fleas progress through several distinct life stages in which the pests transform from eggs into larvae, then into pupae, and then finally into reproducing, blood-sucking adults.

    Fleas can lead to flea allergy dermatitis with itching and skin infections. Fleas are also carriers of tapeworm eggs and your dog can be infested by tapeworm after eating a flea. A large infestation with fleas can also lead to anemia. While dog and cat fleas don't prefer humans, flea bites in two legged family members are possible.

  • 02 of 08


    Parasites in Dogs That You Should Know
    Deer tick, Ixodes scapularis, on a fingernail

    Lauree Feldman/Getty Images

    Ticks can attach themselves to dogs as well as to humans. While you might wear protective clothing when in tick-prone areas, your dog is exposed. Early detection and removal of ticks is important as it takes some time for the tick to transmit tick-borne diseases to their hosts. Diseases spread by ticks to dogs include Lyme disease, Rocky Mountain spotted fever, anaplasmosis, babesiosis, bartonellosis, and ehrlichiosis. Some species of ticks can also cause tick paralysis which will cause a dog to become paralyzed, usually starting at their back end and ascending up towards their head. This can become fatal if the muscles that control breathing become paralyzed, but the paralysis will go away as long as the tick can be found and removed.

  • 03 of 08

    Ear Mites

    Parasites in Dogs That You Should Know
    Ear check

    Isa Foltin/Contributor/Getty Images

    Ear mites are microscopic mites that infect dog’s ears, where they breed and cause thick black debris and discomfort.  Ear mites are highly contagious, and animals become infested by direct contact with another infested animal.

    Your dog may show head shaking, scratching at the ears, and crusty or waxy discharge that looks like coffee grounds. Your veterinarian can diagnose ear mites with an examination and looking at a sample of ear debris under a microscope. Ear mite treatment can require one or more repeated treatments. Ear mites don't infect humans.

  • 04 of 08


    Parasites in Dogs That You Should Know
    Ancylostoma caninum, a type of hookworm, attached to the intestinal mucosa. Image #5205, CDC

    CDC's Public Health Image Librabry/Wikimedia Commons

    Hookworms are small, thin worms that are less than an inch long. These intestinal parasites are common in dogs. There are three species of hookworms that affect dogs. Some can also affect humans, migrating through the skin.

    Dogs pick up hookworms by ingesting the larvae they pick up from the environment, by ingesting other infected animals such as cockroaches, and in puppies, from the mom's milk. Symptoms include diarrhea, loss of appetite, anemia, weight loss, or failure to gain weight.

    A veterinarian can check for hookworm in the stool. Treatment includes deworming medications that must be used repeatedly to eliminate the larvae as they mature. Regular deworming will help prevent recurrence.

    Continue to 5 of 8 below.
  • 05 of 08


    Parasites in Dogs That You Should Know
    Whipworm egg

    Joel Mills/Wikimedia Commons

    Whipworms are intestinal parasites (Trichuris) that are relatively common in dogs and occasionally seen in cats. These small worms have a thin, whip-like front end and a thicker back end. They attach themselves to the walls of the large intestine, feeding on blood.

    Dogs pick up whipworm eggs transmitted through the stool in the environment. A light infection has no symptoms. A heavier infection can result in weight loss, diarrhea, or anemia. A veterinarian can detect the eggs under the microscope during a stool examination.

    Whipworms are resistant to many of the usual dewormer medications, so a different medication is usually used. Keeping the environment clean of feces is the best prevention as the worm eggs take weeks to become infectious.

  • 06 of 08


    Parasites in Dogs That You Should Know
    Toxocara canis adult nematode worms of dog.

    Alan R, Walker/Wikimedia Commons 

    Roundworms, including Toxocara Canis and Toxascara leonina, are intestinal parasites in dogs. They absorb nutrients from the food the dog eats, which results in less being available for the dog. Infection can occur after ingesting eggs shed in stool or from larvae transmitted during pregnancy or in the mother's milk.

    A dog may show vomiting, lethargy, weight loss, diarrhea, and a pot belly. A veterinarian can detect roundworms in the stool. Deworming medication can be used, with a number of treatments in order to clear the roundworms as they mature. A regular deworming protocol is needed to prevent reinfection.

    Roundworms can be transmitted to humans. They cause inflammation and can migrate to various tissues and organs.

  • 07 of 08


    Parasites in Dogs That You Should Know
    Extract from a dog gut during a surgery (found "by accident", nothing to do with the cause of the surgery). Taenia infecting dogs and cats, incidentally humans, benign. Its cycle goes through fleas. (Translated from original Fr.)


    Tapeworms are flat, ribbon-like parasites that live in the intestines. Happily, they rarely cause serious disease. Dipylidium caninum is the most common one for dogs, but there are other species. They are usually transmitted by ingesting fleas, but some species can be transmitted by eating raw meat.

    Tapeworms can cause irritation around the anus, due to shedding of the segments of the worm. A puppy may scoot around on the floor or lick the area. Infestation can result in poor nutrition for the dog or even an intestinal blockage in severe cases.

    A veterinarian can diagnose tapeworms by a stool exam and examination of the hair around the anus. Medication is needed to clear the infection, accompanied by good flea control and keeping the dog from eating dead prey.

  • 08 of 08


    Parasites in Dogs That You Should Know

     Bluering media/Getty Images

    Heartworm disease is caused by a large roundworm parasite that lives mainly in the blood vessels of the lung and in the heart. It is transmitted by mosquitoes. While heartworm is most prevalent in the Southern states, it has been seen in every state.

    Your veterinarian will usually test for heartworm during your dog's yearly check-up. A dog with heartworm infestation may show no symptoms at first, but as it progresses it can be fatal. Dogs can develop a cough (including coughing up blood), become exhausted from exercise, faint, and have severe weight loss.

    Once a dog is infested with heartworm, multiple injections of medication given over a course of several months are needed to kill the parasite. The dog will need complete rest during the treatment period in order to prevent dangerous complications from the dying worms.

    Fortunately, heartworm disease is easy to prevent. Any number of proven, safe preventions exist, which are used to prevent heartworms and several intestinal parasites when administered on a monthly basis. 

    If a mosquito bites an infected dog, the parasite can then produce larvae inside the mosquito, and although it is rare, these can be transmitted to humans. In humans, the parasite most often causes lung lesions. Preventing the disease in your pets can help protect you, as well.

How to Prevent Parasites in Dogs

  • Annual veterinary visits: Preventive care and regular fecal exams are helpful to catch the infestation in its early stages.
  • Keep your pet on flea/tick/ and heartworm prevention year-round: Ask your veterinarian which parasites are a problem in your area.  There are parts of the country where certain internal parasites are less of a concern and others where year-round prevention is imperative. Your veterinarian will be able to tell you what to watch for according to your geographic location, how these parasites can be transmitted to your pet and prescribe the most appropriate preventive products.
  • Clean up after your dog: Pick up your dog’s feces promptly to reduce the risk of environmental contamination. Protect hands while cleaning up the feces and wash hands afterwards.
If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. ParasitesCenters for Disease Control and Prevention

  2. Fleas Of Dogs - Dog Owners - Veterinary ManualVeterinary Manual, 2020

  3. Tick Paralysis In Dogs - Dog Owners - Veterinary ManualVeterinary Manual, 2020

  4. Mite Infestation (Mange, Acariasis, Scabies) In Dogs - Dog Owners - Veterinary ManualVeterinary Manual, 2020

  5. Gastrointestinal Parasites Of Dogs - Dog Owners - Veterinary ManualVeterinary Manual, 2020

  6. Overview Of Heartworm Disease - Circulatory System - Veterinary ManualVeterinary Manual, 2020