Dogs Dog Health & Wellness Dog Parasites

Parasites in Dogs 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

Parasites in dogs are common and may be found internally or externally. These parasites can be extremely irritating to dogs and can cause serious health problems that may affect other pets or even humans. Fortunately, modern medicine makes treatment, control, and prevention of many parasites much easier than in the past. Learn all about the most common parasites in dogs and how to prevent them from causing serious health problems for pets and people. 

What Are Parasites in Dogs?

The Centers 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.” Some parasites are also zoonotic, meaning they can be transmitted from animals to people.

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

  • Internal parasites, such as intestinal worms, 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 in dogs vary depending on the type of parasite, where it lives, and the severity of infestation. Parasites can cause symptoms ranging from mild discomfort and intermittent loose stool to severe issues such as anemia, skin disease, secondary infections, and malnutrition. That's why it’s so important to prevent infestations, and, if they do occur, to treat your pet quickly. 

External Parasite Symptoms

Some external parasites are easier to spot than others. Most dogs will experience skin issues that make it clear there's a problem.

  • 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

Most intestinal parasites won't cause symptoms until the infestation has become severe. Preventive care and regular fecal exams help detect parasites in their early stages. A fecal examination allows your veterinarian to diagnose some intestinal parasites by looking for microscopic eggs or spores in your pet’s stool. Watch for the following signs:

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 pants or shoes.
  • Ticks are acquired 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 get a parasite from their mothers, either in utero or from nursing.
  • Tapeworms can occur when a dog eats an infected flea.
  • Heartworms are transmitted 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 or external parasite, the first step will be to identify the parasite with the help of your veterinarian.

  • External parasites may be visible to the naked eye, but some are microscopic. Your vet may need to examine a sample under a microscope to make a diagnosis.
  • A blood test is needed to detect heartworms. Annual heartworm testing is recommended for all dogs.
  • Fecal testing can detect intestinal parasites in most cases, but not always. Your vet may send a stool sample to a laboratory for further testing. Some veterinarians recommend deworming (administering medication to treat and control infections) even if the fecal test doesn’t confirm the existence of parasites. 

There is no single medication that can treat or prevent all parasites. Once your veterinarian identifies the parasite, they'll recommend the most effective treatment for your dog. In severe cases of internal or external parasites, dogs can also develop dehydration, anemia, breathing issues, or secondary infections. Your veterinarian will recommend treatment for the parasite as well as any secondary issues.

10 Common Parasites in Dogs

  • 01 of 10

    Fleas

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

    Robert Hooke/Wikimedia Commons

    Fleas can make your pet's life miserable because their saliva can induce an allergic skin reaction in many dogs. 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.

    A flea infestation can lead to flea allergy dermatitis, which can cause excessive itching and skin infections. Fleas often carry tapeworm larvae, so your dog can get tapeworms 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.

    The best way to treat dogs with fleas is to use a veterinarian-approved flea control product. These can be given orally or applied topically. It's also important to treat the home environment where eggs, larvae, and pupae may live.

  • 02 of 10

    Ticks

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

    Lauree Feldman/Getty Images

    Ticks can attach themselves to the skin of 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:

    Some species of ticks can also cause tick paralysis, which usually starts at the back end and ascends towards the head. This can become fatal if the muscles that control breathing become paralyzed, but the symptoms will go away as long as the tick can be found and removed.

    The best way to treat and prevent ticks is to use a tick control product recommended by your veterinarian. It's also important to check your dog for ticks regularly, especially after spending time in nature where ticks are found.

  • 03 of 10

    Mange Mites

    small dog with generalized demodectic mange
    Todorean Gabriel / Getty Images

    Mange is a condition where tiny mites live in the skin or hair follicles and cause disease.

    Demodectic mange is the most common type of mange seen in dogs. These mites can live in hair follicles in small numbers without causing problems, but puppies and immune-compromised dogs may not be able to fight them off. Demodicosis causes itching and hair loss. Treatment options include topical applications, medicated baths, and oral drugs.

    Sarcoptic mange, often called scabies, is a contagious type of mange that causes severe itching, redness, scabs, and hair loss. Treatment involves multiple topical and oral medications as well as baths.

    Cheyletiella mites are often called "walking dandruff" because you may see flakes of hair move on the dog, though the mites themselves are microscopic. These contagious mites cause dry, itchy skin and dandruff. Treatment typically consists of topical antiparasitic medications and baths.

  • 04 of 10

    Hookworms

    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 that live in the intestines and suck the host's blood. Three species of hookworms affect dogs. Some can also affect humans by migrating through the skin and causing infection.

    Dogs get hookworms by ingesting larvae in the environment or eating infected animals such as cockroaches. They can also be transmitted to puppies from the mother's milk. Symptoms include diarrhea, loss of appetite, anemia, weight loss, or failure to gain weight.

    A veterinarian can check for hookworm eggs 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 10 below
  • 05 of 10

    Whipworms

    Parasites in Dogs That You Should Know
    Whipworm egg

    Joel Mills/Wikimedia Commons

    Whipworms are small worms with thin, whip-like front ends and thicker back ends. 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 mild infection may have no symptoms, but severe infections can result in weight loss, diarrhea, or anemia. A veterinarian can typically 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 often used. Keeping the environment clean of feces is the best prevention as the worm eggs take weeks to become infectious.

  • 06 of 10

    Roundworms

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

    Alan R, Walker/Wikimedia Commons 

    Roundworms are long worms that live in the intestines and 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 the stool of other animals. Puppies get roundworms from larvae transmitted during pregnancy or in the mother's milk.

    A dog with roundworms may show vomiting, lethargy, weight loss, diarrhea, and a pot belly. A veterinarian can detect roundworm eggs in the stool by using a microscope. Several doses of deworming medication are necessary 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 10

    Tapeworms

    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.)

    Fourrure/Flickr.com 

    Tapeworms are flat, ribbon-like parasites that live in the intestines. Happily, they rarely cause serious disease. They are usually transmitted by ingesting fleas, but some species can be contracted by eating raw meat.

    Tapeworms reproduce by shedding segments in the stool, which can irritate the anus. Dogs may scoot around on the floor or lick their rear ends. Long-term infestation can result in poor nutrition for the dog or, in severe cases, an intestinal blockage.

    A veterinarian can diagnose tapeworms by examining the area around the anus. Their eggs don't usually show up on microscopic analysis. Medication is needed to clear the infection, accompanied by good flea control and keeping the dog from eating dead prey.

  • 08 of 10

    Giardia

    giardia-Eraxion-istock.jpg
    Illustration of Giardia organism © Eraxion/iStockPhoto.com

    Giardia are single-cell organisms (protozoa) that infect the small intestine. Dogs can contract giardia by drinking from streams, puddles, and other contaminated water sources. It can also be acquired through direct contact with the stool of other infected animals.

    Giardiasis can cause diarrhea, vomiting, and weight loss, but some dogs are asymptomatic at first. Giardia can't usually be detected on a standard fecal test, so your veterinarian may send out a stool sample to a laboratory for specific testing.

    Treatment for giardia typically involves more than one medication. Many vets will prescribe a specific dewormer along with the antibiotic metronidazole to kill giardia.

    Continue to 9 of 10 below
  • 09 of 10

    Heartworms

    Parasites in Dogs That You Should Know

     Bluering media/Getty Images

    Heartworm disease is caused by large worms that live mainly in the heart and the blood vessels of the lungs. Mosquitoes can carry and transmit heartworm larvae through their bites. While heartworm disease is most prevalent in the southern United States, it has been seen in every state.

    Your veterinarian typically tests for heartworms during your dog's yearly check-up. A dog with heartworm disease 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.

    Heartworm treatment occurs over several months and involves multiple medications, including to kill the adult heartworms. The dog will need complete rest during the treatment period to prevent dangerous complications from the dying worms.

    Fortunately, heartworm disease is easy to prevent with proven, safe heartworm preventative. These are usually administered monthly to kill heartworm larvae before they can mature into adults and cause disease.

    Although rare, heartworms can be transmitted to humans via mosquito bites. In humans, the parasite most often causes lung lesions. Preventing the disease in your pets can help protect you as well.

  • 10 of 10

    Ear Mites

    Parasites in Dogs That You Should Know
    Ear check

    Isa Foltin/Contributor/Getty Images

    Ear mites are microscopic mites that can live in 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 by looking at a sample of ear debris under a microscope. Ear mite treatment can require one or more repeated treatments. Fortunately, ear mites don't occur in humans.

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 how these parasites can be transmitted to your pet and what to watch for according to your geographic location.
  • 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 afterward.
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.
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  1. About 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. Gastrointestinal Parasites Of Dogs - Dog Owners - Veterinary ManualVeterinary Manual, 2020

  5. Giardiasis in dogs and cats: update on epidemiology and public health significanceTrends in Parasitology.

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

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