Parasites are among the most common reasons for which dogs receive veterinary treatment. However, they can harm the dog directly, transmit various infectious canine diseases, and cause allergic reactions. Parasites of the dog are divided into endo- and ectoparasites.

Endoparasites vs Ectoparasites
Endoparasites vs Ectoparasites

What is the Concept of Parasitism?

Parasitism is the relationship between two different types of living organisms. In this process, the parasite exploits its host for its unilateral benefit. The relationship harms the host but, in most cases, is not killed by it.

An animal parasite lives in or on the host for this purpose and feeds on components of the host, such as skin, hair or intestinal contents. Plant parasites grow on other plants and tap into their nutrients or water supply.

Examples of parasitism:

  • Ticks (parasite) and foxes (host).
  • Tapeworms (parasite) and dogs (host)
  • Mistletoe (parasite) and birch (host)
  • Malaria pathogen (parasite) and humans (host)

Parasitism is one of the biotic environmental factors where one living thing affects another.

Why are Parasites Problematic in Dogs?

Many dog parasites are also infectious for humans, so the dog should not carry parasites in itself if possible. Often healthy adult dogs show no symptoms even though they are infected. Unfortunately, this often leads to the fact that they must be regularly treated for parasites. Especially for young, old and immunocompromised dogs, they can become dangerous.

There is a high density of dogs in many places, so that the parasites can spread easily. This is especially true for boarding kennels, animal shelters or larger groups of dogs in a holding, but also dog parks or areas with a high percentage of dog-owning households. In this way, the little pests reliably find new hosts to multiply. In addition, foxes, by and large, carry the same parasites. They also spread them in the city, where the fox is often native as a cultural successor.

Increasing travel with dogs and importation of animals allows parasites previously considered “exotic,” such as Leishmania or heartworms, to become visible in veterinary practices. In addition, with increasing warmth, their intermediate hosts, such as mosquitoes and ticks, are also becoming native to our latitudes so that these parasites may persist here in the foreseeable future. And: Due to the milder winters, fewer and fewer parasites take their typical “winter break.” Therefore, you should protect your dog from parasites all year round.

dog scratching itself because of Parasites

Endoparasites and Ectoparasites in Dogs

A distinction is made between parasites in terms of their ability to invade the body of the host, resulting in the following two classes:

  • Ectoparasites or external parasites live on other organisms. They penetrate their host organism only with the organs that serve to supply them and feed on skin substances or ingest blood or tissue fluid.

    Examples of ectoparasites include bloodsucking arthropods such as mosquitoes, lice, and ticks. Ectoparasites are also often disease vectors of diseases such as malaria or Lyme disease.
  • Endoparasites (endo- or internal parasites) live inside their host. They colonize cavities, epithelia, the blood or even the tissue of various organs.

    The diseases they cause are called endoparasites. Furthermore, endoparasites can be divided into two groups according to their characteristics in attacking cells.

    Extracellular endoparasites live outside cells (e.g., Giardia on intestinal epithelium), whereas intracellular endoparasites live primarily inside host cells (e.g., malaria pathogens). Many endoparasites reside both extracellularly and intracellularly during their life cycle.

Endoparasites in Dogs


Roundworms, hookworms, tapeworms and whipworms parasitize in dogs’ small or large intestines. For adult animals, they are usually unproblematic. However, puppies, particularly, suffer from diarrhea and emaciation when they are more heavily infested.

In addition to oral ingestion of the eggs or larvae, roundworms, for example, can be transmitted from the bitch to the puppies in the uterus or with the mother’s milk. The latter also applies to hookworms. The dog can additionally become infected with them through the skin, which some species can actively pierce.

Attention: a tapeworm in dogs can also be a small fox tapeworm. Infection with it is life-threatening for humans, which is why good prevention is so important for our pets! Unfortunately, due to fox populations living close to humans, dogs and also cats can get infected with this parasite.

Worms are not just intestinal parasites in dogs. However: canine lungworms live and multiply in the lungs. Their larvae are coughed up, swallowed and excreted in the feces. They cause coughing and fever and are especially dangerous to young animals.

Heartworms parasitize in the heart and pulmonary arteries. They cause respiratory problems, coughing, and reduced exercise tolerance. Mosquitoes transmit them. Heartworm in dogs has been a travel disease, but its intermediate host is becoming more comfortable farther north.

Portrait of a dog with icons of parazites around its head.


Giardia in dogs, like cryptosporidia and other protozoa (single-celled organisms), live in the intestine and cause varying degrees of diarrhea that can be short or long-lasting. Puppies are particularly affected by this; the infections often pass without symptoms in older dogs. The excreted oocysts (reproductive stages, similar to eggs) are ingested orally, e.g., via feces or the contaminated environment. As a result, Giardia Treatment is often lengthy, especially in larger groups of dogs.

Leishmania is also a single-celled parasite that attacks the dog’s immune system. They are mainly transmitted by specific mosquitoes and have been mainly distributed in Southern and Central Europe. However, their range is shifting further and further north. Leishmaniasis manifests itself in various problems of varying severity: Skin lesions and lameness are the most common. Reduced resilience, weight loss and movement disorders are also common. The disease is chronic and permanent. Extensive treatment is necessary.

Babesia transmitted by ticks infects the red blood cells (erythrocytes). Babesia was also previously found in Mediterranean latitudes, but now they are also native to the US. It mainly occurs in parts of the Northeast and the Upper Midwest and usually peaks during the warm summer months.

The clinical course varies depending on the Babesia species with which the dogs are infected and the dog’s condition beforehand. Fever and anemia are often seen, and vomiting and yellowing of the mucous membranes are also possible. Less commonly, respiratory and digestive tract disorders occur. Babesiosis can be life-threatening!

Anaplasmosis is transmitted by ticks. The pathogen attacks cells of the immune system and causes fever. It is detected with a special laboratory test (PCR, polymerase chain reaction) since the detection of antibodies does not reliably indicate an infection.

There are also other infections with protozoa in dogs, such as Neospora and Toxoplasma.

Giardia duodenalis
Giardia duodenalis

Ectoparasites in Dogs

Ticks suck blood but are mainly crucial as carriers of, e.g., Babesia, Anaplasma and Borrelia (tick-borne diseases) and should, therefore, always be removed quickly. They stay in grass, bushes and undergrowth.

Mites cause severe itching, dull coat and dandruff. Some are very contagious, from dog to dog or via blankets and brushes. The clinical picture sometimes resembles that of atopic dermatitis.

A particular disease is demodicosis: Demodex mites live in the hair follicles of healthy dogs. How the disease develops has yet to be conclusively clarified. However, one thing is sure: in immunodeficiency, there is a massive multiplication of mites. As a result, hair loss, pustules and redness occur, which can later become infected with bacteria or fungi and begin to itch.

Ear mites in dogs cause severe itching and ear infection. So a dog with ear mites will scratch his ears, rub his head over the floor and shake. Autumn grass mite larvae usually infest dogs from August through October, often where fallen fruit can be found. They are visible to the naked eye as red spots, often in between toe or ear folds. Severe itching follows. The occurrence is unproblematic to treat.

Fleas are widespread, not host-specific and serve as a vector, e.g., tapeworms. They suck blood and can cause flea saliva allergy. A flea infestation can be recognized by itching, but skin lesions also occur. These first appear due to intense scratching, particularly in the case of allergy. Fleas are visible with the naked eye, in the fur and sleeping places, etc. The flea excrement shows up in dark crumbs. Dissolved in water, it turns red, as a distinction from dirt, which remains gray.

Relatively rarely, meanwhile, one encounters lice in dogs. They cause itching and are transmitted from dog to dog.

Dog tick bloodsucking,Closeup of hands using silver pliers to remove dog tick ,dog health care concept.Focus dog tick.
Dog with bloodsucking tick

Diagnosis of Parasites in Dogs

Relatively typical symptoms can identify many parasites. However, infection in adult dogs can often proceed without signs. In this case, further examinations are helpful:

  • Fecal examination: Provides information about parasites in the gastrointestinal tract. Detection of eggs or metabolites of the parasites, depending on the method.
  • Skin examination: A thorough examination of the skin and coat with a magnifying glass and fine comb is necessary if ectoparasites are suspected. A scraping (removal of skin cells with a scalpel) may also be necessary. Live mites and fleas can be seen under the magnifying glass; flea feces, for example, can be found with the flea comb.
  • Adhesive film preparations: a piece of adhesive film is dabbed on a skin area, and the adhering material is examined under the microscope. This applies to ectoparasites and eggs of, e.g., tapeworms adhering to the fur.
  • Blood test: A blood test is helpful if there is a corresponding suspicion for the detection of antibodies against Leishmania and Babesia or for the detection of typical changes in the blood in case of parasite infestation. 
  • Further examinations, such as biopsies or smears, may be necessary. Puncture of a joint or bone marrow in case of leishmaniasis. 

What Symptoms Indicate Ectoparasites in Dogs?

Generally typical for an infestation with ectoparasites are:

  • Restlessness, irritability
  • Itching
  • Licking and nibbling the fur
  • Scratches and crusts on the skin
  • Dandruff
  • Allergic skin reactions
  • Hair loss

Secondary symptoms such as bacterial skin infections and anemia (are possible if not treated.

What Symptoms do Endoparasites Cause in Dogs?

Endoparasites living in the intestine primarily cause digestive symptoms. These include:

  • Diarrhea
  • Constipation
  • Vomiting
  • Loss of appetite
  • Weight loss
  • Bloating, flatulence
  • Deficiency symptoms
  • Lack of weight gain in puppies

Dogs with heartworms or lungworms show, among other symptoms:

  • Cough
  • Shortness of breath
  • Difficulty breathing
  • Poor circulation
Dog Sick with Parasites

Treatment of Dogs with Parasites

If your dog has caught sub-tenants, there are usually well effective means to get rid of them again.

Individual diseases, such as leishmaniasis, can be very difficult or impossible to treat. It is also essential to treat the environment: If a flea infestation has been detected, the associated home must be thoroughly cleaned, and treatment will extend for six months as the eggs, larvae, etc., are incredibly resistant.

All other pets must also be checked or co-treated. Otherwise, the parasites will return quickly.

Consult With Your Veterinarian!

Only after an accurate diagnosis by the veterinarian is a targeted treatment possible. In the meantime, various agents against parasites in dogs are on the market, used either prophylactically or therapeutically.

These include:

  • Collars
  • Spot-ons
  • Tablets
  • Chewable tablets
  • Suspensions
  • Injection solutions

With ticks, manual, early removal plays an essential role: disease transmission does not occur until 16 to 24 hours after the bite. Therefore, an effective prophylactic method is to check the dog twice daily for ticks and remove them immediately.

Dog treated at vet against Parasites

How can you Prevent Parasites in Dogs?

A regular preventive treatment of the dog against parasites is worthwhile because it is much less costly and unpleasant than the therapy of infections. For this purpose, there are “spot-on” preparations to drop on the skin, pastes, tablets or collars, which are easy to use for you as the owner.

A distinction can be made between repellents and regular preventive treatment. Repellents like collars, and spot-ons keep away fleas and ticks, which do not like the permanently delivered substance on the skin.

In contrast, a regularly administered gastrointestinal worm tablet will kill existing worms; however, it cannot prevent new infections. Pregnant bitches should be especially well dewormed to prevent the puppies from becoming infected with hookworms or roundworms.

In the case of intermediate hosts, eliminating the host will also help:

Ticks should be removed correctly as soon as possible after they are discovered: to do this, grasp the tick as close to the skin as possible with tick forceps and gently twist until it comes off. Alternatively, hook the tick underneath and turn it in as well. Do not pull firmly. Then the front part of the tick remains in the skin and can cause inflammation.

On vacation in the south, take protection against mosquitoes – Stay indoors at dusk and dark, apply insecticide sprays, and attach nets.

Fleas transmit dog tapeworms – so the dog should also be protected from fleas.
With larger groups of dogs or breeding, the importance of prophylaxis and hygiene increases again, as parasites can spread even more here.

There are now vaccinations against Babesia and Leishmania, but they still need to be approved everywhere.

Talk to your vet about the best method for your dog and how often it should be applied. For you as an owner, the following applies: You should wash your hands after every contact with the dog and especially before eating. Also, teach this rule to all children who cuddle with the dog.

Different Dog Parasites, lice, ticks, fleas

Summary Parasitism

  • By parasitism, you mean the relationship between two different species from which the parasite derives a benefit and which harms the host.
  • The parasite feeds on the host and thus is also dependent on it.
  • In addition, parasites have developed particular organs to hold onto the host well.
  • Plant and animal parasites, viruses, bacteria, fungi and protozoa exist.
  • Animal parasites can be further divided into endoparasites and ectoparasites. Endoparasites live in their host’s body, and ectoparasites are found on the skin or in their host’s hair.
  • Plant parasites are divided into holoparasites and hemiparasites. Holoparasites live entirely at the expense of their host. Hemiparasites perform photosynthesis in addition to parasitism.

Parasites in Dogs: Conclusion

There are a large number of parasites in dogs. Protecting your four-legged friend 100% from parasites is certainly not possible.

Nowadays, however, modern diagnosis and treatment options are available, so to avoid damage, your dog should be checked regularly and receive appropriate medical treatment. There are also specific protection options available against different dog parasites.

By treating your dog correctly, you are also protecting yourself. Talk to your veterinarian about the appropriate therapy and the safest protection options!


Dr. Orika Mosquera

Hello, I am Dr. Orika Mosquera Lopez graduated from the free university of colombia sectional Barranquilla as a doctor and surgeon. I work as a General Practitioner with Experience in the Emergency Department, Hospitalization and External Consultation. I love pets, i have 2 cats, Bagheera and Nhala and one Yorkshire Terrier called Princess. I care a lot about the well-being of my animals


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