Canine parasitic diseases – veterinarian Małgorzata Miłosz

Parasites are organisms that live inside or on their host’s surface and benefit from it. Most often they feed on the nutrients of the host, thus causing losses to his/her health. For example, fleas that parasitize a dog in large numbers can contribute to its anemia, in addition to persistent itching and skin problems. Contrary to appearances, the goal of the parasite is not to quickly destroy the host’s organism. The parasite wants to enjoy the benefits of the organism it has attacked for as long as possible. What kind of parasites can we encounter if one of our household members is a dog, how to recognize them and how to deal with them? These and other questions are answered by the veterinarian Małgorzata Miłosz.

Parasites in a dog – symptoms and types

The main division includes external parasites in dogs – such as fleas, ticks, lice, demodicosis or scabies, and internal parasites in dogs, such as roundworms, tapeworms, protozoa, whipworms or, for example, heartworms. Of course, there are many more types of parasites in a dog. However, it is worth discussing those with which we can meet most often in the case of pets.

External parasites in dogs


Probably every dog ​​owner has met them, because they are very widespread in the environment and large enough that you can observe parasites on the dog’s skin with the naked eye. Fleas are hematophages. This means that they feed on the blood of their prey, and their presence in large amounts can cause anemia in the dog. These little jumpers cause itching by locally irritating the skin and secreting saliva which is so strongly allergenic that it is likely that an animal that is not irritating will not be allergic to any other compounds. Additionally, in the case of fleas, we are dealing with secondary inflammation of the skin. A wormed dog that itches, scratches, and bites, causing skin irritation and often even bleeding wounds where bacteria multiply, which can lead to secondary bacterial dermatitis complications.

If a dog has fleas, it is unfortunately very likely that it also has tapeworm, the larvae of which are transmitted through them. A dog that licks its own skin and coat due to itching and bites itself characteristically eats fleas and thus introduces another parasite into the body.

We can tell that our dog has fleas by observing the hair, in which we notice small black worms on the dog. The tiny black dots on a dog’s skin can also be flea feces in the form of lumps of digested blood. To distinguish flea feces from soil, sand, or other contaminants, simply rub the powder on a damp paper towel. Unlike sand, flea feces will smear into rusty spots.

APZS, or flea allergy dermatitis, can be easily identified by the characteristic alopecia in the lower torso and lumbar region. APZS is accompanied by persistent itching, pustules and scaly, darker (due to inflammation) skin. It is a characteristic “picture”, proving in 99% that the dog has been dropped by fleas.

Lice and biting lice

Parasites in a dog appear as small, white grains stuck to the fur, making the white worms in a dog’s fur easily mistaken for dandruff. They feed on blood and epidermis and damage the hair structure. These white worms on a dog’s skin are even smaller than fleas, making them difficult to identify with the naked eye. After using the preparation for fighting fleas, lice, and biting lice, remember to thoroughly brush your pet, which will remove only the worms in the dog’s coat, but also the eggs of parasites, which remain attached to it even after the treatment.


Most of us, if not at home, have seen a tick on our dog. It is worth knowing that you do not have to go on a trip to the forest with your pet to “catch” this parasite. Often a simple short walk to the lawn in front of the block is enough. After drinking blood, the tick acquires the characteristic appearance of a puffy ball, even up to the size of a grape. Despite its characteristic appearance, it sometimes happens that the dog’s parasites are not recognized by the owner. Therefore, it is best to take your dog to the vet in case of any doubts, which will remove the parasite with a special device.

Parasites on the dog’s skin suck blood and tissue fluid from their host, so to prevent them, special preparations in the form of tablets and drops are most often used, which spread mainly in the dog’s tissue fluid. The tick, penetrating the skin, secretes a local anesthetic. Over time, an inflammation in the form of a reddened lump develops around the unremoved tick. It often happens that the owner is unable to pull out the tick, tearing it off and leaving the mouth of the parasite in the dog’s body. In such a situation, you should go with the pet to the vet, who will remove the torn part of it. Of course, it is much safer to pull out the tick completely at once. Then the inflammatory reaction will decrease. However, it should be remembered that at the site of the bite, there will always be a pea-sized inflammation, which may remain on the skin for up to 2 or 3 weeks and does not always indicate that the tick has not been fully removed.

Ticks carry protozoa and bacteria that cause serious diseases. However, Lyme disease is not as common in dogs as it is in humans. The most common disease in dogs caused by protozoa is babesiosis. The intensity of tick-borne diseases in dogs is regionally determined. As it was found based on research, babesiosis is particularly common in the Warmian-Masurian region. A characteristic feature of the protozoa babesiosis is that it appears in the blood of the so-called throws, i.e., in several morphologies taken at intervals of several hours, may alternately appear and disappear. This disease, due to the less obvious symptoms of worming in a dog, causes serious diagnostic problems. Of course, there are additional factors that could suggest that your dog has babesiosis. If he or she “caught” a tick some time ago, has a fever, is depressed, has a very low level of red blood cells, low hematocrit and hemoglobin, low levels of platelets and the beginning of jaundice, we can assume to a large extent that the dog suffers from babesiosis. This protozoan is an aggressive parasite that aims to destroy red blood cells and multiply in huge numbers, destroying the organism of its host.


Demodex mites are found not only as parasites in dogs but also in humans – most often in the hair follicles of the eyelashes. They cause folliculitis and secondary bacterial and fungal infections, mainly when the parasites are diagnosed too late in a dog. Symptoms are most often local, taking the form of dark alopecia, initially without pruritus symptoms, e.g., the so-called scissors glasses, i.e., alopecia around the eyes or slight hair loss the size of a penny on the limbs or on the back. Demodicosis in dogs is a disease whose local form affects especially puppies, due to their fully undeveloped immunity. In the case of adult pets, demodicosis in a dog may suggest the presence of another systemic disease that lowered the animal’s immunity, which allowed Demodex to multiply in his/her body. Some breeds, such as the French bulldog, are particularly predisposed to demodicosis.


We will not see scabies with the naked eye. The presence of ear mites is evidenced by ear discharge that resembles coffee poured into the ear, and by persistent bilateral itching. Scabies is very easily transferred both to the next animal and within one host. The dog can also be attacked by crawfish mites.

The diagnosis of scabies is not the easiest one, because the main symptom of itching is also associated with many other diseases, such as allergies. However, with allergies, the dog scratches himself/herself first, followed by skin lesions. In scabies, the itching and skin lesions are joined together. The most common skin lesions are the ears, elbows, and heel joints.

A useful test in the diagnosis of scabies is the so-called button test that can also be done at home. It is enough not so much to press, but to rub the dog’s ear. If the dog’s parasites are present, we will release the itch reflex and the characteristic scratching motion of the lower limb.

Internal parasites in dogs

Ascarids, whipworms and hookworms

Nematodes, i.e., internal parasites such as the popular dog roundworm, whipworm, and hookworm, are also very common. A dog’s roundworm can develop through infection by ingestion of eggs excreted in the feces by a previous host, through the placenta, or through feeding – from mother to pup.

Internal parasites in dogs can survive in a dog’s body for several generations. From the intestine, the larvae first break through the liver, then pass through the lungs to the bronchi, go up the throat, the dog clears its throat, swallows the developmental stages, they go to the digestive tract and multiply there. Therefore, a cough is characteristic of a dog’s worming infection.

Symptoms of endoparasite infection in a dog include symptoms typical of the gastrointestinal tract – vomiting, diarrhea, constipation. With extremely large worms, it happens that a cluster of parasites clogs the intestine, leading to its obstruction. Other symptoms include the cough, as well as emaciation, lack of appetite or abnormally high appetite, and the general poor condition of the wormed dog’s body.

Capilaria plica

Another, slightly less common nematode in dogs is capilaria plica, a bladder parasite that travels through the kidneys and ureters. Symptoms of infection with this parasite include cystitis and haematuria. Dogs contract Capilariosis most often by eating earthworms. Therefore, special attention should be paid to it and the dog should not be treated with this type of “dessert”, because capilaria plica is difficult to diagnose and capilariosis is difficult to treat.


When talking about nematodes, it is impossible to forget about the popular tapeworm that occurs in various types. The psi tapeworm, transmitted, inter alia, by fleas, it is very characteristic to recognize, since it takes the form similar to rice or fresh cucumber seeds, coming out of the dog’s anus.

Giardia intestinalis

The internal parasites of dogs also include giardia intestinalis, which is invisible to the naked eye. The most characteristic of gardiosis is periodic, intermittent-recurrent diarrhea. A wormed dog may alternate between loose and constant stools in the proportion of time, e.g., 3 days to two weeks. Often in this case, blood and mucus are visible in the stool. Giardia intestinalis is a parasite that is very widespread in the environment and is very difficult to get rid of. Like another protozoan – isospores.


In Poland, dirofilaria immitis and dirofilaria repens are also more and more common in dogs. The first of these nematodes attacks the lungs and heart, obstructing them and causing obstruction of the arteries, and then very often death. The second of these nematodes breaks through the skin, forming nodules on it, in which it parasitizes.

The effects of parasites on a dog vary widely. From mechanical irritation of the skin and digestive tract to its obstruction. As a result of their presence, there is also bleeding from the digestive system, anemia, intestinal damage, digestive disorders, and the absorption of all nutrients, including essential nutrients for the dog’s health, such as iron, the deficiency of which is manifested by pale skin, mucous membranes, brittleness of hair and claws, or silicon. Parasites and worms in the dog also lead to a vitamin deficiency in the body of the quadruped, mainly vitamin B12 (especially in the case of the broad tapeworm), which leads to megaloblastic anemia and vitamin C, consumed mainly by nematodes. Vitamin C deficiency causes a significant decrease in immunity, gingivitis, poor condition of the hair and skin. Parasites also poison the body, secreting all kinds of toxic substances that trigger allergies.

Parasites in dogs – risk to humans

An exemplary flea stays on its host only for the time allocated to mealtimes, i.e., about an hour a day. The rest of the time is spent outside of the host, such as on the couch, in the carpet or on the floor, looking for a dark place where it can multiply. For this reason, it can also attack people, most often their feet, as apart from the host, they mainly move on the floor.

It often happens that the owners use anti-flea preparations on their dog but forget to disinfect the entire environment. In such a situation, the dog’s parasites may leave the host, but they will stay in the apartment and look for another host, not disdaining the human as well. So, if we want to be sure that we have got rid of the unwanted tenant, it is necessary to decontaminate not only the dog, but also the entire apartment

Apart from fleas, we can also be attacked by scabies. His most frequent object of interest, as in the case of dogs, are weakened people with reduced immunity, most often children and the elderly

We are also threatened by roundworm. The dog, or the final host, excretes the immature roundworm eggs along with the feces into the environment. The eggs stay in the environment from several days to several weeks and during this time they mature, becoming invasive. The next host can be the next dog that has eaten the eggs from the ground, or a human, for example, after eating the flesh of a rabbit or other animal that was a carrier of roundworm. However, Demodex is non-contagious for humans. Dog demodicosis is associated with decreased immunity and cannot be infected by other dogs, cats or even humans.

What about tapeworm? The dog expels uterine members through the anus, which contain invasive eggs, which when released into the external environment, pose a threat to humans. They can enter the human body either directly or through an infected intermediate host, for example by eating its flesh. Symptoms of tapeworm infection include gastrointestinal symptoms – vomiting, diarrhea, as well as apathy, weight loss and lack of appetite. As with dogs, also in humans, the tapeworm members come out through the anus in the stool or through the mouth in the vomit. The same thing happens with your dog’s roundworm, but they come out completely. The tapeworm is removed in segments that resemble rice grains.

Dog tapeworm can also be infected by swallowing a flea, which, contrary to appearances, is not uncommon in the case of dog owners. For the worms in the dog’s coat to spread, it is enough to play together, tug or hug the pet. A very dangerous tapeworm for humans is the echinococcal tapeworm, which lives mainly in the liver, forming blisters that spread through the blood throughout the body like a tumor.

So, if you have a dog, clean up after him or her!

The eggs of nematodes that are in the external environment do not become invasive until sometime later, and some of them, such as whipworms, are extremely resistant to external factors and can survive in the environment for up to several years. Hence, sandboxes in which our children play are often mentioned as a source of danger. White porridge in the dog’s poop, invisible to the naked eye, may turn out to be parasite eggs, which, lying in the sand, take on an invasive form over time. Thus, they obviously pose a threat especially to the youngest, who tend to put everything that is within their reach into their mouths.

The invasive form of internal parasite eggs is called toxocara. In humans, the symptoms of infection are much more serious, organ-related, often e.g., ocular. Diagnostics is also difficult here, e.g., due to the frequent lack of digestive symptoms, i.e., low efficiency of the stool test.

Diagnostics, treatment, and prevention

Diagnostics of external parasites in dogs is based primarily on the so-called “Naked eye”. You can also use scrapings or trichograms, i.e., hair collection performed by a doctor at the clinic. Treatment is possible thanks to special preparations in the form of drops, shampoos, collars, or tablets. There are many means to fight external parasites on the market. They have a different duration of action, from four weeks in the case of drops to even several months in the case of collars.

When taking preventive measures and treatment, we consider both the wormed dog and his or her surroundings. They work well here, among others aerosol preparations that can be successfully used in the home, spraying them on sofas, carpets and all other places exposed to the presence of parasites that have found a hiding place in them. In case of definitely bigger problems, it is worth using disinsection.

When it comes to internal parasites, dogs – especially pregnant and nursing dogs – should be dewormed regularly. To detect parasites, microscopic examination of stools, as well as laboratory ELISA tests and PCR tests, are used. The microscopic examination is preceded by information from the doctor on how to properly collect the material for the examination, i.e., how to prepare the so-called representative aggregate sample. Its preparation consists in collecting for 3 days those fragments of stool that look the worst – with the presence of mucus and blood, in which the chance of the presence of possible parasites is the highest. We store such a sample in the refrigerator, in one sterile container.

If the stool test showed nothing, and you still suspect the presence of parasites in your dog, it is worth using more advanced diagnostic tools. Such as, for example, ELISA tests, consisting in the detection of antigens, and PCR tests, in which the genetic material is tested. After diagnosing the presence of parasites, the dog is treated with appropriate drugs selected by a veterinarian. If there are already parasites in the dog, the symptoms will most often appear at the stage when they have already managed to make losses in the pet’s body, so every dog ​​owner must absolutely remember to regularly and preventively deworm. Such a procedure should be performed once every 3 months. It also does not hurt to perform a prophylactic stool examination, which, however, cannot be used as a substitute for deworming, because this examination may have the result of the so-called false negative and is only 100% reliable if the result is positive. In this case, we know exactly which parasite to administer the drugs to. If the fecal test result is negative, the dog should still be treated with a general antiparasitic preparation intended for animals. For this purpose, we do not use preparations for humans or substitutes with low effectiveness, e.g., pumpkin seed oil. Always deworm an animal with an active substance intended for a given species.

An auxiliary test in the diagnosis of parasites in dogs is the EHAA test, i.e., the elemental analysis of the dog’s hair. This test allows you to determine the levels of elements, incl. copper, iron, selenium, silicon, cobalt, zinc, and sulfur, which are elements that are not only eagerly eaten by parasites, but also those whose deficiencies can be noticed because of damage to the intestinal villi responsible for their absorption by parasites. It is worth performing the EHAA test, which is more convenient compared to the blood test, it can be performed without leaving home, without the requirement to be on an empty stomach, and without exposing the dog to unnecessary stress related to the collection itself. Another thing is that to test the levels of the same elements as found in the hair test with a blood test, it would take a lot more blood than with a standard blood count. Parasites always cause nutrient deficiencies – check which ones. This possibility is provided by the EHAA test.


1.What are ectoparasites in dogs?

Among the ectoparasites, i.e., external parasites in dogs, we can distinguish, among others, fleas, ticks, lice and Demodex, and skin and ear mites, such as mites, which are invisible to the naked eye.

2.What internal parasites are in dogs?

The most common internal parasites in dogs are roundworms, tapeworms, hookworms, protozoa, whipworms, and lungworms.

3.What are the symptoms of a parasitic disease in a dog?

Due to the variety of parasites in a dog, symptoms can also vary considerably. Ectoparasites can show up as white or black dots on your dog’s skin and fur and can cause allergy-like skin rashes and redness. Internal parasites may be noticeable in the form of, for example, a white porridge in dog’s poop. Other, less specific symptoms that may indicate the presence of parasites in a dog include weight loss, unusual behavior such as hyperactivity or apathy, convulsions, coughing, flatulence, or sledding.

4.Are parasitic diseases in dogs dangerous to humans?

Yes, some canine parasites are also dangerous to human health. A person can be attacked by fleas, scabies, roundworms, or tapeworms. Due to the ease of infection in daily contact, an important stage in the treatment of parasites in a dog is also appropriate disinfection of the common home space.

Online lecture for PetsDiag on June 7, 2018, Fri “Canine Parasitic Diseases”.

The attending veterinarian Małgorzata Miłosz – from Bydgoszcz, a graduate of UWM in Olsztyn in 2012, a specialist in veterinary laboratory diagnostics. A practitioner with 6 years of clinical experience. On a daily basis working with small animals in the Krakow veterinary clinic. Member of the team.

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