Dogs can be infested by many different types of worms (internal parasites), each settling in different organs or body systems and each producing a different spectra of symptoms characterized by varying degrees of severity. The early recognition of the symptoms of worms in dogs is important not only to provide early treatment and avoid severe, sometimes life-threatening complications in the affected animals, but also to prevent the transmission of worms between dogs and even, in certain cases, from dogs to humans.
Types of Worms That Dogs Can Get
Dogs can be infested by five different types of dog worms: roundworms, hookworms, tapeworms, whipworms (all affecting different sections of the intestines) and heartworms, the latter affecting the cardiovascular system.
Most worms infestations in dogs can cause any or all of the following symptoms, that may be more or less apparent and severe: diarrhea, sometimes with blood in the stool; weight loss; vomiting; appetite loss or sometimes appetite gain; dull, dry coat; coughing; debilitation and general poor appearance. However it is important to notice that these symptoms are not always caused by worms infestations and sometimes can be a sign of a more serious problem.
Roundworms are the most common internal parasites in dogs and often affect puppies under six months of age. They are Toxocara canis and Toxascaris leonina, which have a very similar morphology, being both of them whitish worms, up to 10 cm long. In their adult stage these worms live in the small intestine, where they reproduce releasing eggs into the environment in the feces of the affected dog. It is during this stage that roundworms cause intestinal symptoms such as diarrhea, vomiting (sometimes with worms in the vomit), extension of the abdominal wall (so called barrel belly’) and growth delay in puppies.
The main differences between Toxocara canis and Toxascaris leonina lie in their life cycles and modalities of infestation. While the whole life cycle of Toxascaris leonina (from the larval stages to the adult worm) takes place within the intestinal lumen of dogs, the first larval stages of Toxocara canis live in the respiratory tract. That is why, besides the typical intestinal symptoms caused by the adult worms, massive infestations with Toxocara canis can lead to parasitic pneumonia and respiratory symptoms such as coughing and foamy nasal discharge. This explains the reason of the more pathogenic action of Toxocara canis compared to Toxascaris leonina. As concerns the modalities of infestation, both Toxocara canis and Toxascaris leonina can be transmitted through the feces of affected dogs (i.e. ingestion of worm eggs from contaminated soil) or through the ingestion of accidental hosts such as rodents or lizards. In the case of Toxocara canis, however, the larval stages can migrate to different body tissues and organs where they enter a quiescent state until they are reactivated during pregnancy and are transmitted directly to the fetuses or, after the delivery, to the newborn puppies through maternal milk. All this explains why infestations with Toxocara canis often affect at the same time all the puppies of a litter. In these cases infestations can be serious, sometimes leading to sudden death due to severe parasitic pneumonia.
As concerns the treatment of roundworms infestations, the adult worms are effectively removed by antielmintic therapy (over-the-counter products are also available). Puppies should be treated at two weeks of age and again after 2-3 weeks to remove all the parasites acquired before birth. Lactating bitches should be treated at the same times as puppies, in order to prevent post-partum infestations. The puppies’ treatment should be continued, at 45-day intervals, until they are six-seven months old.
Hookworms (Ancylostoma caninum) are small whitish worms (1-2 cm long) with a characteristic hook shape and, like roundworms, harbor in the intestines. The infestation can occur by penetration of the larvae into the skin, by ingestion of the larvae from contaminated soil or, just as in the case of Toxocara canis, through the maternal milk. The main pathogenic action of hookworms is due to their haematophagous activity, which is responsible for anemia (especially in the puppies) and bleeding of the intestinal wall. Symptoms in puppies include (besides anemia) low energy level and diarrhea with blood and mucus in the stool. In adult dogs symptoms are usually less severe and include weight loss, appetite loss and dull coat. In addition, there can sometimes develop skin lesions (rash, eczema, ulcers) at the site of penetration of the larvae, usually at the interdigital spaces. For hookworm infestations, the antielmintic therapy is similar to that described for roundworm infestations. In addition, the symptoms caused by the anemia can be relieved by the administration of iron supplements and a protein-rich diet.
Tapeworms (Dipylidium caninum) are thin whitish worms, up to 50 cm long, that can harbor in the small intestine of dogs where they usually do not cause any symptoms, except for itching at the perianal area (due to the small broken pieces of the worms that move actively in this body region) and, in case of severe infestation, diarrhea, abdominal pain and weight loss. However, the typical sign of infestation in dogs (whether mild or severe) is the excessive licking of the area around the anus. This is the alarm bell that should lead dog owners to ask for veterinary consultation, remembering that tapeworm infestation cannot be treated with the common over-the-counter products used for the treatment of roundworm and hookworm infestations. It is also important to note that tapeworms are transmitted to dogs through the ingestion of fleas carrying the infective larval stage of Dipylidium caninum. That’s why, in this case, the anti-tapeworm therapy should be always associated with measures of control and treatment of flea infestations.
Whipworms (Trichuris vulpis) are thin, small dog worms, up to 4-6 cm long, that harbor in the large intestine of dogs. The infestation with whipworms often doesn’t cause any symptoms and only in severe cases there can be symptoms of diarrhea with blood or mucus in the stool and weight loss. Whipworm infestations can be effectively treated with appropriate over-the-counter or prescription medications, although the latter are usually more effective.
Due to their location in the cardiovascular system of dogs, heartworms (Dirofilaria immitis) do not cause gastrointestinal symptoms, but they are responsible for a severe, life-threatening medical condition called cardiopulmonary filariasis.’
Heartworm larvae are transmitted by the bite of a mosquito carrying the infective stage of the worm and develop to adult worms within the bloodstream of the infested dogs. The adult stage of heartworms (up to 20-30 cm long) harbor in the right cardiac chambers and the lumen of the pulmonary arteries (the large arterial trunks that carry blood from the heart to the lungs). Here they cause a progressive heart failure characterized by symptoms of coughing, fatigue, effort syncope, ascites (accumulation of fluid in the abdominal cavity) and edema (swelling) to the limbs. Due to the severity of this condition and the difficulties of treatment, which is often a challenge, in this case the veterinary intervention is always unavoidable.
As it has been described, symptoms of worms in dogs are fairly characteristic, although not specific for worm infestation, so they should always require a confirmation for a positive diagnosis through appropriate examinations. This is especially important considering that infestations with different types of dog worms usually require different forms of treatment. Therefore whenever symptoms suggest a possible worm infestation, asking for a consultation with a veterinarian should be always the first thing to do before trying to give to one’s dog any of the over-the counter products available on the market for the treatment or control of common tapeworm and roundworm infestations of dogs.