Dogs can be infested by many different types of worms (internal parasites), each affecting different organs or body systems and producing a distinct spectrum of symptoms with varying degrees of severity. Early recognition of the symptoms of worms in dogs is crucial—not only to provide timely treatment and avoid severe, sometimes life-threatening complications, but also to prevent the transmission of worms between dogs and, in certain cases, from dogs to humans.
Types of Worms That Dogs Can Get
Dogs can be infested by five common types of worms: roundworms, hookworms, tapeworms, whipworms (all affecting different sections of the intestines), and heartworms, which affect the cardiovascular system.
Worm infestations in dogs can cause any or all of the following symptoms, which can vary in severity: diarrhea (sometimes with blood), weight loss, vomiting, loss of appetite (or occasionally an increase in appetite), dull, dry coat, coughing, debilitation, and poor overall appearance. However, it’s important to note that these symptoms are not always caused by worm infestations and may sometimes be a sign of more serious underlying issues.
Roundworms are the most common internal parasites in dogs, particularly in puppies under six months of age. The two most common roundworm species are Toxocara canis and Toxascaris leonina, which are both whitish worms, up to 10 cm long. In their adult stage, these worms reside in the small intestine, where they reproduce and release eggs into the environment via the affected dog’s feces. At this stage, roundworms cause symptoms such as diarrhea, vomiting (sometimes with visible worms in the vomit), a distended abdomen (often called “barrel belly”), and growth delay in puppies.
The key differences between Toxocara canis and Toxascaris leonina lie in their life cycles and infestation methods. While Toxascaris leonina completes its life cycle entirely within the dog’s intestines, the larval stages of Toxocara canis migrate to the respiratory tract. This explains why, in addition to typical intestinal symptoms, a massive infestation of Toxocara canis can lead to parasitic pneumonia and respiratory issues, such as coughing and foamy nasal discharge. This makes Toxocara canis more pathogenic than Toxascaris leonina.
Both worms can be transmitted through contaminated feces (ingested from soil) or via accidental hosts like rodents or lizards. However, Toxocara canis larvae can migrate to different organs and tissues where they enter a dormant state, reactivating during pregnancy and transmitting to puppies either in utero or through maternal milk. This explains why infestations of Toxocara canis often affect all puppies in a litter, sometimes leading to sudden death due to severe parasitic pneumonia.
For roundworm infestations, antelmintic (deworming) therapy is effective. Puppies should be treated at two weeks of age and again at two to three weeks to eliminate parasites acquired before birth. Lactating bitches should be treated at the same time as puppies to prevent post-partum infestations. Puppy treatments should continue at 45-day intervals until they are six to seven months old.
Hookworms (Ancylostoma caninum) are small, whitish worms (1-2 cm long) with a characteristic hook shape and, like roundworms, inhabit the intestines. Infestation can occur through skin penetration by larvae, ingestion from contaminated soil, or, as with Toxocara canis, through maternal milk. The primary pathogenic effect of hookworms is their blood-sucking activity, which leads to anemia, particularly in puppies, and intestinal bleeding. Symptoms in puppies include anemia, low energy, and diarrhea with blood and mucus in the stool. In adult dogs, symptoms are typically less severe and may include weight loss, lack of appetite, and a dull coat. Skin lesions, such as rashes, eczema, or ulcers, may develop at the site of larval penetration (typically between the toes). Hookworm infestations are treated with similar antelmintic therapy to that of roundworms. In addition, anemia can be managed with iron supplements and a protein-rich diet.
Tapeworms (Dipylidium caninum) are long, thin, whitish worms (up to 50 cm) that usually live in the small intestine. Tapeworms typically do not cause symptoms except for itching around the perianal area due to small segments of the worm moving in this region. In severe infestations, symptoms like diarrhea, abdominal pain, and weight loss may occur. The classic sign of tapeworms in dogs is excessive licking of the anus. This behavior should prompt a veterinary consultation. It’s important to note that tapeworm infestations cannot be treated with common over-the-counter dewormers used for roundworms or hookworms. Tapeworms are transmitted when dogs ingest fleas that carry the infective larval stage. Therefore, anti-tapeworm treatment should always be combined with flea control and treatment.
Whipworms (Trichuris vulpis) are small, thin worms (up to 4-6 cm) that inhabit the large intestine of dogs. Whipworm infestations often cause no symptoms, but in severe cases, dogs may experience diarrhea with blood or mucus in the stool and weight loss. Whipworm infestations are effectively treated with appropriate over-the-counter or prescription medications, with the latter usually being more effective.
Heartworms (Dirofilaria immitis) are different from other worms in that they affect the cardiovascular system. Heartworm larvae are transmitted through mosquito bites and develop into adult worms within the bloodstream. Adult heartworms (up to 20-30 cm long) reside in the right side of the heart and the pulmonary arteries, causing progressive heart failure. Symptoms include coughing, fatigue, fainting during exertion, ascites (fluid in the abdomen), and swelling in the limbs. Due to the severity of this condition and the complexities of treatment, heartworm infestations always require veterinary intervention.
As described, the symptoms of worms in dogs can be fairly characteristic, though not exclusive to worm infestations. Therefore, a positive diagnosis requires appropriate tests. Since infestations with different types of worms require different treatments, any suspicion of a worm infestation should prompt an immediate consultation with a veterinarian. It’s important not to attempt treatment with over-the-counter products without proper diagnosis.