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Worms in Cats and Dogs

Updated: Nov 2, 2021


What types of worms infect cats and dogs?

Generally, there are five main types of worms that infect your cat or dog besides many others.

These are:-


Roundworms grow to a length of about 15 cm long and are white in colour. They are round and live in the dog's intestines along with other types of worms. Puppies are infected with roundworms (Toxocara spp and Toxascaris spp) from their mother’s milk. This is prevented by deworming expectant and nursing mothers with a safe, veterinary licensed product. Dogs can also be infected by eating contaminated rodents or soil. Roundworms in dogs are identified as spaghetti-like shapes in the faeces or, in severe cases, in vomit. Roundworms are also zoonotic, affecting humans.



Tapeworms are flat (like ribbons) and can grow up to a length of about 60 cm long. Dogs are infected with tapeworms (Taenia spp., Echinococcus spp., Dipylidium spp.) by fleas or infected carcasses (such as rodents, sheep, or rabbits). Segments of tapeworm in dogs may be seen in faeces or on the dog’s bottom, and they look like grains of rice. Humans are infected by ingestion of eggs (Zoonosis) from dog faeces in soil, on vegetables/fruit, on other food contaminated directly by faeces, or indirectly after fly transfer and from eggs in water.



Hookworms cause heavy infections in suckling puppies and also in young dogs causing severe anaemia, with occasional respiratory distress and deaths. In older dogs, they cause a lighter infection to induce chronic anaemia, dullness, weight loss or poor growth. In other cases, they cause interdigital dermatitis.

Hookworms can also infect humans (zoonosis) causing cutaneous larva migrans in humans, a skin disease caused by the hookworm in tropical and subtropical areas. The hookworms involved are Ancylostoma caninum and Ancylostoma brasiliense.



Lungworms live in the dog’s blood vessels and affect their lungs and the infection is caused by a number of worms. These include Aelurostrongylus abstruse and E aerophilus in cats and Oslerus (Filaroides) osleri in dogs. Others are Capillaria aerophila in foxes and dogs, Angiostrongylus vasorum, Crenosoma vulpis, Eucoleus aerophilus, and Filaroides hirthi in dogs. The adult lungworms live in nodules in the trachea and lung tissues of dogs and cats, and larvated eggs laid by adults hatch there. Puppies become infected from the faeces or when an infected dog (e.g., when an infected mother licks her puppies). Infection is infrequent in dogs. The worms live and lay eggs inside the dog and immature forms pass out into the environment to infect other dogs. Dogs become infected by eating food or drinking water that is contaminated with larvated eggs. After being eaten, the eggs hatch in the intestine and then travel to the lungs through the circulatory system.

The adult worms spend most of their lives in nodules in the trachea. Dogs can also pick up lungworms by eating slugs and snails. Lungworm infection in dogs can be difficult to treat, and it is necessary to continue antiparasitic treatment for up to 2 months.


Heartworm is a potentially serious parasitic disease that can cause heart failure and other complications. Heartworm disease is caused by a worm parasite, Dirofilaria immitis. The organism is transmitted by mosquitoes, which carry the heartworm larvae (called microfilariae) from an infected animal host to another animal host. There are four types of mosquitoes that transmit dirofilariasis, Aedes, Culex, Anopheles and Mansonia mosquitoes. Once in the new host, they grow into adult worms in several months and live in the blood vessels that serve the heart and lungs. Subsequently, the heartworms enter the heart and start stressing the cat's or dog’s heart, causing inflammation of the blood vessels and lungs. Severe complications occur when the number of worms present becomes high or when the heartworms die. Susceptible animals can be reinfected numerous times, so different stages of heartworm infections may be present in the same animal. Where heartworm is prevalent, especially along coastlines, preventive medication is given regularly to dogs and cats. Climate change is also affecting the spread of heartworm disease.


Symptoms of worms in dogs

It’s not always easy to spot dog worms, so it is important to have regular veterinary checkups for cats and dogs.

Signs of dog worms include:

  1. Worms in your pet’s faeces, vomit or on their bottom

  2. Lethargy, weakness and depression

  3. Diarrhoea or vomiting

  4. Weight loss despite a good appetite

  5. An abnormally swollen stomach

  6. Severe vomiting

  7. Loss of appetite

  8. Depression as a result of a large burden causing a blockage of the intestine (normally usually seen in puppies)

  9. Coughing and bleeding problems, among other signs, may suggest Lungworm


Preventing or Treating Worms

  1. Identify and treat worms promptly.

  2. Administer a monthly heartworm preventative if you stay along the coastline.

  3. Keep your dog free of fleas.

  4. Administer a de-wormer regularly.

  5. Maintain regular veterinary visits.

  6. Restrict your dog's access to harmful environments.

    • Keep your dog away from warm, grassy areas shared with other dogs who have not been de-wormed.

    • Do not let your dog come into contact with wild or prey animals.

    • Avoid warm, humid climates that have high populations of bugs such as fleas or mosquitoes.

    • Do not let your dog eat or rub themselves in the faeces of other dogs or wild animals.



Avcioglu, H., & I., B. (2011). The relationship of public park accessibility to dogs to the presence of Toxocara species ova in the soil. Vector Borne Zoonotic Diseases, 11(2), 177-180.

Bowman, D. D., Montgomery, S. P., Zajac, A. M., Eberhard, M. L., & Kazacos, K. R. (2010). Hookworms of dogs and cats as agents of cutaneous larva migrans. Trends in parasitology, 26(4), 162-167.

Elsheikha, H. (2017). Canine angiostrongylosis: an increasing concern. The Veterinary Nurse, 8(8), 424-429.

Levitan, D. M., Matz, M. E., Findlen, C. S., & Fister, R. D. (1996). Treatment of Oslerus osleri infestation in a dog: case report and literature review. Journal of the American Animal Hospital Association, 32(5), 435-438.

Smith, A., Semeniuk, C., Rock, M., & Massolo, A. (2015, July 1 ). Reported off-leash frequency and perceptions of risk for gastrointestinal parasitism are not associated in owners of park-attending dogs: a multifactorial investigation. Preventive Veterinary Medicine, 3–4, 336-348.

Wilcox, R. S., Bowman, D. D., Barr, S. C., & Euclid, J. M. (2009). Intestinal obstruction caused by Taenia taeniaeformis infection in a cat. Journal of the American Animal Hospital Association ., 45(2), 93-96.

Wolfe, A., & Wright, I. P. (2003). Human toxocariasis and direct contact with dogs. Veterinary Record, 152(4), 419-422.

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