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5 Common Parasites in Dogs You Need to Know

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If you’ve noticed your dog scratching, coughing, vomiting, suffering from diarrhoea or losing weight, there may be a parasite to blame.

What is a parasite? Parasites are organisms that live off other organisms, called hosts, in order to survive. There are two main types of parasites in dogs: internal (such as worms) and external (ticks and fleas).

Protection: While it’s almost impossible to prevent your dog from encountering parasites, you can protect them easily by using a suitable product on a regular basis.  

Vets recommend broad-spectrum parasite protection, which essentially refers to using products that protect against multiple parasitic organisms at the same time. 

Ask your vet about a broad-spectrum wormer that protects against multiple worms, including tapeworm, as well as chewable tablets that protect against ticks and fleas.

According to the European Scientific Counsel Companion Animal Parasites (ESCCAP), dogs should have a risk-assessment and receive the appropriate risk-based parasite protection plan. 1,2

Read on to learn about the parasites you should know as a pet owner, as well as important broad-spectrum protection plans.

Internal Dog Parasites and their Symptoms

As mentioned earlier, internal dog parasites are organisms that live inside a dog’s body and can be exhibited through a variety of different symptoms, including diarrhoea, vomiting, weight loss, coughing, lethargy or a distended belly.


What is it? Adult tapeworms are made up of many small segments, which break off and end up in a dog’s stool. These segments contain tapeworm eggs. Different types of tapeworms can affect dogs: the flea tapeworm (Dipylidium caninum), species of Taenia and species of Echinococcus. While some adult tapeworms can be several metres long, adult Echinococcus tapeworms are less than one centimetre long inside a dog’s intestine.

How do dogs get tapeworms? The infective stages of the tapeworm are found in rabbits, rodents, livestock, wildlife and fleas are all potential intermediate hosts, depending on the species of tapeworm. A dog might eat the small host carrying these infective stages, which can then grow into an adult tapeworm inside a dog’s intestines.

What are tapeworm symptoms in dogs? In most cases, dogs can be infected with tapeworms and show no symptoms.  With Dipylidium and Taenia tapeworms, you might see small segments of the worm around an infected dog’s anus or in the stool, owners may also see the segments on bedding or carpets where the dog has been laying. Tapeworms are very easy to miss, even with normal veterinary diagnostic tools. 

How dangerous is it? It depends on the type of tapeworm. Most tapeworm infections are easy to treat with medication, once detected. The vast majority of animals will experience no symptoms, except maybe itching around the anus, and owners may see the segments moving on the carpet on bedding. However, Echinococcus tapeworms in people and sometimes in dogs can cause severe disease, can be difficult to treat and can be fatal.


What is it? Roundworms are very common parasites in dogs. There are two main types of roundworms: Toxascaris leonina and Toxocara canis. The latter is a more serious parasite that can be spread to humans.

How do dogs get roundworms? Most puppies are born with roundworms, contracted through their mother’s placenta or passed along through nursing. It can also be transmitted through eggs in the soil that were deposited from the faeces of infected dogs or by eating smaller infected animals. Low level infections in adult dogs can result in further environmental contamination as they shed eggs in their faeces, putting others at an even greater risk of infection.

What are the symptoms? Typically, symptoms of roundworm include a pot-bellied appearance, weight loss due to malnourishment, coughing, vomiting and diarrhoea. Dead worms may be evident in the faeces or vomited after treatment. 

How dangerous is it? Roundworm can lead to poor development in puppies if left untreated, whereas there are usually no clinical symptoms in adult dogs. 


What is it? Lungworm is a non-intestinal worm that affects dogs. Adult lungworms (Angiostrongylus vasorum) are approximately 14 to 20 millimetres long and live in the large vessels near the heart. They attach here and feed, potentially causing serious problems.

How do dogs get lungworm? Dogs swallow the larvae when they eat an infected slug or snail or eat another animal that has eaten an infected slug. These larvae burrow through the gut wall and migrate to the heart as the larvae turn into adults.

What are the symptoms? Symptoms of lungworm in dogs are non-specific. Signs may include coughing, shortness of breath and blood that doesn’t effectively clot.

How dangerous is it? In extreme cases, lungworm infections in dogs can cause fluid in the abdomen, seizures, collapse and even death. There is no risk to human health.

External Dog Parasites and their Symptoms

At some point in every dog’s life they will come into contact with an external parasite. These parasites can cause mild symptoms such as irritated skin or carry diseases that result in potentially fatal medical problems. 

Broad-spectrum protection and treatment medications are both common methods for dealing with these external parasites. For ticks and fleas, ask your veterinarian about a chewable tablet that protects against ticks and fleas. 


What are they? A flea is an external parasite that feeds on a dog’s blood. Adult fleas hop onto a host like a dog from a contaminated environment and then generally stay on that host. They do not move from animal to animal unless they are in direct contact. 

How do dogs get fleas? Flea eggs hatch into larvae, which then pupate. Pupae (cocoons) can remain dormant in your home for months. Adult fleas emerge from the pupa and wait for a host to walk by to jump onto. Fleas on people almost always come from the contaminated environment and are looking for a host. The flea life cycle is faster when the weather is warm and humid, so flea numbers increase rapidly in warm, humid locations.

What are the symptoms? You may see “flea dirt” (tiny black droppings) on your dog’s coat before you see fleas and you may notice excessive itching, chewing, hot spots or other signs of general discomfort. 

How dangerous are fleas? Some dogs develop mild to severe health problems from scratching or skin conditions such as Flea Allergy Dermatitis (FAD). Fleas may also be carriers of internal parasites or bacterial infections. Severe infestations can lead to anaemia and even death due to excessive blood loss.


tick removal

There are many varieties of ticks that carry serious diseases including Lyme Disease. If you see a tick on your dog, carefully remove it with a tick remover as soon as it is discovered. Dogs should be on year-round tick protection to help prevent the spread of disease. 

After learning about these common parasites in dogs and their symptoms, it’s easy to feel overwhelmed or anxious that your dog will be exposed, but there’s no need to worry. Through sensible ownership and broad-spectrum internal and external dog parasite protection, you can safely enjoy quality time and adventures with your dog. 


For further information call Elanco Animal Health on +44(0)1256 353131 or write to: Elanco UK AH Limited, Form 2, Bartley Wood Business Park, Hook, RG27 9XA, United Kingdom. Elanco is a trademark of Elanco or its affiliates © 2020 Elanco or its affiliates. PM-IE-20-0083. Date of preparation 03/20.



  1. European Scientific Counsel Companion Animal Parasites. Worm Control in Dogs and Cats: ESCCAP Guideline 01 3rd Edition – February 2020 
  2. European Scientific Counsel Companion Animal Parasites. Control of Ectoparasites in Dogs and Cats: ESCCAP Guideline 03 Sixth Edition – March 2018