Worms: Preventing Parasites in Dogs and Cats

Estimated reading time: 6 minutes

Worms found in dogs and cats in the UK are most likely one of two types: Roundworm or Tapeworm. Roundworms can infect humans, whereas Tapeworm are less of a concern. A seemingly healthy dog or cat can show little to no symptoms at all and yet still carry a substantial number of parasites that contribute to the spread of infection through eggs that pass through their system excreted in faeces.

Puppies and kittens are born with a high susceptibility to worms (if not already with them) as they can be transmitted through their mother’s milk. As our furry babies get more adventurous, the chances of them coming into contact with worms increase every time they venture outside. Adults may come into contact with worms in a number of different ways: fleas, lice, soiled grassland, and public areas.

Puppies and kittens are very susceptible to worms.
White kitten and puppy sat together

What are Worms?

Roundworms are the most common parasitic worm found in dogs. The majority of dogs will be infected with these parasites at one time in their life due to the different ways they can be contracted. Known as Toxocara Cati (in cats) or Toxocara Canis (in dogs), roundworms have similar bodies to earthworms and are pinkish, brown, or white in colour and around 2 to 3 inches long.

Eggs are sticky and able to stick to paws or noses, where they stay until ingested through grooming. When ingested, the eggs hatch releasing microscopic larvae into the gut where they burrow into the gut wall to enter the bloodstream.

Dogs can pick up eggs on their nose and paws and ingest them when grooming.
Close up on dog’s nose amongst the grass

Adult roundworms can live in animal intestines without owners knowing. In cases of a large colony, some symptoms may be seen:

  • Weight loss
  • Pot-bellied abdomen
  • Loose stools
  • Sickness
  • Dull coat
  • Cough

Once in the bloodstream, larvae are directed to the muscles, where small cysts encapsulate them. The cycle of these worms is slightly different with adult dogs and cats.

In healthy males, eggs may lay dormant for long periods of time, sometimes never developing into egg-laying adults. When the immune system is compromised through old age, disease, or illness, this gives the larvae the opportunity they need to continue their journey to adulthood resulting in numerous adults laying eggs in the intestines. When adult females become pregnant, the hormone changes can cause their immune system to weaken, resulting in dormant larvae reanimating and continuing their journey once more.

In newborn puppies and kittens, the risk of contracting larvae is still very high. Larvae are able to pass from mother to kitten through the mother’s mammary glands, infecting newborn kittens during nursing. Larvae also pass from mother to puppy but in a slightly different way – whilst still in the womb! Larvae pass through the placenta to infect unborn puppies and, once born, the puppies are also at risk of contracting larvae through their mother’s milk whilst feeding. Once in the bloodstream of a young defenseless host, the larvae travel to organs burrowing and crawling up into the lungs and windpipe causing a cough. This cough is followed by the animal swallowing the larvae which once again end up in the gut. This is now where the larvae will develop into adult egg-laying creatures. These eggs are then excreted out with waste and the cycle starts again.

Frightening facts about Worms

Worm eggs, when expelled, can remain dormant within infected soil or grass for around 2 years without a host! Roundworms are known as “Zoonosis” this means that they are a parasite that can also infect humans!

Always pick up after your dog to help combat the spread of worms.
Dog sat on the grass


Tapeworms are flatworm parasites with long, flat, segmented bodies and small heads with holding hooks and suckers. The tails of these worms develop segments that break off, encasing eggs that are expelled with faeces. There are different species of tapeworms, each requiring a stage in an intermediate host (that needs to be eaten by our pets) to complete their life cycle and resulting in infection.


Taenia uses small rodents and rabbits as their intermediate host. As many cats (and the occasional dog) are known to enjoy the thrill of a rabbit or mouse chase, these worms may be more commonly found in their system. These worms are usually found in the liver which can be an attractive morsel for the determined hunter. Following the tasty meal where worm larvae are ingested, the worm attaches itself to the lining of the intestine using a ring of hooks and suckers and will start to develop a long tail developing segments.

Dipylidium Caninum

Dipylidium Caninum uses fleas as their intermediate host. These tapeworms are more commonly found in dogs although can still be seen in cats due to the way they are contracted. The fleas are ingested while our pets are grooming or trying to rid themselves of irritating fleas from their coat. When our pets ingest the fleas, the digestive enzymes in the stomach breakdown the tapeworm’s host leaving the immature tapeworm unharmed due to its anti-enzyme protection.

Once in the gut, the worm attaches itself to the lining of the intestine using a ring of hooks and suckers. Once secured, the worm then starts to produce a small tape of segments up to 5cm long. When the worm reaches maturity, it will start to shed the egg-filled segments that enlarge to resemble grains of rice and can be seen in the faeces of the animal. They may also get caught in the fur around the animal’s rear end or base of their tail and this can cause irritation. These egg pouches dry and burst in the open air and this releases worm eggs into the surrounding environment waiting to be eaten by passing flea larvae and the cycle starts again.

It is important to treat your cat for both fleas and worms because worms use fleas as an intermediate host.
Ginger cat scratching outside

Treatment & Prevention for Worms

To ensure our pets are worm-free, it is important to treat them with products that target these wriggly worms.

  • Adults should be treated every 3 months.
  • Kittens and puppies should be treated for roundworm from 2 weeks of age, then every 2 weeks until they are 12 weeks old.
  • At 12 weeks worming should continue every 2 to 3 months – this is because their immune system is still developing.
  • Nursing bitches and queens should also be wormed at the same time as their puppies/kittens with matching dose intervals until weaned.

Before administering any dose of wormer, it is vitally important to know the weight of the animal intended. The weight of the individual dog or cat is used to determine the amount of syrup, tablet or granule needed to dose correctly.

Do you need further advice?

If you need any further advice, please contact the Breakthrough Helpline Team on our freephone number 0808 168 3344 or email hello@breakthroughdog.co.uk.


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