Worms And Your Pet

Parasites are not something we really like to think about, but as responsible owners it is important that we safeguard our pets, and our families against them. A heavy burden of worms can cause suffering and illness in our pets, so it necessary to prevent this. Although it is rare, some types of worms also pose a risk to human health if the eggs or larvae are ingested. .

There are two main types of worms affecting dogs and cats 


Dipylidium Caninum (the flea tapeworm)

  • These are long, flat worms with segmented bodies that attach to the wall of the small intestine and absorb nutrients as they flow past
  • Once tapeworms mature, they shed their segments which pass out in the faeces and look like tiny, mobile, grains of rice.
  • The segments dry up in the environment and then break open to release tiny tapeworm eggs.
  • The eggs are then eaten by flea larvae in the environment and and they continue part of their lifecycle in this host until it matures into an adult flea and jumps onto a dog or a cat.
  • If a dog or cat accidentally swallows the infected adult flea while grooming, it will become infected with tapeworms again.
dipylidium Caninum Lifecycle

It is very important to regularly treat your pet for fleas to help prevent tapeworm infestation.

Taenia species

  • These tapeworms need intermediate hosts such as  rabbits, rodents and other animals that may be prey for our dogs and cats.
  • The prey species may ingest the tapeworm eggs from the environment and the tapeworm larvae then starts to develop inside its immediate host.
  • Once the dog or cat has ingested it’s prey, the tapeworm latches on to the wall of the intestine and continues it’s life cycle in much the same way as the flea tapeworm.


Toxocara Cati & Toxocara Canis

  • These worms generally look a lot like small noodles or spaghetti T._canis_adult_worms_wikistrands and live in the intestine
  • Adult roundworms mature, mate and then shed lots of tiny eggs which pass out in the faeces.
  • The eggs have a very tough shell and can remain in the environment for a long time.
  • Animals ingest the eggs through normal grooming or eating an infected host animal.
  • Roundworms can also be passed from mother to puppies or kittens during pregnancy or while nursing.
  • When the eggs reach the animal’s intestines they hatch and the juvenile worm then burrows out of the intestines.
  • If the host is not a dog or a cat then the worm encysts (or encloses) itself into other body tissues and waits until the host is eaten by a dog or a cat.
  • If the host is a dog or a cat, that has either ingested the worm eggs or has ingested a host animal, the juvenile worms migrate through the body until they reach the lungs; here they are coughed up and then swallowed so that they end up in the intestine again.
  • The worms mature in the intestines and eventually produce eggs which are passed out in the dog or cat faeces to begin the life cycle again.

Toxascaris Leonina

  • These Roundworms do not migrate around the body in the same way as the Toxocara species do. The second stage larvae mature in the intestine over a period of  2 to 3 months before they start producing eggs again.

Picture from CDC Website


  • Lungworms live in the pulmonary arteries and an infestation can be fatal
  • They are transmitted to dogs and cats that eat infected slugs, snails and frogs
  • For more information on Lungworm please see the links below

Microscopic views of worms (Courtesy of Novartis)

Other less common worm types 


  • These worms mainly affect dogs and rarely cats.
  • In addition to living in the animal’s small intestine, the hookworm larvae can penetrate skin (usually the feet) and cause infection.
  • Hookworms are thought to infect up to 68% of the fox population.


  • These worms live in the dog’s large intestine. (they don’t affect cats)
  • Dog’s become infected by ingesting eggs in the environment that have been passed in faeces of infected dogs.


  • These worms are not native the UK, but they do now pose a risk because of animals travelling abroad and back home, or animals being imported to the UK.
  • They are transmitted by mosquitoes and live in the pulmonary arteries and heart of infected dogs and cats.

Signs that your pet may have worms

You may not realise you pet has worms at all because not all pets show these signs.  Remember, prevention is easier than cure.

  • Small white segments (roughly the size of a grain of rice) may be seen around your pet’s bottom area or in the faeces
  • Your pet may cough up / vomit Roundworms if he or she has a heavy infestation
  • Itchy bottoms may cause them to ‘Scoot’ along the ground
  • You may see worms in your pets pooWorms
  • Increased appetite
  • Coughing
  • Vomiting and/or Diarrhoea
  • Weight loss
  • Loss of coat condition
  • Pot belly – usually only seen in puppies or kittens
  • Fleas

How often should I worm my dog and cat?

Current guidelines advise worming cats and dogs at least 2-4 times a year, depending on the pet’s lifestyle, We recommend that you worm more frequently if

  • Your pet has regular access to children under 4 years old
  • Your pet is in contact with anyone that may be immunosuppressed
  • Your pet hunts
  • Your pet likes to eat poop from other animals
  • Your pet likes to eat or roll in dead animals

Your vet or veterinary nurse can best advise you on the best worming protocol for your pet.

Worming preparations have a very short duration of action and they do not remain in the body or active against worms after this period, which is why it is important to repeat the treatment at least twice a year.  (See below for fecal egg counts).

The risk to humans

Toxocariasis is thankfully rare in the UK (usually around 4-10 cases a year). Infection happens when Roundworm larvae from an animal are ingested by a human. Usually the larvae will just die off in the human digestive tract, but in some cases the larvae survive and can migrate and encyst in organs or they reach the eye and cause blindness. Children are at a higher risk of infection as they are often close to pets and play in outdoor areas where parasites may have been deposited; infection can also happen in immunocompromised people, whose bodies cannot naturally kill off the larvae in the digestive tract.

Kids and pets

Keep your pet and the environment worm free

  • Use a veterinary recommended wormer. Prescription worming products are generally more effective than over the counter products.  Be very careful about using ‘natural/herbal worming products’ as these products work by removing the worms from the animal’s digestive system but not necessarily killing the worms, meaning any eggs that are passed are still viable and will infect the next host.  It is also worth noting that commonly named ‘natural’ worming products such as Oregon Grape, Black Walnut, Wormwood, Garlic and Onions can all be highly toxic to pets if the dosage is miscalculated! Whichever products you use ensure that you weigh your pet first so that the correct dosage of the product can be given.
  • Use a fecal worm egg counting service. If you would rather not worm your dog or cat as frequently as the guidelines suggest, because you are concerned about unnecessary treatments or overusing medications. We recommend that you do a fecal worm egg count 3-4 times a year to ensure that your pet does not have worms. These can be arranged by your veterinary practice or via an online service such as wormcount.com.
  • Use a veterinary recommended flea treatment. Prescription flea treatments are generally more effective than over the counter products. Spot on treatments and tablets are usually given every 1-3 months, depending on the product and some veterinary recommended flea collars last for up to 8 months . Make sure you use a household spray yearly to kill any flea eggs or larvae in the home environment.
  • Scoop the poop! This is important both on walks and in your own garden – it is also against the law to leave your dog’s faeces in public places. A single mature Roundworm can produce approximately 80,000 eggs a day, which are excreted when the dog or cat has a poo. Unless you clear up after your pet, all of those eggs will remain in the environment and infect other dogs and cats and possibly children too.Cat litter trays/toileting areas should be scooped out daily and properly cleaned at least once a week.
  • Good personal hygiene and making sure children wash their hands, especially after stroking pets and playing outside.  Kissing your pet or letting him or her lick your face will put you more at risk, especially if you are immunocompromised.
  • Speak to your veterinary nurse. They can advise you on the safest and most effective parasite treatments for your pet as well as how often you need to give them.

Useful Links

For more information on the Flea lifecycle

For more information on Lungworm

Novartis Worming information – Worm Patrol

Bayer Animal Health parasite information – Its A Jungle Out There