Worms and your pet's health

There are several types of parasitic worms – or helminth - that can affect your pet and it is often the case that you – and indeed you pet - will not realise that they are present - they are often “silent” parasites.

In general when we say that a pet has worms we mean that they are infected by a parasite, often in the intestines, where they receive nourishment, and therefore disrupt their ability to absorb nutrients, and therefore causes the host harm.

How does my pet get worms?

Your pet can contract intestinal parasites via different routes including:

  • Drinking contaminated water
  • Contact with other infected animals
  • Contact with other infected animal faeces
  • From an infected nursing mother (nursing their young)
  • Swallowing fleas carrying the infective stage of tapeworms
  • Eating an animal (such as a mouse or rat) that is carrying a parasite

Helminths fall into three main types:

  • Roundworms (nematodes)
  • Tapeworms (cestodes)
  • Hookworms (trematodes)

There are other parasites that are also, wrongly, described as worms but are not classified as such and include infections caused by single celled organisms called protozoa such as giardia and coccidia.

Clinical signs of worm infestations can include:

  • Weight loss
  • Gastrointestinal disturbances
  • Diarrhoea
  • Anaemia
  • Scratching, particularly around the base of the tail
  • Vomiting
  • Mild to severe coughing
  • Eating a great deal without putting on weight
  • Bad breath

This, of course, depends upon the agent of infestation so it is worth considering how specific worms present in your pet.

dog roundwormRoundworm - Roundworms are the most common parasite of the digestive tract in dogs and cats. These worms look like spaghetti and continually produce eggs that pass in their faeces and mature for one to three weeks before being infective to others – including humans.

Animals can acquire roundworms from the soil or from eating other carriers such as small rodents. Animals can also be infected in the womb by larvae passed on by their mother depending upon the type of roundworm.

It is vital that you are vigilant with your pet’s health. While animals infected with roundworm don’t always show any signs those with major infestations will have diarrhoea, vomiting, weight loss, dull coat, and abdominal swelling.

Your pet may also have a cough if the roundworms move into the lungs. You may also notice adult roundworms in your dog's faeces or vomit. Occasionally owners mistake roundworms for elastic bands as they are often coiled, as their name suggests, however, in general, they will appear white or light brown in colour and may be several inches long.

Tapeworm - Unlike the other common intestinal worms tapeworms require two different types of animals (hosts) to complete their life cycle. The first host animal – usually fleas - merely carries the parasite around to its new home. The second and final host (i.e., your pet) is the one in which the tapeworm can mature in the intestine and develop its eggs.

While animals infested with tapeworm don’t always show any signs, those with major infestations will have diarrhoea, vomiting (sections of the worm may be vomited), and weight loss.

More commonly smaller infestations will be discovered as a result of the owner observing their pet licking and chewing around their anal area or scooting (dragging their hindquarters along the ground), or observation of segments of the tapeworm on the fur or anus of the pet. These segments contain the eggs of the worm.

lungwormLungworm - Lungworm is becoming increasingly more common, it used to only affect pets in small “hot spots” in the south of the UK but cases are increasingly appearing throughout the country.

Lungworm - Angiostrongylus vasorum - generally affects only dogs but there is another type of lungworm - Aelurostrongylus abstrusus - that can affect cats. However, it infections seem to be rare and has a better prognosis.

Lungworm larvae are carried by frogs, slugs and snails, and dogs can become infected when they accidentally (or purposefully) eat them while eating grass, drinking from water bowls outside, puddles, or even pick them up from their toys.

The worm, as the name suggests, once ingested migrates to the blood vessels of the lungs, and the heart. Like many other parasitic infections, the dog may appear symptom free, particularly if the infection is small. However, signs, when they do appear, include coughing, weight loss, fits, vomiting, diarrhoea and clotting problems. Younger dogs (under the age of two) appear to be more susceptible, although dogs of all ages and breeds can be affected.

Diagnosis is difficult and involves several tests conducted by a vet, which means the infection often goes undiagnosed longer than other infestations. Unfortunately, this means that the disease often gets to its advanced stages before being identified. Even so, prognosis is good, although dogs that have been left untreated may have a residual cough as a result of permanent lung damage.

Heartworm lifecycleHeartworm - Heartworm is spread primarily by infected mosquitos and, as a result, is relatively new to the UK. However, with climate change and a relaxation of European pet travel restrictions the risk has increased.

Heartworms, as the name suggests, live in your dog’s heart, they also live in the surrounding blood vessels and lungs. Signs of heartworm include coughing, difficulty breathing and loss of stamina. These symptoms become most obvious when you exercise your pet and, in severe infestations your dog may faint or even die when very excited or over exerting themselves.

Diagnosis of heartworms is only by a variety of tests, including a blood test, administered by your vet. Treatment often includes a period of rest for a few weeks. This is because, while the medication kills the worms, they may be dislodged from surrounding tissue into the lungs causing a severe pneumonic type reaction. Symptoms can appear a lot worse after treatment and your pet may cough blood.

hookwormHookworm - Your pet can develop hookworms by either ingesting them or by absorbing them through the skin. One of the more common routes is young animals being infected by their mothers.

For example, if a pregnant dog has hookworms, the larvae may be reactivated by the pregnancy. The larvae enter her bloodstream and infect her puppies and once born the puppies may also be infected by suckling on their mother's milk.

Hookworms get their name from the hook like mouth parts that attach themselves to the intestines of your pet. They are around 3mm long and, despite their size ingest a great deal of blood from the blood vessels of the intestinal wall.

The symptoms caused by these parasites include anaemia (due to blood loss) – which can be observed as pale gums, diarrhoea and weakness –and intestinal discomfort.

If untreated and your pet becomes highly infested they may develop skin irritations, especially of the paws, this is because the larvae burrow into the skin and cause itching and discomfort.

In severe infestations the worms may move to the vessels of the lungs and heart which may lead to the animal’s sudden death, particularly in young puppies.

Diagnosis of hookworm is only by a variety of tests administered by your vet and treatment is lengthy, and occasionally – in extreme cases may involve surgery! Unfortunately, your pet may become a carrier and worms may be released in times of stress or illness, thus, it is vital to observe good hygiene precautions, especially if you have a pregnant dog!

Other intestinal parasites

Giardia - Giardia is a single-celled parasite that may be present in standing water or other animals’ faeces. Once ingested the parasite develops into cysts, which then attach to the animal’s intestinal walls. These cysts irritate the walls and disrupt digestion and use up nutrients vital for your pet’s health.

While many animals infected with Giardia are asymptomatic, once they do get Giardiasis, the disease caused by Giardia infection, symptoms usually include loss of appetite and diarrhoea. Long term, undiagnosed giardiasis can cause vomiting, weight loss and other gastrointestinal symptoms

Unfortunately, the parasite is very difficult to identify and, therefore, can only be formally diagnosed by repeated testing by your vet. Your pet can also remain a carrier so it is vital to take they back to your vet should symptoms reappear!

Test for internal parasites in pets Coccidia and Giardia Test for Coccidia and Giardia

Coccidia - Coccidia are single-celled parasites that may be present in other animals’ faeces, soil or in rodents of other prey animals.

Once ingested the parasite develops into cysts, which then attach to the animal’s intestinal walls. These cysts irritate the walls and disrupt digestion and use up nutrients vital for your pet’s health.

Coccidiosis, the illness caused by the parasite, mostly affects younger animals or those with a weakened immune system. Early symptoms include mild diarrhoea, which becomes increasingly more severe until it contains mucus and, eventually blood. This is followed by anorexia, weight loss, and dehydration. This acute phase can last around ten days, and in severe cases may lead to the pet’s death.

Unfortunately, the parasite is very difficult to identify and, therefore, can only be formally diagnosed by repeated testing by your vet. Your pet can also remain a carrier so it is vital to take they back to your vet should symptoms reappear!

Treatment and prevention

Unfortunately, there are no preventative measures for worm infestations; as a result, it is vital that you reduce the risk of infection. Therefore, you must always practice good hygiene such as clearing up and disposing of dog faeces safely, making sure that you don’t share food plates with your pets and wash your hands regularly and thoroughly before meals and after handling. Keep on top of your pet’s flea treatment too!

There are many products that are very effective in killing all stages of intestinal worms these are available as:

Oral treatments: Pastes, tablets or liquids that you can place on their food such as PanacurDrontalWormazole, and Veloxa

Spot on treatments: Applied as drops on the skin between the pet’s shoulder blades such as Dronspot and Droncit


In general, your pet should be wormed every three months if you are treating your pet using tablets and every 4-6 weeks if you are treating your pet with the spot on method.

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