Worm Advice

Types of Parasites

In this guide you will be introduced to 15 of the most common parasites that threaten your pet. Some may be more common than others, but all pose a risk to your pet. You will see these 15 parasites mentioned throughout the guide when we explore other chapters.

Some parasites may sound less of a threat to health than others, but surprisingly, some of the most common and easily treated parasites can cause and carry some dangerous problems, e.g. fleas don’t just bite, but have the ability to carry tapeworm to your pet!

Fleas and flea larvae


Fleas are extremely small and without wings. Well over 2,000 kinds of flea exist across the globe, with the dog and cat fleas Ctenocephalides felis and Ctenocephalides canis being some of the most common. The cat flea is the most widely found species of flea discovered not just on cats, but dogs too.

Their bodies are designed for their biggest talent of all, jumping – one of the reasons why they get around so easily. They can be seen as lively little black specks in the fur or on the skin. Fleas feed on blood, so your dog or cat is the perfect host. But don’t think you are exempt as humans are also on their menu.

A flea’s eggs drop off the infested animal into the surroundings making them easy to catch even without having direct contact with the animal. Many pet owners make the mistake of only giving flea treatments to their pets to find they become re-infested very quickly. Flea eggs are commonly found in dog and cat blankets and beds. Surprisingly, the vast majority of fleas are within the environment, with only approximately 5% living on the animal, and then only when they are feeding. Most of the flea life cycle happens away from the animal.

Fleas can hatch as many as 2,000 eggs in their lives and they are capable of surviving without feeding on blood for some months. They can hold blood weighing considerably more than their body weight.



Ticks are the kings of sucking blood with over 800, possibly over 1,000 species in the world. Ixodes ricinus is the tick species most well known in Britain. This pea-shaped arachnid parasite are known to be a more troubling because they can transmit all kinds of serious diseases, e.g. Lyme’s disease – something that affects both animals and humans.

Dogs are more likely to get ticks because their walks will often been in areas where ticks are rife, particularly in areas with long grass. Cats are have scrupulous self-grooming characteristics, any ticks are less likely to hang around for too long. Either way, you must check for ticks regularly.

Tick larvae are less than 1 mm in length. Fully grown ticks can be between 3mm and 5mm. If you notice ones larger than this, it’s likely they are enlarged with blood, which can extend them to up to 2cm in length. They suck the blood by using their well-adapted mouthparts to penetrate the animal’s skin.

You must be careful if you decide to remove the ticks yourself. You can read up on how to remove them in the treatment chapter on this guide.

Ear mites


Ear mites have eight legs and, unlike parasites that burrow, these ones stay on the surface of your pet’s skin, but within the ear. There are multiple kinds of mite, with the most well-known being the otodectes cynotis. They are normally found in the outer ear canal area. They are attracted to the moisture and like to feed on ear wax and oils.

Ear mites are very contagious between pets, so care needs to be taken in a multi pet household as ear mites commonly re-occur.

Ear mites can cause a lot of irritation for your pet, with excessive head shaking and scratching leading to secondary problems such as aural haematomas.

Luckily, people don’t normally catch ear mites from their pets. Ear mites are most widespread in cats that are allowed outside. From this, they are likely to go indoors and infest other pets, including dogs.



Tapeworms live within your pet’s intestines and appear long and flattened with multiple sections to the body. Adult tapeworms may send out segments of eggs that end up being excreted by your pet. They resemble pieces of white rice and can be found in the faeces or around the anus and surrounding fur.

Dogs and cats are adventurous and like to taste a lot of things, but this just makes them more susceptible to getting tapeworms. More on how pets get tapeworm and other parasites can be read in the next chapter.

Tapeworms can vary in length by quite a bit – they are commonly seen between 8cm and 60cm long!

Noticing your pet has tapeworms is harder than you think, sometimes you will only notice their presence because of the white pieces in your pet’s poo.

Sometimes other symptoms are present in animals and in rare cases tapeworm eggs from pets can infect people causing problems such as cysts.



As their name suggests, roundworms are more tubular in body shape and appear as white or light brown worms big in size. These worms live within the small intestine and feed off of whatever is in the gut of your pet. They can be seen in the vomit or faeces of your pet. Roundworms are commonly a few inches in length.

One roundworm is capable of creating as many as 85,000 eggs every single day.

As with tapeworms, symptoms for roundworms can be minimal in some cases or more noticeable in others. Though the chances of getting disease from roundworm is low, when problems do occur they are often serious and can lead to complications such as blindness.



The name says it all – heartworms are found in the pulmonary arteries and within the heart of the affected pet. They appear white in colour and slim and fine in build. Their sizes can be anything from 12 cm to 30 cm, but are unlikely to be seen as they live inside your pet’s body. The very early life stages of heartworms can be present in the animal’s bloodstream.

Thankfully, heartworms are not known to be within Britain, but would be a risk to any pets travelling to other countries anywhere abroad. Heartworms are transmitted via mosquitoes.

If not attended to, heartworms can cause lots of serious medical problems, with some even leading to fatal consequences.



These irritating flies we avoid getting bitten byare problematic to your pets too. Dogs and cats can be bitten by mosquitoes, which shouldn’t cause any major issues apart from itching and skin irritation. Mosquitoes however, have the ability to carry disease.

Mosquitoes in Britain shouldn’t transmit any disease, but in other countries it can be a risk, so care must be taken if taking your pet to another country.



Lungworm is otherwise known as Angiostrongylus vasorum. These parasites are found in the pulmonary arteries and heart of your pet. They appear as slim worms at about 2cm to 3cm long, but you are unlikely to see these worms as they are internal. The larvae are also not seen, even when excreted, because they are so tiny.

Lungworms can be extremely dangerous to your pet’s health, with fatalities in severe cases. Learn how this worm affects your pet and how it is transmitted in the next three chapters of this guide.

Snails and slugs carry the lungworm parasite and several regions of Britain have infected snails and slugs and because it can kill your pet dog, it needs quick treatment.



Hookworms are found in a pet’s gut. As you can see by their names, hookworms have an anatomy that enables them to fasten themselves onto the walls of the animal’s intestines in order to feed from their blood. They are around 5 and 16 mm long.

Hookworms are found mostly in dogs, with cases in cats being much rarer. Foxes can also be infested with hookworms, with nearly 70% of Britain’s fox population being host to fox hookworm – dogs that frequent areas where there are foxes are able to contract the hookworm through fox faeces so they are at a high risk.

Hookworm larvae can also cause skin infections for both pets and people. For an infested dog, hookworms can have the potential to be dangerous, particularly in puppies.

Biting lice


Lice are insects without wings and their life cycle is spent solely on its host. They appear as little specks on the fur or skin.

Lice, unlike various other parasites, will be exclusive to a particular host – lice on a dog is unlikely to be contagious to a cat and vice versa. This also means humans are not going to be infected.

Puppies, kittens, older cats and dogs or pets with weakened health are most likely to suffer from the effects of lice, whereas healthy pets will suffer skin-based troubles.

Sarcoptic mange mites


These mites have eight legs and only live on the animal. They are the culprits behind the infection called sarcoptic mange – the animal version of scabies – a nasty skin infection that can range from mild to severe in condition.

They are arachnids, which makes them distantly related to other species of parasite such as ticks. Their size is miniscule and they appear white in colour. They feast on the animal’s skin and females can lay between two and three eggs every day.

These mites burrow through your pet’s skin and can cause a lot of irritation, extreme itching and plenty of discomfort if not treated. Unlike some kinds if mites, sarcoptic mange mites can cause hair loss.Sarcoptic mange mites are very contagious, not only between pets but for people too.

Demodex mites


As with sarcoptic mange mites, demodex mites cause mange – a skin infection akin to scabies in humans. The difference between the two is that demodex mites cause skin infections that are less severe than the kind caused by sarcoptic mites. Many dogs have the biological ability to recover or limit demodex mites.

Demodex have eight legs and their bodies are shaped like a cigar. These mites are found feasting in the animal’s hair follicles, as well as the oil glands in the skin.

It’s believed that demodex mites are present in most dogs, but only in small quantities, and this is normal and healthy. It becomes out of control and problematic when the immune system is affected and unable to restrict their existence to the skin.



Whipworms are called whipworms for a reason – as with other parasitic worm names, whipworms have a tail that resembles a whip. Their heads are larger and their length is around two to three inches long.

Whipworms reside in the animal’s large intestine and are only a risk to dogs in Britain. Whipworms live by inserting their heads into the dog’s intestine and using the moisture in the tissue and the blood to feed on.

Whipworms are more to common dogs – the parasite is only seen in cats sporadically. It can be possible for humans to get a whipworm infestation, but it’s only seen in rare cases.

Whipworm can cause mild symptoms, but when severe the infestation can create various health conditions. You can learn about these in the health risk chapter.

Fox Lungworm


Also known as crenosoma vulpis, fox lungworm should not be mistaken with lungworm. This worm is found in foxes and dogs with a risk within Britain.

Fox lungworms reside in the lung airways, with worms being between 6 to 14 mm long – females are typically 11 to 14 mm and males are about 6 mm. Their presence in the airways means breathing problems can occur.

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