External Parasites on pets

Charlotte Howard By Charlotte Howard, 8th Jul 2010 | Follow this author | RSS Feed
Posted in Wikinut>Guides>Pets>Tips & Advice

An overview of external parasites that can be found on pets

Types of external parasites

A parasite is any organism that lives on a host to survive, and there are many that can live on our pets. Some parasites like worms live in the guts of animals, but there are parasites that can live on the skin of our pets, known as ectoparasites. There are several types of external parasites, and if not treated they can cause skin irritations, and many carry diseases that can be passed on to humans.


The most commonly seen parasite is the flea. However, many people do not realise that there are actually several different types of flea. The cat flea is the usual flea to be seen on cats and dogs that can survive on both animals, whilst the dog flea can bite other animals, but rarely survives unless the host is a canine.

Fleas can jump up to 2 meters, meaning that close contact is not really need for this parasite to jump to a new host. The eggs can also survive for many months, and sometimes years, in the fibers of carpets and rugs, not hatching until they sense the warmth of a mammal.

Whilst normally seen during the warmer months, when the summer heat causes the eggs to hatch, they can survive throughout the year and eggs can be caused to hatch by the central heating in homes. Fleas survive by biting the host and drinking their blood. The females lay their eggs which hatch into larvae that then proceed to feed on debris such as skin flakes and feces.

Fleas can cause severe skin irritations and allergic reactions such as Flea Allergic Dermatitis (FAD), which sometimes requires steroids to reduce the serious inflammation and itching. They can also carry diseases and the eggs of other parasites. It is very common to see an animal that is infected by fleas to also have tapeworms. The eggs of tapeworms are often found in the flea’s stomach. As the animal grooms, they swallow the flea, and the egg of the tapeworm is released into the stomach which then moves along to the intestine.

It is easy to diagnose a flea infestation as they can be seen. They also leave feces on the animal, which appear as black flecks. When sprayed with water, these black flecks leave a red stain, which is deemed as proof of a flea infection.


Ticks don’t care who the host is, they will happily live on any animal. They burrow the jaws under the skin and drink blood until they are full before dropping off and moving onto the next victim. However, it is known that ticks can carry diseases such as Lyme disease.


There are two kinds of louse that can be found on pets, the biting louse lives on the skin eating dead skin particles, whilst the sucking louse burrows its jaws into the skin and drinks blood. A skin scraping will be taken from pets with suspected louse infection, and the vet will check the skin under a microscope as these parasites cannot be seen by the naked eye.

Unlike most parasites, lice are host-specific, meaning that they cannot be transferred to other species of animal. They are usually caught by pets who live in close contact with each other. They cause the skin to become irritated, but most injuries seen in pets with a louse infection are self-inflicted from scratching and excessive licking.

The eggs are laid on individual hairs, and often appear as tiny white dots. These ‘nits’ are cemented to the hair and can be difficult to remove. Along with parasitic treatment, grooming with a fine-toothed comb can help to remove the eggs.


There are many kinds of mites that can live off our pets. Some of these mites burrow beneath the skin, whilst others will live on the surface, but they all cause skin irritations and can be passed on to other animals.

The burrowing mite family includes the Sarcoptes mites. These mites are responsible for infections such as mange and scabies, often seen on foxes (mange) and sheep (scabies), they are normally seen on dogs, and rarely seen on cats. It is the Notoedres mite that is usually seen on cats and rats and the Cnemidocoptes mite that is seen on birds, causing ‘scaly legs’. Burrowing mites cause the skin to itch, and are often referred to as ‘itching mites’.

Two surface mites that can be seen in pets are the Otodectes and Cheyletiella mites. The Otodectes mite lives in the ear canal of its host. This mite is normally shown when the pet shakes the head and scratches at their ears frequently. In some cases, the head shaking becomes so violent that blood capillaries within the ear can burst causing an aural hematoma, easily corrected with surgery to release the fluid build up. These kinds of mites are often treated using ear drops.

Cheyletiella is also known as ‘walking dandruff’ as this is what it resembles. Often seen by the naked eye as white flakes wandering around the skin, this little mite feeds off the dead skin cells, but can bite causing small red lumps to appear.

Fungal Infections

Not a true-parasite, but fungi can live on the skin of our pets. Whilst there are many different kinds of fungi, there are two specific varieties that are found on the skin of our pets; moulds and yeasts.

Ringworm is a mould that can be passed on to other animals, including humans. It is commonly seen as a ring or circular shape in a bald area. The mould irritates the skin causing hair loss and inflammation of the skin. Ringworm is usually diagnosed by shining an ultraviolet lamp over the area, as the mould that causes the infection will typically glow an apple-green under the light. Fortunately ringworm can be treated effectively using a medicated shampoo and wash.

The yeast infection, thrush, is commonly seen in animals that have been on long-term antibiotic treatment, especially in pets that are young, sickly or elderly. The yeast usually builds up in a warm, moist area such as the mouth, but it can irritate the skin as well.

Malassezia pachydermatitis is the yeast infection that can grow on perfectly healthy skin. This infection irritates the skin causing it to inflame, with a yellow crust. Yeast infections are often treated with a anti-fungal topical treatment.


Whilst not a common parasite seen on pets, flies occasionally lay eggs on animals, especially those with an open wound. As the eggs hatch, the maggots will eat away at the infected skin tissue. This is called myasis or ‘fly-strike’. Fly strike is a serious infection that can cause an animal to become anemic or send them into shock. If not treated the pet with fly-strike will become seriously ill before dying.

Fortunately, all parasites can be prevented simply by keeping pets healthy and clean. Using regular parasitic treatment can deter them from using your pet as a host, and can kill any parasites that are living on your pet’s body. Make sure that you also wash your pet’s bedding, and keep carpets hovered and floors mopped to further infection, or transmission. It is also important to make sure that pets are kept up-to-date with their vaccinations and health checks to keep them fit and healthy, able to fight any infections that may occur.

Source: BSAVA Veterinary Nursing Second Edition edited by D.R Lane and B. Cooper


Ectoparasites, External, Fleas, Lice, Mice, Parasites, Pets, Ticks

Meet the author

author avatar Charlotte Howard
I write for Helium.com, and am also a published author. Somehow I also manage to be a busy Mum to 2 young children and housewife as well!

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