Dogs suffer from a variety of internal and external parasites. Regular grooming will help you spot early signs of infestation. Even some internal parasites leave telltale signs on the fur and skin. Particular vigilance is needed with puppies, which can inherit parasites from their mothers, and in warm weather when parasite populations explode, making all dogs more prone to attack.

Internal parasites
Dogs have internal parasites ranging in size from microscopic single-celled Giardia to grotesquely long tapeworms. Fortunately, there are effective, safe, and convenient worming medications available from your vet that prevent or eliminate virtually all dog worms.
Parasite Type
How do Dogs get them?
Symptoms and Treatment
Roundworms (common)
Pups can pick up these worms from their mothers before birth, or from suckling on the mother’s contaminated skin.
Severely affected pups are pot-bellied. Pups from 14 days of age and pregnant mothers are wormed routinely using products such as fenbendazole.
Tapeworms (common)
The most common tapeworm (Dipylidium caninum) is picked up by eating an infected flea. Other tapeworms can be contracted from uncooked offal from a variety of livestock, but especially sheep.
Tapeworms rarely cause signs of disease in dogs. The most common sign of infection is dried tapeworm segments that look like grains of rice in the hair around the anus. Worm with praziquantel. Avoid access to animal carcasses or feeding uncooked offal.
Hookworms (uncommon)
One species (Uncinaria) occurs in colder climates and is picked up when dogs lick material contaminated by worm eggs. Another species (Ancylostoma) occurs in warm climates and is also contracted through mother’s milk or by larvae burrowing through the skin.
Weight loss, diarrhoea, blood in the droppings, or skin inflammation, especially around the paws or belly, can indicate infection. To treat, mother and pups are wormed, the environment is cleaned and clinical conditions, such as anaemia, are corrected. Worm with fenbendazole.
Whipworms (uncommon)
Worm eggs build up in the environment where they may survive for years in shaded areas. Eggs are accidentally eaten by dogs. They mature into tiny adult worms that cause severe damage to the intestines.
Signs of infection include diarrhoea, often very smelly and tarry with dark blood. In severe cases, the coat is dull and a dog loses weight and may have abdominal pain. To treat, the environment is cleaned and all dogs wormed. Get veterinary assistance.
Giardia (common)
A microscopic, single-celled parasite, picked up from contaminated water. This is an underdiagnosed cause of diarrhoea in dogs.
Diarrhoea, possibly with blood and abdominal pain is a sign of infection. Treat all waiter while hiking. Give fenbendazole or veterinary recommended treatment.
Heartworms (common in many parts of Europe and Australia, but not the UK)
Eggs are passed on to a dog by mosquito bites. These mature into large worms that reside in the heart.
Coughing and debility do not occur until disease is well advanced. Dogs that live outdoors have a higher risk of infection. Prevent, using selamectin or ivermectin, or treat following your vet’s advice.

External Parasites


Fleas are activated by body heat, vibration, and dog odours. Dormant larvae “come alive”, mature into fleas, then hop on your dog for a blood meal. They spend the rest of the time making baby fleas. Fleas are picked up from the dog’s environment as well as from other animals.

Fleas are the most common external parasites. They leave their eggs and larvae in carpets, which must be treated to prevent reinfection of your dog. Professional sodium borate, tetraborate, or polyborate carpet treatments reliably destroy flea eggs. Do not use laundry grade borax as it may cause eye, respiratory, or kidney problems.

Fleas cause itchiness in most dogs (see p.230). Look for fleas or flea dirt, shiny specks on the skin, especially over the rump. Prevent or treat with effective, safe medications. Always treat the environment as well as all dogs and cats. Use products that prevent the flea lifecycle completing or safe spray or “spot-on” substances that kill fleas.
Ticks(Many are harmless, but some cause paralysis)
Ticks wait in long grass. A shadow, vibration, or even a change in temperature signals a meal has arrived. The tick attaches to the dog, burrows its mouth into the skin and sucks a meal until it
bloats with blood and drops off. Ticks can carry a range of diseases including Lyme disease, Babesia, and Ehrlichia.
Ticks swell enormously and are easily seen when engorged. Apply alcohol to the tick to kill it. Then, using tweezers, twist it at its root in the skin to corkscrew it out. Just pulling may leave the mouthpiece and lead to infection. Prevent ticks by using a recommended product. Avoid squeezing ticks, as this releases more “poison” into the dog.

Ear mites are contracted from another dog, usually the mother, and are most active at night.

Demodex mites are inherited from mother. They cause problems in dogs with weak immunity.
Sarcoptic mites are acquired from another dog, fox, coyote, or wolf. The mite tunnels into the skin, causing a skin disease called scabies.

Cheyletiella mites are most commonly a puppy problem, inherited from the mother.

Dogs with ear mites produce wax and debris in their itchy ears. Treat with a veterinary ear drop or lotion.
Demodex often causes hair loss without itching. Your vet will dispense a prescription treatment.
Scabies is intensely itchy, often affecting the ear tips and elbows. It responds to selamectin and other veterinary treatments.
These mites cause a thick dandruff over the back, often with no itchiness. They are easily killed with anti-flea treatments.
Dog lice are contracted in unhygienic environments such as puppy farms. The lice leave their eggs, called “nits”, glued to the dog’s hair.
Lice cause itchiness and, like fleas, if an infestation is intense they cause blood loss and anaemia. Lice are destroyed by many effective anti-flea treatments.