Two main categories exist, external parasites or ectoparasites, which live outside of the body, in or on the skin, and internal parasites or endoparasites, these are the ones that live within the body, commonly in the intestines.

Some parasites cause disease and are consistently pathogenic, while others are relatively harmless to the dog’s health. Much depends upon the age of the dog, (pups and elderly animals suffer the most effect) the general health of the dog and its nutritional state, and the state of the dog’s immunity- this is reduced in the bitch during pregnancy.

Some parasites spend all their life on the host (dog), such as lice, while others such as fleas and ticks spend only part of their life on the host.

Neospora canium is a protozoan parasite (single celled, and microscopic).
The disease is seen in cattle and can be a major cause of abortion. In the dog, it is most often seen in puppies, and young dogs.

Typically it causes hind limb paralysis,or ataxia (loss of muscle co-ordination). This can progress to affect the fore limbs, as well as swallowing and breathing. In many cases rigid hyperextension (over extension of a limb). Other reported clinical signs are fore limb ataxia (weakness), head tremors, myocarditis, (inflammation of the heart muscle) and pneumonia.

As dog owners the most common worms that concern us are; the round worm, and the tape worm.

Round worms, (toxicara canis) these are slender worms with tapered ends. They are individual males and females. They grow up to 10 centimetres long. The eggs of these parasites produce larvae. The larva moult either inside the host (dog), or outside the host, before becoming adult worms.

Stage one, (L1) the adult female worms living in the small intestine of the dog lay eggs which leave the dog when it goes to the loo. These eggs are capable of travelling great distances via shoes, vehicles, and by being blown around in the wind etc, so their distribution can be over a very wide area.

The dog usually eats the eggs during activities such as fur washing. Stage two (L2) of the round worm, is the most infective stage, they are still in the egg, and will develop into adulthood within two or three weeks. Though they can be dormant for two years.
In a young pup, aged four to six weeks the worms are at stage two, (eggs) living in the lungs, they moult into stage three, and migrate up the wind pipe causing the pup to cough, the pup then swallows the spit, and the parasite then moults to stage four within the pups stomach. Adult worms are then able to mate and the female will produce eggs about a week later. These are then passed as the pup goes to the loo, and the whole process starts again.

In older pups aged about ten to twelve weeks, the stage two moults follows a different route. They leave the lungs via the blood stream, travel around the body, to the left side of the heart; they are distributed to the liver, muscles and lung tissue where they lie dormant for very long periods of time. This is called somatic migration.

When and if, a bitch becomes pregnant, stage two is reactivated, (at about the sixth week of pregnancy) and moves around in the blood stream until they settle down in the placenta or afterbirth, this is usually around the six week gestation period – this is due to the bitch’s lowered immunity during pregnancy. The larvae cross the placenta and enter the foetus (unborn pup); they lodge in the liver and lungs. At birth the whole process starts again, the pup coughs; swallows……….and is passing adult worms by the age of two weeks. The bitch then cleans up after her babies and re-infests her self. This is why worming is so important for the in whelp bitch and the pups as they grow up. There are many worming routines available and your veterinary surgeon will be best able to advise you.

The Demodex mite lives in the hair follicles, said to be present in almost all dogs, but they can and do become a problem when the immune system is down, causing disease ‘Demodectic Mange’. Some times animals don’t develop adequate immunity, and the mites spread and general skin disease is the result. Often very common in the shorthaired dogs - such as the Boxer and Dobermann. The skin reddens, and itches, the hair falls out. There are two main types, localised or dry, usually present on the head and front legs, and feet this settles on its own. Generalised form, common in younger dogs under a year old, the lesions spread over the body and the hair follicles become infected with secondary bacteria, causing small pus filled pimples.

Cheyletiella, or walking dandruff is a fairly common problem in Boxers. Small spider like mites produce a ‘dandruff’ and irritation along the back of the dog, they can just be seen with the naked eye and cause intense irritation to people who are sensitive to them. The adult has combs on the ends of its legs and hooks on the mouthpart. It can be seen in brushings or skin scrapings. Commonly found on rabbits.
It can be very difficult to get rid of, and good husbandry as with all these parasites is essential. Now there are many products available from your vet to treat the condition as well as maintaining condition in the dog through diet and exercise.
Fleas are usually encountered at some time during a dog’s life; the most common flea in England is the cat flea, though all fleas human, rabbit or what ever will have a go!!

They suck the blood of the animal and the bites cause irritation. Some dogs develop allergies to the bites causing dermatitis. They easily move from host to host with their legs they are capable of jumping great heights and distance. Good husbandry again is the answer; they lay their eggs in cracks and crevices, along the skirting boards and in the pile of our carpets. They only spend a short while on the dog to feed then fall off, so keeping on top of the environment is essential. There are many topical products that can be used with very good effect.

It is said that adding garlic to a dogs food will reduce flea infestations, and lavender oil is also effective on dog bedding – and it smells nice.

This has been taken from part of the work I did when at college. It is not intended to be exhaustive and is a guide only. It may not be reproduced in part or whole.

These worms are not round, but segmented parasite that complete their life cycle through an intermediate host. The head of these worms has a number of hooks and suckers that the parasite uses to attach its self on to the small intestine of the host (dog). The segments grow from the head onwards to produce a segmented worm. Each segment contains male and female organs, and fertilisation can occur with the segments, or between the segments of the worm usually at the end of the worm. The end segments are filled with eggs, when the segment is shed; it is passed out of the body as the dog goes to the loo. In addition to this the segments themselves have a muscular action, and can move themselves. If the larvae of a flea eat the egg, it will encyst its self until the flea becomes an adult, dog will then eat the flea, which has the head containing the hooks and suckers, and the process starts over again…
Signs of infestation would include loss of condition, and weight loss despite a good appetite.

Of course there are lots of worms that can infest and infect our dogs, but most are readily treated with the right product. Worming needs to be carried out on a regular basis throughout the dog’s life, and it is important to get a detailed worming history of your puppy when you collect him/her, it needs to be remembered that worming products are essentially a poison so dosage must be correct.

Probably the most common ecto - parasites found on the dog are the scabies mite, demodex mite, ear mite, fur mite (cheyletiella or walking dandruff). Fleas, lice, and ticks. Of course there are many others, as well as various fungi such as those causing ringworm.

Mites commonly found on dogs are permanent parasites and spend all of their life on the host. The life cycle lasts around three weeks, that is the time taken for a newly laid egg to develop into larvae, nymph, and then adulthood.
Some of the mites are sub surface and lie just beneath the skin. They are round, with short legs, such as the sarcoptic mite, (canine scabies), causing hair loss and itching, usually around the ear edges, and elbows then spreading into a more general area affecting the whole body. Often they also cause intense itching to the owners. They are identified with a microscope and relatively easy to treat.