Nematodes can be broken down into many different classes but for our purposes it is easiest to look at them in four different groups according to their shape or where they are found in the body - roundworms (ascarids), hookworms, lungworms and whipworms.
Roundworms are an elongated cylindrical shape growing to about 10-13 cm in length. Hookworms are small worms of only about 1 cm in length with a characteristic 'hook-shaped' head. Lungworms are small worms found either in the lungs or adjacent organs. Whipworms have a slender head and thick tail which gives them a 'whip-like' appearance.

Dogs and cats can acquire nematode infections from their environment, especially places such as the local park.

Certain species can also be transferred in other ways such as through the mother's milk or by eating a bird or mouse that has eaten an infective egg. For more information look in the 'Methods of Infection' section