The gut of chickens and ducks can be infected with a number of different roundworms. They  become infected with worms from soil, feed or water contaminated with worm eggs.Worm eggs survive in warm, damp conditions.  Heavy infections cause weight loss, diarrhea and poor egg production. But worms can be killed by treating the bird with a suitable anthelmintic. Ail worms are killed by tetramisole or levamisole. Birds are either treated separately or the drugs are mixed with the feed or water. Coccidia are treated with several drugs which are added to the drinking water or feed.

Next to internal parasites, a number of lice and mites infect birds and cause severe irritation which leads to loss of feathers, loss of weight and low numbers of eggs. Small ticks feed on the blood of birds and can carry germs which will cause other diseases. External parasites will hide in the walls, floors and bedding of the cages and houses where birds are kept. In order to control the parasites, it is necessary to keep these places clean and kill any parasites there.