Intestinal worms help themselves to your dog's food and can damage the gut causing loss of blood. Worms can also cause diarrhoea, dehydration and anaemia, and this may make your dog run-down and susceptible to other diseases. If there are a lot of worms your dog may cough, lose weight, have a rough, dry coat or a 'pot-bellied' appearance. In puppies a worm infection can be more serious, causing poor growth and sometimes even death. If there are large numbers of worms the intestine can become blocked (although this is rare in an adult dog) and this may be fatal.