It’s possible that you can’t always detect if your pet has parasites. Fleas can conceal themselves under your pet’s fur, and some ticks are so little they are just the size of a pinhead, making them incredibly elusive. Roundworms are an example of an intestinal parasite that can cause diarrhoea, vomiting, dehydration, and other issues, although some infected pets don’t even exhibit any symptoms of sickness.