You can find parasites in different ways depending on their life cycle and the resting place of the parasite in the body. If it is a blood borne parasite like malaria, you take blood samples and you can look for the parasite in blood cells. Or you can look for its DNA using special equipment. If it is a gut parasite you can usually look for eggs in stool samples – although this can be quite a challenge for various reasons. Some scientists are trying to find new diagnostic tools that are more sensitive than sifting through poo.