Threadworms and pinworms are very common amongst schoolchildren and spread through families very easily. They are generally not harmful although an excessive number can cause poor absorption and affect growth and development in children. These parasites lay their eggs at the anus and travel through the gut, usually overnight, to do so. This gives the characteristic itching. Other worms and parasites, such as tropical worms and amoeba, can be very devastating and cause serious illnesses.

Most of these live in the gut, at least initially. Early treatment is advisable and the drugs which are prescribed by doctors stay in the gut and are poorly absorbed. This makes them very effective and non-toxic, although some people can struggle with stomach upsets, nausea and diarrhoea. These drugs should be used if a diagnosis of infestation has been made or if infestation is likely, as in family groups or schools.