Pinworms are parasites -- they survive by feeding off a host -- that affect only a few animals and cannot survive in the digestive tracts of any other species. Because of this, they do not spread between animals and humans. However, one type of pinworm only affects humans.
Pinworms are intestinal roundworms that live in the intestinal tract of certain animals. There are four well-known types of pinworms: Enterobius vermicularis, which infects humans; Oxyuris equi, which infects horses; Passalurus ambiguus, which infects rabbits; and Syphacia obvelata, which infects hamsters. All of these pinworms have round, white bodies that are about a half-inch long. Pinworms don't infest cats or dogs; different pinworm types do not pass among different animal species. For example, pinworms that infest horses cannot pass to humans or rabbits.
Pinworms deposit eggs on the outside of hosts' bodies, near the anal area by adult females. This usually happens at night, when adult females leave the host's body and lay their eggs. The eggs can survive for up to three weeks outside the host body. Eggs that make it back into the animal's digestive system hatch and grow into adults in the large intestine, where they live and reproduce. The total life cycle of a pinworm is about five months long.
In order to continue the life cycle and spread from animal to animal or person to person, a pinworm's eggs need to return to the digestive tract. When the host animal grooms himself or another infected animal, the eggs that were laid near the anal area are picked up by the tongue, swallowed, and make their way to the large intestine. They can also spread through contact and later ingestion. For example, pinworm eggs may spread to a rabbit's paw during one grooming session and be ingested later when he grooms himself again.
Symptoms of a pinworm infestation are usually mild and sometimes nonexistent. The most obvious indication is itching around the anal area where the eggs are deposited. Horses will often rub their tails, while rabbits will chew the area and humans will scratch. Weight loss, nausea and sleeplessness due to intense itching are other common symptoms.
Treatment for pinworms is usually twofold. Oral medication is given in carefully spaced doses to kill adults. The first dose kills existing adults, while the following dose kills those that hatched after the first treatment. The anal area of the infested animal is cleaned daily to remove eggs, and all bedding and objects that come in regular contact with him must also be washed.