Trichuris suis

Trichuris suis
Kingdom	Animalia
Phylum	Nematoda
Class	Enopla
Sub-class	Dorylaimia
Order	Trichocephalida
Family	Trichuridae
Genus	Trichuris
Species	T. suis

Also known as:

Trichocephalus suis Pig Whipworm

Overview

Trichuris suis is a typical whipworm, that primarily infects pigs and can be seen in wild boar. The predeliction site is the large intestine of the pig and the worms are only pathogenic in heavy infections. Heavy infections are rarely seen in the UK as T.suis favours warmer climates, when it is seen it is usually in pigs kept outdoors or in deep-litter systems. The Prepatent period of the worm is 6 - 8 weeks and adults will continue to produce eggs for about 4 - 5 months. When the worm is pathogenic the primary clinical sign is haemorrhagic colitis and may facilitate the invasion of other pathogens, particularly spirochaetes.

Identification

The adult worms are white in colour and about 3- 5cm in length. As with other Trichuris species they have a narrow, fillamentous anterior end becoming broader in the posterior where adult males are coiled. Males possess a single spicule within a protusible sheath though this sheath can vary in length. The eggs are large and characturistically lemon shaped with plugs at both poles and appear yellow/brown in faeces.

Life cycle

The life cycle is typical of the Trichuris worms, the embryonated egg containing the L1 larvae is infective within 1 - 2 of being passed in faeces and under suitable conditions can remain viable of a number of years. Once ingested the L1 larvae hatches and penetrates the glands of the ileum, caecum and colon where 4 moults take place before the adult worm emerges. The pre-patent period of T. suis is 6-8 weeks and the adults can survive for up to 5 months.

Pathogenesis

Most infections are light and asymptomatic but may still be costly to business as they can increase the food conversion ratio of the pig. Heavy infections are uncommon but can cause severe inflammation of the caecal mucosa and haemorrhagic colitis, this irritation is what is believed to allow the invasion of more pathogenic organisms especially spirochaetes.

Use in Human Medicine

In experimental models, Trichuris markedly increases T-regulatory activity, thereby suppressing some immune-mediated diseases (Th2 responses increased; Th1 responses decreased). There is a theory that some human immune-mediated diseases are largely restricted to affluent developed countries (like inflammatory bowel disease and Crohn's disease) occur because the human immune system has evolved with T-regulating helminths constantly present, and therefore tends to go into overdrive in some individuals if this external regulatory influence is lacking. This had led to the hypothesis that strictly controlled exposure of selected human patients to T. suis might ameliorate the symptoms of chronic bowel disease. Large scale clinical trials (placebo-controlled cross-over studies) are currently in progress to test this hypothesis.