4.1 What forms of Ileitis are known?

There are 2 main clinical forms of lleitis commonly seen in pig farming situations around the world: a chronic and acute form. Although they are very different in clinical signs, they are both caused by the same bacterium. Pathology and clinical signs of these forms will be explained and illustrated in this section.

The initial infection is usually at an age of 6 to 20 weeks for chronic Ileitis and 3 to 12 months with acute Ileitis. The incubation period of lleitis is 2 to 3 weeks. Caused by Lawsonia intracellularis, Ileitis is always seen after weaning. Major causes of diarrhoea in neonatal suckling baby pigs include pathogens such as clostridia, coccidia, rotaviruses and enterotoxigenic Escberichia coli, but not Lawsonia intracellularis.

Pigs, that get into contact with Lawsonia intracellularis at later age may develop enhanced clinical signs. The acute haemorrhagic form generally occurs if naive pigs older than approximately 12 weeks contact a significant oral dosage Lawsonia intracellularis. In contrast, chronic and subclinical forms generally develop, if younger pigs (less than approximately 20 weeks-old) contact low to moderate numbers of Lawsonia intracellularis, even when these are derived from the faeces of pigs with an acute form. In common with other oral-faecal transmitted enteric organisms, Lawsonia intracellularis has a low infective dose (only a few bacteria are needed to start the disease in a pig) and it can persist in faeces for long periods under optimum conditions (often around 2 weeks). Increasing dose will result in increasingly more severe disease, progressing through sub clinical, clinical and acute/haemorrhagic disease in naive animals.

Figure 4.1a Forms of PPE (Porcine Proliferative Enteropathy)

A scheme of PPE shows that Porcine Prolifera-tive Enteropathy consists of two main disease forms. The clinical and the subclinical form (see Fig. 4.1 a). The clinical form in itself can be divided into two disease complexes. The first one is the acute disease which is known as Proliferative Haemorrhagic Enteropathy (PHE), the second one is the chronic form. This chronic form is known as Porcine Intestinal Adenoma-tosis (PIA). In some pigs it can lead to Necrotic Enteritis (NE) which can in the end result in a Regional Ileitis (RI).