Background and history

This describes a group of conditions involving pathological changes in the small intestine, associated with a recently identified bacteria called Lawsonia intracellularis. The disease is world-wide in its distribution, the infectious organism exists on most if not all farms and lives inside the cells lining the small and large intestines.

PE is now recognised as having a serious affect on performance including, variations in weight gain, reduced feed efficiency, poorer grading and impaired gut function.

Research has shown that even mild cases may cost $2.00 to $3.00 per pig and in severe cases up to $15.00.

Disease occurs in four different forms;

1. Porcine intestinal adenopathy (PIA) which describes an abnormal proliferation of the cells that line the intestines.
2. Necrotic enteritis (NE) where the proliferated cells of the small intestine die and slough off (necrosis) with a gross thickening of the small intestine (hosepipe gut).
3. Regional ileitis (RI) or inflammation of the terminal part of the small intestine.
4. Proliferative haemorrhagic enteropathy (PHE). In the latter there is massive bleeding into the small intestine, hence the common name bloody gut.

The exact mechanisms of spread are not known but the organism is found in other species including rabbits, birds and rodents. Infected faeces are the major vehicle for movement of the organism around the farm and those herds that have persistent problems are likely to have poor management of faeces, dirty pens and passages and heavily contaminated floor surfaces. Boars and adult pigs act as carriers with transfer of infection to piglets thus maintaining the cycle of infection. The breeding herd can be a source of infection.

Studies suggest that the organism can survive outside the pig for 2-3 weeks. Infected pigs excrete organisms for 6 - 8 weeks and it can be found in the tonsils.

PIA and NE tend to occur in young growing pigs but sudden and severe outbreaks of PHE with high mortality can occur in pigs 60 to 90kg weight and maiden gilts. Gilts either already carry infection as they enter a farm and unknown factors trigger disease or they become infected on the farm for the first time. Ironically PE is more common in high health herds but the reasons for this are unknown.

Clinical signs

Thin pig with ileitis

These are dependent on the nature of the changes that take place inside the small intestine and in many cases disease is so mild that signs are not detected. With PIA the pig appears clinically normal initially eats well but there is a chronic diarrhoea, gradual wasting and loss of condition, followed in some cases by a pot bellied appearance. Necrotic enteritis gives a similar picture but acute disease is manifest by bloody gut or PHE and the pig may die suddenly or appear very pale and anaemic and pass black bloody faeces. Secondary bacterial infections often increase the severity of the disease. PHE occurs frequently in young gilts, particularly within 4 to 6 weeks of arrival on the farm, at the point of service and up to the middle stage of pregnancy. Pigs with the chronic form of the PE recover over a period of four to six weeks, however there can be considerable losses in feed efficiency and daily gain of up to 0.3 and 80g/day respectively. As a consequence there can be marked variations in sizes of pigs.

Diagnosis

Thickened gut wall associated with ileits

This is carried out by the clinical picture, post-mortem examinations, histology of the gut wall and demonstrating the organism in faeces by an ELISA test. A serological test is also available called Ileitest, carried out on blood samples of 11 pigs, 80 - 100 kg in weight. These results can determine the levels of exposure in the herd. They are also an indicator of farm and pen hygiene. Tissue cultures have been recently developed.

Prevention

• Avoid over stocking.
• Strategically medicate incoming gilts with tylosin or other antibiotics if there are problems, commencing one week before signs usually appear. Continue for four weeks as under treatment.
• Reduce environmental stress.
• Reduce the mixing of pigs.
• Make sure pigs have ample water.
• Wash out and disinfect gilt pens between batches. The organism is excreted via the faeces and continual use of pens increases the exposure rate allowing endemic disease to develop.
• Develop all in, all out procedures.
• Where problems continue in growing pigs, pens should be washed out and disinfected between batches and pigs strategically medicated.
• Keep pens as dry as possible.
• Carry over of infection between batches appears to be a significant part of the epidemiology.
• Remove any sick pigs to hospital pens and treat.
• Virginiamycin as a growth promoter will often prevent disease.
• Medicate hospital pens with tylosin or tetracycline in the water for 5 days.
• In severe continuous outbreaks it may be necessary to medicate all feed with 200-400g per tonne CTC or OTC. If using tylosin medicate for 3 weeks at 100g / tonne followed by 40g per tonne continuously.
• Lawsonia intracellularis is susceptible to quaternary ammonium compounds but not particularly so to phenolic disinfectants. Washing pens using a detergent is probably the best method.

Treatment

• The following antibiotics have been shown to be effective against the organism.
  • Tylosin, enrofloxacin and chlortetracycline. Intracellular antibiotics such as tylosin gain access to the organisms in the cells and can eliminate them.
    
  • Virginiamycin - used as a growth promoter could be used to prevent disease.
    
  • Tiamulin and tilmicosin also show activity.
• When gilts are introduced onto the farm preventative medication using 300-500g/tonne of tetracycline or alternatively 100g / tonne tylosin over the first 4 to 6 week susceptible period, are effective means of control.
• Treat individual pigs with injections of tylosin or oxytetracycline and give 300-800mg of iron dextran.
• Offer creep for one to two weeks fed as a gruel.
• In acute outbreaks medicate the water for 2 to 3 days with OTC/CTC or tylosin. Follow this in-feed with 400g / tonne OTC/CTC or tylosin 100g/tonne for 2 - 3 weeks. If using tylosin as a preventive measure medicate at 40g/tonne continuously.

Strategic medication. This is applied at a selected time on the farm to pigs 6 - 8 weeks of age to prevent disease. Intracellular antibiotics are best used because the organism Lawsonia intracellularis lives inside the cells.

Vaccination

An alternative to antibiotic treatment is vaccination with a live attenuated isolate of Lawsonia intracellularis (Enterisol® Ileitis). The vaccine is designed for active immunisation of weaned pigs from three weeks of age to reduce intestinal lesions caused by Lawsonia intracellularis infection and to reduce growth variability and weight gain losses associated with the disease.

The administration of the oral vaccine can be performed by drench or by drinking water.

Vaccination by drench application: Administer a single 2 ml dose orally to pigs (from three weeks of age), irrespective of body weight.

Vaccination via the drinking water: Water systems have to be cleaned and rinsed with untreated water to eliminate residues of antimicrobials, detergents or disinfectants. The final solution containing the vaccine should be consumed within four hours after preparation.

Under field conditions, an improvement in average daily weight gain (ADG) and weight uniformity was seen when vaccinated pigs were compared to non-vaccinates.