Necrotic enteritis (NE) occurs worldwide, especially in high health status herds. It affects weaners, growers and finishers. NE effects are diarrhoea, wasting, pallor, black dung, sudden death.
- Causes of Necrotic enteritis (NE) >
- Effects of Necrotic enteritis (NE) >
- Diagnosis of Necrotic enteritis (NE) >
- Treatment & Control of Necrotic enteritis (NE) >
Causes of Necrotic enteritis (NE)
Proliferative enteropathy is caused by a bacterium, Lawsonia intracellularis, which reproduces in cells. It is a Gram negative, curved, rod-shaped organism with tapered ends and can be grown artificially in cell cultures by a few specialised laboratories worldwide.
The organism can produce microcolonies after seven to 14 days and can survive outside cells for up to two weeks at 5°C but not multiply. Pure cultures of the organism cause all forms of the disease. The bacteria enter cells lining the intestine, usually those of the end of the small intestine (ileum) and sometimes those in the large intestine, and multiply, causing the cells to become immature in appearance, eliminating the absorptive villi and encouraging the crypts between them to lengthen, thus making the intestinal lining non-absorptive, thick and lumpy in infected areas.
Inflammation occurs with loss of red (and some white) blood cells and infected intestinal epithelial cells. Necrotic Enteritis develops as the intestine recovers, and the thick mucosa breaks down to become necrotic, eventually giving rise to thickening of the muscular coats in Regional Ileitis or 'hosepipe gut'. Faster breakdown can cause massive blood loss into the ileum to cause Proliferative Haemorrhagic Enteropathy (PHE). Recovered pigs are immune to re-infection.
Effects of Necrotic enteritis (NE)
Necrotic Enteritis (NE) occurs after Proliferative Enteropathy (PE, Ileitis), and porcine intestinal adenopathy (PIA) - and is accompanied by regional ileitis (RI) and proliferative haemorrhagic enteropathy (PHE).
PE is most commonly seen in recently-weaned pigs and lasts for about six weeks. It has an incubation period of three to six weeks and can occur in animals of any age from three to four weeks to adults.
The first signs are failure to gain weight or loss of weight and varying degrees of inappetence. Affected pigs appear pale, may vomit, are anaemic and may have blackened faeces due to the presence of black, altered blood. Some animals pass loose granular faeces which spread on concrete like portions of wet cement especially where infections with organisms such as spirochaetes are also present.
After four to six weeks affected pigs may recover completely. Some die suddenly at this stage with proliferative haemorrhagic enteropathy These usually appear pale with a low body temperature (37.8°C, 100°F) one to two hours prior to death and may be of any age from six to ten weeks upwards. Twelve percent of a newly infected herd may be affected and 6% may die. Where no effective treatment is given, some animals become stunted. They may appear thin, hairy, pale and may have mild diarrhoea or dark pasty faeces. These are the animals with Necrotic Enteritis (NE) or Regional Ileitis (RI) and can eventually die or develop into stunted adults.
Diagnosis of Necrotic enteritis (NE)
Necrotic Enteritis is a late stage of Proliferative Enteropathy and its related syndromes (PIA, PHE and RI) and all of the clinical signs of these conditions may be present where NE occurs.
Growing pigs become pale with loss of condition and blackened faeces are present in older pigs, these signs and the sudden deaths from proliferative haemorrhagic enteropathy could also be due to gastric ulceration. Diarrhoea or loose faeces is not a reliable indicator of the disease, but commonly occur.
Pigs with NE are older and have usually had some of the above clinical signs. At post-mortem examination of affected pigs, the terminal ileum is thickened, pale and its lining is contoured into folds which resist stretching. Parts of the large intestine may also be affected. The affected gut lining is covered with dead tissue or even eroded completely (Regional Ileitis, RI). Laboratory tests confirm the presence of the disease or infection.
Characteristic changes in the arrangement of the cells of the intestinal lining can be seen by microscopy, but at this stage, the dead tissue may be so extensive that this pattern is difficult to see. The organisms can be demonstrated in, or isolated from, some cells deep in the mucosa and confirmed as Lawsonia intracellularis. L. intracellularis can also be identified in faeces of the affected pig or its group by the Polymerase Chain Reaction (PCR) and antibody to it may be detected in the blood of affected animals using ELISA tests. Other bacteria such as salmonella may also be present.
Treatment & Control of Necrotic enteritis (NE)
As Necrotic Enteritis (NE) is a late stage of Proliferative enteropathy (PE, Ileitis) - treatment and prevention are the same as for that disease).
Individual clinically-affected pigs may be treated with injectable long-acting tetracycline or antimicrobials such as tylosin tiamulin and lincomycin. Water medication of affected groups with tetracycline, tylosin, tiamulin or lincomycin usually results in a clinical cure of mildly affected animals, but very stunted animals may not recover.
Chlortetracycline treatment in feed for two weeks will have the same effect and valnemulin, tiamulin, tylosin, lincomycin or acetylvaleryl tylosin are also effective.
As disease can recur 3 weeks after the end of treatment in infected groups, a second course of treatment is often given 18 days after the end of the first course. When spirochaetosis, salmonellosis or other bacterial disease is present, the treatment should be modified accordingly. Animals which do not regain appetite and begin to grow within 7 days of treatment should be destroyed.
Control based on treatment may be given continuously at low level, but disease will recur after the treatment is discontinued. Most commonly, two courses of treatment at therapeutic level are given, beginning 18 days after entry to a house or earlier if the disease occurs before this.
Disinfection with quaternary ammonium, iodine and oxidising disinfectants at the end of the period of treatment and rodent control reduce the chances of re-infection. Herds founded by hysterectomy and maintained in isolation are usually free from the disease, but may become infected. Breeding stock should come from clean herds. Vaccination with a live attenuated strain of L. intracellularis can be given to recently weaned pigs and prevents clinical disease and reduces or prevents infection with pathogenic L. intracellularis . They must not be receiving antimicrobial at the time.
