Porcine proliferative enteritis (PPE) is characterized by hyperplasia of crypt enterocytes with inflammation and sometimes ulceration or hemorrhage. Lesions always include thickening of the mucous membrane of the small intestine and/or large intestine. The lesions vary considerably by location, extent, and duration. Many terms have been used to describe this disease, including: porcine hemorrhagic enteropathy (PHE), porcine intestinal adenomatosis (PIA), necrotic enteritis (NE), regional or terminal ileitis (RI), ileitis, and garden-hose gut.
There are two main forms of PPE: an acute form called PHE that occurs from 4-12 weeks and a chronic form known as PIA that occurs from 6-20 weeks.
The piggery had 33 breeding sows, several boars, including three introductions within the last 12 months, and home-bred piglets, weaners and growers. Under temporary new management approximately 50 weaners had died in the past six months following intermittent bouts of inappetance, diarrhoea, lethargy and wasting.
Sows were up-to-date with vaccinations for erysipelas, leptospirosis and parvovirus, and all animals were being fed age-appropriate commercial feed. The property had issues with rodent control and flooding in the weaner shed.
A post-mortem was conducted on a weaner pig by the private veterinarian. There was extensive necrosis and autolysis that impaired full histology and no diagnosis was reached.
The district veterinarian was contacted by the private veterinarian to assist with further investigation of this case and a property visit arranged.
The 12-14-week-old mixed sex Landrace cross Large white weaner pigs were examined.
The district veterinarian examined the weaners in a pen in which nine of 12 weaners had died recently including one overnight (pig 1). Two live pigs were examined as they appeared abnormal. One was wasted (pig 2) and one weak (pig 3). The pigs had normal vital signs and no neurological impairment was found on the examination. Pig three was quiet and reluctant to stand. The skin appeared flushed. There was diarrhoea in the pen containing undigested feed, and no blood.
The small and large intestines in all three weaners were grossly thickened, and were lined by diphtheritic membranes in pig 3. Samples were submitted from these weaners.
PCR of faeces (pigs 1 and 2) was positive for Lawsonia intracellularis (LI) and Brachyspira pilosicoli. Samples submitted from pigs 1 and 2 were selective salmonella culture negative, and PCR was negative for Brachyspira hyodysenteriae, porcine delta coronavirus (PDCoV), porcine epidemic diarrhoea virus (PEDV), transmissible gastroenteritis virus (TGE), porcine respiratory coronaviruses, bovine viral diarrhoea virus (BVDV), classical swine fever (CSF) and African swine fever (ASF), and general mammalian virus isolation did not show any cytopathic effect. Blood was porcine circovirus 2 (PCV2) PCR low positive at a level that was not consistent with porcine circovirus associated disease (PCVAD).
The mucosa is diffusely markedly thickened by pseudo-stratified, crowded and mitotically active crypt epithelium, with plump, vesiculated nuclei. Multifocally, villous tips are moderately to severely blunted and fused, or replaced by thick bands of cellular and karyorrhectic debris (necrosis), admixed with granular, lightly basophilic material (bacterial colonies), moderate infiltrations of lymphocytes, plasma cells, neutrophils and fewer eosinophils, and moderate amounts of hypereosinophilic, fibrillar material (fibrin). The mucosa is concurrently expanded by clear space (oedema) and mild lymphoplasmacytic proprial infiltrates.
Variably between sections there are numerous intraluminal, or occasionally proprially invasive, large (30-54 x 36-76 µm), rounded, ciliated protozoa, with a paracentral macronucleus (consistent with Balantidium coli trophozoites).
Special stains: Warthin-Starry Silver stain reveals large numbers of short, comma-shaped, agyrophilic bacteria, clustered apically within enterocytes, free within crypt lumens and occasionally within B. coli trophozoites (consistent with L. intracellularis).
L. intracellularis: There was strong intracellular immunoreactivity at the apical margin of epithelial cells, and to a lesser extent within small numbers of macrophages in the lamina propria.
B. pilosicoli and PCV2: There was no significant immunoreactivity within examined sections.
Intestine: enteritis, proliferative and fibrinonecrotizing, diffuse, severe, chronic, with lymphoid depletion and crypt herniation, cryptitis, intraepithelial, agyrophilic bacteria, aetiology consistent with L. intracellularis, and intralesional ciliated protozoal organisms, pig (Sus scrofa domesticus).
In consultation with the owner and private veterinarian antibiotics were added to the feed. Tiamulin (Tiamulin Fumerate 25 Millpack Liernert Australia) was added to the feed at 120ppm for 14 days. The weaner shed was cleaned and disinfected.
Vaccination for LI was recommended to the owner to reduce further losses both clinical and subclinical and to reduce the ongoing need for antibiotics. Further testing of pigs of different ages was recommended to determine the timing and extent of exposure to LI and to investigate further for the presence of PCV2 within the piggery. There is a vaccine for PCV2.
The owner reported fewer deaths after the antibiotics were commenced, however did not wish to pursue vaccination at this point.
Rodent and fly control, shed hygiene and biosecurity were discussed to assist in reducing the transmission of LI.
Investigating the primary cause of diarrhoea and wasting in growing pigs is complicated by mixed infections, as in this case, where histopathology was used to diagnose porcine proliferative enteropathy (PPE) caused by LI, with concurrent B. pilosicoli, PCV2 and balantidium infections. LI is an obligate intracellular, microaerophilic, non-flagellated, non-spore forming, gram-negative, curved or S-shaped rod bacterium. 1,11,12
The two main clinical manifestations of PPE caused by LI infection in pigs are porcine intestinal adenomatosis (PIA) and porcine haemorrhagic enteropathy (PHE)1.
PIA is most common in post-weaning animals aged 2-5 months, and can progress to necrotic enteritis (NE), usually involving superimposed secondary bacterial infections, and then regional ileitis (RI) if the animal recovers from NE.3,6,10,11-13 Clinical signs of PIA vary from subclinical infection, to reduced growth rate with capricious appetite, to persistent diarrhoea, wasting and mortality.11-13 Mortality rates are usually low and are most often a consequence of secondary bacterial infections.5 The differential diagnoses include brachyspiral colitis, salmonellosis, colibacillosis, Clostridium perfringens type C, yersiniosis, coronaviruses and porcine circovirus-associated disease (PCVAD).4,10,11,13
PHE is acute and most common in finishing pigs, young gilts and boars, typically 4-12 months of age, especially when naïve animals are introduced to a site of endemic LI infection.3,13 PHE is associated with acute to subacute intestinal haemorrhage, which may manifest as melena or haematochezia, weakness and pallor, or rapid death associated with exsanguination, with mortality rates reaching up to 50 percent.3,11-13 The main differential diagnoses include swine dysentery (B. hyodysenteriae, B. hampsonii, and B. suanatina), salmonellosis, gastric ulcers and haemorrhagic bowel syndrome, which is often attributed to intestinal volvulus.13
Macroscopic lesions in PPE are most common in the terminal ileum and also occur in the cecum and colon.11,12 Rarely infection may be restricted to the large intestine. Gross lesions consist of ridges or plaque-like thickened areas that project above the normal mucosa and on the serosal surface the hyperplastic mucosa and oedematous submucosa forms a reticular or cerebriform pattern of projections, which is virtually pathognomonic.11-13 In NE there is more extensive mucosal necrosis, often with diphtheritic membranes and luminal fibrin casts4,11-13 and discrete areas of haemorrhage and ulceration, most common in the ileum.11,12
The diarrhoea observed in PPE is most likely due to loss of functional mucosal surface area, whereas wasting most likely relates to protein-losing enteropathy.8,12,13 As the mucosal thickening in PIA becomes more extensive there is coagulative necrosis of the mucosa, allowing for colonization by pathogenic anaerobic large bowel flora and the formation of diphtheritic membranes and fibrin casts.12 It is unclear if development of PHE relates to the host, infectious dose, virulence of the infecting strain and/or other coinfections.3 Experimental infection of gnotobiotic pigs has shown that PPE will not occur without undefined interactions with other gut bacteria, such as pathogenic E. coli and Salmonella.12,13
As in this case multiple potential pathogens may occur in the same animals, and the relationships between PPE and other diseases are often complex, with LI causing alterations in the composition of the gut microbiome, and either directly or indirectly increasing the likelihood of coinfection with some pathogens such as Salmonella enterica, and decreasing the likelihood of others, such as PCV2.3,6,10 Although B. pilosicoli was identified by PCR in this case, clinical signs and gross changes were not suggestive of porcine intestinal spirochetosis, which typically presents as a watery to mucoid diarrhoea associated with typhlocolitis.7,12 Histologic changes in this case were consist with LI, and not with B. pilosicoli which causes goblet cell hyperplasia, with organisms often forming a ‘false brush border’ of palisading upright bacteria perpendicular to enterocytes, or being observed within colonic crypts and goblet cells.12 A flagellated protozoan, consistent with Balantidium coli, was also observed in this case. B. coli is a facultative pathogen of the intestinal lumen, usually associated with subclinical infection.9 Following injury to the intestinal wall trophozoites may penetrate into the mucosa, usually in the caecum and colon, causing diarrhoea, haematochezia and tenesmus.9,12
The gold standard for diagnosis of PPE is immunohistochemistry (IHC) using LI-specific antibodies.2,13 Other methods of characterizing spirochetal organisms on histologic section include in situ hybridization and electron microscopy.3,11 Cultivation of LI is not routinely performed, and requires live tissues cultures.11,12 Faeces or tissue samples can be used for PCR and faecal smears can also be tested using immunoperoxidase staining.2
Treatment of LI infection is by antimicrobials and control is dependent on biosecurity, vaccination, and antimicrobials. Strict hygiene and biosecurity within and between sheds is also important. Rodent and fly control is also recommended.
Preventing infection through biosecurity is the key. Carrier pigs exist. Isolation, testing, antimicrobials and vaccination can be used prior to introduction. Quaternary ammonium compounds, iodine and Virkon S are effective disinfectants.14
Eradication using early weaning has not been effective, however a control program using PCR testing and antimicrobials showed the number of PCR positive animals in the herd decreased over a 14 week period.3
In the face of clinical disease antimicrobials are necessary. Clinical signs are usually observed when pigs are about 8-11 weeks of age. The preferred treatment is Tiamulin 120ppm or Tylosin 100ppm for 14 days in feed or water. In acute disease in-water medication is more effective.1 The disease is usually treated at the herd level. There is no published information on treatment of individual animals.
Pigs can be vaccinated with an oral ileitis vaccine to prevent infection with LI from 3-12 weeks of age. Administration through drinking water using the water proportioner is a labour saving and efficient method of vaccination.1
Many thanks to Dr. Genevieve Liebich of Orange Veterinary Hospital and the University of Minnesota for their contributions to this case.