Consecutive pathological and immunological alterations during experimentally induced swine dysentery - a study performed by repeated endoscopy and biopsy samplings through an intestinal cannula

Abstract

The development of intestinal lesions after inoculation with Brachyspira hyodysenteriae was followed by repeated endoscopy and biopsy sampling through a caecal cannula. Seven eight-week-old pigs were cannulated and inoculated, two were cannulated but not inoculated, and two pigs were inoculated but not cannulated. Endoscopy, biopsy, and blood sampling to determine SAA (serum amyloid A), haptoglobin, cortisol, and WBC counts were performed at scheduled time-points. At the third day of disease, endoscopy showed a hyperaemic, perturbed mucosa and excessive amount of mucus. Histologically, crypt hyperplasia, depletion of goblet cell mucus, and erosions were noted. Simultaneously, elevated acute phase proteins and circulating monocytes, and decreased number of intraepithelial CD3(+) cells were observed. After five days the pigs recovered. Intestinal lesions were demarcated and interspersed among apparently normal mucosa and blood parameters returned to initial values. Endoscopy through an intestinal cannula made it possible to follow the development of intestinal alterations in vivo and describe the sequential events during the course of swine dysentery. The number of animals used in a study could thus be minimised and the precision of the experiment increased.

Fig. 1

The serum concentrations of the acute phase proteins serum amyloid A (SAA), haptoglobin and cortisol in nine pigs that developed swine dysentery after an experimental challenge with Brachyspira hyodysenteriae. Samples were collected before inoculation, at onset of diarrhoea, when hemorrhagic diarrhoea occurred and once daily thereafter until the day of euthanasia.

Fig. 2

The general endoscopic appearance of the spiral colon of a healthy pig (a) before inoculation and in pigs with overt swine dysentery (b, c, d) after an experimental challenge with Brachyspira hyodysenteriae. (a) Shows the mucosa with a smooth surface, pale colour and distinct vessels before inoculation. (b) Shows the mucosa during the first day of diarrhoea with a perturbed appearance, indistinct vessels and increased amounts of mucus and yellowish material. (c) Shows the mucosa on the third day when haemorrhagic diarrhoea was present. Note the more prominent lesions and areas of haemorrhages. (d) Visualises the gut on the fifth day of disease. The mucosa is still hyperaemic but areas with a smooth appearance and distinct vessels are seen alternating with flecks of yellowish material and demarcated dark spots. (e) Shows the excessive amount of mucus occasionally occurring in the lumen. (f) Shows the intestine of a pig that developed diarrhoea without haemorrhages. On the third day of disease, the mucosa was covered with confluent areas of mucus and yellowish material.

Fig. 3

Histology of biopsies of colonic mucosa. (a) and (b): non-inoculated control pig. Marked predominance of goblet cells throughout the length of the crypts. Some mucin in crypt lumina and on mucosal surface (b). (c) and (d): Brachyspira hyodysenteriae-infected pig, first day of diarrhoea. Goblet cells of lower part of crypts depleted of mucins (d) but crypt length within the variation observed in non-inoculated pigs. (e) and (f): B. hyodysenteriae-infected pig with hemorrhagic diarrhoea, fifth day of disease. (for endoscopical picture, see Fig. 2d). Hyperplastic dilated crypts and markedly attenuated surface epithelium (e). Depletion of goblet cell mucins, mainly in basal crypts areas, and mucin-filled crypt lumina (f). (g): B. hyodysenteriae-infected pig, first day of diarrhoea. Hyperplastic crypts markedly depleted of goblet cell mucins in their major part. (h): B. hyodysenteriae-infected pig, first day of diarrhoea. Superficial erosions with fibrinocellular and haemorrhagic exudation (arrows). a, c, e: H&E × 220; h:H&E, × 275; b, d, f, g: Alcian blue-PAS × 220.