Pathology of bacterial infections in the GI system Flashcards
Cell type in intestine responsible for Absorption
Enterocyte
Cell type in intestine responsible for Antimicrobial proteins
Paneth cell
Cell type in intestine responsible for Mucus production
Goblet cell
Cell type in intestine responsible for microorganisms, particles and macromolecules uptake and transfer
M cell
Cell type in intestine responsible for regulation of
intestinal motility, secretion, appetite etc
Neuroendocrine cell
3 Mechanisms of Diarrhoea
- Secretory
- Osmotic
- Inflammatory
Mechanisms of secretory diarrhoea induced by bacterial toxins
Secretory diarrhea from bacterial toxins involves adenylate cyclase activation, raising cAMP levels, stimulating ion secretion, and inhibiting absorption, resulting in watery diarrhea and electrolyte imbalance.
Mechanisms of malabsorption diarrhoea due to bacterial overgrowth
Excessive growth of bacteria in the small intestine, disrupting normal nutrient absorption. Mechanisms include bacterial fermentation of carbohydrates, bile acid deconjugation, mucosal damage, and competition for nutrients, leading to impaired absorption of nutrients and water, resulting in diarrhea with characteristic features such as steatorrhea (excess fat in stool) and nutrient deficiencies.
3 Consequences of diarrhoea
Dehydration
Electrolyte depletion and imbalance
Metabolic acidosis
What do endotoxins do
Stimulate macrophages and endothelial cells to secrete proinflammatory cytokines and nitric oxide.
Cause cell dysfunction and lysis.
What do exotoxins do
Inhibit biochemical pathways within a cell.
E.coli mechanism of action
Adhere to microvilli on intestinal epithelium
Cl- secretion from enterocytes causing Secretory diarrhoea
Salmonella mechanism of action
bacteria survive within macrophage phagolysosomes
Toxins interfere with closure of Chloride channels secretory diarrhoea
Salmonellosis – pathogenesis of infection
M cells in intestinal epithelium> macrophages in lamina propria
and Peyer’s patches >transferred to mesenteric lymph nodes >via portal circulation to liver
Peracute Septicemic Salmonellosis
Multisystemic vascular lesions with fibrinoid change, thrombosis and necrosis
Disease of calves, foals and pigs – younger animals most sensitive
Usually fatal in animals 1-6 months of age
Signs of Peracute Septicemic Salmonellosis
petechiation and blue discolouration (cyanosis)
of ventral abdomen, extremities (ears commonly affected)
Peracute Septicemic Salmonellosis cause of death
Disseminated intravascular coagulation (DIC)
Acute Enteric Salmonellosis mostly affects….
Horses
Pathogenic effects of Acute Enteric Salmonellosis
Interference with Chloride channels = Secretory diarrhoea
induction of enterocyte apoptosis + recruitment of neutrophils
endotoxins = vascular thrombosis
Button ulcers are commonly caused by
Chronic Enteric Salmonellosis
Lawsonia intracellularis mostly infects
Swine
Swine clinicopathological presentations
Porcine Proliferative Enteropathy (PPE)
- Porcine Intestinal Adenomatosis (PIA)
- Necrotic enteritis
- Proliferative Haemorrhagic Enteropathy (PHE)
Diagnosis of Lawsonia intracellularis
ELISA (serum) L. intracellularis specific IgG
(indicating exposure to infection rather than active disease)
PCR on faeces L. intracellularis DNA
(indicating active infection with faecal shedding)
Distinctive gross PM findings
Immunohistochemistry
Bacteria that causes suppurative bronchopneumonia in foals and ulcerative colitis
Rhodococcus equi
Mechanisms of Clostridial disease
- Local effects of toxins on the mucosa- haemorrhagic, fibrinous or necrotic enteritis
- Secretory effects of locally acting enterotoxin- diarrhoea and minor mucosal lesions
- Systemic absorption of (entero)toxins- affects sites distant from the gut
Causes of massive expansion of enteric populations of clostridia
Changes in the enteric microenvironment
- change in feed, abnormally nutrient-rich digesta – CHO dumping
- antibiotic therapy
- altered pancreatic exocrine function or trypsin inhibitors
- reduced intestinal motility
- primary infections (CPV-2 in dogs or Coccidiosis in piglets & chickens)
Focal symmetrical encephalomalacia (FSE) Pulpy kidney disease is caused by…?
Cl. perfringens type D enterotoxaemia
Haemorrhagic canine gastroenteritis is caused by….?
Clostridium perfringens type A
Necrotising-haemorrhagic enteritis in foals / enterocolitis in adult horses is caused by…?
Clostridium perfringens type A
Potomac Horse Fever (Equine Monocytic Ehrlichiosis) is caused by ..?
Neorickettsia risticii
Idiopathic Inflammatory Bowel Disease (IBD) pathophysiology
Villus blunting (and possible alteration of superficial epithelium)
Variable crypt dilation (filled with mucus and cellular debris)
Possible crypt epithelial hyperplasia
Inflammatory cell infiltration in lamina propria (and variably intraepithelial)
Breeds predisposed to IBD
Basenji
German Shepherds
Boxer (see GCB)
Irish Setter- enteritis associated with familial hypersensitivity to wheat protein
Diagnosis of Inflammatory Bowel Disease (IBD)
Endoscopic biopsies
Diagnostic pathology approach & work up
Histological assessment (revised WSAVA standards / other algorithms)
Differential diagnosis with intestinal lymphoma small cell (EATCL-2)
Immunohistochemistry
