Pathogenesis of Infectious Diarrhea – Bacterial causes

Gram-negative bacterial causes of diarrhea

Salmonella spp.

Pathogenic Escherichia coli

Yersinia spp.

Campylobacter spp.

Lawsonia intracellularis

Gram-neg spirochetes bacterial causes of diarrhea

Brachyspira spp

Gram-positive bacterial causes of diarrhea

Clostridium spp. – Clostridium perfringens,

Clostridioides/Clostridium difficile

Acid-fast bacteria causes of diarrhea

Mycobacterium avium subsp. Paratuberculosis

Transmission and Predisposing Factors of Bacteria which cause Diarrhea

fecal-oral route → Can be present in the feed and water

Inadequate passive immunity (neonates)

Poor management practices: Overcrowding, Abrupt changes in feeding/diet, Poor hygiene

Stressing factors; co-infection with a virus, weaning, social hierarchy, intermingling, transportation, handling and routine husbandry practices.

Salmonella spp.

Salmonella spp: horses and poultry

Pathogenesis of salmonella spp.

ruffling of the cell membranes → uptake of the Salmonella into the Salmonella containing vesicles (SCVs)

• Utilizes the Type III secretory system to inject virulence factors such as toxins into the host cells

Activation secretory pathways and alter ion balance → diarrhea

LPS responsible for endotoxic effect

The local inflammatory response damages epithelial cells - diarrhea

Diagnosis of salmonella spp.

Culture: Most Salmonella species – MacConkey – pale (non-lactose fermenter); Brilliant Green agar – red colonies; XLD – red colony black centers

Serology: Serological tests, Serotyping

Molecular testing: PCR, Gene sequencing

Treatment and control of salmonella spp.

Use of antimicrobials is controversial in clinically normal shedder and patients with the localized enteric form of the disease

Vaccination – commercial killed and live-attenuated vaccines

Competitive exclusion with pre- and probiotics

Good animal husbandry and biosecurity measures on farms

Virulence of E. coli

Endotoxin: LPS – Gram-negative released when the E. coli dies

Pyrogenic activity

Endothelial damage leads to intravascular coagulation and endotoxic shock

Capsules: Inhibits phagocytosis

Structures for adherence and colonization, Enterotoxins

Categories of pathogenic strains of E. coli in animals include

Enterotoxigenic E. coli (ETEC)

Attaching and Effacing E. coli (AEEC)

• Enteropathogenic E. coli (EPEC)

Shiga toxin-producing E. coli (STEC)

• Enterohaemorrhagic E. coli (EHEC)

• Strains producing oedema disease

Enteroaggregative E. coli (EAEC)

Enteroinvasive E. coli (EIEC)

Diffusely adherent E.coli (DAEC)

Enterotoxigenic E. coli

Causes the majority of neonatal colibacillosis of piglets and other domestic animals

Colibacillosis refers to an E. coli infection characterised by one of the following

Diarrhea

Enteritis

Septicaemia

Bacteraemia

Enterotoxigenic E. coli Produce 2 important toxins: Heat-labile (LT)

antigenically related to the cholera toxin of Vibrio cholerae → affects adenylate cyclase system leading to hypersecretion of fluid into the intestines → diarrhea, hypovolemia and metabolic acidosis

Enterotoxigenic E. coli Produce 2 important toxins: Heat-stable (ST)

Two types

STa – a plasmid-encoded toxin affecting the guanylate cyclase system causing fluid accumulation in suckling mice and piglets.

STb – causes diarrhea and fluid accumulation in intestines of weaned pigs

Enterotoxigenic E. coli: Possess fimbrial antigens F4 (K88) and F5 (K99) (adhesins)

Diseases caused by E. coli in domestic animals: Pigs

E. coli in oedema disease (STEC)

Occurs in weaned pigs

E. coli colonize like ETEC – F18 pili

Shiga toxin (Stx2e) absorbed from the intestine → Stx2e damages blood vessels in target tissues - edema

Diseases caused by E. coli in domestic animals: Bovine

Diseases caused by E. coli in domestic animals: Ovine

Diseases caused by E. coli in domestic animals: Canine

Diseases caused by E. coli in domestic animals: Poultry

Lab diagnosis of E. Coli

Culture and Isolation: Pathogenic strains readily grow on ordinary media

Blood agar – often hemolytic

MacConkey agar – pink colonies

Eosin Methylene blue agar – characteristic metallic sheen

Identification: Biochemical tests – manual or automated

Laboratory diagnosis of E. coli: Serological demonstration of

Fimbrial antigens using commercial latex agglutination tests (Fimbrex K88, K99, 987P and F41)

Enterotoxins using a monoclonal antibody-based ELISA assays, DNA probes, tissue culture and suckling mice assays

Shigatoxins – Verocytoxin assays or PCR assays (stx1, stx2, eae and hlyA genes)

Specific serotypes, e.g. O139 and O141 associated with oedema disease

Control and treatment of E. Coli

Antimicrobial sensitivity tests due topresence of transmissible R plasmids which harbour antibiotic resistance genes.

Control: ETEC vaccination of dams to improve maternal levels of antibodies in colostrum

• Poultry and cattle

Yersinia spp. virulence factors

Enter mucosa through M cells → bacteria are engulfed by macrophages → Produce toxins which can form pores and stimulate guanylate cyclase activity → increased cGMP levels and fluid accumulation in lumen

• Type 3 secretory system

Produce effector proteins called Yersinia outer proteins (Yops) – delivered to phagocytes-interfere with phagocytosis and produce reactive oxygen species.

Yersinia spp. Diagnosis

Histological examination of intestinal lesions – clusters of organisms in micro-abscesses in the mucosa

Culture and identification: Blood and MacConkey agar incubated aerobically at 37°C for 72 hours → Plate feces directly on selective plates

Serotyping: PCR-based methods

Treatment and control of yersinia spp.

Fluid replacement

Formalin killed vaccine

Good animal husbandry practices

Campylobacter species in dogs: Pathogenesis and Clinical Signs

Intermittent diarrhea may persist for up to 2 weeks sometimes up to months

Diarrhea is most severe in young dogs

Pregnant dogs can miscarry her inborn puppies

Virulence factors in campylobacteriosis in dogs

Cytolethal Distending Toxin

Lipopolysaccharides

Microcapsule or S layer (C. fetus subs fetus, and subsp. venerealis)

Outer membrane proteins

Flagella genes – for motility

Type IV and VI secretion system

Mucus-laden, watery, bile-streaked diarrhea (with or without blood)

Diagnosis of diseases caused by Campylobacter species: Sample

feces or blood - airtight container containing a transport medium like modified Cary- Blair medium

Diagnosis of diseases caused by Campylobacter species: culture and ID

require microaerophilic atmosphere for growth

Culture on selective medium (Campy agar: Skirrow, Butzler, Preston agar)

Strictly microaerophilic (5-10% O2, 1-10 CO2, 85% N2)

Stain smears from cultures and clinical specimens with Dilute Carbol Fuchsin (DCF) for 4 minutes

Treatment of campylobacteriosis

Lawsonia intercellularis pathogenesis

Lawsonia intracellularis clinical signs in weaned pigs(6-12 wks)

Porcine Intestinal Adenomatosis

• Chronic intermittent diarrhea with a reduction in weight gain

• Acute hemorrhagic enteropathy

Lawsonia intracellularis clinical signs in foals

Equine proliferative enteropathy (EPP)

• Rapid weight loss

• Diarrhea

• Colic

• Depression

• Fever

• Subcutaneous ventral edema

Lawsonia intracellularis: Treatment and Control

Antimicrobial agents such as tylosin or tiamulin may be used prophylactically or therapeutically in feed and water

Cleaning and disinfection of contaminated premises

Vaccination

Brachyspira spp.: General characteristics

Anaerobic intestinal bacteria, 6-14 spirals

Pathogenic Brachyspira spp. can be found in the intestines of both clinically affected and normal pigs

Can survive in moist feces for weeks (about 2 months) → Susceptible to desiccation

Brachyspira spp. and conditions

Brachyspira hyodysenteriae: Transmission

Fecal-oral route

Disease spreads slowly through pens

Dogs, rats, mice and flies may act as vectors

Brachyspira hyodysenteriae: Clinical signs

Weaned pigs 6 to 12 weeks old

Decreased appetite/Increased thirst

Emaciation/Loss of condition

Profuse muco-hemorrhagic diarrhea

Brachyspira hyodysenteriae: Virulence factors

Motility

Chemotactic capacities

Lipopolysaccharide

Haemolysin(s)

Enzymes such as NADH oxidase

Brachyspira hyodysenteriae: Pathogenesis

Brachyspira hyodysenteriae: Diagnosis

Darkfield microscopy on abnormal mucosa or fecal swabs

Culture: Blood agar with antibiotics incubated at 42°C for at least 3-5 days, anaerobically

• Complete hemolysis around colonies

PCR: Immunofluorescence

Serological tests- ELISA

Brachyspira hyodysenteriae: Treatment and control

Improved sanitation and hygiene

Medication of drinking water → Tiamulin, lincomycin and nitroimidazoles

Depopulation, Cleaning and disinfection

Vaccination using the whole cell bacterin: Questionable efficacy

Clostridium perfringens virulence factors: α toxin

produced by all strains

acts on cell membrane & cause hemolysis/cell necrosis

Clostridium perfringens virulence factors: β toxin

produced by strains B&C

necrotizing enteritis & contraction of intestinal smooth muscle

Clostridium perfringens virulence factors: ε & ι toxin

ε (strains B&D), ι (strain E)

produced as a pro-toxin which is activated by proteolytic enzymes

Canine Hemorrhagic Gastroenteritis

Caused by overgrowth of Clostridium perfringens type A

Necrotic enteritis in chickens (rot gut) agent and transmission

C. perfringens type A and less frequently type C

fecal-oral route

Necrotic enteritis in chickens(rot gut)

Predisposing factors: Dietary, Mucosal damage, Coccidia usually occurs concurrently

Clinical signs: Sudden death

• Depression, ruffled feathers, diarrhea

Hemorrhagic Enteritis in Pigs

C. perfringens type C

Distribution: Worldwide in newborn piglets

Pathogenesis: β-toxin → binds to vascular endothelial cells → vascular necrosis + necrosis of villi

Clinical signs: Sudden death

• Dullness, anorexia, blood-stained feces, perianal hyperemia

Hemorrhagic Enteritis in Pigs: postmortem findings

Hallmark lesion-segmental mucosal necrosis with marked hemorrhage in the small intestines

Necrosis of the intestinal mucosa with blood-stained contents in the terminal small intestines, cecum and colon

Serosanguineous fluid in the pleural and peritoneal cavity

Pulpy kidney (Overeating disease) Thriving lambs 3 to 10 weeks of age

C. perfringens type D

Distribution: worldwide

Predisposition: Excessive consumption of high grain and low roughage diet

• immunocompromised animals

• GI parasites

• Decreased intestinal motility

Pulpy kidney(overeating disease) pathogenesis

Gorging on high grain diet or succulent pasture

High starch content of the food is suitable for the rapid proliferation of clostridial organisms

Ingestion of excessive quantities of food leads to the entry of partially digested food from the rumen to the intestine

Production of toxins – mainly ε toxin

Pulpy kidney (Overeating disease) Clinical signs

Lambs often found dead

CNS – Dullness, opisthotonos, convulsions and terminal coma, blindness and head pressing

GI – bloating (later stages)

Hyperglycemia and glycosuria are constant features

Pulpy kidney postmortem finding

Acute disease: endocardial hemorrhage, excess pericardial fluid

Rapid kidney autolysis – pulpy (friable/soft) cortex

Focal symmetrical encephalomalacia – subacute effects of ε toxin → symmetrical hemorrhagic lesions in the basal ganglia and midbrain

Diagnosis of pulpy kidney

Clinical signs & post-mortem findings

ELISA assay for toxin

Toxin neutralization in mice

PCR for toxin producing genes

Diseases caused by various types of Clostridium perfringens

Diagnosis of C. perfringens enterotoxemias

Direct smears from the mucosa or intestinal from postmortem samples

Mouse inoculation tests

ELISA tests can be used as an alternative to in vivo assays

Culture and Isolation of C. perfringens

PCR can be used to detect toxin coding genes

Treatment and control of C. perfringens enterotoxaemias – Large animals

Hyperimmune serum

Acute nature of disease so antibiotic therapy is generally ineffective

Vaccination is the principal control method

Good animal husbandry practices

Avoid sudden dietary changes

Clostridioides difficile Habitat:

usually found as normal flora of the gut

Disease conditions associated with C. Diff

Pseudomembranous colitis

Chronic diarrhea in dogs

Hemorrhagic enterocolitis in foals without prior antimicrobial therapy

Neonatal diarrhea in pigs in the USA

Nosocomial infections in humans

Antibiotic associated: use of clindamycin, lincomycin, ampicillin, amoxicillin, cephalosporins and fluoroquinolones

Clostridioides difficile virulence factors: Toxin A (enterotoxin)

Stimulates fluid secretion

Diarrhea

C. diff virulence factors Toxin B (potent cytotoxin)

Damages enterocytes in the gut causes hemorrhage

Pathogenesis of C. diff

Antimicrobials causes a disruption in the normal flora of the intestine

Overgrowth of C. difficile from persistent spores

Toxin production and diarrhea

Clostridioides difficile overview

Pathogenesis of Johne’s disease

Paratuberculosis: Granulomatous proliferation of ileo-cecal mucosa (also in local

lymph nodes)

Diagnosis of paratuberculosis

Live animals

Observation of history and clinical signs confirmed by the demonstration of MAP in the feces by

Microscopy-scrapings or pinch biopsies from infected animals

Culture – special media required can take weeks, also rapid media with radiometric detection

If your not going to explain the rest of them idgaf

Diagnosis of paratuberculosis at necropsy

Finding of the pathognomonic lesions of the disease in the intestines, either grossly with the demonstration of typical acid-fast organisms in impression smears of the lesions or histologically

Isolation of MAP in culture

Control of Johnes

Isolate animals with clinical signs suggestive of Johne’s

Affected animals should be slaughtered promptly – shed large numbers of the organism

Bacteria can contaminate buildings and pasture

Detect and eliminate subclinical animals

Treatment of Johnes

Vaccines: Adjuvanted and live attenuated whole cell vaccines or subunit vaccines

Vaccinated animals become sensitive to tuberculin

Based on the immunodominant protein antigens – stimulate a strong Th1 response

Fungal causes of diarrhea in dogs and cats: Moldy food – mycotoxins

Consumption of contaminated food items including dairy products, walnuts, peanuts, stored grains, pasta

Rummage through garbage cans → Encountering decomposing substances

Clinical presentation of mycotoxins in dogs and cats

Early signs: Diarrhea, vomiting, agitation

Intermediate signs: Seizures, tremors, stiffness, weakness

Severe signs: Pneumonia, hypothermia, abnormal clotting

Types of Mycotoxins: Penitrem-A (tremortin)

Produced by Aspergillus, Claviceps and Penicillium

Most common type of mycotoxin frequently found in mold growing on bread, nuts, cheese and other spoiled products

Types of mycotoxins: alfatoxins

Produced by Aspergillus spp.,

Can also be a component of many types of molds

Can affect liver function

Types of mycotoxins: vomitoxin

A trichothecene mycotoxin produced by Fusarium spp. Which grows on grains such as those used to make bread or dog food

Infrequent cause of poisoning in dogs mainly caused by contaminated dog food

Types of mycotoxins: Roquefortine

A tremorgenic mycotoxin frequently found with penitrem-A