GASTROENTERITIS

Gastroenteritis

• Inflammation of stomach or intestines– Inhibits nutrient absorption and excessive H2O and

electrolyte loss

• Bacterial • Viral• Parasites • Poisoning by microbial toxins

– food borne intoxication

• Signs and Symptoms:– General features: diarrhea, loss of appetite, abdominal

cramps, nausea, vomiting and possibly fever– Dysentery – Typically self Limiting

• Enteric fevers – Systemic with severe headache, high fever, abscesses,

intestinal rupture, shock and death

• Epidemiology– Occurs worldwide– Oral to fecal route of transmission

• Water common reservoir • Overcrowding & poor sanitation are risk factors • Animals may be source of infection

• Prevention – Hand washing– Proper food handling and complete cooking– Pasteurization of milk and juices – Adequate sanitation– Safe water supplies

• Treatment– Rapid replacement of fluids and electrolytes– Anti-nausea medication – Antimicrobials may be used in severe cases

Bacterial Gastroenteritis

• 3 groups of gram negative bacteria account for most bacterial intestinal infections: – Vibrio cholerae (Cholera) – Enterics (Salmonella, Shigella, E. coli)– Campylobacter jejuni

Cholera

• Causative agent: Vibrio cholerae • High infectious dose

– Bacteria sensitive to stomach acid – Adheres to small intestine and multiply– Bacteria don’t enter cells

• Cholera toxin– Potent exotoxin – Causes intestinal cells

to rapidly pump out electrolytes

– Passive osmotic H2O loss follows

– Metabolic acidosis – Shock

• Heavy loss of fluid – “rice-water stool”

• Up to 20L of fluids lost per day• May discharge 1 million bacteria per ml of feces

• Untreated cases potentially fatal – Fluid/electrolyte replacement – Tetracycline reduces toxin production

Shigellosis

• Causative Agent: Shigella sp.– S. dysenteriae, S. flexneri, S. boydii, S. sonnei

• Low infecting dose – Bacteria not sensitive to stomach acid

– Characterized by fever and dysentery

• Infects cells of large intestine and initiates intense inflammatory response

• Dead cells slough off• Produces areas covered with

pus and blood

• All species produce enterotoxin and type III secretion systems

• S. dysenteriae produces powerful endotoxin– shiga-toxin

• Ciprofloxacin, rifampin or azithromycin may reduce duration and infectivity

Traveler’s Diarrhea

• Causative Agent: Escherichia coli– Multiple antigenic strains (O, H, K)– Virulent strains have fimbriae, adhesions and

multiple toxins

• Enterotoxigenic E. coli – Enterotoxins – Type III secretion system– Typically self limiting

• Enterohemorrhagic E. coli – O157:H7– Produce potent Shiga-like toxins and type III secretion

systems

• Antimicrobials cause increase in toxin production

Salmonellosis and Typhoid Fever

• Causative agent: Salmonella enterica – 2000 strains (serotypes) – Typhimurium and Enteritidis commonly cause

Salmonellosis – Typhi and Paratyphi cause Typhoid Fever

• Common intestinal flora of many animals

• Contaminated animal products are reservoir

• Reptiles, eggs and undercooked poultry

• Virulent strains tolerate stomach acid and pass to intestines

• Toxin induces phagocytosis in intestinal cells

• Pathogen reproduces inside phagosome killing host cell

• Bacteria (Typhi) may pass 倠䁝 through intestinal cells into bloodstream

Campylobacteriosis

• Causative agent: Campylobacter jejuni – Leading cause of bacterial diarrhea in United States– Estimated 1million cases annually with ~100 deaths

• Associated with poultry– Low infecting dose

• Virulent strains possess adhesions, cytotoxins and endotoxin – Induce endocytosis in cells of intestine and initiate

inflammation and bleeding lesions

• Non-motile mutants are avirulent

• Severe cases treated with ciprofloxacin or azithromycin

Bacterial Food Intoxication

• Staphylococcus aureus – Halotolerent; grows well in foods at room temp– Associated with cafeterias and social functions

• 5 heat stable enterotoxins:– 1000 for up to 30 min– Stimulate muscle contractions, nausea and intense

vomiting, diarrhea and cramping – Acute and self limiting

• symptoms begin 4-6 hrs after consumption and end within 24 hrs

Botulism

• Causative agent:– Clostridium botulinum

• Obligate anaerobic, Gram +, spore forming bacillus

– Produce 7 different neurotoxins • One of most deadly toxins known

• Signs & Symptoms– Dizziness, dry mouth, blurred vision– Abdominal symptoms include pain, nausea,

vomiting and diarrhea or constipation– Progressive paralysis

• Paralysis of respiratory muscles most common cause of death

• 3 forms of botulism:– Food-borne botulism – progressive paralysis of

all voluntary muscles due to toxin production

– Wound botulism – similar symptoms

– Infant botulism – bacteria grow in the intestines, producing non-specific symptoms• “floppy baby syndrome”