Microbial Diseases of the Digestive System: Study Guide

Diseases of the Digestive System

Overview of the Digestive System

The digestive system is responsible for the breakdown and absorption of nutrients, as well as the elimination of waste. It consists of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and accessory organs such as the liver, pancreas, and gallbladder.

• Mouth: Entry point for food; site of mechanical and chemical digestion.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water and forms feces.

Infection vs. Intoxication

Diseases of the digestive system can result from either infection or intoxication:

• Infection: Caused by the growth of a pathogen in the GI tract. Symptoms usually appear after an incubation period.

• Intoxication: Caused by ingestion of preformed toxins. Symptoms appear rapidly, often within hours.

Definition: Gastroenteritis

Gastroenteritis is the inflammation of the stomach and intestines, typically resulting in diarrhea, vomiting, abdominal cramps, and sometimes fever.

Bacterial Diseases of the Digestive System

Dental Caries

• Organism: Streptococcus mutans (primary agent)

• Signs/Symptoms: Tooth decay, pain, visible holes in teeth.

• Prevention: Good oral hygiene, reduced sugar intake, fluoride.

Periodontal Disease

• Gingivitis: Inflammation of the gums, caused by plaque accumulation.

• Periodontitis: Progression of gingivitis; destruction of supporting bone and tissue.

• Organisms: Various anaerobic bacteria, including Porphyromonas spp.

Staphylococcal Gastroenteritis

• Organism: Staphylococcus aureus

• Key Feature: Produces heat-stable enterotoxin.

• Symptoms: Rapid onset vomiting, diarrhea, abdominal cramps.

• Temperature Abuse: Allowing food to remain at room temperature enables bacterial growth and toxin production.

• Prevention: Proper food handling and refrigeration.

Shigellosis (Bacillary Dysentery)

• Organism: Shigella spp.

• Pathogenesis: Invades M cells in the intestinal mucosa, multiplies, and spreads to neighboring cells, causing tissue destruction and inflammation.

• Symptoms: Bloody diarrhea, fever, abdominal pain.

Salmonellosis

• Organism: Salmonella enterica

• Symptoms: Nausea, vomiting, diarrhea, abdominal cramps.

• Typhoid Fever: Caused by Salmonella typhi; more severe, with high fever, weakness, and sometimes a rash.

Cholera

• Organism: Vibrio cholerae

• Symptoms: Profuse watery diarrhea ("rice-water stools"), dehydration, shock.

• Mechanism: Cholera toxin causes secretion of water and electrolytes into the intestine.

• Treatment: Oral rehydration therapy, antibiotics in severe cases.

E. coli Gastroenteritis

• Organism: Escherichia coli (various pathotypes)

• Enterohemorrhagic E. coli (EHEC): e.g., O157:H7; secretes Shiga-like toxin, can cause bloody diarrhea and hemolytic uremic syndrome (HUS).

• Enteropathogenic E. coli (EPEC): Causes diarrhea in infants.

• Enterotoxigenic E. coli (ETEC): Produces enterotoxins; major cause of traveler's diarrhea.

Campylobacteriosis

• Organism: Campylobacter jejuni

• Symptoms: Diarrhea (often bloody), fever, abdominal cramps.

• Complication: Guillain-Barré syndrome (autoimmune paralysis) can rarely follow infection.

Peptic Ulcer Disease

• Organism: Helicobacter pylori

• Symptoms: Abdominal pain, nausea, sometimes bleeding ulcers.

• Treatment: Antibiotics and acid-suppressing drugs.

Clostridium perfringens Gastroenteritis

• Organism: Clostridium perfringens

• Symptoms: Abdominal cramps, diarrhea.

• Source: Often associated with meat dishes kept warm for long periods.

Clostridium difficile Diarrhea

• Organism: Clostridium difficile

• Symptoms: Mild diarrhea to life-threatening colitis.

• Risk Factor: Often follows antibiotic therapy that disrupts normal gut flora.

Viral Diseases of the Digestive System

Rotavirus

• Symptoms: Severe watery diarrhea, vomiting, fever (especially in infants and young children).

• Prevention: Vaccination.

Norovirus

• Symptoms: Acute gastroenteritis with vomiting and diarrhea.

• Transmission: Fecal-oral route, highly contagious.

Mumps

• Organism: Mumps virus (a paramyxovirus)

• Symptoms: Swelling of parotid glands, fever, headache.

• Complications: Orchitis (inflammation of testes), oophoritis (ovaries), meningitis, deafness.

• Prevention: MMR vaccine.

Hepatitis Viruses

Type	Transmission	Symptoms	Complications
Hepatitis A	Fecal-oral	Fever, jaundice, malaise	Usually self-limited
Hepatitis B	Blood, sexual	Fever, jaundice, joint pain	Chronic infection, cirrhosis, liver cancer
Hepatitis C	Blood	Often asymptomatic	Chronic infection, cirrhosis, liver cancer

Fungal Diseases of the Digestive System

Ergot Poisoning

• Cause: Ingestion of alkaloids produced by Claviceps purpurea (on grains).

• Symptoms: Hallucinations, convulsions, gangrene.

Aflatoxin Poisoning

• Cause: Ingestion of aflatoxins produced by Aspergillus flavus (on peanuts, grains).

• Symptoms: Liver damage, increased risk of liver cancer.

Protozoan Diseases of the Digestive System

Giardiasis

• Organism: Giardia lamblia

• Symptoms: Prolonged diarrhea, greasy stools, abdominal cramps.

• Transmission: Contaminated water.

Cryptosporidiosis

• Organism: Cryptosporidium spp.

• Symptoms: Watery diarrhea, stomach cramps.

• Transmission: Contaminated water; resistant to chlorine.

Helminthic Diseases of the Digestive System

Tapeworms

• Organisms: Taenia spp., Diphyllobothrium spp.

• Symptoms: Often mild; abdominal discomfort, weight loss.

• Cysticercosis: Infection with larval cysts; can affect eyes (ophthalmic) or brain (neurocysticercosis).

Hookworms

• Organisms: Necator americanus, Ancyclostoma duodenale

• Symptoms: Anemia, fatigue, abdominal pain.

• Transmission: Larvae penetrate skin, migrate to intestines.

Pinworms

• Organism: Enterobius vermicularis

• Symptoms: Perianal itching, especially at night.

• Transmission: Fecal-oral route; common in children.