1. Diseases of the gastrointestinal tract
Components of digestive tract (and sites of infection)
Normal flora and other protective mechanisms
Pathogenesis
many candidates: notice all of the tables in this
chapter!

2. Structure of the digestive system
Ingestion (mouth)
Digestion (mouth, stomach, small intestine)
Accessory organs (liver, pancreas, gall bladder)
Absorption (small, large intestine
Excretion (large intestine)

3. The oral cavity Many resident bacteria
Some bacteria cause plaque (e.g., S. mutans, Actinomyces)
Caries- breakdown of enamel
Periodonal disease
Can cause systemic complecations

4. Other infections of the mouth
Mumps
spreads from upper respiratory tract to salivary glands; can spread to meninges; testes
Vaccine available since 1967 (MMR)
Thrush (C. albicans)
Herpes simplex type 1 (cold sores)

5. Bacterial infections of the GI tract
“Food poisoning”- toxins, other contaminants
toxins are already formed so onset is rapid
Termed intoxication)
S. aureus toxin is problematic because it is heat-stable
Symptoms: diarrhea, pain, nausea, vomiting
usually no immunity established
“When in doubt, throw it out”

6. Bacterial (gastro-)enteritis: organism causes disease,
not exotoxin
Diarrhea- small intestine affected
Dysentery- large intestine (blood, pus)
Enteric fever- systemic
Salmonella
many distinguishable types (serovars)
very common; usually spread by improperly
perpared food
symptoms occur about 48 hours after infection
invades mucosa in small, large intestines

7. Shigella- not as invasive as Salmonella, but very
contagious
bloody diarrhea
S. dysenteriae produces a neurotoxin
Vibrio- cholera outbreaks occur when sanitation is
disrupted
Enterotoxin makes interstines permeable to water;
patients lose massive amounts
fluid replacement, vaccination
Many other organisms produce enterotoxins (E. coli,
Campylobacter, etc.

8. Intestinal pathogens have different modes of activity
Cholera toxin
Invasiveness of Shigella

9. H. pylori First cultured in 1982 (Marshall and Warren)
Generates ammonia from urea
Causes peptic ulcers
Linked to chronic gastritis, stomach cancer

10. Most infectious enteritis probably caused by viruses
Rotavirus (esp. young children)
tends to be seasonal
Norwalk virus
very common in adults
2-day incubation period
Poliovirus: introduced by fecal-oral route but does
infect digestive system

11. Comparison of types of viral hepatitis

12. Parasitic diseases of the digestive system
Often transmitted from other animals
Food (beef, fish, pork, etc.)
Incidental contact (soil, insects, feces)
Helminths: Flukes, tapeworms (cestodes) roundworms (nematodes)
Often symptoms are subtle or nonexistent
Can infect diverse tissues
Requires antihelminthic drugs for treatment

13. Infections by protozoans
Giardia, etc.
Cyst is hard to eliminate
Clean drinking water is important
Have complex life cycles
Invasion of tissues; inflammation

14. Fungal toxins can be deadly
Aflatoxins (moldy grain, peanuts)
Strong carcinogens
Ergot (rye, wheat) can cause hallucinations; can be medicinal
Mushroom toxins mainly produced by Amanita; toxic to liver

15. Summary Substantial opportunities for infection
Bacterial/viral: no cure or lasting immunity
Drugs for protozoan or helminthic infections pretty toxic
Vaccines limited (and often inappropriate)
Avoidance
Hydration therapy