Diseases of the gastrointestinal tract

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 complications

4
Other infections of the mouth

• Mumps
• spreads from upper respiratory tract to salivary
  glands can spread to meninges and/or 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
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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
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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.
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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 (now
norovirus) very common in adults 2-day
incubation period See Table 25.11 Poliovirus
introduced by fecal-oral route but does infect
digestive system
11
Comparison of hepatitis viruses (now table 25.12)
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, Cryptosporidium, Cyclospora, Entamoeba,
  etc.
• Cyst is hard to eliminate
• Clean drinking water is important
• Cyclospora spread on contaminated food
• Have complex life cycles
• Invasion of tissues inflammation

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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

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Summary

• Substantial opportunities for infection
• Bacterial/viral no cure or lasting immunity
• Drugs for protozoan or helminthic infections are
  toxic
• Vaccines limited (and often inappropriate)
• Avoidance
• Hydration therapy