Presentation on theme: "Diseases of the gastrointestinal tract Components of digestive tract (and sites of infection) Normal flora and other protective mechanisms Pathogenesis."— Presentation transcript:
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!
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)
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
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)
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”
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
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.
Intestinal pathogens have different modes of activity Cholera toxin Invasiveness of Shigella
H. pylori First cultured in 1982 (Marshall and Warren) Generates ammonia from urea Causes peptic ulcers Linked to chronic gastritis, stomach cancer
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
Comparison of types of viral hepatitis
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
Infections by protozoans Giardia, etc. Cyst is hard to eliminate Clean drinking water is important Have complex life cycles Invasion of tissues; inflammation
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
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