Microbial Diseases of the Digestive System

Chapter 23: Microbial Diseases of the Digestive System

1. Gastrointestinal Tract

  • Description: The gastrointestinal (GI) tract is a continuous tube that extends from the mouth to the anus, responsible for the ingestion, digestion, absorption of nutrients, and elimination of waste.

2. Main Components of the Gastrointestinal Tract

  • Components:

    • Mouth

    • Esophagus

    • Stomach

    • Small intestine

    • Large intestine

    • Anus

3. Accessory Organs of the Digestive System

  • Accessory Organs:

    • Salivary glands

    • Liver

    • Gallbladder

    • Pancreas

4. Candida albicans

  • Mucosal Disease: Candida albicans is responsible for oral thrush (mucosal disease).

    • Spread: It is spread through the oral route, frequently occurring in individuals with weakened immune systems.

    • Signs and Symptoms: Symptoms include white patches on the tongue and inner cheeks, difficulty swallowing, and soreness in the mouth.

5. Dental Caries and Related Diseases

  • Bacteria Responsible:

    • Streptococcus mutans

    • Lactobacillus species

  • Cavity Development: Cavities develop due to the demineralization of tooth enamel caused by acids produced from the metabolism of sugars by oral bacteria.

6. Taeniasis

  • Parasites Responsible:

    • Taenia saginata (beef tapeworm)

    • Taenia solium (pork tapeworm)

    • Longevity: Taenia solium lives longer in humans compared to T. saginata.

  • Accidental Host Disease: When humans ingest the eggs of Taenia solium, they contract cysticercosis.

  • Transmission: Taeniasis is transmitted via ingestion of undercooked meat infected with cysticerci.

7. Enterobius vermicularis (Pinworm)

  • Common Name: Enterobius vermicularis is commonly known as the pinworm.

    • Most Common Helminth Infection: It is the most common helminth infection in the US.

    • Transmission: Pinworm is transmitted via the fecal-oral route, often from contaminated surfaces or hands.

    • Flashlight Test: A diagnostic method where a flashlight is used to illuminate the perianal area at night to spot female pinworms.

    • Scotch Tape Test: A method of adhesive tape used to collect eggs from the perianal area for microscopic examination.

8. Dysentery

  • Definition: Dysentery refers to a gastrointestinal infection characterized by severe diarrhea with the presence of blood or mucus in the stool.

9. Giardiasis

  • Common Name: Giardia lamblia is the causative agent of Giardiasis, commonly referred to as beaver fever.

    • Zoonotic Disease: Yes, it is considered zoonotic, with transmission from animals like beavers and muskrats.

    • Prevention: To prevent Giardiasis, drink treated or boiled water, wash hands, and avoid unwashed produce.

    • Signs and Symptoms: Diarrhea, gas, stomach cramps, bloating, and nausea are common symptoms.

10. Cryptosporidiosis

  • Causative Protozoa: Cryptosporidium parvum is the pathogen responsible for Cryptosporidiosis.

11. Entamoeba histolytica

  • Diseases: Causes amoebic dysentery and amoebiasis.

    • Feeding Cells: E. histolytica grows and feeds on red blood cells and intestinal epithelial cells.

12. Bacterial Gastroenteritis

  • Transmission: It is transmitted through contaminated food or water, often due to poor sanitation practices.

13. Traveler’s Diarrhea

  • Causative Bacteria: Caused by enterotoxigenic E. coli (ETEC) and other bacterial pathogens.

    • Definition: Traveler's diarrhea is diarrhea that occurs in travelers due to exposure to unfamiliar pathogens.

    • Food Sources for E. coli O157:H7: Found primarily in undercooked or contaminated ground beef and unpasteurized dairy products.

    • Zoonosis: Yes, E. coli O157:H7 is zoonotic.

14. Campylobacteriosis

  • Causative Bacteria: Caused by Campylobacter jejuni.

    • Transmission: It is transmitted primarily through undercooked poultry, unpasteurized milk, and contaminated water.

15. Listeriosis

  • Transmission: It is transmitted through contaminated food, particularly unpasteurized dairy, deli meats, and smoked seafood.

    • Prevention: Prevented through proper cooking and food handling practices.

16. Salmonellosis

  • Causative Bacteria: Caused by Salmonella species.

    • Common Food Sources: Found in undercooked poultry, eggs, and unwashed fruits and vegetables.

    • Zoonosis: Yes, Salmonella is zoonotic, transmitted from animals to humans.

17. Vibriosis

  • Prevention: Vibriosis can be prevented by cooking seafood properly and avoiding raw or undercooked shellfish.

18. Peptic and Stomach Ulcers

  • Causative Bacteria: Due primarily to Helicobacter pylori infection.

    • Blood Type Influence: People with O blood type are more susceptible due to certain molecular adhesion properties of the bacteria.

    • Favorable Conditions: Condition such as increased stomach acid and changes in the stomach environment favor H. pylori colonization.

19. Clostridium difficile

  • Characteristics: It is a Gram-positive, spore-forming bacterium associated with antibiotic-associated diarrhea and Pseudomembranous colitis.

    • Signs and Symptoms: Symptoms include severe diarrhea, abdominal pain, and fever. A colonoscopy may reveal pseudomembranes on the colon lining.

20. Shigella Species

  • Disease Caused: Shigellosis, an intestinal infection that causes diarrhea.

    • Toxins Production: Yes, Shigella species produce Shiga toxin, leading to severe complications.

    • Transmission: Transmitted through contaminated food or direct person-to-person contact.

    • Vaccine Status: No widely available vaccine for Shigellosis as of now.

21. Cholera

  • Causative Bacteria: Caused by Vibrio cholerae.

    • Prevalence in the US: Cholera is rare in the US but outbreaks can occur following contaminated water incidents.

22. Hepatitis A

  • Virus Description: A virus that causes infectious hepatitis, classified as a non-enveloped RNA virus.

    • Transmission: Transmitted through the fecal-oral route, often via contaminated food or water.

    • Prevention: Prevented with vaccinations and good hygiene practices.

23. Hepatitis B

  • Transmission: Serum Hepatitis is transmitted through blood, sexual contact, and from mother to child during childbirth.

    • Chronic HBV in Babies: Yes, infants can develop chronic HBV if infected at birth.

    • Prevention: Vaccination against HBV is a key preventive measure.

24. Hepatitis C

  • Transmission: Transmitted primarily through blood-to-blood contact, including sharing needles.

    • Cancer Association: Hepatitis C is associated with the development of liver cancer (hepatocellular carcinoma).

    • Prevention: Preventive measures include avoiding sharing needles and ensuring safe blood transfusions.

25. Viral Gastroenteritis

  • Causative Viruses:

    • Norovirus

    • Rotavirus

    • Treatment: Treatment primarily involves hydration and symptomatic relief as there are no specific antiviral treatments.

    • Outbreak Sources: Norovirus is implicated in most outbreaks in restaurants and catered events.

    • Infant Deaths: Rotavirus is responsible for a significant number of infant deaths globally due to diarrhea.

26. Food Poisoning

  • Intoxication Disease: Food poisoning is described as an intoxication disease due to the preformed toxins produced in food by pathogens.

    • Other Intoxication Diseases: Botulism is another notable intoxication disease.

    • Common Food Poisoning Bacteria:

    • Staphylococcus aureus

    • Bacillus cereus

  • Fungi Causing Food Poisoning:

    • Amanita muscaria (a toxic mushroom)

    • Amanita phalloidea (death cap mushroom)

    • Aspergillus flavus (produces aflatoxin)

    • Treatment for Mycotoxicoses: Treatment includes supportive care, and in severe cases, use of activated charcoal can be beneficial.

    • Aflatoxin Production: Aspergillus flavus is known to produce Aflatoxin, a carcinogenic compound.

    • Aflatoxin Sources: Commonly found in grains and peanuts, especially under improper storage conditions.