Chapter 25 - Digestive System

GI Tract or Alimentary Canal

• Mouth

• Pharynx (throat)

• Esophagus

• Stomach

• Small and large intestine

Accessory Structures of the GI Tract

• Teeth and tongue

• Salivary glands

• Liver

• Gallbladder

• Pancreas

What is the structure and function of the digestive system?

• Absorption of foods

  • 25 tons of food pass through the GI tract in a lifetime

• 70% of the immune system is located in the intestinal tract

• Gut-associated lymphoid tissue (GALT)

  • Lymph nodes

  • Peyer’s patches

Normal Microbiota of the Digestive System

• Millions of bacteria per mL of saliva

• Few microorganisms in the stomach

  • Due to HCl production

• Small intestine

  • Paneth cells

    • Granule-filled phagocytic cells; produce defensins

• Large numbers of bacteria in the large intestine

  • Anaerobes and facultative anaerobes

• 100 billion bacteria per gram of feces

A Healthy Human Tooth: 3 Main Aspects

Root, neck, and crown

Dental Plaque

Biofilms involved in the formation of dental caries

Dental Caries (Tooth Decay)

Pathogen → Primarily streptococcus mutans

Symptoms → Discoloration or hole in tooth enamel

Treatment → Removal of decayed area

Prevention → Brushing, flossing, reducing dietary sucrose

*Decay can reach pulp, which contains the blood supply and nerve cells, which may advance to the soft tissues and lead to abscesses

Periodontal Disease

Pathogen → Various, primarily Porphyromonas spp.

Symptoms → Bleeding gums, pus pockets

Treatment → Removal of damaged area; antibiotics

Prevention → Plaque removal

The Stages of Periodontal Disease

1. Healthy gingivae

2. Gingivitis → Inflammation and infection of the gums

3. Periodontal pockets → Bone and tissue supporting the teeth are destroyed

4. Periodontitis

Acute Necrotizing Ulcerative Gingivitis (trench mouth)

Pathogen → Prevotella intermedia

Symptoms → Pain with chewing, halitosis (bad breath)

Treatment → Removal of damaged area; antibiotics

Prevention → Brushing & flossing

Staphylococcal Food Poisoning

Pathogen → Staphylococcus aureus

Symptoms → Nausea, vomiting, and diarrhea

Intox/Infec → Intoxication (enterotoxin)

Diagnostic Test → Phage Typing

Treatment → None

*Toxin produced when the organism is allowed to incubate in food (temp abuse)

*S. aureus outgrows most bacteria in high osmotic pressure & high temp

Shigellosis (bacterial dysentary)

Pathogen → Shigella spp.

Symptoms → Tissue damage and dysentery (blood in feces)

Intox/Infec → Infection (endotoxin and Shiga toxin, exotoxin)

Diagnostic test → Isolation of bacteria on selective media

Treatment → Usually none needed

*Oral rehydration

*Membrane ruffle

Salmonellosis

Pathogen → Salmonella enterica

Symptoms → Nausea and diarrhea

Intox/Infec → Infection (endotoxin)

Diagnostic test → Isolation of bacteria on selective media, serotyping

Treatment → Oral rehydration

*Replicates in macrophages

*Incubation of 12-36 hours

*Membrane ruffle → Lymph node → Bloodstream

Typhoid Fever

Pathogen → Salmonella Typhi

Symptoms → High fever, significant mortality

Intox/Infec → Infection (endotoxin)

Diagnostic Test →Isolation of bacteria on selective media, serotyping

Treatment → Requires antibiotic-susceptibility testing

Preventative → Vaccine

*Spread through phagocytes

*1-3% of patients become chronic carriers and harbor organism in the gallbladder

Cholera

Pathogen → Vibrio cholerae; O:1 and O:139

Symptoms → Diarrhea with large water loss

Intox/Infec → Infection (exotoxin)

Diagnostic Test → Isolation of bacteria on selective media

Treatment → Rehydration; doxycycline

*Associated with salty waters

*Causes “rice water stools”

*Increases when sanitization and sewage disposal systems are compromised

Vibrio parahaemolyticus Gastroenteritis

Pathogen → V. parahaemolyticus

Symptoms → Cholera-like diarrhea, but generally milder

Intox/Infec → Infection (enterotoxin)

Diagnostic Test → Isolation of bacteria on 2-4% NaCl

Treatment → Rehydration

*Saltwater

*Raw oysters and crustaceans

Escherichia coli Gastroenteritis

Pathogen → EPEC, EIEC, EAEC, ETEC

Symptoms → Watery diarrhea

Intox/Infec → Infection (exotoxins)

Diagnostic Test → Isolation on selective media, DNA fingerprinting

Treatment → Oral rehydration

*Reservoir = cattle

*Causes the host cells to form pedestals where bacteria attach

Shiga Toxin-Producing Enterohemorrhagic E. Coli

Pathogen → E. coli O157:H7

Symptoms → Shigella-like dysentery; hemorrhagic colitis, HUS

Intox/Infec → Infection, Shiga toxin (exotoxin)

Diagnostic → Isolation, sorbitol fermentation test, DNA fingerprinting

Treatment → Intravenous rehydration, serum electrolyte monitoring

Campylobacter Gasteroenteritis

Pathogen → Campylobacter jejuni

Symptoms → Fever, abdominal pain, diarrhea

Intox/Infec → Infection

Diagnostic Test → Isolation in low O2, high CO2

Treatment → Azithromycin

*Leading cause of foodborne illness in the US → intestines of poultry

Helicobacter Peptic Ulcer Disease

Pathogen → Helicobacter pylori

Symptoms → Peptic ulcers

Intox/Infec → Infection

Diagnostic Test → Ultra breath test, bacterial culture

Treatment → Antibiotics

*Leads to ulceration of the Stomach wall

Yersinia Gastroenteritis

Pathogen → Yersinia enterocolitica

Symptoms → Abdominal pain and diarrhea, usually mild; may be confused with appendicitis

Intox/Infec → Inection (endotoxin)

Diagnostic Test → Culture, biochemical or molecular tests

Treatment → Oral rehydration

*Transmitted by uncooked meat and pork

*Grows at 4 degrees celcius

Clostridium perfringens Gastroenteritis

Pathogen → Clostridium perfringens

Symptoms → Usually limited to diarrhea

Intox/Infec → Infection (exotoxin)

Diagnostic Test → Isolation of 10^6 endospores/g feces

Treatment → Oral rehydration

*Obligately anaerobic rod, causes gas gangrene

*Symptoms 8-10 hours after ingestion

C. difficile-Associated Diarrhea

Pathogen → Clostridium difficile

Symptoms → Mild diarrhea to colitis; 1-2.5% mortality

Intox/Infec → Infection (exotoxin)

Diagnostic Test → Cytotoxin assay

Treatment → Vancomycin, fidaxomicin

Bacillus cereus Gastroenteritis

Pathogen → B. cereus

Symptoms → May take form of diarrhea, nausea, vomiting

Intox/Infec → Intoxication

Diagnostic Test → Isolation of > 10^5 B. cereus/g food

Treatment → None

*Spores survive heating

*Common in soil and vegetation

Hepatitis A

Pathogen → Hepatitis A virus, Piornaviridae

Symptoms → Mostly subclinical; fever, headache; malaise, jaundice in severe cases; no chronic disease

Incubation Period → 2-6 weeks

Transmission → Ingestion

Diagnostic Test → IgM antibodies

Treatment → Immunoglobulin

Vaccine → Inactivated virus; postexposure = immune globulin

*Entry via the oral-fecal route

*Multiplies in the epithelial lining of the intestinal tract → liver, kidneys, and spleen

Hepatitis B

Pathogen → Hepatitis B virus, Hepadnaviridae

Symptoms → Frequently subclinical; similar to HAV, but no headache; more likely to progress to severe liver damage; chronic disease occurs

Incubation period → 4-26 weeks

Transmission → Parenteral; sexual contact; blood and bodily fluids

Diagnostic Test → IgM antibodies

Treatment → Interferon and nucleoside analogues

Vaccine → Genetically modified vaccine produced in yeast

*dsDNA; resembles retrovirus

*The spherical and filamentous particles are unassembled components of the virion without nucleic acids

Incubation period

How long it takes for you to develop symptoms after exposure to an infectious disease

Food intoxication

Consuming toxins already present in food

• Symptoms appear quickly - after a few hours

• Antibiotics are NOT helpful, because it’s caused by the toxins produced, not the bacteria itself

Food infection

Caused by microorganisms that have to grow and multiply in the body

• Symptoms appear after a longer period of time

Hepatitis C

Pathogen → Hepatitis C virus, Flaviviridae

Symptoms → Similar to HBV, more likely to become chronic

Incubation Period → 2-22 weeks

Transmission → Parenteral, often transfusion-transmitted

Diagnostic Test → PCR for viral RNA

Treatment → Enzyme inhibitors, interferon, and ribavirin

Vaccine → None

*Kills more in the U.S. than AIDS

Hepatitis D

Pathogen → Hepatitis D virus, Deltaviridae

Symptoms → Severe liver damage; high mortality rate; chronic disease may occur

Incubation Period → 6-26 weeks

Transmission → Parenteral; requires coinfection with Hep B

Diagnostic test → antibodies with PCR for viral RNA

Treatment → None

Vaccine → HBV vaccine is proactive

*Acute = coinfection; chronic = superinfectionH

Hepatitis E

Pathogen → Hepatitis E virus, Caliciviridae

Symptoms → Similar to HAV, but pregnant women have high mortality; no chronic disease

Incubation period → 2-6 weeks

Transmission → Ingestion

Diagnostic test → Antibodies against HEV or HEV RNA

Treatment → None

Vaccine → None

*Spread by fecal-oral transmission

Mumps

Pathogen → Mumps virus, Paramyxoviridae

Symptoms → Painful swelling of parotoid glands

Incubation period → 16-18 days

Diagnostic Test → Symptoms; virus culture

Prevention → Attenuated vaccine (MMR vaccine)

*Transmitted in the saliva and respiratory secretions

*May cause orchitis (swelling of testes), meningitis, ovary inflammation, and pancreatitis

Viral Gastroenteritis (rota)

Pathogen → Rotavirus

Symptoms → Vomiting, diarrhea for 1 week

Incubation period → 1-3 days

Diagnostic test → enzyme immunoassay for viral antigens in feces

Prevention → Attenuated vaccine

Viral Gastroenteritis (nora)

Pathogen → Norovirus

Symptoms → vomiting, diarrhea for 2-3 days

Incubation period → 18-48 hours

Diagnostic test → PCR

Prevention → Handwashing

Ergot Poisoning (fungal)

Pathogen → Claviceps purpurea

Symptoms → Restricted blood flow to limbs (gangrene); hallucinogenic

Reservoir → Mycotoxin produced by fungus growing on grains

Diagnostic Test → Finding fungal sclerotia in food

Treatment → None

Aflatoxin Poisoning (fungal)

Pathogen → Aspergillus flavus

Symptoms → Liver cirrhosis; liver cancer

Reservoir → Mycotoxin produced by fungus growing on food

Diagnostic Test → Immunoassay for toxin in food

Treatment → None

*Likely found on peanuts

Giardiasis (protozoan)

Pathogen → Giardia intestinalis

Symptoms → Protozoan adheres to intestinal wall, may inhibit nutritional absorption; diarrhea

Reservoir → Water; mammals

Diagnostic Test → FA
Treatment → Metronidazole; nitazoxanide

Cryptosporidiosis (protozoan)

Pathogen → Cryptosporidium hominis, C. parvum

Symptoms → Self-limiting diarrhea; may be life-threatening in immunosuppressed patients

Reservoir → Cattle; water

Diagnostic Test → Acid-fast stain

Treatment → Nitazoxanide

*Transmitted through drinking water

Cyclosporiasis

Pathogen → Cyclospora cayetanensis

Symptoms → Water diarrhea

Reservoir → Humans; birds; usually ingested with fruits and vegetables

Diagnostic test → acid-fast stain

Treatment → Trimethoprim and sulfamethoxazole

*Oocysts are ingested from drinking feces-contaminated water

Amebic Dysentery (amebiasis)

Pathogen → Entamoeba histolytica

Symptoms → Ameba lyses epithelial cells of intestine, caused abscesses; significant mortality rate

Reservoir → Humans

Diagnostic test → Microscopy; EIA

Treatment → Metronidazole

*Feces contain blood and mucus

Tapeworms (helminthic)

Pathogen → Taenia saginata (beef), T. solium (pork), Diphyllobothrium latum (fish)

Symptoms → Adults cause few symptoms; pork tapeworm larvae may encyst in many organs (neurocysticercosis) and cause damage

Reservoir → Intermediate host: cattle, pigs, fish

• Definitive host: humans

Diagnostic test → Microscopic exam of feces

Treatment → Praziquantel; niclosamide

*Taeniasis: adult tapeworm infects the intestine; Cysticercosis: infection with the larval stage by ingesting eggs; Ophthalmic cysticercosis: larvae lodge in the eye; Neurocysticercosis: larvae develop in the central nervous system

Hydatid Disease (helminthic)

Pathogen → Echinococcus granulosus

Symptoms → Larvae form in body; may be very large and cause damage

Reservoir → Intermediate host: sheep, humans

• Definitive host: dogs

Diagnostic test → Serology; X-ray exam

Treatment → Surgical removal; albendazole

*Develops a hydatid cyst that can grow and hold up to 15 liters of fluid; May rupture, causing anaphylactic shock

Pinworms (helminthic)

Pathogen → Enterobius vermicularis (tiny nematode)

Symptoms → Itching around anus (eggs laid around anus)

Intermediate & definitive hosts → humans

Diagnostic test → microscopic exam

Treatment → Pyrantel pamoate

Hookworms (helminthic)

Pathogen → Necator americanus, Ancylostoma duodenale

Symptoms → Large infections may result in anemia

Reservoir → Larvae enter skin from soil; definitive hosts: humans

Diagnostic test → Microscopic exam

Treatment → Mebendazole

*Attaches to the intestinal wall and feeds on blood and tissue

Ascariasis (helminthic)

Pathogen → Ascaris lumbriocoides

Symptoms → Helminths live off undigested intestinal contents, causing few symptoms

Intermediate & definitive hosts → humans

Diagnostic test → microscopic exam

Treatment → Mebendazole

*Thirty percent of the worldwide population is infected

*Larvae develop into adult worms in the intestinal tract and emerge from the anus, mouth, or nose

Whipworm (helminthic)

Pathogen → Trichuris trichiura

Symptoms → Diarrhea, malnutrition

Intermediate & definitive hosts → Humans

Diagnostic test → Microscopic exam of feces

Treatment → Albendazole, mebendazole

*Eggs are ingested and enter the intestinal glands.

*Feeds on cell contents and blood

Trichinellosis (helminthic)

Pathogen → Trichinella spiralis, T. nativa

Symptoms → Larvae encyst in striated muscle; usually few symptoms, but large infections may be fatal (Fever, eye swelling, gastrointestinal upset)

Intermediate & definitive hosts → mammals\

Diagnostic test → Biopsy; ELISA

Treatment → Mebendazole; corticosteroids