Digestive System Diseases and Infections

Chapter 24: Digestive System Infections

Historical Context

• Cholera Origins

  • Documented in Sanskrit writings, likely originated in the Far East thousands of years ago.

  • Increased shipping and mobility in the 19th century enabled its spread from Asia to Europe and North America.

  • Major epidemics occurred during the 19th century.

• John Snow's Contribution

  • Demonstrated in 1854 that cholera was transmitted through contaminated water.

  • Observed that victims drank from a particular well on Broad Street, while neighbors elsewhere remained unaffected.

  • Despite the absence of germ theory at the time, Snow’s intervention of removing the well handle led to a decrease in new cases.

  • In 1883, Robert Koch isolated Vibrio cholerae.

• 2008 Cholera Outbreak in Zimbabwe

  • An outbreak reported to WHO saw about 100,000 cases and ~2,300 fatalities by July 2009.

  • Medical facilities set up by Médecins Sans Frontières; WHO and Red Cross supplied filtered water and health education, treated patients with rehydration fluids.

  • Contributing factors included lack of public health resources and political instability.

Anatomy, Physiology, and Ecology of the Digestive System

• Digestive Tract Overview

  • A hollow tube extending from mouth to anus, major boundary with the environment.

  • Gastrointestinal tract refers specifically to the stomach and intestines, where most microbial interactions occur.

  • Mucous membrane separates microbial populations from underlying tissue; damage allows pathogen entry.

• Accessory Organs

  • Includes salivary glands, liver, pancreas: responsible for enzyme production and food breakdown.

• Organ Functions

  • Oral Cavity: Mechanical processing via teeth; saliva aids digestion.

  • Esophagus: Connects mouth to stomach; peristalsis pushes food.

  • Stomach: Breaks down food, highly acidic environment prevents most bacterial survival.

  • Small Intestine: Main digestion and nutrient absorption site; contains villi for increased surface area.

  • Large Intestine: Absorbs water and vitamins; host to bacteria that can help synthesize certain vitamins.

Bacterial Diseases of the Upper Digestive System

• Dental Caries (Tooth Decay)

  • Causative Agent: Streptococcus mutans, thrives in acidic environments.

  • Pathogenesis: S. mutans adhere to teeth, produce acids from sugars that lower plaque pH and promote decay.

  • Prevention: Dental care, reduced sucrose intake, and fluoride usage.

• Periodontal Diseases

  • Gingivitis: Inflammation of gums; can progress to chronic periodontitis characterized by bad breath and loose teeth.

  • Acute Necrotizing Ulcerative Gingivitis: Severe cases leading to painful swollen gums.

• Helicobacter pylori Gastritis

  • Linked to stomach ulcers; produces urease neutralizing stomach acid, allowing survival in the stomach's harsh environment.

  • Can lead to chronic infection, inflammation, and reduced mucus production leading to ulcers and potentially stomach cancer.

Bacterial Diseases of the Lower Digestive System

• General Characteristics

  • Symptoms include diarrhea, nausea, and vomiting; categorized as gastroenteritis.

  • Major causative agents: Shigella, Salmonella, E. coli, etc.

• Cholera

  • Transmission: Via fecal-contaminated water; severely affects intestinal function.

  • Symptoms: Severe watery diarrhea, termed "rice-water stool"; dehydration can lead to organ failure.

  • Causative Agent: Vibrio cholerae, produces a powerful exotoxin that affects intestinal ion transport.

  • Treatment: Fluid replacement; sanitation efforts are critical for prevention.

Viral Diseases of the Lower Digestive System - Liver

• Hepatitis A

  • Causes acute illness; typically spreads through the fecal-oral route.

  • Vaccination recommended for children and high-risk populations.

• Hepatitis B

  • Can result in both acute and chronic infections; chronic infections may lead to serious liver disease.

  • Transmitted through body fluids; vaccination available.

• Hepatitis C

  • Majority of infections remain asymptomatic initially; can lead to chronic infections.

  • Transmitted primarily through blood; no vaccine available.

Activities of the Normal Digestive System Microbiota of Value to the Host

• Competition with pathogens for nutrients and attachment sites, reducing pathogen colonization.

• Fermentation of dietary fibers to short-chain fatty acids, providing energy to host cells and contributing to gut health.

• Synthesis of essential vitamins (e.g., Vitamin K, certain B vitamins).

• Modulation of immune response and maintenance of intestinal barrier function.

Pathogen Characteristics, Causes, Pathogenesis, Prevention, and Treatment for Dental Caries

• Pathogen Characteristics: Caused by Streptococcus mutans, a gram-positive bacterium.

• Causes: High sugar diet, poor oral hygiene.

• Pathogenesis: Adheres to tooth surfaces, metabolizes sugars to produce acids, leading to enamel decay.

• Prevention: Regular dental care, reduction of sucrose intake, use of fluoride.

• Treatment: Dental fillings, restorative procedures.

Pathogen Characteristics, Causes, Modes of Transmission, Pathogenesis, Prevention, and Treatment for Stomach Ulcers

• Pathogen Characteristics: Caused by Helicobacter pylori, gram-negative bacterium.

• Causes: Infection with H. pylori, chronic NSAID use, alcohol, smoking.

• Modes of Transmission: Oral-oral or fecal-oral route.

• Pathogenesis: Produces urease, neutralizing stomach acid and causing inflammation of the stomach lining.

• Prevention: Good hygiene practices, avoiding excessive use of NSAIDs.

• Treatment: Antibiotics paired with proton pump inhibitors to reduce stomach acid.

Pathogen Characteristics, Causes, Modes of Transmission, Pathogenesis, Prevention, and Treatment for Shigellosis

• Pathogen Characteristics: Caused by Shigella species, gram-negative bacteria.

• Causes: Contaminated food or water.

• Modes of Transmission: Fecal-oral route, very low infectious dose.

• Pathogenesis: Invades epithelial cells of the intestine, causing damage and inflammation.

• Prevention: Hygiene, sanitation, safe food handling.

• Treatment: Supportive care, antibiotics in severe cases.

Pathogen Characteristics, Causes, Modes of Transmission, Pathogenesis, Prevention, and Treatment for Salmonellosis

• Pathogen Characteristics: Caused by Salmonella species, gram-negative rods.

• Causes: Contaminated food sources, particularly undercooked meat and eggs.

• Modes of Transmission: Fecal-oral route.

• Pathogenesis: Invades intestinal lining, causing inflammation and diarrhea.

• Prevention: Proper cooking of food, hygiene, vaccination in some cases.

• Treatment: Fluid replacement, antibiotics in severe infections.

Pathogen Characteristics, Causes, Modes of Transmission, Pathogenesis, Prevention, and Treatment for Cholera

• Pathogen Characteristics: Caused by Vibrio cholerae, curved gram-negative bacillus.

• Causes: Contaminated water sources.

• Modes of Transmission: Fecal-oral route, often through contaminated drinking water.

• Pathogenesis: Produces an exotoxin affecting intestinal ion transport, leading to severe diarrhea.

• Prevention: Improving sanitation, access to clean water, vaccination in endemic areas.

• Treatment: Rehydration therapy, antibiotics if necessary.

Symptoms, Causes, Pathogenesis, Modes of Transmission, Treatment, and Prevention for Hepatitis A

• Symptoms: Fatigue, nausea, abdominal pain, loss of appetite, and jaundice.

• Causes: Caused by Hepatitis A virus (HAV).

• Pathogenesis: Virus infects liver cells, causing inflammation.

• Modes of Transmission: Fecal-oral route, often through contaminated food or water.

• Treatment: Supportive care, no specific antiviral therapy.

• Prevention: Vaccination recommended for high-risk populations and good sanitation practices.

Symptoms, Causes, Pathogenesis, Modes of Transmission, Treatment, and Prevention for Hepatitis B

• Symptoms: Fatigue, jaundice, abdominal pain, and dark urine.

• Causes: Caused by Hepatitis B virus (HBV).

• Pathogenesis: Virus causes inflammation and can lead to chronic liver disease.

• Modes of Transmission: Blood and body fluids (sexual contact, sharing needles).

• Treatment: Antiviral medications for chronic infections.

• Prevention: Vaccination and safe practices to prevent transmission.

Symptoms, Causes, Pathogenesis, Modes of Transmission, Treatment, and Prevention for Hepatitis C

• Symptoms: Often asymptomatic initially; chronic infection can lead to liver disease.

• Causes: Caused by Hepatitis C virus (HCV).

• Pathogenesis: Virus infects liver cells, leading to chronic inflammation.

• Modes of Transmission: Primarily through blood (sharing needles, less common sexual transmission).

• Treatment: Direct-acting antivirals for chronic infections.

• Prevention: No vaccine, but measures to avoid blood exposure are recommended.

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Activities of the Normal Digestive System Microbiota of Value to the Host

• Competition with pathogens for nutrients and attachment sites, which is crucial in preventing pathogen colonization and overgrowth, thereby maintaining overall gut health. The microbiota utilizes nutrients from the host, making them less available to pathogens.

• Fermentation of dietary fibers into short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, which serve as a significant energy source for colonocytes, help regulate gut motility, and act as signaling molecules that influence metabolism and inflammation.

• Synthesis of essential vitamins, particularly Vitamin K (which is vital for blood clotting) and several B vitamins (such as B12 and B9), necessary for red blood cell formation and DNA synthesis.

• Modulation of the immune response and maintaining intestinal barrier function, which helps to control inflammation and promote tolerance to non-harmful antigens, aiding in the prevention of autoimmune diseases and allergies.

Dental Caries

• Pathogen Characteristics: Caused primarily by Streptococcus mutans, a gram-positive bacterium that can thrive and produce acid in the presence of sugars.

• Causes: Predominantly linked to a high sugar diet and poor oral hygiene, which allows plaque formation and increases acidity in the oral cavity.

• Pathogenesis: S. mutans adheres to tooth surfaces and metabolizes sugars to produce acids, leading to a drop in plaque pH. This acidic environment demineralizes enamel, promoting tooth decay.

• Prevention: Regular dental check-ups and treatments (e.g. fluoride applications), reduction of sucrose intake, and effective oral hygiene practices such as brushing and flossing.

• Treatment: Dental fillings to restore tooth structure, alongside restorative procedures as necessary to address decay.

Stomach Ulcers (h. pylori) cagA

• Pathogen Characteristics: Primarily caused by Helicobacter pylori, a gram-negative spiral-shaped bacterium known for its ability to survive in acidic environments.

  • produces the protein cagA

• Causes: Infection with H. pylori, chronic NSAID (non-steroidal anti-inflammatory drugs) use, high alcohol consumption, and smoking exacerbate the vulnerability of the gastric mucosa.

• Modes of Transmission: Spread predominantly through oral-oral or fecal-oral routes, with close contact and inadequate sanitation increasing risk.

• Pathogenesis: H. pylori produces urease, which neutralizes gastric acid, allowing it to colonize the stomach lining and cause inflammation, leading to ulcer formation.

• Prevention: Good hygiene practices, such as handwashing and consuming well-cooked food, while avoiding excess NSAID use is crucial.

• Treatment: A combination of antibiotics to eradicate H. pylori and proton pump inhibitors to reduce gastric acid secretion, enabling healing of the ulcer.

Shigellosis

• Pathogen Characteristics: Caused by Shigella species, which are gram-negative bacteria that can cause significant intestinal damage with as little as 10-100 organisms.

• Causes: Primarily due to consumption of contaminated food or water, especially in areas with poor sanitation.

• Modes of Transmission: Transmitted through the fecal-oral route, emphasizing the importance of hygiene as the infectious dose is very low.

• Pathogenesis: Shigella invades epithelial cells of the intestine, disrupting cellular functions and triggering inflammatory responses that lead to severe diarrhea.

• Prevention: Emphasizes the need for strict hygiene practices, proper sanitation efforts, and safe food handling to reduce outbreaks.

• Treatment: Supportive care with hydration; antibiotics may be necessary for severe cases to mitigate infection severity.

Salmonellosis

• Pathogen Characteristics: Caused by diverse Salmonella species, which are motile gram-negative rods that can reside in gastrointestinal tracts of animals and humans.

• Causes: Often results from ingestion of contaminated food, particularly undercooked meat, poultry, and eggs, along with unpasteurized dairy products.

• Modes of Transmission: Primarily spreads through fecal-oral route, highlighting the importance of food hygiene.

• Pathogenesis: Salmonella species invade the intestinal lining, leading to inflammation, which manifests as diarrhea, abdominal cramps, and fever.

• Prevention: Proper cooking of food, maintaining hygiene practices, and vaccination of livestock in certain cases can help minimize risks.

• Treatment: Fluid replacement for dehydration, with antibiotics reserved for severe cases or vulnerable populations.

Cholera

• Pathogen Characteristics: Caused by Vibrio cholerae, a curved, gram-negative bacillus known for its ability to produce potent cholera toxin.

• Causes: Contaminated water sources, notably in regions lacking adequate sanitation, are major contributors to cholera outbreaks.

• Modes of Transmission: Fecal-oral, primarily through consumption of contaminated drinking water or food.

• Pathogenesis: The cholera toxin disrupts intestinal ion transport, leading to extreme fluid loss and severe watery diarrhea, known as "rice-water stool."

• Prevention: Improving sanitation infrastructures, providing access to clean water, and vaccinating at-risk populations in endemic regions are key prevention strategies.

• Treatment: Rehydration therapy using oral rehydration solutions or intravenous fluids; antibiotics may also be warranted in severe cases to shorten course duration.

Hepatitis A

• Symptoms: Commonly manifest as fatigue, nausea, abdominal pain, significant loss of appetite, and jaundice as the infection progresses.

• Causes: Resulting from Hepatitis A virus (HAV), it is often self-limiting but can cause acute illness.

• Pathogenesis: The virus specifically infects liver cells (hepatocytes), leading to pronounced inflammation and impairment of liver function.

• Modes of Transmission: Primarily via the fecal-oral route, often from contaminated food or water supplies.

• Treatment: Supportive care is the mainstay, as there is no specific antiviral therapy for HAV.

• Prevention: Vaccination is advisable for high-risk populations, alongside ensuring good sanitation practices.

Hepatitis B

• Symptoms: Typically presents with fatigue, jaundice, abdominal pain, darker urine, and in chronic cases, can lead to liver cirrhosis.

• Causes: Initiated by the Hepatitis B virus (HBV), known for its chronic infection potential.

• Pathogenesis: HBV causes significant liver inflammation and can result in chronic liver disease and associated complications.

• Modes of Transmission: Transmitted through blood and body fluids via sexual contact or sharing needles.

• Treatment: Chronic cases are managed with antiviral medications to suppress virus replication.

• Prevention: Vaccination coupled with safe practices is vital in preventing transmission.

Hepatitis C

• Symptoms: Frequently asymptomatic initially; chronic infections can eventually lead to severe liver disease, including liver cancer.

• Causes: Resulting from infection with the Hepatitis C virus (HCV), primarily impacting liver health.

• Pathogenesis: HCV infiltrates liver cells, instigating chronic inflammation and damaging hepatic architecture over time.

• Modes of Transmission: Primarily via blood (especially through the sharing of needles), with sexual transmission being less common.

• Treatment: Management of chronic HCV involves direct-acting antiviral regimens that can lead to sustained virologic response.

• Prevention: There is no vaccine; hence, avoiding blood exposure and adhering to safe practices are critical preventive measures.