Chapter 21
Infectious Diseases Affecting the Digestive System
21.1 The Structure and Indigenous Microbiota of the Digestive System
• The digestive system is composed of two separate categories of organs
• Gastrointestinal (GI) tract
• Accessory digestive organs
• Chemical, mechanical, and cellular defenses protect the GI tract from pathogen
colonization
• The human intestinal microbiome has not been well studied
• The microbiota of mouth and large intestine represent extremely complex
communities
21.2 Diseases of the Oral Cavity
• Oral Diseases Cause Pain and Disability for Affected Individuals
• At least 600 species of bacteria inhabit the human mouth
• Plaque is a biofilm, containing salivary proteins, food debris and bacterial
cells and products
• Dental caries (tooth decay) results from
• plaque building
• dietary carbohydrates
• acidogenic bacteria
• A major cause of caries is Streptococcus mutans
• They ferment dietary carbohydrates into acids
• Fluoride and diet can prevent dental caries
• Periodontal disease (fusospirochetal disease) results from the
inflammation of periodontal tissue
• Poor oral hygiene leads to increased subgingival plaque, which can
be populated by bacteria
• It is characterized by
– ulcers and bleeding along the gingival margin
– degradation of periodontal ligaments and bone
– loosened or lost teeth
Mumps is a viral infection affecting parotid glands
• Mumps spreads easily from person to person through infected saliva
• Infectious parotitis is alternative name for the disease
• Mumps is characterized by enlarged jaw tissues caused by swollen
salivary glands
• The swelling is caused by blockage of ducts leading from the parotid
glands
• It is spread by respiratory droplets or contact with contaminated objects
• In males, swelling and damage may occur in the testes (orchitis)
21.3 Introduction to Bacterial Diseases of the GI Tract
• Many Foodborne and Waterborne Diseases Have a Bacterial Cause
• Intoxications are illnesses in which bacterial toxins are ingested with food
and water
• Infections are illnesses in which live bacterial pathogens are ingested and
grow in the body
•
The incubation period is the time between
• consumption of contaminated material
• appearance of symptoms
• Clinical symptoms and duration of illness depend on
• the toxin or microbe
• the infectious dose
• Demographics can make individuals more or less prone to
food/waterborne illness
• For example, age or sanitary conditions
• There Are Several Ways Foods or Water Become Contaminated
• Meat can be infected during improper slaughter procedure
• Fruits and vegetables can be washed with contaminated water
• Infected humans can contaminate food they handle through the fecal-oral
route
• Cross-contamination can occur
• between foods
• via knife, cutting board, etc.
• Water contamination can occur by defecation of infected individuals in
public water sources
• Improperly stored foods can contain large numbers of pathogens because
of rapid multiplication
21.4 Foodborne Intoxications
Caused by Bacteria
• Food poisoning illnesses are the result of enterotoxins
• Staphylococcus aureus causes staphylococcal food poisoning
• Toxins are often consumed in protein-rich foods such as
– meat and fish
– dairy products
• The enterotoxin causes gastroenteritis for several hours
• Food is often contaminated by
• boils or abscesses on a handler’s skin
• through sneezing
• Proper handling, refrigeration, and heating help decrease the risk of
contamination
• Clostridium perfringens causes clostridial food poisoning
• C. perfringens commonly contaminated meat, poultry, and fish
• Clinical symptoms require a high infectious dose and take 8–24
hours to appear
• Bacillus cereus can cause diarrhea or vomiting
• Infections usually occur from eating contaminated cooked grains
21.5 GI Infections Caused by Bacteria
• Bacterial GI infections have a longer incubation period than intoxications because
bacterial cells must establish themselves in the body after ingestion
• Bacterial gastroenteritis often produces an inflammatory condition
• Dehydration is a common but serious complication of
gastroenteritis
•
Cholera Can Involve Enormous Fluid Loss
• Cholera is caused by Vibrio cholerae
• V. cholerae are often consumed with raw oysters and water
• The cells are susceptible to stomach acid
• A large infectious dose is needed to colonize the intestines
• Cholera toxin causes unrelenting loss of fluid and electrolytes through
diarrhea (up to 1 L/hour)
• In untreated, fluid loss thickens the blood, leading to shock and coma
• Antibiotics and restoration of water and electrolyte balance are effective in
treatment
• Vaccines using dead V. cholerae are available
• E. coli Diarrheas Cause Various Forms of Gastroenteritis
• Escherichia coli is normally found in the human intestine, but certain
serotypes are pathogenic
• Transmission occurs through the fecal-oral route
Healthcare-associated infections
• Clostridium difficile
• Major cause of pseudomembranous colitis
• Vibrio species other than V. cholerae can cause illness
• V. parahaemolyticus is a common problem where large amounts of
seafood are consumed
• V. vulnificus is transmitted by oysters and clams
– It can cause a deadly systemic infection
• Several bacteria can cause an invasive gastroenteritis
• Typhoid Fever Involves a Blood Infection
• It is caused by Salmonella enterica serotype Typhi (S. Typhi)
• S. Typhi is transmitted by the five Fs:
• Flies
• Food
• Fingers
• Feces
• Fomites
• Several bacteria can cause an invasive gastroenteritis
• S. Typhi is acid resistant
– It passes through the stomach to the small intestine
» It causes ulcers, bleeding, and pain
• Invasion of the blood can occur
• Rose spots indicate blood hemorrhage
• Vaccines contain dead or attenuated S. Typhi or polysaccharides from S.
Typhi capsule
• Salmonellosis Can Be Contracted from a Variety of Foods
• Salmonellosis is usually caused by S. enterica serotype Enteritidis or
Typhimurium
• Gastroenteritis occurs 6–48 hours after a large infectious dose
• Salmonella serotypes are often found in unpasteurized milk or poultry
products
• They can also be transmitted by live animals
• Shigellosis (Bacterial Dysentery) Occurs Where Sanitary Conditions Are Lacking
• Shigellosis is primarily caused by Shigella sonnei
• S. dystenteriae causes epidemics in the developing world
• Contaminated foods commonly include
• Eggs
• Vegetables
• Shellfish
• Dairy
• An infectious dose requires fewer than 200 S. sonnei individuals
• Shiga toxin production in the intestinal epithelium triggers gastroenteritis
• Infection of the large intestine can lead to fatal dysentery
• No vaccine is available
• Enterotoxigenic E. coli (ETEC) penetrate the intestinal epithelium and
produce a toxin that causes gastroenteritis
• a.k.a. traveler’s diarrhea
• Enterophatogenic E. coli (EPEC) cause diarrhea in infants, particularly
where sanitation is lacking
• Campylobacteriosis Results from Consumption of Contaminated Poultry or Dairy
Products
• Campylobacteriosis is the most common cause of bacterial gastroenteritis
in the United States
• Campylobacter jejuni is transmitted through the fecal-oral route, usually
by poultry
• Yersinia enterocolitica is transmitted by consuming food that came in
contact with
• infected animals
• raw pork
• Gastric Ulcer Disease Can Be Spread Person to Person
• Helicobacter pylori is involved in gastric ulcers
• It is unknown how H. pylori is transmitted, but it likely involves
contaminated food or water
• The bacteria produce urease, which in turn produces ammonia
• Ammonia neutralizes acid in that area of the stomach, allowing the
bacteria to survive
• Colonization of the intestine occurs during a 2- to 7-day incubation period
• Guillain-Barré Syndrome is a rare nervous system disease that may develop
• The ammonia, and an H. pylori cytotoxin destroy mucous-secreting cells
• This creates a sore
• A urea breath test is used to detect H. pylori presence
21.6 Digestive System Infections and Intoxications Caused by Viruses and Eukaryotic
Microbes
• Rotavirus infections can be a deadly infection in children
• Transmission occurs through ingestion of contaminated food or
water
• The viruses invade the small intestine, inducing diarrhea
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• Two vaccines are available
• Norovirus infections are a common cause of nonbacterial gastroenteritis in
adults
• Transmission occurs through
– the fecal-oral route
– direct person-to-person contact
– contact with infected surfaces
• Recent outbreaks have been seen on cruise ships
• They are highly contagious
• Dehydration is the most common complication
• The Coxsackie virus is an enterovirus infection
• Different strains of Coxsackie viruses cause gastroenteritis, as well
as several other serious diseases
• The echovirus is also an enterovirus
• It occurs in many strains
• It can cause
– gastroenteritis
– aseptic meningitis
– exanthemas
Hepatitis Viruses A and E Are Transmitted by the Gastrointestinal Tract
• Hepatitis A is an acute inflammatory liver disease
• It is commonly transmitted by food or water contaminated by the
feces of an infected individual
– Transmission can also occur by raw shellfish
• Hepatitis A virus (HAV) belongs to the Picornaviridae family
Enlargement of the liver and jaundice may follow initial symptoms of hepatitis A
High standards of personal and environmental standards are needed to prevent
transmission
Three vaccines are available for different age groups
There is no known treatment
• Hepatitis E is an opportunistic, emergent disease
• It is caused by a member of the Caliciviridae family
• Young adults and pregnant women are most susceptible
Viral Gastroenteritis Is Caused by Several Unrelated Viruses
• Viral gastroenteritis is a general name for illnesses involving
• diarrhea
• nausea
• vomiting
• fever
• cramping
• headache
• malaise
Several Hepatitis Viruses Are Bloodborne
• Hepatitis B virus (HBV) is a global health problem
• HBV is a member of the family Hepadnaviridae
• Virions consist of
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– a nucleocapsid surrounded by a core antigen (HBcAg)
– an envelope containing a surface antigen (HBsAg)
Transmission usually involves direct or indirect contact with a bodily fluid
• Giardiasis is caused by Giardia intestinalis
• Transmission occurs through food or water contaminated with
sewage containing cysts
• Trophozoites emerge and attach to the intestinal lining
• Symptoms appear after about 7 days
– nausea
– cramps
– flatulence
– diarrhea
• Cryptosporidiosis is caused by Cryptosporidium parvum and C. hominis
• It is transmitted through contaminated water and physical contact
• Diarrhea lasts 1–2 weeks
• In immunocompromised patients, cholera-like diarrhea can occur
• Cyclosporiasis is caused by Cyclospora cayetanensis
• Transmission occurs through contaminated fresh produce and
water
• Symptoms include
– diarrhea
– nausea
– cramping
– bloating
– vomiting
• Symptoms can last more than a month and can return later
Several Protozoal Parasites Cause Diseases of the Digestive System
• Amoebiasis is the second leading cause of death from parasitic disease
• It is caused by Entameoba histolytica
• Cysts enter the body through food or water contaminated with feces
• Trophozoites emerge in the intestines, causing
• loose stools
• stomach cramping and pain
• Lesions may form, causing amoebic dysentery
• pain
• bloody stools
• fever
• Rarely, parasites can spread to other organs and cause fatal abscesses
• Some flatworms and roundworms are human pathogens
• Dog tapeworm disease is caused by Echinococcus granulosus
• Humans can be an intermediary host
• Parasites form hyatid cysts in the liver
Humans Are Host to at Least 50 Roundworm Diseases
• Pinworm disease is caused by Enterobius vermicularis
• Infection of the intestines leads to diarrhea and anal itching
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Reinfection can occur if contaminated hands contact food or the
mouth
Worms die in a few weeks, even without treatment
Trichinellosis is caused by Trichinella spiralis
• T. spiralis lives in pig intestines and can encyst in skeletal muscles
• Transmission to humans occurs by eating raw or poorly cooked
pork
• Symptoms include:
– pain
– vomiting
– nausea
– constipation
• Larvae can migrate to the tongue, eyes, and ribs
Ascariasis is caused by Ascaris lumbricoides
• Females produce a large number of eggs that can remain viable in
soil for months
• Transmission occurs by consuming contaminated food or water
• Worms mature in the intestine, causing blockage and perforation
• Larvae can move to the lungs
– This causes pneumonia and reinfection if coughed up
larvae are swallowed
Hookworms have a set of hooks or suckers to attach to the upper intestine
• Hookworms suck blood from intestinal capillaries
– This cause blood loss and anemia
• Humans are the only host
• Larvae in soil penetrate the skin of bare feet and enter the
bloodstream