Chapter 21



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

• 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

– 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

• 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

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download