Touro PA Microbiology Lectures #7, #8.pdf

Microbiology Lecture #7-8 Food And Waterborne Diseases Foodborne Illness • Foodborne illness (food poisoning) is due to consumption of pathogen or toxin it produces • Millions of cases annually 3 Disease Transmission • Food and water: can become contaminated • Animal products (meat, eggs, she...

Microbiology Lecture #7-8 Food And Waterborne Diseases Foodborne Illness • Foodborne illness (food poisoning) is due to consumption of pathogen or toxin it produces • Millions of cases annually 3 Disease Transmission • Food and water: can become contaminated • Animal products (meat, eggs, shellfish, etc) from animal’s intestines, undercooked • Cross-contamination: transfer between foods • Municipal water systems can distribute to large numbers • Cryptosporidium hominis outbreak in Wisconsin (1993) affected over 403,000 people • Cryptosporidium oocysts passed through the filtration system • 2-week period, 403 000 of the estimated 1.61 million • 54 deaths • the elderly and immunocompromised persons, such as AIDS patients. • ©Glow Cuisine/ Getty Images 4 Foodborne Illness • Foodborne intoxication results from consumption of exotoxin produced by microorganisms growing in food • Staphylococcus aureus • Many strains produce toxin that causes nausea, vomiting • Heat-stable: survives cooking, unlike most exotoxins • Most spoilage microbes outcompete, but if they are killed (cooking) or inhibited (salt), S. aureus can thrive • Creamy pastries, starchy salads, ham • Contamination usually via human carrier • • (left): Scott Bauer/ARS/U.S. Dept of Agriculture; (right): ©Gaetano/Corbis Access the text alternative for slide images. 5 Foodborne Intoxication Clostridium botulinum • Ingestion of neurotoxin (botulinum toxin) produced by anaerobic, endospore forming, Gram-positive rod C. botulinum causes deadly paralytic disease • Botulinum toxin is one of the most powerful poisons known • Found naturally on many foods • Endospores survive cooking and inadequate canning procedures • If conditions are favorable (anaerobic, nutrient-rich, a pH above 4.5, temperature above 4°C), endospores germinate, and vegetative cells multiply and produce the toxin 6 Foodborne Infection • Foodborne infection requires consumption of living organisms • Symptoms of illness usually do not appear for at least a day; usually include diarrhea • Thorough cooking will kill, thereby prevent infection • Salmonella and Campylobacter (in raw milk too) • Two genera commonly found in poultry products • Inadequate cooking or crosscontamination of other foods can result in foodborne infection • • Access the text alternative for slide images. (left): villagemon/iStock/Getty Images Plus/Getty Images; (right): alisali/123RF 7 Foodborne Infection 1 Shiga toxin-producing Escherichia coli (STEC) • Cause bloody diarrhea; sometimes results in hemolytic uremic syndrome (HUS), which is life-threatening • Can colonize intestinal tract of healthy livestock; shed in feces; meats can easily become contaminated • Searing exterior of meats destroys; grinding meat to produce patties distributes pathogen throughout product • Hamburgers particularly troublesome, must be cooked sufficiently to heat center to kill all E. coli cells • Outbreaks also linked to unpasteurized milk, various produce contaminated with animal manure 8 Focus on Diarrheal Diseases 1 • Gastroenteritis; “stomach flu” (not influenza) • Hundred of thousands of children die around the world due to diarrheal illnesses. All ages can be affected, though most are infants. • Signs and Symptoms: diarrhea, loss of appetite, nausea, vomiting, perhaps fever; incubation period 1 to 2 days • Small intestine: abundant, watery diarrhea • Large intestine: small amounts of diarrhea with mucus, pus, and sometimes blood • Dysentery: blood and pus in feces 9 Focus on Diarrheal Diseases 2 • Pathogenesis • Virulence genes • Infectious dose related to acid tolerance; organism must survive passage through stomach • Attachment of pathogen typically needed for infection • Disrupts fluid exchange in small intestine; can result in dehydration; potentially fatal • Often elicits a strong inflammatory response in large intestine • Mechanisms include alteration of intestinal epithelial cells, cell invasion, exotoxin production • Enterotoxins cause water and electrolyte loss • Cytotoxins cause cell death • Some absorbed into bloodstream; systemic effects 10 Focus on Diarrheal Diseases 3 • Epidemiology • Transmitted by fecal-oral route • Commonly through food or water contaminated with animal or human feces • Sexual practices with oral-anal contact • Microbes with low infectious dose can be transmitted by person-toperson contact • Sewage treatment, handwashing, chlorination of drinking water are important control measures 11 Focus on Diarrheal Diseases 4 • Treatment and Prevention • Oral rehydration therapy (ORT): appropriate liquids counteract loss of fluid and electrolytes • Plain water cannot be absorbed enough to keep pace • Glucose increases absorptive capacity of intestine • ORS (solution) is mixture of glucose and salts; premeasured packets added to clean water • Antimicrobial medications often prolong bacterial infection as they suppress normal microbiota • No specific treatment for viral diarrhea • A few pathogen-specific vaccines are available 12 Vibrio cholerae • Vibrionales • Found in aquatic habitats • V. cholerae causes cholera • V. parahaemolyticus causes gastroenteritis Vibrio Cholerae Bacterial Diseases of the Lower Digestive System 1 Cholera • Causes diarrhea so severe that it can be fatal within hours • In 2011 Haiti had the highest number of recorded cases in a country in a single year • Due to earthquakes, natural disasters, the civil war disrupting sanitation, water treatment, and access to health care 15 Cholera 1 Signs and Symptoms • Incubation period of 12 to 48 hours • Classic example of severe watery diarrheal disease • “Rice water stool” appearance; can amount to 20 liters/day; dehydration can lead to organ failure and death • Vomiting often occurs at onset; severe muscle cramps result from loss of fluids and electrolytes Causative Agent: Vibrio cholerae • Curved, Gram-negative rod • Several serotypes grouped by O antigen 16 Cholera 2 Pathogenesis • Sensitive to acid, so large numbers must be ingested • Adhere to epithelial cells of small intestine, establish infection, produce cholera toxin, an A-B toxin • B portion attaches irreversibly to specific receptors of the microvilli of the epithelial cells facilitating entry of the A portion • A portion enters cells, locks the G protein into the “on” position resulting in nonstop activity of adenylate cyclase which converts ATP to cAMP • High levels of cAMP cause cells to secrete chloride and other electrolytes yielding outpouring of fluid and salts from cells • Toxin does not affect large intestine, but volume of fluid is too much to be absorbed, causing diarrhea 17 Vibrio cholerae Pathogenesis • ©London School of Hygiene & Tropical Medicine/Science Source • Access the text alternative for slide images. 18 Cholera 3 Epidemiology • Fecally contaminated water most common source • Foods including crab, oysters, vegetables implicated • A person can discharge a million or more V. cholerae cells in each milliliter of feces • Relatively common worldwide; most cases in U.S. involve international travel • Can spread quickly in untreated wastes • Effective wastewater treatment can eliminate spread 19 Cholera 4 Treatment and Prevention • Rapid replacement of fluids and electrolytes given before damage to vital organs can occur • Intravenous or oral rehydration therapy can decrease mortality from over 30% to less than 1% • Clean water and adequate sanitation are key control measures • Travelers should cook food immediately before eating and avoid fruit and ice contaminated with local water • Vaccines available in many parts of world • In 2016 FDA approved live attenuated oral vaccine intended for travelers to endemic areas 20 Bacterial Diseases of the Lower Digestive System 2 • Shigellosis • Found all over the world, most commonly in areas lacking sewage treatment • Estimated 80 to 165 million cases occur resulting in about 600,000 deaths per year • Signs and Symptoms • • • • • Incubation period 1 to 3 days Usually dysentery (bloody, mucoid diarrhea), some species cause watery diarrhea Headache, vomiting, fever, stiff neck, convulsions, joint pain Often fatal for infants in developing countries Causative Agents • Four species of Shigella, Gram-negative rods: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei • S. dysenteriae most virulent, S. sonnei least virulent • S. dysenteriae and S. flexneri most common in developing countries • S. sonnei causes over two-thirds of cases in U.S. 21 Shigellosis 1 Pathogenesis • Shigella take advantage of M cells which deliver microbes from intestinal lumen to macrophages • Multiply inside macrophages (in the cytoplasm), induce apoptosis in host cell • Attach to specific receptors, induce uptake by epithelial cells, multiply, cause actin polymerization to propel cell to cell • Invasion results in death of epithelial cells, sloughing of patches of epithelium; strong inflammatory response • Some strains produce Shiga toxin, an A-B toxin responsible for hemolytic uremic syndrome (HUS) • B subunit binds to endothelial cells lining small blood vessels • A subunit halts protein synthesis, leading to cell death • HUS may cause anemia and kidney failure; often fatal 22 Shigella Pathogenesis • ©Dr. Philippe J. Sansonetti, Professeur Institut Pasteur 23 Shigellosis 2 Epidemiology • Disease of humans; fecal-oral route • Small infectious dose; Shigella resistant to stomach acid • Spreads rapidly in populations with poor sanitation • Fecally contaminated food and water cause outbreaks • Anal intercourse Treatment and Prevention • Antimicrobials shorten duration; some strains resistant • Sanitary measures control spread 24 Bacterial Diseases of the Lower Digestive System 3 • Escherichia coli gastroenteritis • Signs and Symptoms • Depend on strain • Some cause watery diarrhea, others dysentery • One group causes hemolytic uremic syndrome (HUS) • Causative Agent: Escherichia coli • Gram-negative rod closely related to Shigella • Unlike Shigella, most strains ferment lactose 25 Bacterial Diseases of the Lower Digestive System • Escherichia coli Gastroenteritis • Pathogenesis • Variety of mechanisms • Strain dependent • Strains grouped into six pathovars (pathogenic varieties) based on their virulence factors • Access the text alternative for slide images. 26 Escherichia coli Gastroenteritis 1 Epidemiology • STEC strains foodborne; epidemics have involved ground beef, unpasteurized milk, bean sprouts • Initial source often untreated cow manure • Infectious dose low • (Toxigenic) ETEC strains cause diarrhea in infants in developing countries, also visitors (LT and ST toxins) • (Invasive) EIEC primarily cause disease in young children in developing countries • (Pathogenic)EPEC strains important in infants; antibodies in breast milk protective; relatively low infectious dose • (Aggregative)EAEC strains infect children, travelers, AIDS patients 27 Escherichia coli Gastroenteritis 2 Treatment and Prevention • Replacement of lost fluid • Most cases self-limiting, so antibiotics not routinely used • Worsen outcome in patients with STEC infections • Handwashing, pasteurization of juices, cooking of food thoroughly • Traveler’s diarrhea usually prevented with bismuth preparations (Pepto-Bismol) • Widespread use of antibiotics to prevent diarrhea has promoted development of resistant strains 28 Bacterial Diseases of the Lower Digestive System 4 • Salmonella gastroenteritis • About 1.2 million cases in U.S. each year • Outbreaks due to foods contaminated by animal feces • Signs and Symptoms: Diarrhea, abdominal cramps, nausea, vomiting, headache, fever • Incubation period 6 hours to 3 days • Often short-lived and mild depending on strain • Causative Agent: Salmonella enterica • Gram-negative rod; Enterobacteriaceae • More than 2,400 serotypes • Significant in terms of epidemiology and disease 29 Salmonella Gastroenteritis 1 Pathogenesis • Most sensitive to acid, so high infectious dose • Attach to epithelial cells of distal small intestine; effector proteins via type III secretion system induce endocytosis • Some bacteria escape the phagosome and multiply in the cytoplasm, but others are released by exocytosis • Inflammatory response causes diarrhea • Inflammation also produces tetrathionate that Salmonella can use in anaerobic respiration 30 Salmonella Gastroenteritis 2 Epidemiology • Most cases from nonhuman animal sources • Bacteria sometimes survive for months in soil and water • Untreated manure can spread • Poultry, eggs often contaminated; many other products (for example, tomatoes, alfalfa sprouts) have started outbreaks • Children commonly infected by pet reptiles 31 Salmonella Gastroenteritis 3 Treatment and Prevention • Most recover without antibiotics; many strains antibiotic resistant • Likely due to subtherapeutic levels in animal feed • Sanitary handling of food; cooking to 160 degrees Fahrenheit 32 Bacterial Diseases of the Lower Digestive System 5 • Enteric Fever (Typhoid and paratyphoid fevers) • Examples of enteric fevers: systemic diseases that originate in the intestine • Signs and Symptoms • Incubation period of 1 to 4 weeks • Progressively increasing fever over several days, severe headache, constipation, abdominal pain • In severe cases, intestinal rupture, bleeding, shock, death • Causative Agents • Salmonella serotypes Typhi and Paratyphi • Cases confirmed by blood culture 33 Enteric Fever 1 Pathogenesis • Enteric fevers caused by bacteria that colonize intestines, cross mucous membrane via M cells, multiply within macrophages, and are carried in bloodstream throughout the body • Systemic infection causes fever, abscesses, sepsis, and shock, often with little or no diarrhea • Peyer’s patches sometimes destroyed, leading to rupture of intestine, hemorrhage, and death • Toxin produced when cells are within a host cell • Role of toxin in disease under study 34 Enteric Fever 2 Epidemiology • Humans only known host, so spread person to person often via contaminated food or water • Some survivors remain colonized in gallbladder; can shed high numbers for years (for example, “Typhoid Mary”) Treatment and Prevention • Antibiotics; some strains resistant, susceptibility testing must be done • Surgical removal of gallbladder and months of antibiotic therapy often necessary to rid carriers of infection • Two vaccines against Salmonella Typhi, each approximately 50 to 75% effective: attenuated live oral or injectable capsular polysaccharide • No vaccine against Salmonella Paratyphi 35 Bacterial Diseases of the Lower Digestive System • Campylobacteriosis • First isolated in 1972, took 5 years to selectively culture • Signs and Symptoms • Incubation period 1 to 11 days; usually 2 to 5 days • Fever, vomiting, diarrhea, abdominal cramps • Dysentery occurs in about half the cases • Causative Agent: Campylobacter jejuni • Curved, Gram-negative rod • Can be cultivated under microaerophilic conditions with a selective medium • Photo by De Wood, digital colorization by Chris Pooley, USDA-ARS 36 Campylobacteriosis 1 Pathogenesis • Penetrate epithelial cells of small and large intestines, cause localized inflammatory reaction • In rare cases individuals with campylobacteriosis go on to develop an autoimmune complication called Guillain-Barré syndrome Epidemiology • Estimated 1.3 million cases each year • Numerous foodborne and waterborne outbreaks reported involving as many as 3,000 people, although most cases are sporadic • C. jejuni lives in intestines of domestic animals; poultry is common source of infection, with up to 90% containing it • Raw milk is also a source of C. jejuni • Low infectious dose (approximately 500 organisms) 37 Campylobacteriosis 2 Treatment and Prevention • Typically self-limiting, patients’ immune • Antibiotics used to treat severe cases • Cooking and proper handling of raw poultry to avoid crosscontamination • Handwashing after contact with animal feces • Keeping outdoor play areas free of bird droppings • Chlorinating drinking water, pasteurizing beverages 38 Listeriosis 1 Signs and Symptoms • Infections asymptomatic or mild in most healthy people • If symptomatic, characterized by fever, muscle aches, sometimes nausea or diarrhea • The cases requiring medical attention have meningitis with fever, headache, stiff neck, and vomiting • Pregnant women often miscarry or deliver terminally ill infants • Babies infected at birth usually develop meningitis after incubation of 1 to 4 weeks, shorter if infection takes place in utero 39 Listeriosis 2 Causative Agent • Listeria monocytogenes: Motile, non-spore-forming, facultatively anaerobic, Gram-positive rod • Can grow at 4 degrees Celsius (refrigerator) even if vacuum-packed Pathogenesis • Primarily foodborne pathogen • Induce phagocytosis, survive and reproduce within host cells, protected from immune system, enter bloodstream • can cause host cell actin to polymerize, forming a “tail” that propels the organism with enough force to push it into an adjoining cell • Bacteremia is source of meningeal infection • L. monocytogenes crosses placenta in pregnant women; produces widespread abscesses in fetal tissues 40 Listeriosis 3 Epidemiology • Widespread in natural waters, vegetation; can be carried in intestines of asymptomatic humans, other animals • Pregnant women, elderly, those with underlying illnesses especially susceptible • Outbreaks have resulted from contaminated food (coleslaw, non-pasteurized milk, pork tongue in jelly, some soft cheeses, hot dogs, cantaloupe) • Can grow in commercially prepared food stored at refrigeration temperatures, so thousands of infections can originate from a single food-processing plant 41 Listeriosis Treatment and Prevention • Most strains susceptible to antibacterials • Often mild in pregnant women, but prompt treatment important to protect fetus • Cook food thoroughly; avoid cross-contamination by keeping food separate • Pregnant women, others at risk should avoid soft cheeses, refrigerated meat spreads, raw or smoked seafood • Bacteriophage mixture that lyses L. monocytogenes can be sprayed on meats during production • Increased safety 80 to 99% • (top): ©Tomas Del Amo/Photo Library/Getty Images; (bottom): ©Intralytix, Inc. 42 Botulism 1 Signs and Symptoms • Begin 12 to 36 hours after ingesting toxin-contaminated food • Dizziness, dry mouth, blurred or double vision • Abdominal symptoms can include pain, nausea, vomiting, and diarrhea or constipation • Progressive paralysis involves all voluntary muscle • Respiratory paralysis most common cause of death Causative Agent • Clostridium botulinum: Strictly anaerobic, Gram-positive, endospore-forming rod • Different strains produce different types of neurotoxin • Endospores survive boiling; can germinate in favorable environment (nutrient-rich, anaerobic, pH above 4.5, temperature above 4 degrees Celsius) • Types A, B, and E are responsible for most human cases of disease 43 Clostridium botulinum • Canning processes designed to destroy endospores (commercial sterilization) • Rare in commercially canned foods; most botulism due to improperly processed home-canned food • Toxin destroyed by heating; home-canned foods should be boiled at least 10 minutes before eating • Damaged or bulging cans should be discarded 44 Botulism Pathogenesis • Vegetative cells release powerful botulinum toxin • Circulating botulinum toxin attaches to motor neurons, stops transmission of signals to muscles, paralysis. • A-B toxin; B portion binds to specific receptors on motor nerve endings, A portion enters nerve cell, inactivates proteins regulating release of neurotransmitter. • stops muscle contraction, resulting in flaccid paralysis • • prevents nerve transmission to muscles, applications: Botox is used to prevent headaches and provide relief from a variety of conditions involving muscle contractions • Cosmetic use to reduce wrinkles • 45 Richard Gross/McGraw-Hill Education Botulism • Epidemiology • Endospores widely distributed in soils, aquatic sediments • Fewer than 30 cases/year of foodborne botulism in U.S. • Most from preserved fish or home-canned foods • Commercial canners strictly controlled • Intestinal (infant) more common in U.S. • Still <150 cases/year • Honey implicated • Most wound botulism in U.S. due to abuse of injected drugs 46 Botulism 2 • Treatment and Prevention • Intravenous antitoxin; only neutralizes toxin in blood • Affected nerves slowly recover over weeks or months • BabyBIG for infants, HBAT for anyone older than 1 year • Mechanical ventilator may be needed • Intestinal botulism: respiratory, feeding support until normal microbiota replace pathogen; antitoxin • Proper sterilization, sealing of food • Toxin is heat-labile; cooking can destroy • Avoid feeding honey to babies under 1 year of age • Immunity does not develop 47 Bacterial Diseases of the Upper Digestive System 3 • Helicobacter pylori gastritis • Barry Marshall drank culture of Helicobacter pylori in 1980s, demonstrated association with stomach ulcers • Signs and Symptoms • Most infections asymptomatic • Gastritis, typically asymptomatic, can result in belching, loss of appetite, nausea and sometimes vomiting may occur • Chronic gastritis can lead to stomach cancer • Peptic ulcers produce localized abdominal pain, tenderness, bleeding • Causative Agent: Helicobacter pylori • Short, curved, Gram-negative microaerophile with multiple polar flagella 48 Helicobacter pylori Gastritis 1 Pathogenesis • H. pylori survives acidic environment of stomach • Produces urease, which converts urea in gastric juices to ammonia, creating alkaline compound that neutralizes stomach acid in microenvironment • Burrows within mucus layer that coats stomach lining • • • • • Avoids recognition by immune system receptors VacA (vacuolating cytotoxin) has multiple effects on cells, including damaging mitochondria, inducing apoptosis in epithelial cells, interfering with T cells CagA (cytotoxin-associated gene) in strains with higher risk of cancer; alters host cytoskeleton, cell signaling Damage to epithelial cells and inflammatory response resulting in decreased mucus production, cell damage Infections persist for years, often for life; 90% of those with stomach cancer are infected 49 Helicobacter pylori Pathogenesis • • Science Photo Library/Getty Images Access the text alternative for slide images. 50 Helicobacter pylori Gastritis 2 Epidemiology • About 35% of adults in U.S. infected with H. pylori; incidence increases to approximately 80% for those over 75, clusters in families • Infection rates highest in low socioeconomic groups • Likely transmitted via fecal-oral route • Bacteria found in well water Treatment and Prevention • Antibiotics plus medication to inhibit acid production 51 Bacterial Diseases of Blood and Lymphatic Systems 6 • Brucellosis (“Undulant Fever” or “Bang’s disease”) • Signs and Symptoms • Symptoms start gradually, are vague • Mild fever, sweating, weakness, aches and pains, enlarged lymph nodes, weight loss • Recurrence of fevers over weeks or months • Recovery within 2 months without treatment; some develop chronic illness • Causative Agent: Brucella melitensis • Small, aerobic, non-motile Gram-negative rods • At least four varieties cause brucellosis in humans 52 Brucellosis 1 Pathogenesis • Penetrates tissues through mucous membranes or wounds, weak initial immune response • Grow within phagocytes, avoid antibodies • Infected macrophages carry to other parts of body where they infect mononuclear phagocytes • Low mortality rate; death generally from endocarditis or meningitis; osteomyelitis (bone infection) is complication Epidemiology • Typically, chronic zoonotic infection of domestic animals • Contaminates milk • Causes millions of dollars in agricultural losses globally • Occupational exposure; consumption of unpasteurized milk products; hunting, eating meat from infected animals 53 Brucellosis 2 Treatment and Prevention • Can be treated with doxycycline for 6 weeks along with oral rifampin for 6 weeks or intravenous streptomycin for 2 to 3 weeks • Some chronic cases may require 6 months or more • Pasteurization of dairy products; inspection of domestic animals for evidence of disease • Protective gear (goggles or face shield, gloves) for veterinarians, butchers, slaughterhouse workers • Attenuated vaccine controls disease in domestic animals 54 Protozoan Diseases of the Lower Digestive System 1 • Protozoa—single-celled eukaryotes—important causes of human intestinal diseases • All transmitted via fecal-oral route • Giardiasis • Signs and Symptoms • About two-thirds of exposed individuals develop symptoms; incubation is 6 to 20 days • Symptoms mild (indigestion, “gas,” nausea) to severe (vomiting, explosive diarrhea, abdominal cramps, fatigue, weight loss) • Usually resolve without treatment in 1 to 3 weeks; some cases become chronic • Long-term carriers excrete infectious cysts in feces 55 Giardiasis Causative Agent: Giardia lamblia • • Flagellated protozoan with two side-by-side nuclei, adhesive disc on undersurface Two forms: growing, feeding trophozoite and dormant cyst • Cysts: thick protective chitin-like polysaccharide walls • Source: Janice Haney Carr/CDC 56 Giardiasis 1 Pathogenesis • Cysts infectious, survive stomach acid, unlike trophozoites • Trophozoites emerge from each cyst that reaches upper part of small intestine • Some attach to epithelium by adhesive disc • Others use flagella to move freely in intestinal mucus • Some migrate to gallbladder, cause cramping or jaundice • Trophozoites interfere with intestine’s ability to absorb nutrients, secrete digestive enzymes • Result in bulky feces containing fat, intestinal gas from bacterial fermentation, and malnutrition • Trophozoites detach, are carried to large intestine • If transit time is long, trophozoites develop into cysts • If person has diarrhea, trophozoites are eliminated in feces 57 Protozoan Diseases of the Lower Digestive System • (3): Dr. Stan Erlandsen/CDC; (4): Dr. Stan Erlandsen/CDC • Access the text alternative for slide images. 58 Giardiasis 2 Epidemiology • Low infective dose (10 cysts); easily spread • Water contaminated with human feces common source of infection; feces from other animals also implicated • Cysts infectious, remain viable in cold water >2 months • Hikers drinking from streams are at risk • Person-to-person transmission, especially in daycare centers where hands contaminated while changing diapers • Sexual practices involving oral-anal contact can transmit • Transmission by fecally contaminated food reported • Good personal hygiene and handwashing minimize spread 59 Giardiasis 3 Treatment and Prevention • Treatment not necessary if mild and no risk of transmission • When appropriate: Tinidazole, metronidazole (Flagyl), and nitazoxanide • Municipal chlorination does not destroy cysts, so water generally filtered to remove • Hikers most effective water treatment is to boil for 1 minute or use portable filter 60 Protozoan Diseases of the Lower Digestive System –Figure 24.22 • Cryptosporidiosis (“Crypto”) • One of the most common waterborne diseases in the United States. Health risk to both general public and those with immunodeficiency • Signs and Symptoms • Fever, loss of appetite, nausea, abdominal cramps, profuse watery diarrhea begin after 4 to 12 days • Symptoms last 10 to 14 days; can last months and may be life-threatening in immunocompromised individuals • Causative Agent: Cryptosporidium hominis (formerly parvum) • An apicomplexan • Oocyst stage is an environmentally resistant with four sporozoites • ©Michael Abbey/Science Source 61 Cryptosporidiosis 1 Pathogenesis • In the small intestine, sporozoites released from ingested oocysts, which then invade epithelial cells of small intestine • Cause inflammation, water and electrolyte secretion increases, decrease in nutrient absorption • Cell-mediated immunity is important in controlling the infection Epidemiology • Infectious dose as few as 10 oocysts; can easily spread person-toperson • Responsible for many cases of traveler’s diarrhea • Oocysts can survive up to 6 months in food, water • Resistant to chlorine; too small for some filtration methods • Feces from dogs, pigs, cattle can contaminate food, water 62 Cryptosporidiosis 2 Treatment and Prevention • Nitazoxanide may be used in those with healthy immune systems; most recover without treatment • Sanitary disposal of human, animal feces • Treat water with filtration, UV, or ozone • Pasteurize liquids • Wash hands with soap, water • Immunodeficient individuals should avoid animals, boil or filter water, avoid recreational water activities 63 Protozoan Diseases of the Lower Digestive System 2 • Cyclosporiasis • Signs and Symptoms • Fatigue, loss of appetite, slight fever, vomiting, and watery diarrhea begin after about 1 week, followed by weight loss • Diarrhea subsides in 3 to 4 days; relapses up to 4 weeks • Causative Agent: Cyclospora cayetanensis • An apicomplexan; oocysts similar to C. parvum but larger, and not infectious in feces • With favorable conditions outside the body oocysts mature to become infectious. Mature oocysts contain sporozoites within structure called sporocysts 64 Cyclosporiasis Pathogenesis • Little known; no known hosts other than humans • Biopsies confirm sexual and asexual forms are both present in intestinal epithelium • Epidemiology • No person-to-person transmission • Warm, moist conditions favor maturation of oocysts • Fresh produce implicated in epidemics • Has been found in natural waters; source undetermined • Treatment and Prevention • Co-trimoxazole • No specific preventive measures; boil or filter drinking water, thoroughly wash produce during outbreaks 65 Protozoan Diseases of the Lower Digestive System • Amebiasis • Believed to infect up to 50 million people worldwide and in crowded, unsanitary living conditions as estimated 55,000 people die from the virulent strains each year • Signs and Symptoms • Commonly asymptomatic; some suffer from chronic, mild diarrhea lasting months or years • In severe cases, acute dysentery can be fatal • May also spread to the liver causing liver abscesses; results in fever, nausea vomiting, abdominal pain, and liver enlargement • Incubation period varies from a few days to a few months • ©Centers for Disease Control and Prevention 66 Amebiasis 1 Causative Agent: Entamoeba histolytica • An amoeba that can sometimes lyse tissue. Life cycle involves active trophozoite stage and infectious cyst. • Trophozoite cannot survive in the environment. Cysts have four nuclei and can survive in the environment. Pathogenesis • Cysts survive passage through stomach, release trophozoites, which are passed to large intestine • Trophozoites feed on mucus, bacteria to multiply; cause cramps, diarrhea; many strains produce cytotoxic enzyme • May penetrate intestinal lining, causing ulceration and bloody diarrhea called amebic dysentery • Sometimes penetrate blood vessels and are carried to liver or other organs resulting in amebic abscesses 67 Amebiasis 2 Epidemiology • Low infectious dose; most commonly spread by fecal-oral route • Most common in tropical areas with poor sanitation but distributed worldwide • In U.S., mainly in poverty-stricken areas, among migrant farm workers, and men who have sex with men • Humans only important reservoir Treatment and Prevention • Asymptomatic infections are often left untreated. If treatment is given, a luminal agent is used (paromomycin) as it is poorly absorbed, and its action is limited to the gut lumen • For symptomatic infections, metronidazole is administered with Tinidazole as an alternative and followed by paromomycin • Sanitary measures prevent 68 STOP! Enjoy your weekend!