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Intestinal Infections Flashcards

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1
Q

What types of damage can be caused by gastrointestinal pathogens?

A
  • Local inflammation
  • Ulceration / perforation of mucosal epithelium
  • Disruption of normal microbiota
  • Pharmacological action of bacterial toxins
  • Invasion to blood or lymphatics
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2
Q

Describe the consequences of GI epithelial perforation.

A
  • Ruptured ulcer / perforated ulcer.
  • Lining of the mucosa wall is perforated due to untreated ulcers.
  • May result in leaking of food and gastric juices to the peritoneal or abdominal cavities.
  • Treatment requires surgery.
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3
Q

What are the incubation periods for the pathogens which cause diarrhoea, specifically campylobacter and shigella?

A
  • Campylobacter - 2-11 days
  • Shigella - 1-4 days
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4
Q

What are the durations of diarrhoea caused by campylobacter and shigella?

A
  • Campylobacter - up to 3 weeks
  • Shigella - 2-3 days
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5
Q

Describe the variable symptoms caused by the pathogens which cause diarrhoea, specifically campylobacter, shigella, EPEC and cholera.

A
  • Campylobacter and shigella - bloody stools.
  • EPEC and cholera - watery stools.
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6
Q

Describe the characteristics of vibrio cholerae.

A
  • Gram negative
  • Comma-shaped rod
  • Flagellated
  • Characterised by epidemics and pandemics
  • Human-only pathogen
  • Flourishes in communities with no clean drinking water / sewage disposal
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7
Q

What are the available vaccines for V. Cholerae?

A
  • Parenteral vaccine: low protective efficiency.
  • Oral vaccine: effective and suitable for travellers.
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8
Q

Describe the pathogenesis of V. cholerae.

A
  • Only infective in large doses.
  • Many organisms killed in the stomach.
  • Colonisation of small intestine involving flagellar motion, mucinase, attachment to specific receptors.
  • Production of multicomponent toxin.
  • Loss of fluid and electrolytes without damage to enterocytes.
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9
Q

Describe the characteristics of the cholera toxin (CTx).

A
  • Oligomeric complex of 6 protein subunits:
    • 1 copy of A subunit (enzymatic)
    • 5 copies of B subunit (receptor binding)
  • Responsible for the characteristic, watery cholera diarrhoea.
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10
Q

Describe the consequences of being infected by cholera.

A
  • Fluid loss of up to 1L per hour.
  • Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalaemia.
  • Hypovolaemic shock.
  • 40-60% mortality.
  • <1% mortality if given fluid / electrolytes (ORT).
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11
Q

Describe the characteristics of Escherichia coli.

A
  • Gram negative.
  • Bacillus.
  • Member of normal GI microbiota.
  • Some strains possess virulence factors enabling them to cause disease.
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12
Q

What are the types of E. coli which cause GI infections?

A
  • EPEC - enteropathogenic
  • ETEC - enterotoxigenic
  • VTEC / STEC - verocytotoxin-producing
  • EHEC - enterohaemorrhagic
  • EIEC - enteroinvasive
  • EAEC - enteroaggregative
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13
Q

Describe the different GI infections caused by the different types of E. coli.

A
  • EPEC: sporadic cases and outbreaks of infection in under 5s.
  • ETEC: ‘travellers’ diarrhoea’ (occurs in 20-50% of travellers).
  • VTEC / EHEC: sporadic cases and outbreaks of gastroenteritis.
  • EIEC: food-borne infection in areas of poor hygiene (often persistent diarrhoea).
  • EAEC: resource-poor countries.
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14
Q

Describe the factors which aid the adherence of E. coli.

A
  • Pili / fimbriae are used to attach the bacteria onto enterocytes.
  • Pedestal formation - this happens normally even in the absence of infection.
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15
Q

Describe the mode of action of E. coli enterotoxins.

A
  • LT = heat-labile toxin
  • STa = heat-stable toxin
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16
Q

Describe the characteristics of campylobacter jejuni.

A
  • Gram negative.
  • Helical bacillus.
  • Large animal reservoir.
  • Causes food-associated diarrhoea.
  • Commonest cause of diarrhoea in the developed world.
  • Transmission through comsumption of raw / undercooked meat, contaminated milk.
  • Mucosal inflammation and fluid secretion.
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17
Q

Describe the histological appearance of C. jejuni infection.

A
  • Inflammation involves entire mucosa.
  • Villous atrophy.
  • Necrotic debris in crypts.
  • Thickening of basement membrane.
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18
Q

Describe the characteristics of Salmonella spp.

A
  • Gram negative.
  • Bacilli.
  • >2000 serotypes of Salmonella spp.
  • Causes food-associated diarrhoea.
  • Transmission through consumption of raw / undercooked meat, contaminated eggs and milk.
  • Secondary spread can be human - human.
  • Important species:
    • S. typhi
    • S. paratyphi
    • S. enteritidis
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19
Q

Describe the pathogenesis of Salmonella infection.

A
  • Ingestion of large numbers of bacteria.
  • Absorption to epithelial cells in terminal section of the small intestine.
  • Penetration of cells and migration to lamina propria.
  • Multiplication in lymphoid follicles.
  • Inflammatory response mediates release of prostaglandins.
  • Stimulation of cyclic AMP.
  • Release of fluid and electrolytes causing diarrhoa.
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20
Q

Describe the consequences of S. typi and S. paratyphi infections.

A
  • Cause enteric fevers: typhoid and paratyphoid.
  • Systemic infections initiated in gastrointestinal tract.
  • Species restricted to humans.
  • Multiply within, and are transported around the body in, macrophages.
  • Patients can excrete S. typhi in faeces for several weeks after recovery.
  • 1-3% become chronic carriers, most common in women and the elderly.
  • Public health concern: it is a notifiable disease.
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21
Q

What are the available vaccines for typhoid?

A
  • Oral; live attenuated
    • Booster after 5 years
  • Parenteral; capsular polysaccharide
    • Booster after 2 years
  • 50-80% effective.
  • Recommended for travellers to endemic areas.
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22
Q

Describe the characteristics of shigella spp. and name the 4 species.

A
  • Bacillus.
  • Causes shigellosis (bacillary dysentery).
  • Human-only pathogen.
  • 4 species:
    • S. dysenteriae: most serious
    • S. flexneri: severe disease
    • S. boydii: severe disease
    • S. sonnei: mild infections
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23
Q

Describe the pathogenesis of shigella infection.

A
  • Attaches to mucosal epithelium of distal ileum and colon.
  • Causes inflammation and ulceration.
  • Rarely invasive.
  • Produces Shiga toxin (STx).
  • Diarrhoea watery initially, later can contain blood and mucous.
  • Disease is usually self-limiting.
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24
Q

Describe the characteristics of listeria monocytogenes.

A
  • Coccobaccillus.
  • Causes listeriosis.
  • Food-borne pathogen associated with paté, soft cheese, unpasturised milk, hummus.
  • <1000 organisms may cause disease.
  • Population at risk:
    • Pregnant women (with possibility of infection of the baby in utero or at birth).
    • Immunosuppressed individuals (e.g. those with AIDS or on cancer / immunosuppressive drugs).
    • The elderly.
  • Usually presents as meningitis.
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25
Describe the characteristics of antibiotic-associated diarrhoea.
* Does NOT involve ingestion of pathogen or toxin. * Can arise from disruption of gut microbiota following antibiotic therapy. * Tetracycline - allows colonisation by *Staphyloccocus aureus & Candida sp.* * Clindamycin suppresses gut microbiota and allows Clostridium difficile to multiply - overgrowth. * *C. difficile* infection is now associated with resistance to vancomycin.
26
Describe *C. difficile* infections.
* Produces spores for survival. * Produces an enterotoxin and a cytotoxin. * Nosocomial infections largely responsible for increase in cases.
27
Describe *Clostridium perfringens* infection.
* Usually caused by type A strains from animal guts and soil. * Contamination of raw meat products. * Spores survive cooking and germination takes place. * Multiplication in large intestine, production of spores and enterotoxin. * Damage to intestinal epithelium. * Diarrhoea.
28
Describe Rotavirus.
* 'Rota' = wheel. * 11 separate segments of double-stranded RNA. * Infects many mammals. * Infection commonest in children \<2 years old. * As few as 10 ingested particles can cause disease. * Seasonal ocurrence (commonest in cooler months). * Transmission is faeco-oral, but may also be faeco-respiratory.
29
Describe the pathogenesis of rotovirus infection.
* Incubation period of 1-2 days. * Replication of virus in small intestinal epithelial cells at tips of villi. * Results in villous atrophy. * Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes. * Onset of vomiting, diarrhoea lasting 4-7 days. * Up to 1010 - 1011 virus particles / gram faeces released.
30
What are the available vaccines for rotavirus?
* RotaRix; RotaTeq * Oral administration (2-3 doses) * First dose at 6-10 weeks of age * Live, attenuated virus * Introduced in UK from 2013.
31
Describe norovirus.
* Winter vomiting disease. * Accounts for most non-bacterial outbreaks worlwide. * Past infection in 60% of adults. * Human-only pathogen. * Transmission is faeco-oral, contaminated water / shellfish, fomites. * \<100 virions can establish infection.
32
What vaccines are available for norovirus?
* NONE YET * Still ~4-5 years away. * Good hand washing instead goes a long way.
33
Describe enteric adenovirus.
* Accounts for 10% of community-acquired diarrhoea in young children. * No seasonal incidence. * Asymptomatic infections common. * Mild, but prolonged diarrhoea.
34
Describe the transmission of intestinal protozoa and helminths?
* Complex life-cycle stages. * New infections depend on contact with faecal-derived material. * Infection levels reflect hygiene / sanitation standards. * Usually acquired through ingestion of contaminated food or water. * Symptoms usually present as acute to chronic diarrhoea and inflammation. * Occasionally, spread of parasites into other organs may occur.
35
Describe Giardia lamblia.
* Giardiasis is a frequent cause of travellers' diarrhoea globally. * Detected in both drinking and recreational water. * Can be passed from person to person. * Infective dose is small: 10-25 cysts. * Diagnosis by microscopy of stool samples.
36
Describe the life cycle of G. lamblia.
**​​2 stages:** * **Trophozoite** * Flagellated and bi-nucleated. * Lives in upper part of the small intestine. * Adheres to the brush border of epithelial cells. * **Cyst** * **​**Formed when trophozoite forms a resistant wall. * Passes out in stools. * Can survive for several weeks.
37
Describe the pathogenesis of G. lamblia.
* Present in the duodenum, jejunum and upper ileum. * Attaches to the mucosa via ventral sucker. * Does not penetrate the surface. * Causes damage to the mucosa and villous atrophy. * Leads to malabsorption of food, especially fats and fat-soluble vitamins. * May swim up the bile duct to the gall bladder.
38
What are the clinical manifestations of G. lamblia?
* Mild infections are asymptomatic. * Diarrhoea is usually self-limiting (7-10 days). * Chronic diarrhoea presents in immunocompromised patients. * **Stools** are characteristically **loose**, **foul-smelling** and **fatty**.
39
Describe cryptosporidium parvum.
* Significance grew during the early years of AIDS epidemic (opportunistic infection). * Transmission through faecally-contaminated drinking water. * Animal reservoir (usually cattle). * Infective dose: as few as 10 oocysts.
40
Describe the life-cycle of C. parvum.
* Asexual and sexual development within the host. * Ingestion of resistant oocysts. * Release of infective sporozoites in the small intestine. * Invasion of microvillus border of intestinal epithelium. * Division to form merozoites which re-infect cells. * Aftersexual phase, oocytes are released.
41
Describe the clinical manifestations of C. parvum.
* Moderate to severe profuse diarrhoea. * Up to 25L of watery faeces / day. * Usually self-limiting disease. * In HIV positive individuals with CD4+ T-cell counts of \<100/mm3, diarrhoea is prolonged and may become irreversible and life-threatening.
42
Describe *Entamoeba histolytica.*
* Common in tropical and sub-tropical countries: prevalent in \>50% of population. * Transmission via ingestion of contaminated food or water. * Transmission also occurs through anal sexual activity. * Cysts pass through stomach and excyst in the small intestine giving rise to progeny. * These adhere to epithelial cells and cause damage mainly through cytolysis. * After mucosal invasion, cysts invade RBCs giving rise to amoebic colitis. * Trophozoite stages live in large intestine and pass out as resistant, infective cysts.
43
Describe the pathogenesis of *E. histolytica.*
* Adheres to epithelium and acute inflammatory cells. * Resists host humoral and cell-mediated immune defence mechanisms. * Produces hydrolytic enzymes, proteinases, collagenase and elastase. * Produces protein that lyses neutrophils, the contents of which are toxic to the host.
44
What are the clinical manifestations of E. histolytica?
* Small localised superficial ulcers leading to mild diarrhoea. * Entire colonic mucosa may become deeply ulcerated leading to severe amoebic dysentery. * Complications include intestinal perforatin. * Trophozoites may spread to the liver, and other organs. * Rarely, abscesses spread to overlying skin.
45
What are the protozoal infections of the GI tract?
* *G. lamblia* * *C. parvum* * *E. histolytica*
46
What are the treatments for *C. parvum*?
* Nitazoxanide * Spiramycin
47
What are the treatments for *G. lamblia*?
* Mepacrine hydrochloride * Metronidazole * Tinidazole
48
What are the treatments for *E. histolytica*?
* Metronidazole
49
What are the ways of preventing protozoal infections of the GI tract?
* Improved hygiene and water supplies. * Eating only freshly prepared food served hot. * Avoiding salads and fuit which cannot be peeled. * Avoiding tap water and ice cubes.
50
Describe nematode intestinal infections.
* Nematodes are the most clinically important intestinal worms. * Often soil-transmitted. * Infections occur by either: * Swallowing infective eggs (*Ascaris lumbricoides, Trichuris trichiura).* * Active skin penetration by larvae and systemic migration through lung to intestine (*Strongyloides stercoralis*). * Diagnosis by stool microscopy.
51
Describe *Strongyloides stercoralis.*
* Pinworm * Disruption of small intestinal mucosa * Villous atrophy * Marked loss of elasticity of intestinal wall
52
What are the clinical manifestations of *S. stercoralis*?
* Dysentery (persistent in immunocompromised hosts). * Dehydration * Malabsorption syndrome * Analpruritis * Association with appendicitis
53
Describe *Trichuris trichirua.*
* Whipworm * Can live for 3 years in the gut * Acquired through ingesting eggs on vegetables * 10,000 eggs produced daily * 800 million cases worldwide
54
Describe *Ascaris lumbricoides.*
* Giant roundworm * Large thick white worm 20-30cm * Females produce approximately 20,000 eggs/day from 65 days after infection. * Adults live in the gut for 2 years. * Causes 1 million cases per year, with 20,000 deaths.
55
What are the clinical manifestations of *A. lumbricoides?*
* Allergic reaction in sensitised people. * Digestive upsets. * Protein / energy malnutrition. * Intestinal blockages. * Worm may invade mouth, nose etc.
56
Describe *Enterobius vermicularis.*
* Threadworm. * Small cylindrical nematodes \<1cm. * Female migrates to anus at night to lay approximately 10,000 eggs, which may develop to infective stage within hours. * Intense itching, secondary bacterial infection - mild catarrhal inflammation and diarrhoea, slight eosinophilia.
57
Describe *Ancyclostoma duodenale.*
* Hookworm. * Often picked up walking barefoot in infected areas. * Attaches to small intestine, suck blood and protein, often present in huge numbers. * Cause hypochromic anaemia. * Blood loss 0.03ml/day/worm (often 500-1000 worms).
58
Describe *Taenia solium* (tapeworm).
* Acquired from ingesting worms or eggs in undercooked pork. * Reside in large intestine. * Can grow up to 7m long. * Scolex - for attachment.
59
Describe the treatment and prevention of intestinal helminth infections.
* Improved hygiene and sanitation are important in prevention of infection. * Specific drugs: * Mebendazole * Praziquantel * Ivermectin * Piperazine
60
There are antiprotozoal and antihelminthic agents. What are the particular problems posed when treating with these?
* Pose particular problems because of: * Large variety of species * Complexities of their life cycles * Differences in their metabolic pathways * Drugs active against protozoa are inactive against helminths
61
Describe the use of oral rehydration therapy (ORT) in treatment of intestinal infections.
* Involves the replacement of fluids and electrolytes lost during diarrheal illness. * 90-95% of cases of **acute**, watery diarrhoea can be successfully treated with an oral rehydration solution (ORS). * ORS increases the resorption of fluids and salts into the intestinal wall.

Gastrointestinal (10 decks)

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