Gastrointestinal Pathogens Flashcards
(173 cards)
1
Q
What can be classed as enteric pathogens? What do they cause?
A
• Bacteria, viruses, protozoa • Gastroenteritis
2
Q
What defines gastroenteritis?
A
- Inflammation of stomach and intestines
- Results in diarrhoea, vomiting, fever, abdominal pain
3
Q
What characterises diarrhoea and dysentery and how do they differ?
A
Diarrhoea
- Abnormal faecal discharge (not just liquid)
- Frequent and/or fluid stools
- Forcible expulsion of pathogen (beneficial for pathogen because of dissemination)
- Watery = secretory
- Lose water from tissue due to disruption to mucosal ion pumps
- No damage to mucosal cells, little/no inflammation
Dysentery
- Bloody diarrhoea
- Inflammatory disorder of GIT
- Damages mucosal cells (by pathogen/inflammation preventing water absorption)
- Sever damage causes the bloody diarrhoea
4
Q
How does the impact of GE differ between the developing and developed worlds?
A
Developing World
- Major cause of morbidity and mortality in children under 5
- Dehydration deaths
- Long term effects on growth, development, immunity
Developed World
- Common, not life threatening
- Annoying, but self-limiting (clears itself up)
5
Q
What is a reservoir of infection?
A
- Person/animal/plant/soil/substance which infectious agent normal lives and multiplies
- Can harbour infectious agent without harm to source
- Reservoir often needed for survival of pathogen
6
Q
What are the main 7 sources of GE infection?
A
• Faeces, fluids, fingers, food, flies, fomites, fornication
7
Q
What can be a source of GE infection with faeces?
A
• Humans, contaminated water/food, animals, contaminated meat
8
Q
What bacteria are poultry, cattle and pigs sources of?
A
- Poultry: salmonella, campylobacter
- Cattle: salmonella, E. coli EHEC ETEC)
- Pigs : Yersinia
9
Q
How can GE infection be contracted via fluids?
A
• Drinking, ice, natural disasters, poor sanitation, swimming, pasture runoff, shellfish grown in contaminated water
10
Q
Why is hand washing important?
A
- Fingers can convery microorganisms or faeces to the mouth or food
- Bacteria are shed onto fingers
- Important for food handling
- Touching animals can pick up bacteria
11
Q
What are causes of food associated infections?
A
• Poor food handling, cooking, storage, post cooking contamination
12
Q
What is intoxication?
A
• Ingest a toxin in food which causes the problem rather than the microorganism
13
Q
What characterises a microorganism that supplies pre formed toxins in food? What is the main symptom of intoxication?
A
- Organism contaminates food, multiples in food, produces heat and acid stable toxin
- Toxin ingested with good and has immediate effect on intestinal mucosa
- Vomiting main symptom
14
Q
What must a microorganism do to cause GE infection? Is the affect immediate?
A
- Survive through stomach
- Evade host defences (reach intestine)
- Adhere to intestine and multiply to cause damage
- Not immediate
15
Q
What can predispose someone to GE infection?
A
- pH changes
- normal flora alterations
- food provides protection of acidic environment
16
Q
What is the most common outcome of GE infection?
A
• Diarrhoea
17
Q
What can cause damage to mucosal cells as a result of GE infection?
A
• Dysentery, not diarrhoea
18
Q
What can cause the symptoms of GE?
A
- Toxins
- Damage during microorganism growth (microorganism needs to multiply after adhering to gut mucosa)
- Microorganism invading intestinal cells (blood, pus)
19
Q
How do short and long incubation periods differ?
A
Short
- 2-6 hours
- Suggests preformed toxin ingested
Long
- 12-48 + hours
- Suggests microorganism needs time to multiply
20
Q
How do small and large infectious doses differ?
A
Small ID
- Acid stable usually
Large ID
- Ensure enough survive to pass through stomach
- Means need to multiply to big numbers in food to cause disease
- Relates to food safety
21
Q
What can act as clues to the cause of GE?
A
- Symptoms
- Incubation period (IP)
- Type of food/food handling or storage
- Associated activities
- Patient history
- Specimens (faecal, food, vomit)
- Processed to liquid
22
Q
What kind of pathogens would be examined using electron microscopy?
A
• Viruses
23
Q
What are examples of routine, specialised and enrichment media?
A
Routine medium (e.g. MAC)
Specialised media (e.g. selective, BCSA)
- Often has antibiotic to suppress growth of other bacteria
Enrichment media (e.g selenite broth for salmonella)
24
Q
What are the main families of GIT bacterial pathogens?
A
• Enterobacteriaceae and Vibrionaceae
25
How are Enterobacteriaceae and Vibrionaceae similar and different?
Enterobacteriaceae
* Family
* Gram negative Rods
* Facultative anaerobes
* Oxidase negative
* Grow on simple media
* Fermentative metabolism of glucose
* Sometimes motile
* Differentiated biochemically
Vibrionaceae
* Genus
* Gram negative slender curved rods
* Facultative anaerobes
* Oxidase positive
* Need 1% salt in media
* Fermentative metabolism
* Motile
* Differentiated biochemically
26
What are examples of Enterobacteriaceae pathogens?
• E.coli, salmonella, shigella, yersinia
27
What are examples of Vibrionaceae pathogens?
Campylobacter, vibrio cholera
28
Why does C. jejuni grow well at 42 degrees C?
• It’s the temperature of chicken gut
29
What is a mesophile?
• Optimal growth temperature is 37C
30
What are the main steps involved in the identification process?
1. Culture on selective or specialised media and incubate
2. Examine for characteristic growth
3. Relevant biochemical tests from ID charts
4. Further characterisation and confirmation
* Serological tests (ELISA, agglutination)
* Strain comparison (PFGE)
* Molecular methods (PCR, electrophoresis)
31
What are characteristics of MacConkey agar?
* Routine media
* Selective indicator (bile salts, neutral red, lactose)
* Lactose Fermenters (LF) make acid, pink colonies
* Lactose Non-Fermenters (LNF) alkali, yellow or colourless colonies
* Incubate aerobically 35-37°C
32
What are characteristics of Desoxycholate Citrate Agar?
* Routine media
* Highly selective indicator (bile salts, citrate, neutral red, lactose)
* LF pink colonies (E.coli grow poorly because of citrate)
* LNF yellow or colourless colonies o Has sodium thiosulphate (H2S producers can grow as colonies with black dot in middle)
* Incubate aerobically 35-37°
33
What are characteristics of Baird Parker Medium (BP)?
* Specialist medium
* Very specific selective and diagnostic
* Isolation of staphylococcus aureus
* Has egg yolk emulsion and selective agents
* Colonies would be grey/black, white margin, zone of clearing surround
* Incubate aerobically 37°C
34
What are characteristics of B. cereus Selective Agar (BCSA)?
* Specialist medium
* Indicator, selective
* Has egg yolk emulsion, polymyxin B antibiotic, mannitol and pH indicator
* Incubate aerobically at 37°C o Colonies don’t ferment mannitol so are turquoise with precipitate
35
What are characteristics of Campylobacter Medium (CAMP)?
* Specialist medium
* Highly selective and enriched (blood)
* Has blood, pyruvate, vitamin B6, antibiotics
* Colonies shiny with metallic sheen
* Incubate 42°C for 48hours in micro-aerophillic conditions
36
What coloured colonies are produced by lactose fermenters and non-lactose fermenters?
• LF pink, LNF yellow/colourless
37
Which three pathogens are associated as being LNF?
• Salmonella, shigella, Yersinia
38
Are all LNF pathogens?
• No, but they are not normal gut flora
39
What is selenite brother and when is it used?
* Selenite Broth used if no growth on primary culture
* Enrichment media (enrichment of salmonella)
* Has sodium biselenite (inhibits growth of many bacteria)
* Reduction of selenite sometimes causes red precipitate
40
What do you do if you don’t see a red precipitate in your selenite broth?
• If no colour change, subculture on selective medium like DCA and look for LNF
41
Why are antibiotics put in selective media?
• Suppress growth of other bacteria
42
What happens during an enzyme immune assay? What kind of test is it?
* Serological test
* 1. Coat with antibody
* 2. Block unbound sites
* 3. Capture antigen from sample
* 4. Add know antibody conjugated with enzyme
* 5. Add substrate for enzyme
* 6. Read colour
43
How does an agglutination reaction test work?
• Mix bacteria with antibody against it and visible clumps should form
44
What are the steps in phage typing? Are the results conclusive?
* 1. Plate bacteria
* 2. Use panel of phage dotted on plate
* 3. Incubate
* 4. Read the pattern of lysis
* Can give preliminary conclusions, need more tests
45
What characterises intoxication by staphylococcus aureus?
* Short IP (2-6 hours)
* Source from normal human flora or food high in salt/sugar
* Produce heat stable enterotoxin which causes the issue
* Only small quantities needed
* Toxin binds neural receptor in upper GIT, vomiting happens
46
What characterises intoxication of the emetic type with bacillus cereus?
* Short IP (1-5 hours)
* Fried rice and starchy foods common source
* Produce spores, survive boiling and can germinate
* Heat stable toxin produced
47
What characterises intoxication of the diarrhoeal type with bacillus cereus?
* Longer IP (6-15 hours)
* Associated with meat, dried vegetables, milk products contain spores
* Spores germinate after cooking and grow
* Heat labile toxin produced
* Activate adenylate cyclase enzymes (intestinal fluid secretion)
* Watery diarrhoea
48
How does Clostridium perfringens cause food poisoning?
* Foods have spores and are slowly cooked then not refrigerated. Spores survive cooking, germinate and grow as the food cools to ambient temperature.
* Stomach acid environment causes heat labile enterotoxin to be produced in intestine
* Toxin inhibits glucose transport, damages intestinal epithelium and causes protein loss to lumen
49
What must pathogens do to cause disease?
* Enter body
* Colonise host
* Evade defences
* Multiply (maybe disseminate)
* Damage host
50
What role does stomach acid have in regards to pathogens entering the body? What characteristics of organisms let them overcome this?
* Acidic environment, barrier to entry
* Should be acid resistant, in large numbers, protected by food or stomach has higher than usual pH (antacid) Why are peristalsis and mucous important?
* Peristalsis can push out pathogens (they must be able to adhere)
* Mucous provides a barrier that pathogens must penetrate to reach epithelium
51
Which gastrointestinal disease causing bacteria are extracellular and which are invasive?
* Extracellular: vibrio cholerae, ETEC, EPEC, EHEC
* Invasive: Shigella, salmonella, campylobacter, Yersinia
52
What are the two biotypes of serotype O1 Vibrio cholerae?
• Classical and el tor
53
What are characteristics of vibrio cholerae?
• Environmental o Free living in water
* Also human intestinal pathogen
* Spread in contaminated food or water
* Voluminous watery diarrhoea
* Easy to die from dehydration
54
What happens in the infection cycle by vibrio cholerae?
* 1. Ingested large numbers
* 2. Sensitive to acid so needs large numbers to pass stomach
* 3. Colonisation with pili and toxin as virulence factors
* 4. Massive fluid and electrolyte loss
55
What adhesisn is on the pili of vibrio cholerae? Why are they needed?
* Adhesion is TCP (toxin co regulated pili)
* Need for colonisation of intestine (bacteria bind each other and bind enterocytes)
56
What is the cholera toxin and how does it cause diarrhoea?
* A-B (A catalytic, B binding)
* Pentameric (AB5)
* Bind to GM1 gangliosides on surface of intestinal cells and A subunit internalised
* Does NOT invade intestine (toxin does)
* 1. A1 subunit causes ADP ribosylation of GTPase o Regulates adenylate cyclase activity o GTPase permantely ‘on’
* 2. Increased adenylate cyclase activity so increased cAMP levels
* 3. Can’t absorb Na, secrete more Cl
* 4. Lots of NaCl in lumen so water secreted osmotically
57
How can v. cholerae be diagnosed in the lab? What colours do other vibrios form on the media?
* Forms yellow colonies on TCBS agar (selective indicator)
* Other vibrios green
* Further serological and biochemical identification
58
What are characteristics of vibrio parahaemolyticus and how does differ to vibrio cholerae?
* Marine waters (e.g. contaminated oysters)
* IP 12-24 hours
* Explosive watery diarrhoea
* Invasive pathogen (not toxin producing)
* Green on TCBS agar
59
What type of countries is EHEC most associated with?
• Industrialised
60
What is another common name for ETEC?
• Travellers’ diarrhoea
61
What can cause ETEC?
• Food or water contaminated with faecal matter
62
What is the pathogenesis of ETEC? Is it like cholera?
* Pathogenesis like cholera
* Adhesin is pilus with colonisation factor antigen (CFA)
* Makes toxins (heat stable ST and heat labile LT)
* Pathology resulting from ETEC due to change in cells internal biochemistry
63
Does ETEC invade cells?
• No
64
How are ST and LT similar and different?
* Heat Labile Toxin (LT)
* Identical structure and function to cholera toxin
* Change in cell permanent
* AB5 toxin which is cytotonic
* Heat Stable Toxin (ST)
* Different structure, similar function to cholera toxin
* Change in cell not permanent
65
What are the characteristics of EPEC?
* Infant diarrhoea
* Adults infected if ID high
* Developing countries
* Contaminated food and water
* Extracellular pathogen
66
What is the pathogenesis of EPEC?
* Extracellular pathogen
* Adhesin is bundle forming pilus (bfp)
* Loose attachment to enterocytes
* No toxins
* Produces attaching and effacing lesions (A/E lesions)
* Diarrhoea due to malabsorption (villi damaged), or A/E formation, intestinal permeability
67
What is T3SS and how does it work? What is characteristic of A/E lesions?
* Type III Secretion System (T3SS)
* Needle and syringe method to transmit proteins microbe to host cell o Injects virulence/effector proteins
* Common among gram negative pathogens
1. BFP loose adhesion
2. T3SS secretes Tir (receptor protein) into enterocyte
3. EPEC outer membrane protein Intimin mediates intimate adherence to host cell by binding to Tir
4. Other effector proteins from T3SS activate actin polymerisation. Host cytoskeleton rearranges and forms pedestal (characteristic of A/E lesions) A/E lesions have pedestal with intimately adhering EPEC atop
68
What are the characteristics of EHEC? What is the main reservoir and major serotype?
* Bloody diarrhoea
* Can cause haemolytic Uraemic Syndrome (HUS)
* Transmitted from animals (unaffected) via poorly cooked meat or contaminated foods
* Cattle main reservoir
* More common in developed countries (factory farmed animals)
* Major Serotype O157:H7
* Attaching and effacing pathogen (no invasion)
69
What is the pathogenesis of EHEC? What are Shiga toxins and what can they do?
Attaching and effacing pathogen (no invasion)
* Unknown colonising antigens/adhesion
* T3SS injects Tir and other effector proteins (Tir interacts with intimin)
* Pedestal formation and actin rearrangement
Produce shiga toxins
* AB5
* Cytotoxic (same structure to cholera toxin, different function)
* 1. Toxin binds receptor Gb3 on Endothelial cells (goes through tight junction of epithelial cells)
* 2. A subunit is N-glycosidase that stops protein synthesis
* 3. Endothelial cells are damaged in intestine, bloody diarrhoea
* 4. Can damage blood vessels in renal glomeruli (HUS)
70
What does N-glycosidase do?
• It is an A subunit in the shiga toxin that removes nucleic acid from ribosomes to stop protein synthesis
71
What lab methods are used to diagnose EHEC, EPEC and ETEC?
Lab Diagnosis EHEC
* Sorbitol MacConket Agar (SMAC)
* Serological Tests with EIA for shiga toxins
* PCR for eae gene (intimin)
* PCR for stx1 and 2 genes
EPEC
* PCR for BfpA gene
* Immunofluorescent Microscopy
* PCR for eae gene
ETEC
* PCR for LT gene
* PCR for ST gene
72
What are characteristics of Shigella pathogen?
* Bloody diarrhoea/dysentery
* LNF (very similar to E.coli except E.coli LF)
* Non motile
* Species
* Shigella dysenteriae
* Shigella flexneri
* Shigella boydii
* Shigella sonnei
* Low ID o Very acid stable (acid resistant phenotype)
* Invade gut cells from basal surface, move cell to cell without becoming extracellular
* Human only
* Person to person spread, contaminated food water
* Virulence plasmid
73
How can shigella be distinguished from E.Coli?
• Very similar, but shigella is LNF and E.coli is LF
74
Which form of shigella produces the mildest infection?
• Shigella sonnei
75
What are the four species of shigella and what are their characteristics?
Shigella dysenteriae
* Developing countries
* Shiga toxin
Shigella flexneri
* Young males
Shigella boydii
Shigella sonnei
* Industrialised countries
Mildest infection
76
Why is a low ID needed to be infected by shigella?
* Very acid stable and has an acid resistant phenotype
* Can pass through stomach acid
77
What is the benefit of shigella invading the basal surface of epithelial cells?
* It can move cell to cell without becoming extracellular
* Hidden from immune response
78
What are the characteristics of shigella’s virulence plasmid? What does it encode?
* Large
* Encodes T3SS
* Encodes Ipa (invasion plasmid antigens) proteins
* Translocated via T3SS
* Cause membrane ruffling
* Encodes an outer membrane protein
* IcsA (Intracellular spread)
* Recruits actin, allows spread
79
How do Ipa proteins enter a host cell and what do they do?
• Translocated via T3SS and induce membrane ruffling
80
What is the IcsA protein? What does it do?
* Intracellular spread protein on outer membrane that recruits host cell actin and allows cell to cell spread
* Produced at pole of cell
81
How do T3SS’s differ between shigella, salmonella, Yersinia and EPEC?
Shigella
* Deliver effector protein (Ipa’s) for uptake by epithelial cells
Salmonella
* Encodes 2 of them
* Invasion and intracellular survival
Yersinia
* Deliver proteins to disrupt innate immune system
EPEC
* Use Tir to bind intimin on EPEC membrane
82
What is intimin?
• Protein on the outer membrane of EPEC that allows it to bind to Tir, thus the host cell
83
What are M cells?
• Antigen sampling cells over lymphoid follicles
84
What happens during the infection cycle of shigella?
* 1. Approach intestinal cells (non-motile mechanism)
* 2. Invade M cells
* Intestinal epithelial cells resistant to Shigella invasion on luminal surface o Invade via basal surface
* Can also penetrate through leaky tight junctions
* Invade by injecting Ipa (invasion plasmid antigen) proteins via T3SS (membrane ruffles)
* Bacteria taken up via fliopods
• 3. Bacteria released to lamina propria
* Engulfed by macrophage
* Can induce macrophage apoptosis
* Inflammation triggered by stimulation of IL1 and IL8 cytokines and neutrophils migrating
• 4. Gut becomes leaky
* Neutrophils move through mucosal tissue and separate tight junctions
* More bacteria can invade
• 5. Some bacteria leave macrophages and invade enterocytes through basal surface by inducing uptake by cell
* Use phagolysosome then escape it to replicate in cytoplasm
• 6. IcsA protein produced at on pole of cell
* Intracellular spread protein
* Cause polymerisation of actin which propels bacteria to neighbour cells
• 7. Adjacent cells die and ulcer can form
85
Which chemokine’s and cytokines are stimulated to trigger inflammation during infection by shigella?
• IL-1 (inflammation) and IL-8 (chemokine)
86
What is the role of Ipa proteins in invasion by shigella?
* Ipa (invasion plasmid antigen) proteins injected via T3SS
* Causes membrane to ruffle and bacteria taken up via filopods
87
How does shigella damage the host?
* Cells die, focal ulcer
* Inflammatory cells and RBC into lumen causing bloody diarrhoea
* Polymorphs recruited to contain infection but can destroy tissue
* Shigella dysenteriae produces shiga toxin
* Bind Gb3 receptor endothelial cells
* Inhibit protein synthesis o Intestinal damage
88
How is shigella diagnosed in the lab?
* LNF (distinguish from E.coli)
* Biochemical tests
* Serotype O antigens
* Non motile, no flagella/H antigens
* No H2S made (unlike salmonella)
89
How do AB5 toxins differ between shiga toxin from EHEC and shigella dysenteriae and toxins from cholera and ETEC (LT)?
Identical structure, different functions
Shiga toxin (EHEC, Shigella dysenteriae)
* Act on endothelial cells (inhibit protein synthesis)
* Cytotoxic
Cholera toxin and LT toxin from ETEC
* Act in intestine, increase cAMP (cGMP)
* Secretory diarrhoea
* Cytotonic
90
What are the characteristics of Salmonella?
* LNF
* Human pathogens : Salmonella enterica
* Serovars typed by O and H antigens
* Not all equal (human only or cross host)
* Normal flora in many animals
* Contaminated food and water
* Acid labile/sensitive so high ID needed Which serovars cause human GE?
* Serovar Typhimurium
* Serovar Enteritidis
91
What kind of ID is needed to be infected by Salmonella? Why?
• High because it is acid labile/sensitive
92
What happens in the infection cycle of salmonella? What causes diarrhoea?
• 1. Invade M cells AND enterocytes
* Invasion proteins = Sip
* Cause membrane ruffling, organism uptake
* 2. Mediators for uptake induce electrolytes/NaCl to accumulate in lumen
* 3. Bacteria transcytose to basal membrane (vesicular transport)
* 4. Escape at basal surface (don’t harm gut cells, just a barrier they need to cross)
* Can be engulfed by macrophages
* Can escape to blood (transient bacteraemia)
* 5. Dendritic cells capture bacteria and transport to lymph nodes (replication)
* Pathogenesis
* Inflammatory response leads to release of prostaglandins and stimulation of cAMP, active fluid secretion
93
What are Sip? What so they do? Where are they encoded?
* Salmonella Invasion Proteins
* Induces cellular mediators and mobilise intracellular Ca2+
* Causes membrane ruffling and uptake of organisms
* Encoded for on pathogenicity island
94
What is a pathogenicity island?
* Large part of bacterial chromosome
* Encode virulence genes
* Absent from non-pathogenic
* Different G/C content to host DNA
* Discrete genetic unit
* Unstable
* Get by HGT
95
What kind of pathogenicity islands does salmonella have? What do they encode?
* SPI-1 for T3SS and Sip proteins for membrane ruffling
* SPI-2 for T3SS and Salmonella Survival Antigens (SSA) proteins for survival in macrophage vacuoles)
96
What are the roles of Ssa Proteins?
• Salmonella Survival antigens, allow survival inside macrophage vacuole
97
Where can salmonella bacteria go after escaping at the basal surface?
* Can be engulfed by macrophages
* Can escape to blood (transient bacteraemia)
* Ultimately Dendritic cells capture bacteria and transport to lymph nodes (replication)
98
How is salmonella diagnosed in the lab?
* LNF so yellow colonies on MAC, DCA
* Grow on DCA selective media and black colonies (H2S production)
* Biochemical tests (slide agglutination, O/H antigens)
* Strain comparisons (phage typing, PFGE)
99
What are the characteristics of Yersinia enterocolitica?
* Symptoms mistaken for appendicitis
* Food borne (cattle)
* Virulence Factors
* Complications like post-infectious reactive arthritis
100
How can Yersinia adhere to cells? Which molecules are involved?
* Adhesion using Invasin protein
* RGD tri-peptide motif, bind host cell β1 integrin
* Mimic natural binding process
101
What is in the Yersinia plasmid?
* Encodes T3SS
* Encodes Yop protein (Yersinia outer protein) translocated to host cell
102
What are Yop proteins? What do they do? How do they enter host cells?
* Yersinia outer protein
* Translocated to host cell using T3SS
* Cytotoxicity
* Regulate genes for cell cycle/growth (YopM)
* Counteract pro-inflammatory response (YopP) which prevents phagocytosis by macrophages
103
What is involved in the infection cycle of Yersinia? What can it do within a macrophage?
* 1. Invade M cells
* 2. Invade epithelial cells, enter macrophage
Different options within macrophage
* Form pore, inhibit phagocytosis, inhibit TNF production
* Dissemination
* Macrophage apoptosis, bacteria released
104
How is Yersinia diagnosed in the lab?
* LNF, urease positive, oxidase negative
* Psychotroph (likes low temperatures, incubate at 25, think of pasteurised milk)
* Grow on selective media CIN with “bulls-eyes” colonies
105
What are the characteristics of campylobacter?
* Microaerophillic (lower than normal O2)
* Curved/bird wing gram negative rods
* Animal reservoirs
* Not acid resistant (high ID, long IP)
* Can produce bloody diarrhoea, Guillain Barre Syndrome
106
Why does campylobacter have a high ID? What is it’s IP like?
* Not acid resistant
* IP is long (2-4 days possible)
107
How can campylobacter infect humans?
* Grow in chicken gut (42) but chicken not diseased
* Go to humans via poor cooking
* Goes to water supply then contaminates then human eats
108
How can campylobacter be diagnosed in the lab?
CAMP medium
* Highly selective, enriched
* Blood, pyruvate, vitamin B6
* Antibiotics
Incubate 42 degrees for 48 hours, microaerophillic
109
Who is most likely to be affected by rotavirus?
• Infants
110
Who is most likely to be affected by norovirus?
• Adults
111
How does the use of symptoms to distinguish GE causes differ between bacteria and viruses?
• You can’t distinguish viral sources of GE by symptoms alone
112
What are characteristics of GE causing rotavirus?
* High risk are infants
* Seasonal (winter)
* Person to person spread (Low numbers needed)
* 2 day IP
* Diarrhoea
113
When can excretion of rotavirus occur?
* With symptoms, in faeces (large amount of virions)
* Asymptomatic excretors
* Virions in stool
* Excretion weeks before and days after symptoms
114
What is beneficial about the structure of Rotavirus? What is it like?
* “wheel with spokes”
* Reoviridae family
* Icosahedral, double capsid protein coat (beneficial to withstand stomach acid)
* Ds RNA and segmented genome What is a segmented genome?
* Made up of fragments of nucleic acid (not circular genome)
115
How does rotavirus replicate and spread?
• Entry
* Binding, penetration and RME
* Enhanced by proteolysis of outer capsid protein spikes by stomach enzyme trypsin
* Exit phagolysosome
* Un-coating
* Viral RNA made
* In cytoplasm NOT nucleus
* Assembly
* Transit through RER
* Infected cell lysis and viral release
116
What enzyme does rotavirus need for replication? Where does it come from?
* Needs RdRp (RNA dependent RNA polymerase) to make mRNA from RNA genome
* RdRp imported as part of virion
117
What is involved in the pathogenesis of rotavirus?
* Virus infects mature villi cells (tip)
* Infected cells lyse, virus released to lumen and infects more cells
* Villi are blunted/shortened as result of lysis (reduced absorption of sugar, water, salt)
* Virus produces enterotoxin (protein NSPA) that affects enterocytes o Cl and H2O secreted to gut (diarrhoea)
* Fluid accumulates in lumen
• Virus replication ends and crypt cells repopulate villi restoring function/structure
118
How can rotavirus be diagnosed in the lab?
* Antigen detection assays (ELISA, latex agglutination)
* Electron microscopy
119
What is needed to see rotavirus microscopically?
• High virus titre or virus specific antibody to form clumps of viruses
120
What is used as vaccination for rotavirus? When is it administered?
* RotaTeq
* Oral live attenuated vaccine
* Childhood vaccine (12 weeks age)
121
What are the characteristics of GE causing norovirus?
* Caliciviridae family
* Explosive outbreaks
* Winter peak
* IP 1-2 days
* Very stable in environment
* Faecal oral transmission (contaminated food and water, aerosols from vomit)
* Mild, self-limiting
* Asymptomatic infection common
* Viral shedding 2-3 weeks after
122
What is the pathogenesis of norovirus?
• Bind histo-blood group antigens
* Carbohydrate epitopes common on mucosal cells in gut
* Blunt villi but intact intestinal epithelium
* Diarrhoea because malabsorption of fat and lactose
123
Which histo-blood group antigen is more likely to be bound by norovirus?
• A and O best
124
What is a difference in pathogenesis between rotavirus and norovirus?
• No enterotoxin (unlike rotavirus)
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How can norovirus be diagnosed?
* RT-PCR for viral RNA in stool
* Electron microscopy
* EIA for antigen
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What are the characteristics of GE causing adenovirus?
* Adenoviridae family
* Non enveloped, dsDNA
* Stable in environment
* Faecal oral spread
* Shed for months after infection
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How can adenovirus be diagnosed?
• Using antigen detection
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What is the benefit of a virus being non-enveloped?
• Survive well in the environment and bile (Hep A)
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How does Hep A spread and cause infection?
• Faecal oral spread • Mouth → GI tract → bloodstream → liver → virions in bile → faeces
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Does Hep A cause GE?
• No
131
What are some common characteristics of rotavirus, adenovirus and norovirus?
* Pathogenesis mechanism not well understood
* Stable in the environment
* Can be shed from asymptomatic carriers
132
How are protists characterised?
• By motility and replicative cysts
133
How can infection by protists be acquired?
• Ingestion of cysts
134
What does Entamoeba histolytica cause? How?
• Mild
* Loose stool, cramps
• Amoebic dysentery
* Blood stool, fever, pain
* Can invade deeper tissue (abscess forms)
• Ulcerates small intestine
135
What parts of the word does Entamoeba histolytica dominate?
• Developing countries
136
What is the life cycle of Entamoeba histolytica and what are the two stages?
Life Cycle
* Cyst stage (dormant, infectious, resistant)
* Trophozoite stage (growing, cause disease)
* Extreme cases: spread to liver, form abscess
* Ingest mature cyst → spread in faeces
* Mature cyst → excystation to trophozoite → multiply to more trophozoites or cysts
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How does Entamoeba histolytica cause infection?
• Adhere to Gal-galNAc sugars on intestinal cells using parasite lectin
* Can be inhibited by mucous
* Attachment then contact-dependent killing of host cell using pore forming proteins (amebapores)
* Kill macrophages and neutrophils (less phagocytosis)
* Make cysteine protease
138
What does cysteine protease do?
• Breaks down IgA (mucosal) and IgG (circulatory)
139
How is Entamoeba histolytica diagnosed in the lab?
* Microscopy (cysts, trophozoites, iodine stain)
* Serology with antigens in stools, antibodies in patient sera (won’t distinguish from past infection)
140
How is Entamoeba histolytica treated? How does the drug work? How does treatment differ between deep infection and gut infection?
* metronidazole
* Get parasite anaerobic metabolism for invasive deep tissue infection
* Pro-drug, activated by pathogenic amoebae
* If just gut infection, need extra anti-parasitic drugs
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What causes Giardiasis? What are the characteristics of the illness and protist?
* Giardia lamblia
* Zoonosis
* Faecal oral route (chlorine resistant)
* Watery, grumbly diarrhoea
* Gut malabsorption
* Non invasive
* Cysts acid resistant (low ID)
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What characteristics of Giardia lamblia cysts are beneficial for the organism?
* Acid resistant and chlorine resistant
* Low ID needed
* Can spread in water more easily
143
What is the life cycle of Giardia lamblia?
* Cyst stage
* Trophozoite stage
* Ingest cyst, form trophozoite in body, cysts (sometimes trophozoites) in faeces
144
How does Giardia lamblia cause infection? What are the symptoms?
* Non invasive
* Trophozoite adheres to intestinal wall (ventral sucking disc)
* Decreases absorption capacity
* Host immune response with infiltration of inflammatory cells
* Microvilli damaged/shortened
* Nutrients not absorbed
* Watery diarrhoea
145
How is Giardia lamblia diagnosed in the lab?
* Microscopy (cysts, trophozoites in stool)
* Antigen detection (immunoassay)
146
How can Giardia lamblia be treated and prevented?
* Treatment with metronidazole
* Prevention by filtering/boiling water
147
What does Cryptosporidium cause?
• Cryptosporidiosis, watery diarrhoea
148
What is beneficial about the properties of Cryptosporidium cysts?
• Highly chlorine resistant (recreational water spread)
149
What are key points about the Cryptosporidium life cycle?
* Complex
* Sexual and asexual stages
* Oocyst is dormant, infectious
150
How does Cryptosporidium cause infection?
* Adherence using surface glycoproteins and lectins
* Non invasive
* Epithelial damage due to enterocyte disturbance
* Makes proteases
151
How can Cryptosporidium be diagnosed in the lab?
* Microscopy (oocysts and acid stain)
* Antigen detection with immunoassay
152
How can Cryptosporidium be treated? How does severity and treatment differ between normal and immunocompromised people?
Normal
* 2-10 days after infection
* Watery diarrhoea, resolves in couple of weeks
* Treat with nitazoxanide (like metronidazole)
Immunocompromised
* Severe dehydration
* Life threating illness
* Need supportive therapy too (rehydration, anti-motility drugs)
* If AIDs, boost immune system
153
Why do cases of GE in Australia seem low?
• Lack of reports, don’t often visit doctor for it
154
Who can be affected by the cost of GE?
• Individuals, business, healthcare, government
155
What is epidemiology?
* Study occurrence, spread, control of disease
* Who, where, when, why, how
* Collect data, aim to limit further spread
156
What is the difference between endemics, epidemics and pandemics?
Endemic
* Always present in community, low frequency
Epidemic
* More cases of disease than expected in given area for given group of people for particular time period
Pandemic
* Endemic covering large area (multiple countries/continent) and often affecting large proportion of population
157
How did epidemiology come about?
London 1850’s
* Overcrowding, no sewers, cholera outbreaks
* Believed in miasmas and spontaneous generation
John Snow linked cholera to water pump
* Believed human cause of cholera (NOT germ theory)
158
Why was John Snow so important?
* Showed that disease causing agents may come from human body
* Track cholera to water pump, closed it down
159
How can a disease outbreak be investigated using epidemiology? What steps are involved? Investigating Outbreaks
Describe
* Time
* Place
* Use rate calculations
* Person
* Demographic, social characteristics
* Measure of outcome (e.g. death, self-limiting)
* Pathogen
* Genotypic, phenotypic analysis
Develop and test hypotheses for cause
* Analytical epidemiology
* Case controlled study
* Identify source, find commonalty
* Microbiological investigation
Intervene, control outbreak
Prevent future outbreaks by implementing mechanisms
160
What are the types of epidemic curves? What features do they have?
Point Source
* Rapid peak, moderate decline, shorter time frame
Continuing Source
* Slow to peak and decline, longer time frame, relatively flatter (if no person to person spread)
Person to Person Spread
* Waves and peaks (IP = gaps between peaks)
* Earlier cases are sources to infect new people
* Continue until no more people susceptible or interventions occur
161
Why may an epidemic curve graph fall quickly?
• Quick fall if no person-person spread
162
When will a continuing source epidemic curve end?
• Ends when fault fixed or all susceptible are infected
163
How does person to person spread affect the way an epidemic curve looks?
* The graph has waves
* Gaps between peaks due to IP
164
How can an outbreak be described?
• In terms of time, place, person and the pathogen
165
How can the responsible pathogen be found?
* Genotypic, phenotypic analysis
* Molecular (PFGE)
* Genomic sequencing
166
What is analytical epidemiology? What type of study is used?
* Identify source, find commonalty, use cause and effect
* Case controlled study
167
At what levels can food borne GE be controlled?
* State health (MDU)
* National (FSANZ, OzFoodNet)
* International (WHO, Enternet)
* ‘Paddock to plate’ (HACCP)
* Consumer education
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What is HACCP? What steps are involved?
* Hazard analysis and critical control point
* 1. Analyse hazards
* 2. Identify critical control points
* 3. Establish preventative measures with critical limits for each control point
* 4. Establish procedures to monitor critical control points
* 5. Establish corrective actions to be taken when monitoring shows critical limit not met
* 6. Establish procedures to verify system working properly
* 7. Establish effective record-keeping to document HACCP system
169
What are WHO’s rules for safe food preparation?
* Choose foods processed for safety
* Cook thoroughly
* Eat cooked foods immediately
* Store cooked foods carefully
* Reheat thoroughly
* Avoid raw and cooked contact
* Wash hands repeatedly
* Keep surfaces clean
* Protect from vermin/animals
* Use safe water
170
What are the challenges of controlling food borne GE?
* Developing vs developed countries (easier to follow rules)
* Food production distribution (large, complex)
* Food industry globalisation (import, export, different standards)
* Patterns of food consumption changing
* Vulnerable groups (immunocompromised)
* Antibiotics in animals (resistant microbes)
171
Where do 99% of deaths by diarrhoea occur?
• Developing world
172
What are the common causes of deaths for children under two in developing world?
• Dehydration, dysentery, malnutrition
173
How can the effects of food borne GE be prevented in the developing world?
* Better housing, sanitation
* Less crowding
* Waste disposal
* Clean water
* Improve maternal education and health care
* Longer breastfeeding
* Supply oral rehydration therapy, nutrition, vaccination
* Better food hygiene
