GE: viruses and protozoa Flashcards
1
Q
Structure of rotavirus
A
- Non-enveloped, icosahedral virus
- Multilayered protein coat that makes it hardy to the acidic environment of the stomach
- Capsid encloses double stranded RNA
Segmented genome
2
Q
Rotavirus infectious profile
A
Low ID > 10 virions
IP: 2 days
Very high density of virions in faeces, can be excreted before and after onset of symptoms
symptoms: diarrhoea
3
Q
Nucleic acid of rotavirus
A
- Double stranded RNA
- segmented genome (11)
- capsid contains RNA dependent RNA polymerase (transcriptase) > translated dsRNA into mRNA
4
Q
Rotavirus invasion
A
- entry by membrane penetration > enhanced by outer protein spikes (VP4) that are ‘cleaved’ via proteolysis by enzyme trypsin, which makes it more infectious
- taken into phagosome
- exits phagosome and loses a capsid layer
- mRNA made from viral genome
- proteins produced by host cell and assembled in the cytoplasm
- virus released, cell lysed
5
Q
Parthenogenesis of rotavirus
A
- blunting of villi
> destruction of mature absorptive cells (younger less effective)
> immature cells less effective at producing disaccharidases = malabsorption of carbs - virus produces a toxin that stimulates chloride and water secretion into the gut
- enteric nervous system is activated
6
Q
rotavirus diagnosis
A
viral antigen detection assays for stool samples
Electron microscopy, needs high virus titre
7
Q
rotavirus treatment
A
vaccine available with low chance of intussusception
8
Q
Norovirus infectious profile
A
- most frequently effect school-aged children or adults
- prolonged virus shedding (3-6 weeks)
symptoms: vomiting, cramps, diarrhoea
IP: 1-2 days
9
Q
pathogenesis of norovirus
A
- virus binds preferentially to histo-blood group antigens (which are on all cells) for type A and O
- some people lack a gene that produces an enzyme which means that the antigens that the virus needs to bind to aren’t on the right cells
- blunting of villi but intact intestinal epithelium (x ulcers)
- no toxin
10
Q
Diagnosis/treatment of norovirus
A
- no vaccine
- enzyme immuno-assay
electron microscopy to locate virions in faeces
or RT-PCR assays to look for viral RNA
11
Q
Entamoeba histolytica infectious profile
A
- forms ulcers in SI
- humans are reservoirs for infection
- can cause mild disease or amoebic dysentery (bloody stools, fever, stomach pain)
12
Q
Entamoeba histolytica life cycle
A
- cysts are ingested and de-cysts in small intestine
- trophozoite attaches and engulfs cells in SI, cause abscesses by burrowing in
- cysts further down the small intestine
13
Q
virulence of entamoeba histolytica
A
- contact dependent killing: binds to specific sugars (glycoproteins) before making pore forming proteins
> which can be inhibited by mucus - kills lymphocytes, neutrophils
- breaks down antibodies
- can cleave complement components
14
Q
Giardia lamblia virulence
A
- adheres to intestinal cell wall by ventral sucking disk
> thought that this stops the absorptive capacity of the gut
> malabsorption of nutrients, esp fat - inflammatory cells (CD8) can cause further damage to microvilli
15
Q
Giardia lamblia infectious profile
A
- zoonosis
- chlorine resistant ~ associated with ingestion of contaminated water
- low ID required
- IP: 1-14 days
