Viruses 4 - Classification Flashcards
look at the graphs on the PowerPoint - These cards focus mainly on Avian Influenza (35 cards)
What are acute self-limiting infections?
and
What are examples?
- virus causes rapid, self limiting infection
- infection cleared by the immune system, leading to recovery
- influenza virus
- rotavirus
Whare are chronic infections with a carrier?
- viruses can persist fir many months in animal after symptoms have cleared such as FMDV in cattle = 24 months
- will eventually be eliminated
- doesn’t tend to kill the host so we have to
What is a latent infection?
- Virus persists at very low levels
- limited recognition by immune system of infected cells
- no/few viral proteins expressed
Where do latent infections replicate?
- in immune privileged sites
- special relationship between tissue and immune system
Latent infections have the potential to reactivate - what does this mean and what is this usually due to?
- switch from latent to productive infection
- usually due to immunosuppression/external stimuli (sunlight/stress)
Name some examples of latent viruses?
- IBR virus invades via nasopharynx or genital tract - proceeds to ganglionic neuron - latency
What is a chronic infection?
- virus persists at very low levels in immune privileged sites, with slow growth
Name toe examples of chronic infection?
- FeLV - retrovirus in oncornavirus group - causes cancer - slow, progressive disease, can persist after initial infection
- Jaagsiekte “chase disease” = slow continuous growth
Classification is the same for all organisms how are they classed?
- species
- genus
- family
- order
- class
- phylum
- kingdom
- realm
What is the Baltimore system of classification based on?
- based on system of messenger RNA (mRNA) synthesis
The Baltimore system of classification has 7 groups what are the specifications for each of these groups?
- group I = double stranded DNA viruses - DsDNA
- Group II = single stranded DNA viruses ssDNA
- Group III = double stranded RNA viruses dsRNA
- Group IV = positive sense single stranded RNA viruses = ssRNA (positive sense)
- group V = negative sense single stranded RNA viruse = ssRNA (negative sense)
- Group VI = single stransed RNA viruses with DNA intermediate in lifecycles = ssRNA (positive sense, reverse transcribing)
Group VII = double stranded DNA viruses with an RNA intermediate in their lifecycle = dsDNA (reverse transcribing)
What is Avian Influenza?
- 7 genera but only 1 (A) known to infect birds
- highly contagious disease if birds - domestic and wild
- significant economic impact
- potential zoonosis
What is the mortality rate in affected flock? (AI)
- up to 50% mortality
How is AI spread?
- spread by migratory wild birds
What are the two forms of AI?
- highly pathogenic
- low pathogenic
How do you determine if AI is highly or low pathogenic?
- determined by IVPI (intravenous pathogenicity index)
How do you asses Intravenous pathogenicity index?
- inoculate virus into wing vein of 10 x6 (4-8) week old chicks
- examine every 24hrs for 10 days
- score number if birds on symptoms = normal, sick, paralysed or dead
- add up score after 10days = have an index
- IVPI > 1.2 = HPAI (max 3)
- or H5 or H7 with specified amino acid at Haemagglutinin cleavage site)
Group VI -Group VI viruses have a positive sense, single-stranded RNA genome (so normally would replicate in cytoplasm as can be read directly into the ribosome and translation into proteins) but what do they do instead?
- but replicate through a DNA intermediate.
- The RNA is converted to DNA by reverse transcriptase
- then the DNA is spliced into the host genome for subsequent transcription and translation using the enzyme integrase.
Group VII - viruses have a double-stranded DNA genome, but unlike Class I viruses, how would they replicate?
- they replicate via a ssRNA intermediate.
- The dsDNA genome is gapped, and subsequently filled in to form a closed circle serving as a template for production of viral mRNA.
- To reproduce the genome, RNA is reverse transcribed back to DNA.
What is Haemagglutinin?
- homotrimeric (3 identical polypeptide chains) glycoprotein on the surface of influenza viruses
- amino acid sequence of the connecting peptide that cleaves H - critical factor
What is Haemagglutinin important for?
- HA important for entering cells
What is Neuraminidase important for?
- NA important for exiting cells
How is an genome released into cytoplasm?
- As pH dops , structure of HA changes, virus and ,lysosome membranes fuse and release genome into cytoplasm
What is HA essential for? and how dies this work in AI?
- binding viruses to cell surface
- binds to sialic acid-containing receptors in target cells in respiratory tract
- results in endocytosis - internalisation of the virus
- creates endosome =- cell digests contents - dropping pH transformation to lysosome
