Viruses 4 - Classification Flashcards
look at the graphs on the PowerPoint - These cards focus mainly on Avian Influenza
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
Where is the HA cleavage site?
- protein cleaved unit HA1 and HA2
What happens if there is no cleavage?
- no fusion
- no cell penetration
What does cleavage require?
- require specific enzyme
What is LPAI HA?
- Single type of amino acid = arginine at the hemagglutinin cleavage site
- trypsin-like proteases catalyse the cleavage process
What happens in LPAI HA acquires multiple amino acids?
- open to multiple proteases (e.g., furin, PC6)
- virus can then multiply systemically (proteases elsewhere)
- significant increase in replication , virulence, pathogenicity
What does virulence mean?
- Virulence, a term often used interchangeably with pathogenicity, refers to the degree of pathology caused by the organism.
What is the extent of virulence usually correlated with?
- The extent of the virulence is usually correlated with the ability of the pathogen to multiply within the host and may be affected by other factors
What is the difference between ducks and chickens AI?
- Chickens – excessive, delayed cytokine response; poor cellular immune response
- Ducks - fast, lower cytokine response; strong cellular response
What are the general carrier of AI?
- In general: waterfowl and waders – carriers – disseminate virus; get localised/widespread outbreaks in wild birds
Where do outbreaks of AI in poultry mostly occur?
- Outbreaks in poultry mostly occurred in areas where the location of farms or trade areas overlapped with habitats for wild birds
Where do outbreaks in wild birds mainly occur?
- Outbreaks in wild birds…mainly found in areas where food and shelters..” Spread to poultry via both poultry and wild birds
- Contact with wild birds alone seems to drive the outbreaks in wild birds.
