Introduction to Virology Flashcards
Viruses are responsible for ____ disease worldwide
50%
Why else are viruses important?
they are linked to 15-20% of cancers; they can be used as future tools for vaccines
Virus
disease causing entity at the boundary of life and non-life; all of nucleic acid genome; all are obligate parasites
Features of all viruses + features that some have
all = DNA or RNA + capsid some = matrix, lipid envelope, glycoproteins
Many viruses use what type of capsids
icosahedral, with 3 capsomeres per face and a minimum of 20 faces
2 examples of naked capsid viruses
bacteriophage and adenovirus
you can classify viruses by nature of capsid
naked capsid (which can be helical or icosahedral) or enveloped (which can be helical, icosahedral, or complex)
you can also classify by nature of genome
DNA or RNA (which both break down into SS or DS)
Group IV viruses are + strand RNA viruses…what does this mean for their infectivity and replication strategy
the positive strand RNA is infectious because it can be introduced into the cell and directly translated into proteins
replication strategy- they will make a negative strand to serve as a template for making more positive strands
Group VI viruses like HIV have a particular genome that leads to their replication strategy…
they have a positive stranded RNA with extra sequences for genome amplification and packaging…reverse transcription into dsDNA is a must
Group III viruses are weird (rotavirus = example)…
they come in a vesicle, they have their own RNA-dependent RNA pol, they make a positive strand which leaves the vesicle to be packaged or translated. In a capsid, the positive strand is used to make a negative strand (hence dsRNA). The cells can’t melt the dsRNA (which is good because you want the cells to be very good at recognizing dsRNA as foreign to maintain the IFN-innate response) but the viral enzymes can.
sense strand
mRNA made from the DNA template strand (the anti-sense strand)..it is the positive strand and it will read directly the same as the complementary DNA strand to the template
So, if you have a positive mRNA sense strand, you can find the DNA template by matching the complementary bp to it
Negative strand viruses must
have their RNA copied by a RNA dependent pol into a positive sense strand- it is am amplification step to make lots of mRNA and lots of protein
Picornaviruses (polio) and flaviviruses (west nile, dengue)
genome = positive-strand RNA
virion RNA dependent polymerase? no
initial event in cell= translation
genome infectivity = infectious
orthomyxovirus (flu) and paramyxovirus (measles and mumps)
genome = negative-strand RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = non-infectious
reovirus (rotavirus)
genome = ds RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = no
retrovirus (HIV)
genome = positive strand RNA
virion RNA dependent polymerase? yes
initial event in cell = reverse transcription
genome infectivity = no
6 basic steps of viral replication
- attachment
- entry/ penetration
- uncoating
- protein expression/ gene replication
- assembly
- release
Steps that have to deal with viral receptors
1 and 2 (attachment and entry)
Viral receptors allow virus to:
- find the appropriate host cells
- interact with virus to allow for absorption
- interact to facilitate entry
- facilitate disassembly of viral capsid
absorption is aided by charged molecules on the surface….what are they
sialic acid- flu, coronavirus, rhinovirus
heparin sulfate proteoglycans- herpes, dengue, adeno-associated viruses
charged lipids - VSV
examples of cell surface proteins that serve as receptors or co-receptors for viruses
integrins- adenoviruses, Kaposi's sarcoma, cocksackie NAChR - rabies HAVCr-1 - hep a/ ebola/ dengue CD4- HIV and herpes 7 PVR/CD155- poliovirus
3 main modes for uncoating
- uncoating at plasma membrane (paramyoxvirus - RSV and mumps)
- uncoating in endosomes (alpha virus- Chikungunya and semiliki forest virus)
- uncoating at the nuclear membrane (adenovirus)
transcription and replication of genome (step 4)
many different methods; can copy using viral or host enzymes; can occur in cytoplasm or nucleus
proteins encoded by viruses
structural- capsid, envelope
enzymatic- proteases, integrases
proteins encoded by viruses can be made and used within the host cell
enzymatic functions necessary for virus
to block innate and adaptive immune responses
to affect host cell growth and survival (viral oncogenes)
regulate cellular or viral gene expression
3 mechanisms of release
enveloped- budding
non-enveloped- lysis of cell
shedding into mucosal linings
4 major ways that viruses cause disease
- direct tissue damage (like in the liver with hep b or nerve damage in poilio or herpes)
- inflammation (cytokines associated with viral infection cause flu like symptoms)
- cancer (deregulated growth like with papilloma virus)
- loss of immunocompetency (HIV with depletion of CD4 cells)
Pathogenic outcomes of infection
cytopathic effects (CPE)
death of the host cell (cytocidal)
non-lethal shedding
abortive infection
persistent infection (latency) - herpes or HIV
cellular transformation (HPV, EBV, KSHV can immortalize and transform the cell and give rise to tumors)
Our immune system operates constantly with a background of
viral infection and chronic inflammation- for example ERV and CMV are common and normally with us
Where do emerging viruses come from?
reassortment with existing viruses and from zoonosis (jump from animals to humans)
Example of zoonosis
Ebola- fruit bats eat fruit and infect it with ebola. Duiker eat the fruit and then humans hunt the duiker
Zoonosis is facilitated by
modern transport and pushing into more remote areas
more than _____ % of infectious disease agents are zoonosis
60
Explain the meaning of intermediary species
for example, the host of Mers-CoV is a bat, but transmission to humans is via camels and many times the intermediary between those two is a mosquito
Bats harbor
haemorraghic fever viruses (Ebola, Marburg) respiratory viruses (SARs and MERS-CoV) Henipah viruses (hendra, Nipah)
Primates
HIV
monkeypox
Chikungunya, dengue, yellow fever
Bird
avian flu and west nile virus
Rodents
hantavirus, lassa fever
initiative to closely address animal-human-ecosystem interface
OneHealth
