Introduction to Virology Flashcards
What are 3 general ways you can classify a virus?
- on it’s genome structure
- general structural characteristics (enveloped/ shape?)
- Infection characteristics - the disease it causes and how it causes it
Wha tis the final taxonomic classification of viruses?
the genome sequence
What is the capsid? What is the nucleocapsid?
the capsid is a protein shell that surrounds the genome of a virus particle
the nucleocapsid is the capsid complexed with the nucleic acid of the virion
What is the capsid composed of?
protein subunits called capsomere
What lies between the envelope and the capsid in an enveloped virus?
the integument (not all)
What are the two main shapes of capsids?
helical (rod-shaped viruses)
icosahedral (spherical viruses - this is the most efficient arrangements of subunits in a closed shell)
Give details about the measles virus…
genome (group)
segmented?
shape?
enveloped?
ssRNA - (group 5)
nonsegmented
helical nucleocapsid
enveloped
(paramyxoviridae, morbillivirus)
Provide details about the Coxsackievirus B…
genome (group)
segmented?
capsid shape?
enveloped?
ssRNA +
(group 4)
Nonsegmented
icosahedral nucleocapsid
nonenveloped
(picornaviridae, enterovirus)
What are the two characteristics of a virus that the baltimore classification system takes into account?
the type of nucleic acid it uses
the steps the nucleic acid takes to be replicated
What are the 3 classes of DNA viruses?
- and 7.
1 - dsdNA with classical semiconservative replication
2 - ssDNA + with classical semiconservative replication, but you discard the negative strand when packaging
7 - dsDNA, but the mRNA is used as a template for reverse transcriptase to make genome copies to be packaged
What do class 3 viruses have?
dsRNA
transcription of the minus strand gives mRNA for proteins
What do class 4 viruses have?
ssRNA +
where the ssRNA+ is used directly for mRNA to translate proteins.
What do class 5 viruses have?
ssRNA -
transcribe the minus strand to make mRNA
What do class 6 viruses have?
they’re the retroviruses!
they have ssRNA + that is reverse transcribed to a dsDNA intermediate
the minu strand is then transcribed to make mRNA
What determines the tropism for the virus?
what cells have the appropriate receptors the virus needs to bind and enter
What are the 5 general steps in a viral infection?
after exposure….
- attachment
- penetration and absorption
- synthesis
- assembly
- release
and then it continues in secondary infeections…
or you can do it this way…
- pathogen exposure to mucosal surface
- invasion
- primary replication/imune reponse
- dissemination
- secondary infections
- secondary replication and immune response
- tissue destructoin
- shedding
What does HPV cause?
warts and carcinoma
What are the characteristics of HPV?
genome/group
arrangement of genome
capsid shape?
enveloped?
dsDNA (group 1)
circular genome
icosahedral
nonenveloped
(papovaviridae, papillomavirus)
How does HPV get the host cell to replicate?
It has two proteins - E6 and E7 - that will block p53 and Rb. Both of these would normally keep an infectec cell from entering S phase, but without them the cell will enter uncontrolled proliferation resulting in warts and carcinoma
Describe the progression of HPV through the skin layers.
It enters the skin through a foriegn body or a microabrasion
In the lysogenic state it will infect basal cells and transform them using E6 and E7
In the lytic cycle the virus will either infeect the upper keratinized epithelium or it will just progress with the basal cell from below as it rises and differentiates
In the keratinized layer the virus is able to replicate its DNA and assemble new virions
How does one diagnose HPV?
1% acetic acid will turn lesions white in colposcopy
you can then biopsy the white lesions or use PCR
What strains of HPV does gardasil protect against?
6, 11, 16, and 18
WHat are the general characteristics of poxviruses?
genome/group/arrangment
nucleocapsid?
envelope?
dsDNA (group 1)
linear genome
complex nucleocapsid
enveloped
What is special about transmission of poxviruses?
can be zoonotic - form animals
What does a complex nucleocapsid look like?
it’s more of a barbell shape
What are the 3 poxviruses we talk about?
molluscipoxvirus (mulluscum contagiosum)
orthpoxvirus (smallpox)
parapoxvirus (orf virus)
What are the 4 herpesviruses we’re interested in?
- herpes simplex (HSV 1 and HSV2)
- Herpes varicella (chicken pox)
- Cytomegalovirus (CMV)
- Lymphocyrptovirus (EBV)
How are herpesviruses classified within the group?
alpha, beta, or gamma depending on where they survive in latency…
alpha - in nerve cells (varicella and HSV)
beta - in macrophages (CMV)
gamma - in B cells (EBV)
What are the general characteristics of herpesviruses?
genome/group/arrangement?
shape?
enveloped?
dsDNA (group 1)
linear
icosahedral
enveloped
What does parvovirus B19 cause?
Fifth disease - erythema infectiosum
also aplastic crisis (infection gets into bone marrow and kills precursor cells)
WHat are the characteristics of parvovirus?
genome/group/arrangement
shape?
enveloped?
ssDNA (group 2)
linear genome
icosahedral
nonenveloped
(parvoviridae, erythrovirus)
Parvovirus is a biphasic disease, meaning…
has 2 phases…
1st phase: flue like symptoms with viral shedding during viremia
2nd phase: rash, arthralgia and arthritis. aplastic crisis
What are the characteristics of picornaviruses?
genome?
segmented?
shape?
envelope?
ssRNA + (group 4)
nonsegmented
icosahedral
nonenveloped
(picornaviridae, enterovirus)
What are the 5 picorna viruses we talk about?
- poliovirus
- coxsackievirus A and B
- Echovirus
- Rhinovirus
- Enterovirus
How are picornaviruses usually transmitted? What’s the exception?
usually fecal-oral except the rhinoviruses which are respiratory droplets
What are the characteristics of the measles virus (rubeola)?
genome/group
segmented
shape
enveloped?
ssRNA - (Group 5)
nonsegmented
helical
enveloped
(paramyxoviridae, morbillivirus)
What is the pathogenicity of measles?q
- infects epithelial cells of respiratory tract
- spreads in lymphocytes and by viremia
- replicates in conjunctiva, respiratory tract, urinary tract, lymphatics, blood vessels and CNS
- T cell-response to the virus infected capillary endothelial cells causes the rash! (diffuse morbiliform)
complications: otisi media, croup, bronchopneumonia, encephalitis, SSPE
What are the characteristics of rubella (german measles)?
geome/group
semented?
icosaheral
enveloped?
ssRNA + (group 4)
nosemgneted
icosahedral
enveloped
(togavirus, rubivirus)
What do you get with a rubella infection?
robeola - a rash
What are the characteristics of flaviviruses?
genome, group
segmented?
shape?
envelope?
ssRNA + (group 4)
nonsegmented
icosahedral
enveloped
What are the two types of flaviviruses w talk about?
dengue fever and west nile
How are flaviviruses transmitted?
moquitoes
