Lytic Viral Lifestyles Flashcards
What stage of viral lifecycle is associated with a decrease in virion number?
Infection; an “investment” of virus particles must be made to infect a host.
Picornaviruses
Are they naked or enveloped?
What is their capsid morphology?
What baltimore class are they?
Picornaviruses
Naked.
Icosahedral.
Group IV (+ssRNA).
What picornaviruses can cause polio?
Which can cause the common cold?
Which can cause gastroenteritis?
Enteroviruses (to which polioviruses belong).
Rhinoviruses.
Parechoviruses and Kobuviruses.
What does the cellular receptor “CAR” attract?
What other surface proteins can attract viruses?
Coxsackie and Adenoviruses.
Lipid receptors, integrins, more or less anything.
Note: “Cluster of differentiation” (CD) proteins are often such targets. However, they encompass many classes of proteins.
Describe the progressive series of polio infections. Which is most common? Least common?
Subclinical infections comprise over 90% of infections.
Minor illness including flu-like or GI symptoms constitute 4-8%.
Aseptic meningitis due to CNS invasion occurs in 1-2%.
Poliomyelitis involves the grey spinal matter, causing flaccid paralysis especially of the lower extremities (sometimes bulbar paralysis). This causes lifelong disability and occurs in less than 2% of infections.
How does poliovirus disseminate to cause CNS symptoms?
Poliovirus can invade tonsillar and gut-associated lymphoid tissue. Dissemination occurs via the lymphatics, and can affect multiple organs and the CNS.
You suspect a patient has a picornavirus infection. How do you confirm your diagnosis?
The virus can be isolated via cell culturing* of stool, CSF, or throat swabs. However, serology and PCR are preferable.
How is poliovirus spread?
When were infection rates worst?
Why weren’t polio epidemics observed before the 1900s?
Fecal-oral route, facilitated by asymptomatic carriers.
During summer months (eg at the local swimming pool)
Before indoor plumbing, many children developed immunity to the virus due to early contact with it.
What are the gene products of poliovirus replication?
A single polypeptide, which is cleaved into capsid (P1), proteases, RNA polymerases and other enzymes (P2/P3).
Describe 3 methods of antiviral treatment.
Prevent its entry/release (Pleconaril)
Block its proteases (Ruprintrivir)
Block its RNA-dep RNA pol (Ribavirin)
The immune system also neutralizes the virus using antibodies. Not sure if IVIG is a treatment option for picornavirus.
Distinguish between the Salk and Sabin vaccines.
Which is used in the US?
Salk’s is an inactivated vaccine. Sabin’s is live-attenuated.
In the US, Salk’s is primarily used because of the nil risk of infection.
Adenovirus
Are they naked or enveloped?
What is their capsid morphology?
What baltimore class are they?
Adenovirus
Naked.
Icosahedral, but more complex than picornaviruses. Note the penton spikes.
Type I (dsDNA)
What diseases are caused by adenoviruses?
Describe their tissue tropism.
Upper respiratory infections mostly. Also conjunctivitis, urinary infection, and rarely organ and CNS infections. Types 40 and 41 can cause gastroenteritis.
It closely matches picornavirus–upper respiratory and intestinal cells. The same path of dissemination is also observed.
What is “viral surfing”?
Why does CAM disruption occur in epithelial adenovirus infection?
Adenoviruses use penton spikes to adhere to cell membranes until they encounter an appropriate receptor (eg CAR) to facilitate entry.
The progeny virions, which are secreted basally, return to the apical surface by disrupting these junctions (paracellular).
Why does adenovirus have to relocate to the host cell nucleus?
As a DNA virus, it must gain access to the host’s DNA polymerases, which will not be found outside the nuclear envelope.
