2 - Viral Lifecycles 1: Lytic Replication Flashcards
How fast can viruses replicate within cells?
After initial infection in cell, there is an eclipse period while macromolecular synthesis occurs, then a burst size in which progeny are released from the cell via lysis.
In less than 8 hours, some viruses have gotten to 100,000 particles/cell
What is the outcome of infections caused by lytic replication?
Productive infection - generally leads to cytopathic effect with a burst of virus production
Causes an acute infection
Most RNA viruses are _____.
Lytic.
What are the diseases associated with Picornaviruses and what illness each is associated with?
- Enteroviruses: paralysis (polio and non-polio), common cold, meningitis, diarrhea, hand-foot-mouth disease
- Rhinoviruses: common cold
- Hepatoviruses: hepatitis
- Parechovirus: gastroenteritis, myocarditis, encephalitis.
- Kobuvirus: gastroenteritis
What factors contribute to Picornaviruses pathogenesis and disease?
Cellular receptors
Permissiveness of the cell
Induced cell/host factors: cytokine and immune response
Speed of virus replication
Spread of infection between tissues and organs
What are the picornavirus cellular receptors?
Coxsackie: Car Poliovirus: Pvr Rhinovirus: Icam-1 Echovirus: CD55 Hepatitis A: HAVcr-1
Describe the infection and disease associated with polio virus?
Inapparent (subclinical) infections (90-95%) - virus recovered from throat or stool, asymptomatic.
Mild illness (4-8%): minor undifferentiated febrile illness with occasional URI or gastroenteritis
Aseptic meningitis (non-paralytic polio) (1-2%): minor illness progresses to CNS invasion, stiffness in neck/back, disease 2-10 days. Rapid and complete.
What are characteristics of paralytic poliomyelitis?
Initial non-specific febrile illness. Asymmetric flaccid paralysis, lower extremities involved more than upper, larger muscle groups involved more.
Bulbar paralysis from CN involvement, medulla, and respiratory compromise.
Recovery slow: 2 years for 100%. Can cause residual paralysis.
Describe the stages in the progression of poliovirus infection?
Digestive stage in pharynx and small intestine, shed in feces.
Lymphatic stage in cervical and mesenteric lymph nodes.
Viremia: virus in blood and extraneural tissues - crosses BBB
Neural stage: Virus enters CNS
Describe the sites of poliovirus infection in the order they occur? What other enteroviruses can do this?
- Oral ingestion
- Alimentary tract
- Blood
- (crosses BBB) Central nervous system
- Skeletal muscle
All other enteroviruses can do this, they just don’t do it as often as poliovirus does.
What are the ways to diagnose picornavirus?
Virus isolation from stool, rectal swab, throat swab, or CSF. Specific, sensitive, time consuming. See the cytopathic effects (lysis).
Serologic: look for increased antibody response to virus
PCR (multiplex) most common, fast and very specific.
What is the epidemiology of polio? How and when is it spread?
Poliomyelitis is a human disease only.
Fecal-oral transmission enhanced by persons with subclinical infections who shed virus in stool.
Summer epidemics in temperate climates (true for many other enteroviruses).
What are the three major epidemiological phases of polio?
- Endemic: children encounter at early age, maternal Ab protects then. High rate of subclinical infection, low paralytic disease.
- Epidemic: 1800-1900s US. Advent of indoor plumbing. Patients are older when first encounter virus and have higher incidence of paralytic disease.
- Post-vaccine: small # of cases, most all cases are vaccine related (from reverting attenuated virus).
What type of virus is picornavirus? What pH are they stable at?
ssRNA (+)
Enteroviruses stabel at pH 3-9
Rhinovirus: unstable below pH 6
What is the size and structure of picornavirus?
22-30 nm, Icosahedral, with NO lipid envelope and NO tegument.
Four structural proteins: VP1-4.
