Picornaviruses ate.edu



Picornaviruses

3/27/13

Small, RNA viruses

+ strand RNA acts as mRNA

7400 bases

has poly A tail

VPg attached to 5'end

Genome-translated as one polypeptide

Viral protease self-excises then aids host proteases in cleavage

Replication-

Bind surface structures (ICAM1) is common

Genome injection into cytoplasm

Binds ribosome and alters to decrease translation of host mRNA

Members-

Enteroviruses-only found in humans but can reside in standing water -ponds are common

Coxsackieviruses A&B and poliovirus

Polio

More severe in adolescents than children

Attacks Anterior Horns of CNS

most infections are assymptomatic

Begins with mild symptoms

Paralytic polio 0.1-2% of infections

Vaccination very successful-some incidents of paralysis as a result of oral strain regaining virulence

Coxsackievirus A-

Herpangina-oral lesions of soft palate and uvula

Hand-foot & mouth disease-causes vascular lesions

Coxsackievirus B-

Pleurodynia-aggravation of outer membrane of lung

Myocardia-most severe in neonates

Rhinovirus-cannot survive stomach and intestinal tract

Usually limited to upper respiratory tract

Causes 60% of colds

Transmitted by aerosol or fomites

typically introduced to nasal epithelium

may also infect conjuctiva

Undergoes genetic drift so surface presentation always changing

Short term immunity-18-24 months

Over 100 serotypes exist anyway

+ strand RNA acts as mRNA

7400 bases

has poly A tail

VPg attached to 5'end

Icosahedral capsid-60 structural units comprising 240 polypeptides

One of the four polypeptides is not exposed to external environment

acts as pseudoscaffold

Deep cleft present at axis of 5-fold symmetry called canyon

Infection-

Canyon interacts with ICAM of host epithelium

ICAM usually facilitates adherence of leukocytes to endothelium

ICAM shaped like a Flintstone hand (one thumb and three fingers)

Leukocytes bind to the thumb, but rhinovirus cleft binds to fingers

Binding causes endocytosis

Genome-translated as one polypeptide

Viral protease self-excises then aids host proteases in cleavage

Host ribosomes are altered limiting translation of host transcripts

Replication takes place in cytoplasm-up to 400,000 copies of viral genome/cell

Viruses result in lysis of host cell

Immune response:

Most symptoms are a result from immune response

Infected cells increase expression of pro-inflammatory cytokines

Recruit leukocytes and increases ICAM on adjacent cells

Mast cells and basophils produce histamine

Results in increased mucus production (rhinorrhea)

Sialic acid in mucus interferes with virus/host binding

Virus swept away in mucus flow

Temp increases to above 33°C inhibiting viral replication

Damaged cells are extruded

Treatments-most only diminish histamine response and fever resulting in longer infection

New therapies in testing that bind to canyon and prevent viral binding

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download