DNA Viruses: Poxviridae Flashcards
(6 cards)
What are some Unique Properties of Poxviruses?
Largest virus (300nm)
Almost visible under compound light microscope
Enveloped (But resistant to inactivation)
dsDNA genome 130-375 kb
Bricked shape
Has dumbbell core ( Contains Nucleic Acid)
Possess Lateral bodies (Unknown function)
Produce more than 100 polypeptide
Replicates in the cytoplasm
Highly species-specific
Under exploration for gene therapy
Discuss it’s replication
Viral Replication is divisible into those controlled by:
Early (Pre-replicative) gene products
Late (Post-replicative) gene products
The replication starts with Attachment & Penetration
This is subsequent to viral & host cell Membrane fusion
Naked DNA is not infectious
Viral core dissociates to release
Viral DNA
Viral enzymes
Core enzymes (including DNA-dependent RNA polymerase play key roles in viral replication
Virally-encoded RNA polymerase ( prepackaged) synthesizes the Early mRNA
From the Early mRNA is formed the Early Proteins:
DNA polymerase
Thymidine kinase
Recombinase
This gives room to uncoating, DNA replication and synthesis of Late mRNA
Initial uncoating is due to cellular enzymes but full uncoating is by viral enzymes
Late mRNA leads to late proteins (Structural proteins) synthesis
Virus Maturation follows assembly with synthesis & incorporation of Viral membranes
Some of the mature virus exits by budding (exocytosis) but most is by cytolysis
80-9% are released by cell rupture
How is it transmitted
There are some peculiarities in the mode of transmission
Small pox virus transmission is respiratory
Other poxviruses are largely transmitted by contact
Zoonotic transmission is common
Nosocomial transmission?
Pathogenesis
Poxvirus replication occur locally in the infected cells after acquisition
This manifest as dermal hyperplasia & leukocytes infiltration
And then, primary viraemia follows
Dissemination is especially to lymph nodes via:
Lymphatics and
Cell (macrophages) mediated spread
Virus multiplies further in seeded lymph nodes
This leads to:
Secondary viraemia
Another dermal inoculation
Characteristic Skin eruption (Pocks)
Clinical manifestations
Poxviruses produces characteristic skin rashes
Most poxvirus typically have a primary lesion
Generalized lesion develops in human monkeypox & molluscum
Cowpox & parapox infections develop at inoculation site (hands usually)
They then spread other sites (face , genitals by scratching)
Human monkeypox resembles mild smallpox
Parapox and molluscum are painless & cause little disturbance
Human cowpox is very painful & cause fever, lymphadenopathy
It often also require hospitalization especially in children
Encephalitis may complicate cowpox
Erythema multiforme is a complication of parapox
Severe infection with generalized illness can be precipitated by:
Immunocompromised state
eczema
Monkey pox is controlled by what vaccine
Vaccinia virus
