Pox Viridae Flashcards
Yt plus lecture notes
What are the two subfamilies of pox viridae
Chordopoxviridae(mammals)
Entomopoxviridae(insects)
Which 2 are the human diseases
Smallpox
Molluscum contagiosum
List 5 properties of pox viruses
.largest and most complex virus
.brick shaped virion
.the virion is a complex virion as there’s no nucleocapsid
.the outermembrane of tubular shaped lipoprotein(synthesized denovo) encloses a dumbell shaped core and 2 lateral bodies
.the core contains viral Dna which is double stranded and associated proteins
.poxviruses are resistant to ambient temperature and may survive years in dried scabs
Briefly explain the viral replication
Replication occurs in the cytoplasm hence these viruses have evolved to encode the dozens of enzymes required for transcription and replication
.
After fusion of the virion with the plasma membrane or via endocytosis ,the viral core is released into the cytoplasm
Transcription is intiated by the viral :transcriptase, transcription factor , capping and methylating enzymes and poly(A) polymerase which are carried in the core of the virion
These factors allow functional capped and polyadenylated mRNAs to be produced without splicing within minutes after infection .
The polypeptides produced by translation of these mRnas complete the uncoating of the core and transcription of the early genes
Early proteins include Dna polymerase and thymidine kinase which are required for the replication of the genome
Transcription of intermediate and late genes is controlled by binding of specific viral proteins to characteristic promoter sequence
Virion assembly occurs in circumscribed areas of the cytoplasm known as guarnieri bodies
The outer bilayer becomes the outer membrane of the virion and the core and lateral bodies
differenciate within it
The outer membrane is synthesized denovo
Some of the mature particles move to the vicinity of the golgi complex,acquire an envelope and are released from the cell by exocytosis
Most particles are not enveloped but are released later by cell disruption
Between the enveloped and nonenveleoped particles ,which are infectious?
Both are infectious bt enveloped are more rapidly taken up by cells and are important in the spread of virions through the body
Describe the clinical manifestations of pox viruses
Skin lesions
Human cowpox are usually localized
Human monkeypox is a severe generalized infection involving organs eg lungs
Pathogenesis of pox viruses
Infection is usually by invasion through broken skin .it replicates at the site of innoculation and causes dermal hyperplasia and leukocytes infiltration
Human infection is acquired by contact or by airborne transmission to a resp mucosa( human monkeypox)
Incubation period spread the infection to internal organs and a second viremia spreads to the skin
Spread to the skin initiates the clinical phase and the lesions progress through the classical stages ie: macule
Papule
Vesicle
Pustule
Crust
Host defences against pox viridae
First line of defence is unbroken skin
Initial response after infection involves interferon and inflammation
Cell mediated and humoral responses to viral antigens are induced by the infection important for recovery and subsequent immunity
Briefly explain the diagnosis of pox viruses
Suggested by :presence of skin lesions
History of contact with human or animal cases
Diagnosis is confirmed by electron microscopy and/or virus isolation
Which features made smallpox eradicable
.effective vaccine .one stable serotype .no animal reservoir .easily diagnosed .long incubation period .it was infectious only after incubation period
Which features made smallpox eradicable
.effective vaccine .one stable serotype .no animal reservoir .easily diagnosed .long incubation period .it was infectious only after incubation period
Which pox virus disease is often painless
Milker’s nodes virus
Orf viruses
Molluscum contagiosum
Which pox virus disease is often painful
Cowpox
Which one produces generalized lesions
Human monkeypox
Molluscum contagiosum
Which one produces localized lesions
Cowpox
