Poxvirus

Question 1

Poxvirus structural characteristics vaccinia Three strucutral features

Answer 1

vaccinia is prototype for the other poxvirus and has been studied most at the molecular level. Poxviruses are the largest and most complex animal viruses known with dimesnions of 250x350 nm and having an overall oval or brick shape.

Envelope (tightfitting and ether resistant). Biconcave core. and Lateral bodies that fit into the indentations of the bi concave core

Question 2

Poxvirus structural genome

Answer 2

double stranded DNA with covalently linked termini. It is located inside the core structure of the virus particle.

Question 3

Poxvirus genetic modification

Answer 3

Within its core, the poxvirus particle can accomodate a genome with additional DNA sequences (genes) artifically or naturally added to its standard genome length.

Question 4

Vaccinia disease

Answer 4

does not cause smallpox buit may cause its own disease manifestations in certain individuals who are immunocompromised and otherwise impaired.

Question 5

Vaccinia culture

Answer 5

cultured in embryonated hen’s egg and tissue cultures

chorioallantoic membrane of chick embryo, which produces lesions called pocks

farming vaccainia can be used for bioterrorism or for smallpox vaccine

Question 6

Vaccinia Replication cycle location

Answer 6

Viral replication in guarnieri bodies.

Vaccinia can replicated entirely in the cytoplasm.

Question 7

Vaccinia inclusion bodies

Answer 7

guarnieri bodes for small pox virus that correspond to viral replication sites within the cells.

Question 8

Stages of vaccinia replication: 1 attachment

Answer 8

virus attaches to cell surface recpotrs GAG and is internalized via vacuole formation (viropexis) and therein uncoated through a two step process

Question 9

Stages of vaccinia replication: 2 uncoating

Answer 9

the virus particle must be disassembled in order to release viral DNA into the cytoplasm of the cell.

First step: host cell enzymes remove outerenvelope and lateral bodies causing distension of core and activation of core enzymes. Within the core syntehsis of viral m-RNA occurs during viral DNA-RNA polymerase that is resident in the core. VIral mRNAS that are syntehsized within the core are designated immediately early mRNAS. Immediately early mRNAs are translated into immediate early proteins taht are responsible for initiating step 2 of the uncoating process.

uncaoting proteins of viral origin then cause the release of the viral DNA from the viral core structures into the cytoplasm.

Question 10

Stages of vaccinia replication 3 and 4

Answer 10

3. early events: uncoated viral (parental) is then transcribed into “early” mRNAS which are translated into early proteins.

Early proteins have eenzymatic activities which are required for viral DNA replication. (DNA dependent DNA polymerase, thymidine kinase, exonnucleases)

4. DNA replication occurs in defined regions of the cytoplasm to yield progeny DNA molecules

Question 11

Stages of vaccinia replication: 5 and 6

Answer 11

5. Progeny DNA is transcribed into “late” mRNAs, which is translated into “late” proteins. Late viral proteins are mostly structural proteins. Pox viruses are unusual in that they syntehsize one layer of theri own envelope (de novo syntehsis) and acquire another layer from cell membrane.
6. Progeny virus particles form and accumulate in the cytopalsm to yield infectious particles. Microtubules enable progeny virus partciles to move to the surface of cell to egress.

Question 12

Disease: smallpox erradication

Answer 12

model for eradication of a disease with a worldwide disease

Question 13

Small pox clinical transmission and stages

Answer 13

variola virus enter into the UR as an aerosol to initiate the infection process. Virus multiplies in the respiratory mucosa and regional lymph nodes.

A transiet viremia then develops which enable virus to spread to an replicates in cells of internal organs and bone marrow. Virus is released into the blood after this process and

2nd viremia > infection moves to cell of skin, skin rash begininng usually first on the face then spreading centrifugally (exanthem and enathem)

Question 14

Exanthem

Answer 14

rash or lesions of skin

Question 15

Enanthem

Answer 15

lesion of mucous membranes

Question 16

small pox clinical considerations: Reason for erradication

Answer 16

Time period between first exposure to virus and infection of internal organs w/ overt symptoms represent a long incubation period of about 6-17 days. Long incubation period is a very consistent feature, allows enteded time for vaccination during incubation period. The sooner vaccination is begun after SPV exposures (first 4 days is best), the better the chance for blocking infection (reason for erradication)

Question 17

Smallpox SX

Answer 17

severe fever 1-4 days prior of onset of rash, >101 F, PRODROMAL SYMPTOMS

Question 18

Smallpox Rash developmented

Answer 18

Macule > papule > umbilicated vesicle > pustule > crust and scarring, involves all leayers of epidermis and dermis, crust are infectious which is unlike some other skin lesions caused by other viruses. (umbilicated indicates an indented top surface). most lesions develop first on face and then distal portion of extremities. SPV infection includes cells in all layers of skin. One crop of lesions per area of skin, ie lesions arise in a syncrhonous manner at each site. Lesions seen on palms of hands and soles of feet.

Question 19

Reasons for erradication

Answer 19

long incubation period

guarnieri bodies are identifiable

spread only in mad

person to person contact but not easily transmitted: ruptured pustules are infectious after which a scab may form. Upper respiratory secretions contain virus. Contagious of all are individauls who are partially immune and who have few lesions, escape detection, yet are infected by virus. Ruptured pusutles more infective than scabs but the latter may transmit smallpox.

Question 20

Small pox vaccine

Answer 20

first generation found stockpiled and still immnogenic. Second generation . Third generation vaccine more avirulent

Question 21

Vaccine responses

Answer 21

Primary response: follows same lesion progression as seen in actual smallpox infection; indicates no prior immunity. 8-10 days (max response) maximum size of vesicle by ninth day

accelerated response: same lesion progression as a but faster. Indicates partial immunity. 3-7 days (max response)

c. Early or immediately rponse. hypersensitivity reaction; immunity not certain 2-3 days

Question 22

vaccinia gangrenosa or vaccinia necrosum

Answer 22

seen in those with thymic dysfucntions

spreading lesions with necrosis of skin and muscles

show importance of t lymphocytes in controlling viral infections

patients with AIDS were given experimenal vaccinia vaccine. Since their immune system was malfunctioning vaccinia infection was disseminated causing a fatal disease.