Pox viruses

Question 1

What subset of the population experiences the highest mortality from pox viruses?

Answer 1

children

Question 2

Go over the taxonomy of pox virus>

Answer 2

Family: Poxviridae

Subfamily:Chordopoxvirinae

Genus: Orthopoxvirus

Species: Variola

Question 3

Smallpox is caused by what two strains?

Answer 3

Variola major—more common, causes a severe form of the disease
(30-40% mortality rate)

Variola minor—causes a mild form of disease (1-2% mortality rate)

Question 4

What are the important characteristics of poxvirus?

Answer 4

Largest of all animal viruses

Brick-shaped

Enveloped (2 types)

• mature virion (MV)= 1 envelope
• extracellular enveloped virion (EEV) = 2 envelopes

Nucleoid core shaped like a dumbbell

Large dsDNA genome within the core

Many viral enzymes also found within the core

• Brings own DNA dependent RNA Polymerase
• everything occurs in cytoplasm

Question 5

What is the vaccinia virus?

Answer 5

Used to vaccinate individuals against smallpox

Question 6

WHat are the 3 classes of vaccinia mRNAs transcribed by vaccinia virus?

Answer 6

Early mRNAs 
 - encode enzymes and factors needed for transcription of the intermediate class of mRNAs and DNA replication.

Intermediate mRNAs
- encode enzymes and factors required for late gene expression.

Late mRNAs
- expression occurs after DNA replication.
Encodes factors and enzymes package into the virion
- Structural proteins

Question 7

Go over vaccinia assembly, maturation, release.

Answer 7

After the late gene products are synthesized, infectious particles are assembled

The particles are double-wrapped with a Golgi-derived membrane and transported to the periphery of the cell

Fusion of the IEV with the plasma membrane results in release of an EEV with 2 membranes

IMV remain inside until cell lyses (contain a single membrane)

Question 8

What are the types of variola major?

Answer 8

Ordinary—accounts for about 90% of cases, 30% mortality rate

Modified (vaccine)—mild, occurred in 2% of previously vaccinated persons, less than 10% mortality rate the ppl who were infected but had received the vaccination

Flat or malignant pox—rare, very severe, represents about 5% of cases, 80% mortality rate

Hemorrhagic—rare, very severe, less than 1% of cases, 96% mortality rate

Question 9

What are the clinical signs of ordinary smallpox (variola major) vs chickenpox?

Answer 9

centrifugal pattern

• concentrated on hands, face, feet
• not as concentrated on abdomen/trunk
• virus pattern in extremities
• lesions (pox) are uniform in size

chicken pox

• uncommon to see lesions on hands/feet
• lesions (pox) are different sizes

Question 10

Go through the clinical presentation of smallpox.

Answer 10

Average incubation period is 10-14 days
- asymptomatic during the incubation period

First symptoms (Prodromal period)

• Fever, headache, backache
• then feel better
• rash appears and become bedridden
• ruptured lesions contain alot of virions

Question 11

Why was smallpox a good candidate for eradication?

Answer 11

• narrow host range
• no carriers
• no animal reservoirs
• effective and inexpensive vaccine
• Surveillance of the disease was easy (centrifugal rash).
• WHO created a program to eradicate it

Question 12

How is smallpox transmitted?

Answer 12

respiratory tract secretions

Question 13

Go through the pathogenesis of smallpox.

Answer 13

Spread via respiratory tract or skin

spreads to nearest draining lymph node
- replication

Spreads to bloodstream
- primary viremia

Spreads to liver and spleen
- replication

Spreads back to bloodstream
- secondary viremia

Skin lesions appear
- release