Viral Pathogens

Question 1

Describe virus coat/capsid, nucleocapsid, nucleocapsid symmetry, virus particle/virion, enveloped virus and envelope-free viruses.

Answer 1

Virus coat/capsid = protein shell

Nucleocapsid = nucleic acid + capsid

Nucleocapside symmetry: helical-appears rod shaped, Icosahedral-naked virus with 20 triangular faces, Complex-surface structure consisting of tubular proteins and bound by external membrane

Virus particle/Virion - extracellular viral particle, not living but can be killed by destroying its infectivity

Enveloped Virus - Nuc. Acid + protein + lipid envelope(stolen from host)

Naked Virus - Nuc. Acid + capsid

Question 2

Explain routes by which viruses enter the body and the most common forms of virus transmission.

Answer 2

Viruses enter body via mucosa of digestive, respiratory, reproductive sites

*Enveloped virus cant invade through digestive tract b/c bile dissolves lipid membrane

Transmission: Oral(food,drink,saliva), droplet (inhalation), transplacental, sexual transmission, direct (injection, insect bites)

Question 3

Explain key elements in virus infection of host cells including virus attachment/adsorption, virus receptors, host specificity and viral entry.

Answer 3

Attachment - viral ligand binds to a cellular receptor
Receptors - receptors determine host and tissue specificity
Host specificity - most viruses infect specific host cells (HBV only infects humans)
Viral Entry - all viruses can enter via receptor mediated endocytosis, some viruses (polio) forms a pore and injects viral RNA/DNA

Question 4

Explain the process of virus replication including synthesis of virus mRNA, translation and processing of virus proteins, replication of virus nucleic acid and the assembly and release of virus particles.

Answer 4

1. Attachment
2. Penetration
3. Uncoating - endocytosed viruses (enveloped) have the membrane dissolved in low pH environment, naked virus dissolve capside to release Nuc. Acid
4. Gene expression - 3 types of RNA viruses: dsRNA, ssRNA, and retrovirus

*Viruses often have one promoter region on mRNA so it is translated as one long protein and proteases cleave it into smaller functional pieces

dsRNA - if neg. - transcribed by RdRP into positive strand
- if pos. - directly translated by ribosome
ssRNA - see dsRNA
retrovirus - positive DNA transcribed by viral reverse transcriptase

Question 5

Distinguish between DNA virus, dsRNA virus, ssRNA virus and retrovirus.

Answer 5

DNA virus - virus that has DNA as genetic material + replicates using DdDP
dsRNA - similar to DNA - copy neg. strand to make + strand (ex: rotovirus)
ssRNA - similar to dsRNA
retrovirus - copies + RNA strand into DNA with reverse transcriptase

Question 6

Compare and contrast the mechanisms by which dsRNA viruses, positive and negative sense ssRNA viruses and retroviruses synthesize mRNA and replicate genomic RNA.

Answer 6

dsRNA - if neg. - transcribed by RdRP into positive strand
- if pos. - directly translated by ribosome
ssRNA - see dsRNA
retrovirus - positive DNA transcribed by viral reverse transcriptase

Question 7

Compare and contrast lytic, persistent and latent viral infections.

Answer 7

lytic = cell dies - nonenveloped niruses always cause lytic infections

Persistent = cell “enslaved” by virus

Latent = dormant viral genome, no viral replication (Ex: chicken pox - latent infection - shingles)

Question 8

Explain the mechanisms of viral oncogenes and the process by which viruses can transform host cells into cancer cells.

Answer 8

Examples of Oncogene Virus = E6 + E7 (in HPV)
E6 - ubiquitinates p53
E7 - competes with Rb (protein that stops cell division)

overactive mitosis-promoting genes kicks cell past G1-S transition

Question 9

Explain how viruses are classified into families based on the type of nucleic acid in the genome, number and polarity of nucleic acid strands, mode of replication and size, structure and symmetry of the virus particle.

Answer 9

Enveloped/Naked
DNA/RNA Viruses
ssDNA + ssRNA/dsDNA + dsRNA
\+sense/-sense RNA viruses
Retrovirusses - have rever transcription step
Serotypes - based of viral antigens
Genotypes - based on viral genomes

Question 10

Explain latent infection of herpesviruses

Answer 10

establishes episomal latency in dorsal ganglion root and leave linear genetic material in cytoplasm. travels down nerve to infect cells when active

episome = plasmid that is capable of integrating in to the chromosome. The integrative plasmids may be replicated and stably maintained in a cell through multiple generations, but always at some stage they exist as an independent plasmid molecule

Question 11

Identify the clinical and laboratory manifestations of HSV and VZV infections

Answer 11

HSV-1 (herpes labialis) - enveloped, dsDNA genome, characterized by groups of vesicles around hips, latency in trigeminal ganglion neurons and travels up sensory nerve fibers
DX: Tzank test = skin scrape - multinucleated giant cells

VZV-2 = chicken pox and shingles
primary infection = chicken pox, zoster = vesicle along a nerve