Introduction to virology

Question 1

Describe the basic structure of a virus

Answer 1

• obligated intracellular parasites
• Viral genome can either be DNA or RNA but never both
• Viruses can either have a naked capsid or envelops
• Viruses contain outer glycoproteins ( receptors )

Question 2

Differentiate between the enveloped virus and non-enveloped virus

Answer 2

> An enveloped virus: Contains an outer wrapping lipoprotein derived from the cell that is infected with an inner nucleocapsid and a genome

> non-enveloped virus: A virus that lacks an outer envelope and contains only a nucleocapsid that covers the genome

Question 3

Describe the types of virus classification (ICTV vs Baltimore classification,(mention the 7 groups as well )

Answer 3

> ICTV is based on the number of strands, the polarity of genome , shape of capsid , presence of envelope and DNA or rna

> Baltimore classification: A classification system based on how an mRNA is produced and places a virus in one of the 7 groups based on :

• DNA or RNA
• Strandedness ( ss or ds)
• Sense ( positive sense mRNA or negative sense mRNA)
• Method of replication ( transcription or reverse transcription )

Group 1; dsDNA
Group 2: ssDNA 
Group 3: dsRNA
Group 4 : +ssRNA 
Group 5 : -ssRNA 
Group 6 : RT- RNA 
Group 7 : RT -DNA

Question 4

How are viruses transmitted?

6 marks

Answer 4

• inhalation
• ingestion
• direct contact with mucous membrance
• indirect contact
• transplacental
• Organ transplant

Question 5

List the 2 types of viral infection

2 marks

Answer 5

1. Inapparent infection
   * asymptomatic /subclinical
2. Apparent infection
   * acute /persistant (chronic)

Question 6

How do viruses spread in the body

3 marks

Answer 6

lymphatic, blood, and neuronal

Question 7

List 3 techniques used to diagnose viral infections

Answer 7

1. Serology
2. Molecular
3. Culture

Question 8

List the 3 different viral shapes/symmetry

Answer 8

1. Icosahedral eg herpes
2. Helical eg influenza
3. Comple eg neither purely icosahedral nor helical

Question 9

Discuss the viral genome configuration and polarity

Answer 9

• continuous or segmented
• positive sense ( nucleotide have the same polarity as mRNA, such nucleic acid can be used mrna without being transcribed ) or negative sense (mrna is used as a template )

Question 10

What is the difference between chronic and latent infection and slow virus infection?

Answer 10

> Chronic infection :

• Virus s constantly detectable
• May be symptomatic or non-symptomatic
• Shedding continues and therefore infection is in varying degree

> Latent infection :

• Persistent in host
• There is little or no replication of virus = in no disease
• Remains undetectable diagnostically and immunologically
• Disease may occur if the virus is activated

> Slow virus infection
*Due to prolonged incubation, the virus continues to replicate without causing disease. The disease may occur at end of the infection