Viral diseases

Question 1

Which are the criteria allowing to categorize viruses

Answer 1

The structure and type of nucleic acids the virus contains and its replication strategy

The structure of the virus capsid (= the protein coat that houses the viral genome)

Whether the virus is enveloped or non-enveloped
- non-enveloped virus: calicivirus, feline panleukopenia virus

Question 2

Explain how viruses can conceptually be thought of

Answer 2

Viruses can conceptually be thought of as two separate components:
- the part that allows the virus to survive in the environment and attach to host cells (this is usually shed once the virus enters the host cell)
- this part usually also determine the mode of transmission: enveloped viruses are sensitive to destruction by the environment thus are typically directly transmitted in secretions (e.g., nasal droplets, saliva); non-enveloped viruses are typically more resistant in the environment and are often transmitted via the faecal-oral route

- the part that contains the genome and components that facilitate replication (e.g., enzymes)
    - viral genomes may consist of DNA or RNA, single or double stranded

Question 3

Explain the two mechanisms permiting viruses to enter in the host cell

Answer 3

Non-enveloped viruses attach via direct attachment proteins

Enveloped viruses attach via surface glycoproteins

The particular receptors required by the virus determine host specificity, and also tissue or target cell tropism
- these cellular receptors are often normal cell surface molecules

Question 4

Explain how a virus enter a host cell once attached to its receptor

Answer 4

Once the virus has attached, it enters the host cell and undergoes disassembly of the capsid

The virus enters the cell either by fusion of the viral enveloppe with the cell membrane or via endocytosis