Virology 1

Question 1

What is a virus?

Answer 1

An infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy and is able to multiply only within the living cells of a host.

Question 2

How many viruses are there?

Answer 2

We do not know

Question 3

What hosts can viruses be found in?

Answer 3

• Humans
• Animals (including insects)
• Plants
• Bacteria

humans, animals, non-mammels, mammels, vertebrates and invertebrates

animal to human or between insects plants and humans

Question 4

What is the term for where a virus is found?

Answer 4

Host range

Question 5

Describe the transmission cycle for viruses

Answer 5

• Viruses replicate in reservoirs or amplifying hosts – here they replicate but do not cause disease. E.g swine
• These animals get bitten by insects known as vectors – it does not cause disease.
• Horizontal transmission – transmitted between the same species and vertical is between mother to child in the same species.
• These vectors can reintroduce the virus into the new environment
• Vectors interact with dead end hosts e.g in horse but they don’t effect the horse.
• It is then transmitted into humans, then passed on vertically or horizontally

Question 6

In what tissues can viruses can organs be found?

Answer 6

Viruses can be found in multiple tissues and organs of their host. The tissues that viruses can be found in can be referred to as their “tissue tropism”.
Through processes of evolution viruses evolve to replicate in tissues that favor transmission of between hosts and allow them to evade the immune system of the host;
For example; Some viruses replicate in the lungs and are transmitted in the air by breathing, coughing and sneezing. Some viruses replicate in tissues required for pro-creation and are transmitted by sexual intercourse.
For example; Some viruses replicate in cells of the immune system, preventing immune function. Some viruses choose not to replicate immediately and cannot be detected by the immune system.

Question 7

Describe how viruses can be spread directly or indirectly

Answer 7

• Viruses cause a range of disease, either directly or indirectly.
• Viruses cause disease directly as a product of their host range and tissue tropism.
• Viruses can cause disease indirectly by promoting or inhibiting cell function.

Question 8

Give an example of viruses

Answer 8

cancer
immunodeficiency
respiratory
acute or chronic disease

Question 9

Describe bacteria, prions and virus structure

Answer 9

Bacteria contain nucleic acids (DNA) surrounded by proteins and have a polysaccharide wall made of sugars and replicate outside of cells.

Prions are proteins that do not contain nucleic acids and replicate within cells.

Viruses have nucleic acids covered by proteins, no cell wall and may or may not have a lipid coat and they are obligate cellular parasites.

Question 10

What are the essential features of virus structure?

And describe the structural features of them

Answer 10

1. Viruses have a different structure, but the same organisation.
2. It determines there tissue tropism and host range

Question 11

Describe the 5 essential features of virus replication

Answer 11

Entry into the cell - attachment/entry receptors – direct fusion or endocytosis.

Genome movement within the cell - intracellular structures.

Genome replication - see next lecture.

Genome packaging into protein shells – “Packaging” sequences in viral DNA or RNA.

Exit from the cell – budding or lysis.