Question

Please answer the last two bullets and the blank space in the second bullet.

Pre Assemble, on their hosts' they metabolic machinery for replication, viruses are not considered living. A. Viral Infections Some viruses are merely nuisances while others can cause fatal infections. When a virus causes a worldwide epidemic, this is referred to as a punana An example of this would be: inFuuenza pandurni or vai8 While certain viruses can be prevented by vaccination, others cannot. In particular, that use as their genetic material tend to change frequently making vaccination efforts futile. Why is this the case? Most viruses are specific to a single type of host cell that they can infect. However, there are viruses that can infect multiple types of cells and even multiple species. Using Influenza A as an example, explain how this virus can jump from species to species. c 2009, 2013, 2015 WH Freeman & Co. Used by permission.

Answer 1

1) World-wide epidemics are called Pandemics. Year 1918 out break of influenza virus is an example.

2) Viruses that use RNA as genetic material tend to change genetically, making vaccine development difficult.

Replication or synthesis of DNA/RNA is error prone. There is a high chance of mutations occuring during RNA synthesis to be left corrected/fixed due to lack of effective proof reading mechanisms.

This chance is less for DNA because of availability of proofreading. This applies to viruses as well. For the same reason, viruses having RNA as genetic material will accumulate more mutations. Mutations result in change of aminoacids in encoded proteins resulting in variations. Therefore, targeting these proteins for vaccine development is very challenging. In addition, new variants may occasionally confer increased fitness, resulting more aggressive viruses that can make the vaccines ineffective.

3) Generally, during viral infection, virus binds to a specific cell surface protein/receptor on the host cell. Each virus use a specific receptor to which it would bind to cause infection. Ability of a virus’ host cell and host species range depends upon availability/distribution and abundance of the cell surface receptor. Influenza A virus contains hemagglutinin (HA) on its surface. It uses uses sialic acid-containing molecules as receptors which are very abundant and ubiquitous. This allows the virus to infect multiple cell types and species.