Viruses
- Understand htat the classification of viruses is based on structure and nucleic acid types as illustrated by lambda, phage, tobacco mosaic virus and Ebola (RNA) human immunodeficiency virus (RNA retrovirus)
- Know the lytic cycle of a virus and latency
- Know that viruses are not living cells and so antivirals must work by inhibiting virus replication
- Know that as viruses can be difficult to treat once infection has occurred, the focus of disease control should be on preventing the spread, as exemplified by the Ebola outbreak in West Africa
Viruses
Obligate intracellular parasites – they can only exist and reproduce as parasites in the cells of living organisms
Endocytosis – the host cells digests the capsid
Exocytosis – how the viral particles leave the cell
Structure
- Some may have a lipid envelope
- Easier for viruses to pass from cells to cell but makes them vulnerable
- Protein capsid made up of capsomeres
- The repeating unit is easier for reproduction
- DNA viruses
- Genetic material is DNA is used as a template for new viral DNA and mRNA to induce synthesis of viral proteins
- RNA viruses
- More likely to mutate then DNA viruses
- Positive single stranded RNA that can act directly as mRNA and be translated
- Negative single stranded viruses must be transcribed before it is translated
- RNA retroviruses
- The single strand of RNA uses reverse transcriptase to make DNA from the viral RNA this is then inserted into the host cell DNA to produce new viral proteins
- DNA virus replication
- Latency / The lysogenic pathway
- Insert the DNA into the host DNA so that when the cell reproduces lots of cells have the DNA. One gene stops transcription of viral DNA so it does not do any damage or is it noticeable Non- virulent, provirus, latent
- The lytic pathway
- The genetic material is replicated independently of the host DNA straight after entering. Viruses are made and the host cells bursts with all the viruses within which invade other cells. Virulent, lytic
- Latency / The lysogenic pathway
- RNA virus replication
- Positive ssRNA
- The single strand of RNA is used directly for translation into viral proteins
- Negative ssRNA
- Has to be transcribed into a sense strand. RNA replicase uses free bases in the host cell to transcribe a sense strand which can be translated into viral proteins
- Positive ssRNA
- RNA retrovirus replication
- It is translated into DNA by reverse transcriptase, it is then inserted into the host cells which creates new viral proteins
Treating viral diseases
- Target the receptors by which viruses recognise their host cells
- Target the enzymes that help to translate or replicate the viral DNA or RNA
- Inhibit the protease enzymes that enable new virus particles to bud from host membranes
- Rapid identification
- Nursing in isolation
- Preventing transmission
- Sterilising or disposing of equipment and bedding after use
- The wearing of protective clothing by health workers
- Identifying points of contact
Dependency on whether a drug should be fast tracked for an epidemic
- The severity of a drug
- The availability of other treatments
- The effectiveness of standard disease control measures
- Transparency of the process and consent of the people taking the drug
- Collection of clear clinical data
- Some people feel that it is unethical under any circumstances to use untested drugs
- May produce expected side effects
- You have to decide who to give the vaccine
- Corruption may arise
- Informed consent is an issue