Topic 2 Microbiology - Virology and Viral Infection Flashcards
(36 cards)
What are characteristics of viruses?
Viruses lack independent metabolism
Need a host to replicate
cannot regulate internal conditions (no organelles)
wide range of organisms infected by viruses
cannot react to external factors
Do not grow, produced fully formed
Very small in size - typically 20-300 nm
Generally, very small genomes
What are characteristics of a viruses life?
Homeostasis - regulation of the internal environment e.g. sweating to reduce temperature
Organisation - being structurally composed of one or more cells
metabolism
growth
adaptation
response to stimuli
reproduction
Different viruses have different genetic materials. What are these genome compositions?
Some double stranded DNA
Some double stranded RNA
Some single stranded DNA
Some single stranded RNA
Describe a viruses structure?
The genetic material is within the virus
There is a protein coat around the genetic material. Protein coat is protecting the genetic material
Generally, an outer lipid membrane as well
The energy required for replication comes from the host
The viral particles tend to be highly symmetrical in appearance
The virus has some genes-often required for own replication e.g. reverse transcriptase
Why do viruses have a very limited range of host organisms (often only one)?
Due to the small number of genes present in a virus
What does a limited number of genes in a virus reduce potential for?
reduces potential for diversity and therefore a mutation is required to jump species barrier
What are some examples of viral infection routes?
Aerosols e.g. measles
Faecal-oral e.g. GI tract viruses (Norovirus)
Direct contact e.g. sexually transmitted (HIV)
Via Blood e.g. rabies, hepatitis B
Insect Bites e.g. Dengue fever
What are some viral infection factors?
In addition to ensuring correct infection mechanism, other factors may also be important:
Temperature range
Humidity levels
sunlight (UV) levels
Host specific-microbiome, genetic factors, co-morbidities, immune system
What needs to happen for a successful infection to occur?
there needs to be contact initiated between the host and the viral particle.
Therefore there is the initial contact, but then it must be followed by the interaction.
If for some reason the hosts surface has changed, then recognition might not take place. If recognition does not take place, then infection will fail.
The contact must also be with the correct type of tissue e.g. Influenza A virus needs epithelial tissue
Describe virus infection events
- Once contact has been made with the cell, the virus becomes engulfed by the cell.
- The viral coat (capsid) is removed
- The genome can then be transported to the nucleus in the case of DNA viruses, however, for RNA viruses this may have to have a reverse transcription step before being moved to the nucleus for replication
- Any expression of viral genes can now take place. This will often include expression of the genes responsible for producing the capsid of the virus
- Replication of the viral genome. This will all result in new viral particles being produced. In some cases these may be budded out of the host cell - and so will not be fatal to the cell. In other cases the replication of the viral particle is accompanied by cell lysis (a method in which the outer boundary or cell membrane is broken down or destroyed in order to release inter-cellular materials such as DNA, RNA, protein or organelles from a cell?), with the virus killing its host cell
- Release of viral genome from nucleus
- Coating of viral genome to form new mature virus
- Release of viral particle (killing cell????)
What is taxonomy?
Taxonomy involves the identification and naming of organisms and their classifications into groups based on shared characteristics
What is Human Cytomegalovirus (HCMV)
HCMV is classified within the herpesviridae group (Herpesvirus 5)
It is a double stranded DNA virus
How is HCMV transmitted?
The precise mode of transmission is unclear, but it is thought to be passed on through bodily fluids. it is believed to be most commonly spread by kissing or sexual activity, but also appears to be spread via tears, urine, blood and saliva.
HCMV is not tissue specific, but what tissues does it mainly affect?
Most tissues can be infected, but mainly salivary glands and leucocytes.(white blood cells???)
What problems can HCMV cause for immunocompromised individuals?
Colitis (inflammation in your colon?)
Increased susceptibility to other symptoms
In neonates (newborns) there can be congenital abnormalities following exposure to the virus
What are the treatments for HCMV?
No vaccine is available
Antiviral treatments exist. Generally uses Gancicovir
Ganciclovir is a synthetic analogue of 2′-deoxy-guanosine and so as ganciclovir triphosphate it is a competitive inhibitor of deoxyguanosine triphosphate (dGTP) incorporation into DNA. While this could pose problems for the host’s own DNA replication, it actually preferentially inhibits the viral DNA polymerases more than cellular DNA polymerases and so preferentially prevents replication of the viral DNA.
What are some examples of cancer-associated viruses?
Epstein-Barr Virus (EBV) -nasopharyngeal carcinoma
Hepatitis B (Hep B)-hepatocellular carcinoma
Hepatitis C (Hep C)-hepatocellular carcinoma
Human Papillomavirus (HPV)-cervical cancer
Herpes virus-Kaposi’s sarcoma
Human T-lymphotropic virus Type 1 (HTLV-1)-adult T cell leukaemia
Merkel cell polyomavirus (MCPyV)-Merkel cell carcinoma (skin)
How is the Zika virus (ZVD) transmitted?
Transmitted through mosquitoes in the genus Aedes
What does the ZVD cause?
Typically causes mild fever, rash, conjunctivitis which last around 2-7 days
Neonatal malformation with small head size
Babies may develop epilepsy, learning disabilities, hearing problems, vision problems
Many will develop normally
What is ZVD an example of?
This is an example of a positive sense RNA virus, and after infection it has to be able to make a double-stranded RNA version of its genome
The Aedes aegypti (mosquito) is known to spread ZVD, what else is it also involved in spreading?
Dengue fever
Chikungunya
Mayaro virus
Yellow fever virus
What treatments are there for ZVD (zika virus)?
No vaccine available
No specific treatment
Best way to avoid ZVD is to avoid being bitten
Found in many tropical/sub-tropical areas
What are characteristics of Corona virus?
RNA virus
Infect mammals and birds
Cause respiratory problems
Some very mild, others more severe
Long-term effects unknown
They have a positive-sense, single-stranded RNA genome. They are typically in the range of 50-200 nm (approximate mean size = 120 nm) with a genome size of around 30,000 nucleotides. There are several different types of coronaviruses and they are able to infect both birds and mammals. Some are specific to a single species, while others can infect a number of species. Infections vary in terms of severity and affect the respiratory tract, and in some other cases other systems as well.
What does the H and N stand for in H1N1 and what do they do?
H = Haemagglutinin - helps with initial attachment
N = Neuraminidase - Helps with release of new virus particles
