Microbiology – Viruses
- Viruses basically invade cells, cause colds, influenza, HIV, small pox, MMR, warts, polio and many more.
- Some viruses are asymptomatic= don’t show symptoms
- Viruses have particular cells they can infect, lock and key
- Host soecificity = lock and key
- In Latin, virus means poison.
- Existence proven by Ivanowski (Russian Scientist) 1892 – first started with plants
- Virus are: self-reproducing particles that enter hosts and reproduce inside cells
Is a branch of Microbiology that looks at viruses.
- Can only be seen by electronic microscope
- Simplest form of life
- Neither prokaryotes or eukaryotes
- Smaller than bacteria
- Can’t be cultures in labs
- Huge diversity
- They live inside cells – feeding, reproducing and growing = they need organisms to live = cant carry out metabolic reaction alone, viruses take over ribosomes
- Potentially infectious = dependant on Host
- Capside = protein layer that protects RNA or DNA, composed of protein unit called capsomeres.
- Capsides have different shapes:
Lacks ribosomes and other replication equipment. Our bodies can recognise the antigenic properties and build antibodies.
v Some viruses have an additional protective layer , a lipid usually (envelope) – makes it weaker to environment change, naked viruses are more stranger to pH change
v Viral enzymes are used to infect, they are targets for antiviral therapy
v Outside the host cell, they are unable to carry out any metabolic reaction
Virion: mature virus; will have nucleic acid and capsid or nucleic acid, capsid and envelope: they are capable of transmission from one host to another
Virus: intracellular infectious particle consisting of nucleic acid and protein coat (capsid)
Viroids: Infectious agent, don’t have a capsid. Only have a closed circular RNA molecule
Prion: consists only of protein : not alive, lacks genetic material. BUT it can go to a host cell and infect it.
v Shape is used for classification
v Genetic Material found will depend on the nature and function of the virus
v Division based on genetic material:
- Single or Double strand
Types of Viral Infection:
v Acute lytic:
- Virus infects host cell > new viruses are created > host cell dies> virus spread to neighboring cells.
- Identifiable symptoms and signs (You know they are sick)
- Eg common cold, mumps, flu
- No recognisable symptoms or signs : swollen glandsand a sligh fever
- Can harm a fetus if mum is incontact with it during pregnancy
- Possible no symptoms
- Virus lives in host at a low level carrier state
- Unlikely to be cured
- Eh HIV and HepB
- Virus lies dormant- will reactivate later
- Common in herpes virus
- Initial symptoms >apparent recovery> virus will still be there
- Eg. Chickenpox, Shingles, G – fever
Infection of host:
v Inhaled droplets : rhinovirus, influenza
v In food or water: HepA, Norovirus
v Direct transfer: HIV, HepB
v Vector: Yellow Fever, West Nile Virus
v Viruses have a host specificity, restricted range of hosts. Thank Lock and Key Fit
Adsorption = Virus attaches to host receptor
Penetration = genetic material enters host cell
Uncoating = genetic material of virus hijacks the cell, taking cell away from it’s usual job
Synthesis and Assembly = using host cell make new virus
Release = new virus released (lysis or budding), host cell is destroyed
Infection of nearby cells
v As some viruses affect dna of host cell = it most usually helps cancer,
v Cell replicates too much and gets cancerous (after the altercation of host dna, the host cell looses control over the replication)
- HPV and STD = cause cervical cancer
- HepB and C = are linked to liver cancer
Once a virus has hijacked a cell and used it’s ribosomes and cellular material to reproduce, host cell will produce many viruses and infect nearby cells. Certain proteins must fit to the receptors of a host cell surface in order to infect.
The replication process is depending on Single strand or double strand.
DNA: viral DNA wants to replicate so it goes into the host nucleus = replication and production of mRNA = sits on ribsosome and produce protein. Host cell left for dead after replication.
Single Strand RNA: viral DNA is synthesised from the ssRNA using a viral enzyme called: reverse transcriptase = the new DNA is transcribed into viral mRNA protein and new viral RNA.
Some viruses sit in chromosomes and pretend to be part of us = with us in our genes forever, 5% of our genes are virus.
The more the cell replicates, the higher chance of mutation= a new virus
|Rhinovirus/ Adenovirus||Common cold|
|Arbovirus / Herpes Virus||Encephalitis|
|Varicella zoster||Chickenpox and Shingles|
|Rubella||German Measles, can cause arthritis later on in life, is a major problem on fetus.|
Virus – Disease
|Retrovirus (RNA virus)||Promotes Tumour Growth|
|Filovirus||Bleeding and coagulation and viral hemorrhagic fever|
|Paramyxovirus||Measles and mumps|
- Caused by a virus
- Antibiotics wont work
- Affects liver
- Will be in feaces a lot (checkable – any unhygienic act can be transmitted – by poo)
- Unsanitary conditions
- Found in water and food
- Can be immunised against
Prevention: vaccine, past exposure, good hygiene
v From symptoms
v presence of other cases at the same time
v blood test and cultures from blood samples, bodily fluid
v PCR and ELISA = used to look at the Polmerase chain reaction = used to detect dna of other microbes.
v Examination of blood or tissue under electronic microscope
Little way to attack viruses unless they take their own enzymes “Reversetase” then we can attack.
v Drugs (antiviral) – but can be very toxic to human cells
v Viruses build up a resistant to antiviral drugs very easily.
- Inferon Drugs=Protein (synthetic) that slows the replication process
- Immune Globulin = antibodies produced by others
- Vaccines = help prevent infection
Host Defence Mechanism: