Killing Viruses 101 Flashcards
Survival: Non-enveloped vs. Enveloped
Non-enveloped viruses (e.g. parvovirus, rotavirus, circovirus) generally highly resistant - can survive in enviro or @ room temp. for periods
Enveloped viruses (e.g. retrovirus, coronaviruses) are fragile - survive only short periods
*Have spikes on lipoprotein - if it breaks, can’t attach to host
What we can attack
- Integrity of nucleic acid genome
- The integrity & bio activity of surface coat proteins (& envelope glycoproteins) involved in functions such as attachment & penetration
*Viral envelope pretty easy to destroy - once destroyed, attachment proteins lost & virus rendered non-infectious (inactivated)
Using Detergents & Surfactants
Detergents & Surfactants (& soaps) inactivate 2 ways;
-effect on the lipoprotein envelop
-protein denaturing activity
(Both take time)
Using Alcohols
- Denatures proteins
* either Ethanol or isopropanol used (Best conc. is 70% - water helps the denaturing process)
Using Oxidants (3)
Sodium hypochlorite (Bleach)
-Derivatives of hypochlorous acid are strong oxidizing agents
-activity reduces in alkaline pH & w/ organic material
Potassium Peroxymonosulfate
-Principal ingredient in Virkon (disinfect. used in labs, human & vet hospitals)
Chloramines
-They don’t combine w/ organic material as readily as hypochlorites
-can be quite effective anti-viral agents
Using Iodophors
- are organically bound iodine - active against enveloped viruses
- Low toxicity for humans, but can stain skin, plastics, fabrics & corrosive to metals
- Rapid activity (further increased by warm, acidic water - tho this is less stable) Needs contact time (10 mins)
- Organic material inactivates iodophors (esp. if abundant protein present)
Using Alkylating Agents (2)
- Not suitable for skin
- Glutaraldehyde - v. effective, active at conc of 1-2%. Remains effective in moderate conc. of organic material, chemically stable & moderately corrosive.
- Formaldehyde: disinfect. active against all viruses (& can be used for soil). Can be used as a gas, but is an irritant & toxic.
Using Heat
*Most viruses inactivated by moderate temp in liquid suspension (56-60 deg C)
Reaction varies;
-Circoviruses, parvoviruses and Newcastle disease Virus (NDV) all fairly resistant to heat.
- Moderate temperatures denatures proteins
- High Temperatures inactivate nucleic acids
Using Dessication
(Drying)
- Many are quickly inactivate, but are some that can survive
- i.e. poxviruses (still infectious in dried scabs for long periods)
- Humidity also affects survival - enveloped generally more sensitive
Using Radiation
- Ionising Radiation (X-rays, gamma radiation): Removes electrons from proteins & nucleic acids [can create dimers, induce breakages, cross-linking - basically inhibiting replication]
- can also generate reactive oxygen species causing oxidative damage to lipid membranes
- Larger the genome, the more sensitive the virus
- Non-Ionising Radiation (UV Radiation): Short wavelength (Type C) more damaging - creates thymine-thymine dimers that inhibit DNA replication & increase risk of mutation.
- used to sterilise open surfaces - needs to be directly exposed
- most of sun’s shorter rays absorbed by ozone layer
Overview of the Immune System
*Is the defense against infection by micro-organisms;
Divided into 2 arms:
1. Innate immune System
2 Adaptive Immune system
*Micro-organisms have evolved ways to evade or overcome the immune systems of their hosts
Innate Immune System Components
- Are all physical barriers*
- Skin, scales, hair, horn
- mucociliary escalator (in lungs), peristalsis (gut movement)
- stomach acid
- gastrointestinal proteases (breaks down proteins)
- bile & other surfactants
- sweat, sebum, mucus, tears, lysozyme (eye secretions)
Toll Like receptors: recognise pathogen-associated molecular patterns (are molecules on surface of cells to sample external enviro.
-can initiate inflammatory response (redness, swelling, heat)
Innate Immune system Components
- Cells (neutrophils, macrophages, monocytes, dendrtic cells, eosinophils, basophils, natural killer cells, mast cells)
- Cytokines (interferons, interleukins)
- Complement
- Defensins
- Collectins
Adaptive Immune System (2 cells)
- T-Lymphocytes: turn into either cytotoxic T-cells or Helper T-Cells
- Is the cell mediated immune response
- B-lymphocytes & plama cells - arise from activated B-cells which have been costimulated by helper T-cell. Each plasma cell dedicated to production & secretion of specific antibody
- Afterwards, come T- & B- lymphocytes become long-lived memory cells
- is the humoral immune response
- Afterwards, come T- & B- lymphocytes become long-lived memory cells
Antiviral Chemotherapy - Can they be Clinically useful?
-Aim of successful antiviral drugs
2 major probs. in antiviral chemotherapy:
- Viruses depend on host cell - most subs. that inhibit virus replication interfere w/ cellular metabolism
- Viral production well advanced when clinical signs present
- Aim of any successful antiviral drug = target unique events in replication of virus, e.g.:
- Viral attachment to host cell
- Block unique virus enzymes (e.g. reverse transcriptase)
