Reaction to Physical & Chemical Agents Virolory lec.3
Lecture objectives:
To understanding of different physical and chemical factors affected viruses such as:1-Heat & Cold, 2- Stabilization of Viruses by Salts, 3-pH, 4-Radiation, 5-Photodynamic inactivation, 6-Ether Susceptibility, 7-Detergents, Formaldehyde, Antibiotics & Other Antibacterial Agents.
Heat & Cold
There is great variability in the heat stability of different viruses.
- Icosahedral viruses tend to be stable, losing infectivity after several hours at 37°C. Enveloped viruses are much more heat-labile, rapidly dropping in titer at 37°C.
-Viral infectivity is generally destroyed by heating at 50–60°C for 30 minutes, exceptions (eg, hepatitis B virus, polyomaviruses).
Viruses can be preserved by storage at deep-freezing temperatures, and some may withstand lyophilization and can thus be preserved in the dry situation at 4°C or even at room temperature. Enveloped viruses tend to lose infectivity after prolonged storage even at -90°C and are particularly sensitive to repeated freezing and thawing.
Stabilization of Viruses by Salts
Many viruses can be stabilized by salts in concentrations of 1 mol/L. The mechanism by which the salts stabilize viral preparations is not known. Viruses are preferentially stabilized by certain salts.
MgCl2, 1 mol/L, stabilizes picornaviruses and reoviruses;
MgSO4, 1 mol/L, stabilizes orthomyxoviruses and paramyxoviruses;
Na2SO4, 1 mol/L, stabilizes herpesviruses.
pH
Viruses are usually stable between pH values of 5.0 and 9.0. Some viruses (eg, enteroviruses) are resistant to acidic conditions. All viruses are destroyed by alkaline conditions.
Radiation
Ultraviolet, x-ray, and high-energy particles inactivate viruses. The dose varies for different viruses. Infectivity is the most radiosensitive property because replication requires expression of the entire genetic contents.
Photodynamic Inactivation
Viruses are penetrable to a varying degree by vital dyes such as toluidine blue, neutral red, and proflavine. These dyes bind to the viral nucleic acid, and the virus then becomes susceptible to inactivation by visible light.
Ether Susceptibility
Ether susceptibility can be used to distinguish viruses that possess an envelope from those that do not
29-1 As shown in table
Detergents
Nonionic detergents—eg, Nonidet P40 and Triton X-100—solubilize lipid constituents of viral membranes. The viral proteins in the envelope are released (denatured).
Anionic detergents, eg, sodium dodecyl sulfate, also solubilize viral envelopes; in addition, they disrupt capsids into separated polypeptides.
Formaldehyde
Formaldehyde destroys viral infectivity by reacting with nucleic acid. Viruses with single-stranded genomes are inactivated much more rapidly than those with double-stranded genomes. Formaldehyde has minimal adverse effects on the antigenicity of proteins therefore it has been used frequently in production of inactivated viral vaccines.
Antibiotics & Other Antibacterial Agents
1- Antibacterial antibiotics and sulfonamides have no effect on viruses. Some antiviral drugs are available.
2- Larger concentrations of chlorine are required to destroy viruses than to kill bacteria, especially in the presence of extraneous proteins. For example, the chlorine treatment of stools adequate to inactivate typhoid bacilli is inadequate to destroy poliomyelitis virus present in feces.
3- Alcohols, such as isopropanol and ethanol, are relatively ineffective against certain viruses, especially Picornaviruses.