Effects of Physical Agents

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Effects of physical and chemical agents on viruses

3rd lecture of Medical Virology for 3rd year students- college of Medicine

Presented by Dr. Mohammed J. M. Shallal
References: Main textbook: Medical Microbiology, Jawetz, Melnick, 26th ed.,2013

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Susceptibility of viruses to Physical and Chemical Agents
1- Disinfectants
The viruses are usually more resistant than bacteria to chemical disinfectants. Most viruses are relatively resistant to phenol.


The oxidizing agents, such as hydrogen peroxide, potassium permanganate, hypochlorite, and organic iodine compounds, are most active antiviral disinfectants.


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Susceptibility of viruses to Physical and Chemical Agents
1- Disinfectants

The chlorination of drinking water is useful for killing most of the common viruses with exception of hepatitis A and polioviruses.

These two viruses are relatively resistant to chlorination.

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 stool adequate to inactivate typhoid bacilli but it is inadequate to destroy poliomyelitis virus present in feces.
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2- Temperature (Heat & Cold)

Most of the viruses with few exceptions are highly heat labile.

There is a great variability in the heat stability of different viruses.

They are inactivated within seconds at 56C°, within minutes at 37C° and within days at 4C°
* The viruses such as influenza, measles, and mumps are very labile and may survive outside the host only for a few hours.


Other viruses, such as polio and hepatitis A, are relatively much stable and may survive for many days, weeks, or even months in the environment
*Viruses, such as hepatitis B and polyomaviruses, show resistance to heating at 60C°for 60 minutes; slow viruses, such as scrapie virus, are resistant to autoclaving at 121C° for 15 minutes.

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Icosahedral viruses tend to be stable, losing infectivity after several hours at 37C °

Enveloped viruses are much more heat-labile, rapidly dropping in titer at 37C °

*The viruses are stable at low temperature. They can be stored by freezing at 35C°or 70C°

Lyophilization or freeze-drying is useful for long-term storage and preservation of viruses.

The poliovirus is an exception, as it does not withstand freeze-drying.

Enveloped viruses tend to lose infectivity after prolonged storage even at -90C ° and are particularly sensitive to repeated freezing and thawing

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3- pH
The viruses usually remain viable in a pH range of 5 - 9, but are sensitive to extremes of acidity and alkalinity. Rhinoviruses are very susceptible to acidic pH, while enteroviruses are highly resistant.


4- Lipid solvents
Ether, chloroform, and detergents are active against enveloped viruses but are not active against non-enveloped, naked viruses.

5- Radiations

The viruses are readily inactivated by sunlight, ultraviolet (UV) radiations, and ionizing radiations.

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.

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6) 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.

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7) 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.

9)Detergents

Non-ionic detergents—eg, Nonidet P40 and Triton X-100—solubilize lipid constituents of viral membranes.

The viral proteins in the envelope are released (denatured).

Ionic detergents, eg, sodium dodecyl sulfate, also solubilize viral envelopes; in addition, they disrupt capsids into separated polypeptides.

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10) Formaldehyde and propiolactone

Formaldehyde and propiolactone destroy viral infectivity by reacting with nucleic acid.


Viruses with single-stranded genome are inactivated much more rapidly than those with double-stranded genomes.

Formaldehyde and propiolactone has minimal adverse effects on the antigenicity of proteins are also active virucidal agents, which are commonly used for preparation of killed or inactivated viral vaccines.


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11) Antibiotics & Antibacterial Agents

1- Antibacterial or antibiotics and sulfonamides have no effect on viruses. They are replaced by antiviral drugs which are effective against viruses.

3- Alcohols, such as isopropanol and ethanol, are relatively ineffective against certain viruses, especially Picornaviruses.

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Thank you