Susceptibility to Physical and Chemical Agents

◗ 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. Formaldehyde and b-propiolactone are also active virucidal agents, which arecommonly used for preparation of killed viral vaccines.

The chlorination of drinking water is useful for kill-ing most of the common viruses with exception of hepatitis A and polioviruses. These two viruses are relatively resistant to chlorination.

◗ Temperature

Most of the viruses with few exceptions are highly heat labile. They are inactivated within seconds at 56°C, within minutes at 37°C, and within days at 4°C.

·           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, show resistance to heating at 60°C for 60 minutes; slow viruses, such as scrapie virus, are resistant to autoclaving at 121°C for 15 minutes.

The viruses are stable at low temperature. They can be stored by freezing at 235°C or 270°C. Lyophilization or freeze-drying is useful for long-term storage of the viruses. The poliovirus is an exception, as it does not withstand freeze-drying.

◗ 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.

◗ Lipid solvents

Ether, chloroform, and detergents are active against envel-oped viruses but are not active against nonenveloped, naked viruses.

◗ Radiations

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