Disinfection virus

Careful consideration should be given to the validation of methods for sterilization, disinfection, virus removal and inactivation. 

Unrestricted use of reclaimed wastewater for drinking water, however, requires careful examination. While practically a complete barrier to viruses, bacteria, and other toxic entities that must be kept out of a potable supply, RO membranes could pose serious problems should any defect develop in their separation mechanism. Given the purity and clarity of RO-treated wastewaters, however, it might be advantageous to use RO and then subject the product to well-established disinfection procedures. 

The current concept of disinfection is that the treatment must destroy or inactivate viruses as well as bacillary pathogens. Under this concept, the use of coliform counting as an indicator of the effectiveness of disinfection is open to severe criticism given that coliform organisms are easier to destroy than viruses by several orders of magnitude. 

Sodium hypochlorite is one of the best disinfectants known, capable of killing bacteria, yeasts, fungus, spores, and even viruses. Because it is an excellent disinfectant as well as a bleaching agent, it is used in many household cleaners. Sodium hypochlorite is also used to disinfect water supplies and swimming pools (although calcium hypochlorite in powder or pellet form is often used as a substitute, due to the convenience of its solid form). 

Heat is the most reliable method of virus disinfection. Most human pathogenic viruses are inactivated following exposure at 60°C for 30 minutes. The virus of serum hepatitis can, however, survive this temperature for up to 4 hours. Viruses are stable at low temperatures and are routinely stored at -40 to -70°C. Some viruses are rapidly inactivated by drying, others survive well in a desiccated state. Ultraviolet light inactivates viruses by damaging their nucleic acid and has been used to prepare viral vaccines. These facts must be taken into account in the storage and preparation of viral vaccines (Chapter 15). 

Viruses that contain hpid are inactivated by organic solvents such as chloroform and ether. Those without hpid are resistant to these agents. This distinction has been used to classify virases. Many of the chemical disinfectants used against bacteria, e.g. phenols, alcohols and quaternary ammonium compounds (Chapter 10), have minimal virucidal activity. The most generally active agents are chlorine, the hypochlorites, iodine, aldehydes and ethylene oxide. 

Susceptibility of viruses to antimicrobial agents can depend on whether the viruses possess a lipid envelope. Non-lipid viruses are frequently more resistant to disinfectants and it is also likely that such viruses cannot be readily categorized with respect to their sensitivities to antimicrobial agents. These viruses are responsible for many nosocomial infections, e.g. rotaviruses, picornaviruses and adenoviruses (see Chapter 3), and it may be necessary to select an antiseptic or disinfectant to suit specific circumstances. Certain viruses, such as Ebola and Marburg which cause haemorrhagic fevers, are highly infectious and their safe destruction by disinfectants is of paramount importance. 

There is much concern for the safety of personnel handling articles contaminated with pathogenic viruses such as hepatitis B virus (HB V) and human immunodeficiency vims (HIV) which causes acquired immune deficiency syndrome (AIDS). Some agents have been recommended for disinfection of HBV and HIV depending on the circumstances and level of contamination these are hsted in Table 10.4. Disinfectants must be able to treat rapidly and reliably accidental spills of blood, body fluids or secretions from HIV infected patients. Such spills may contain levels of HIV as high as lO" infectious units/ml. Recent evidence Irom the Medical Devices Agency evaluation of disinfectants against HIV indicated that few chemicals could destroy the vims in a... 

Table 10.4 Chemical disinfection of human immunodeficiency virus (HIV) and hepatitis B virus (HBV). Adapted from ACDP (1990) and Anon (1991)...

Ethanol (CH3CH2OH) is widely used as a disinfectant and antiseptic. The presence of water is essential for activity, hence 100% ethanol is ineffective. Concentrations between 60 and 95% are bactericidal but a 70% solution is usually employed for the disinfection of skin, clean instruments or surfaces. At higher concentrations, e.g. 90%, ethanol is also active against most viruses, including TUV. Ethanol is also a popular choice in pharmaceutical preparations and cosmetic products as a solvent and preservative. 

Of the other peroxygen compounds with antimicrobial activity, potassium monoperoxysulphate is the main product marketed for disinfectant use. It is used for body fluid spillages and equipment contaminated with body fluids, but its activity against mycobacteria and some viruses is limited. 

Sterilization, Disinfection and Cleaning of Medical Equipment Microbiology Advisory Committee (1993) Guidance on Decontamination fixMnttie Microbiology Advisory Committee to Department of Health Medical Devices Directorate. Part 1 Principles. London HMSO. van Bueren J., Salman H. Cookson B.D. (1995) The Efficacy of Thirteen Chemical Disinfectants against Human Immunodeficiency Virus (HIV). Medical Devices Agency Evaluation Report. 

The testing of disinfectants for virucidal activity is not an easy matter. As pointed out earlier (Chapter 3), viruses are unable to grow in artificial culture media and thus some other system, usually employing living cells, must be considered. One such example is tissue culture, but not all virus types can propagate under such circumstances and so an alternative approach has to be adopted in specific instances. The principles of such methods are given below. 

A standardized viral suspension is exposed, in the presence of yeast suspension, to appropriate dilutions of disinfectant in WHO hard water. At appropriate times, dilutions are made in inactivated horse serum and each dilution is inoculated into tissue cell culture or embryonated eggs (as appropriate for the test virus). The drop in infectivity of the treated virus is compared with that of the control (untreated) virus. 

Plaque assays, at present, apply to only a very limited number of viruses, e.g. poliovirus, herpes virus, human rotavirus. The principle ofthese assays is as follows test virus is dried on to coverslips which are immersed in various concentrations oftest disinfectant... 

Fig. 11.7 A, diagrammatic representation of plaque assay for evaluating virucidal activity and B, monolayers of baby hamster ki(hiey (BHK) cells C, virus tte untreated virus (o represents a plaque-forming unit, pfu, in BHK cells) D, virus titre disinfectant-treated virus (before plating onto BHK, die disinfectant must be neuh alized in an appropriate manner). Note the greatly reduced nimiber of pfu in D, indicative of fewer iminactivated virus particles than in C. 

For assaying herpes virus, monolayers of baby hamster kidney (BHK) cells are used. Virus titre is expressed as the number of plaque-forming units (pfu) per millilitre before and after exposure to a disinfectant, so that the virucidal efficacy of the test agent can be determined. A diagrammatic representation is given in Fig. 11.7. 

The hepatitis B virus (HB V) does not grow in tissue culture and an acceptable animal model has been found to be the chimpanzee. This is observed for clinical infection after inoculation with treated and untreated virus, care being taken in the test series that residual disinfectant is removed by adequate means before inoculation into the animal. 

Duck hepatitis B virus (DHBV) has been proposed as a possible model for the inactivation of human HBV by chemical disinfectants. The principle of the test method uses viral DNA polymerase (DNAP) as a target, total inhibition in vitro of DNAP by chemical disinfectants being predictive of inactivation of infectivity in vivo. 

The human immunodeficiency virus (HIV lymphadenopathy-associated virus, LAV human T-cell lymphotrophic virus type 3, HTLV III) is responsible for acquired immune deficiency syndrome (AIDS see Chapter 3). Because of the hazard and difficulties of growing the virus outside humans, a different approach has to be examined for determining viral sensitivity to disinfectants. 

Studies have demonstrated that one such method is to examine the effects of disinfectants on endogenous RNA-dependent DNA polymerase (i.e. reverse transcriptase) activity. In essence, HIV is an RNA virus after it enters a cell the RNA is converted to DNA under the influence of reverse transcriptase. The virus induces a cytopathic effect on T lymphocytes, and in the assay reverse transcriptase activity is determined after exposure to different concentrations of various disinfectants. However, it has been suggested that monitoring residual viral reverse transcriptase activity is not a satisfactory alternative to tests whereby infectious HIV can be detected in systems employing fresh human peripheral blood mononuclear cells. 

Tyler R. Ayliffe G.A.J. (1987) A surface test for virucidal activity of disinfectants preliminary study with herpes virus. J Hasp Infect, 9, 22-29. 

Beekes, M., Lemmer, K., Thomzig, A., Joncic, M., Tintelnot, K., and Mielke, M. (2010). Fast, broad-range disinfection of bacteria, fungi, viruses and prions. /. Gen. Virol. 91, 580-589. 

Solomon, E. B., Fino, V., Wei, J., and Kniel, K. E. (2009). Comparative susceptibilities of hepatitis A virus, feline calicivirus, bacteriophage MS2 and bacteriophage PhiX-174 to inactivation by quaternary ammonium and oxidative disinfectants. Int. J. Antimicrob. Agents 33, 288-289. 

Different mechanisms to explain the disinfection ability of photocatalysts have been proposed [136]. One of the first studies of Escherichia coli inactivation by photocatalytic Ti02 action suggested the lipid peroxidation reaction as the mechanism of bacterial death [137]. A recent study indicated that both degradation of formaldehyde and inactivation of E. coli depended on the amount of reactive oxygen species formed under irradiation [138]. The action with which viruses and bacteria are inactivated by Ti02 photocatalysts seems to involve various species, namely free hydroxyl radicals in the bulk solution for the former and free and surface-bound hydroxyl radicals and other oxygen reactive species for the latter [139]. Different factors were taken into account in a study of E. coli inactivation in addition to the presence of the photocatalyst treatment with H202, which enhanced the inactivation... 

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