Viruses physical agent effects

The effect of chemical and physical agents on viruses 9 The problems of viral chemotherapy... 

Prions are responsible for the so-ealled slow virus diseases, a distinet group of unusual neurologieal disorders. They are believed to be markedly resistant to inactivation by many ehemieal and physical agents but because they have not been purified, it is at present diffieult to state whether this is an intrinsic property of prions or whether it results fkm the proteetive effect of host tissue present. Certainly very high coneentrations of a bioeide aeting for long periods may be necessary to produee inactivation. 

Normal healthy people are generally not free from the action of mutagens, such as chemicals, physical agents, viruses, lifestyle habits including smdring and alcohol consumption. There is also scanty information on the variability of spontaneous rate of chromosomal aberrations in lymphocytes, which establishes the uppo level of normal variability in adults and children, so that a positive effect of exposure can be recognized more exactly. It is not clear at all how national rates can be different, or how urban or rural lifestyle (or environment) may affect the somatic cell aberration yield. 

The physical process of filtration is rather effective in removing pathogens from water. During the 1800s, before chlorine came into widespread use, filtration with simple sand filters employed in just a few cities cut down significantly on the incidence of waterborne cholera in those cities. With modern membrane technology (see Section 5.10), ultrafiltration can remove even viruses from water. Small amounts of chlorine or chloramines (see Section 5.11.3) can be added to maintain sterile water in distribution systems, but much less of these agents are required for membrane-filtered water than are required for total disinfection. 

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