LIFE STYLE OF VIRUSES

The viruses become active and   reproduce within the cells  of other organisms  but they remain inert outsides the cells ,showing  no activity .Evidently ,they are obligate parasites .While  infecting  or attacking  other organisms  they show host  specificity .In general ,viruses are  specific in  attacking hosts, a particular  virus attacks a particular host ,choosing one and the same  organ  or closely  related organs .However  ,a few viruses ,for example ,rabbies virus and vaccinia virus  can infect man as well as cows  ,sheep,rabbits,monkeys ,rat ,mice ,guinea pigs,hamsters ,chick embryos ,etc.                                                                                                             In certain  instances  ,there is much  precision in host specificity ;there are some viruses  which attack only a particular  kind of  tissue .For example ,viruses of pox  and measles attack  and tomato-wilt virus attacks only leaves of tomato .Certain viruses ,attack bacteria infect  only male cell  but not the female cell.                                         Many viruses remain concealed within the host cell for a very  short to a long  period without  showing  any adverse effect on the host .Sch viruses are  known as latent virus .Some viruses that infect  two hosts ;remain  latent  in one host  but become virulent  in another .For  example  a virus known to  exist and  reproduce  in potato  without  showing  any pathogenic  symtoms .become  effective on transfer to tomatoes .                                                                                                                                                             Nomenclature of Viruses                                                                                                                           It  appears that the virus  nomenclature  is more arbitrary  and in confused  state.Instead of  adopting  the binomial  nomenclature ,viruses are named after the disease they cause ,for  example ,pox virus,polio  virus , tobacco -mosaic virus ,tomato wilt virus ,cherry-ringspot virus ,etc ., or  after the tissue or organ  they attack ,for example ,the ,the adeno-virus  that attacks adenoids .In certain  cases ,the naming is  more arbitrary ,for example ,the polyoma virus is  named so because it is  able to cause  numerous kind of tumors .The code number are often  used to name  the bacterial viruses .For example ,viruses that attack the  intestinal bacteria,Escherichia coli have  been  named  by using  T with  numeral  as suffix from 1to 7 [T,toT1]  .