Since viruses have characteristics of both living and non-living objects with very simple organization as very minute particles of nucleo- protein , it may be concluded that the primitive life was like viruses .Their posession of the characteristics of both the living and non-living objects suggests that non-living inorganic substances evolved into organic substances before the origin of the primitive life.Further , since viruses may synthesize DNA and protein in the host cell , they may be taken as the first forms of life as per Oparin's explanation of the origin of life .However , the modern view about the viruses is that they have originated from the early existing cellular form of life and therefore , they can not be taken as the early primitive forms of life .Moreover,C.F.Luria [1971] ,the noble prize winner , has called them bits of heredity , looking for a chromosome. ECONOMIC IMPORTANCE OF VIRUSES Viruses are responsible for several diseases of plants and animals. In plants , they cause leaf roll of potato , rugose mosaic of potato, leaf curl of tomato , leaf curl of papaya ,mosaic of papaya ,yellow ringspot of lady finger ,mosaic of tobacco ,etc. In man ,the viruses cause small pox ,influenza,common cold ,mumps ,measles ,rabies,poliomyeletis [polio],etc. The HIV [Human immuno deficiency virus] cause AIDS [acquired immune deficiency syndrome ] which drastically cut the life of men and women .Besides , the viruses are supposed to cause cancer and tumor formation.
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