1. According to the famous scientist Pleczar, any non-cellular microscopic infectious entity composed of proteins and nucleic acids and capable of multiplying only in living host cells is called a virus.
2. According to scientist Bawden (1947), viruses are obligate parasites invisible to the naked eye.
3. According to scientist (A. Lwoff (1952), Virus is a virus.
4. According to scientist George (1983), viruses are microscopic harmful substances composed of nucleoprotein core and protein coat, which cause disease in plants and animals. Dr. Siddiq Publications