Viruses are nucleoproteins. The genetic material is protected with in a protein coat. The protein coat is called capsid. The capsid consists of a number of subunits called capsomeres. The capsids are arranged in helical, polyhedral or geometric form. The genetic material, i.e., DNA or RNA may be single-stranded or double-stranded.
e.g., Poliomyelitis, rinderpest, dengue, potato mosaic, etc.