|Measles virus particles, animation. Viruses are non-cellular particles that invade living cells in order to reproduce. Viruses consist of a core of genetic material surrounded by a protein coat and surface proteins. Once inside a cell, they use the cell machinery to replicate themselves. The release of the replicates usually destroys the host cell. This virus, from the Morbillivirus group of viruses, consists of an RNA (ribonucleic acid) core surrounded by an envelope studded with surface proteins that are used to attach to and penetrate a host cell. Measles is a highly infectious itchy rash with a fever. It mainly affects children, but one attack usually gives life-long immunity.