Virus is from the Latin word for poison, and paramyxovirus is a blended word that means something like “beyond slime virus.” Interestingly, the "paramyxo" part is from the Greek. Scientists haven't determined the origins of viruses, or even whether they can even be classified as living beings.

A virus is an entity, much smaller than any bacteria. Many can only be seen with an electron microscope. A virus doesn't have its own metabolism and can only reproduce inside of a living cell, which is why scientists aren't sure it's truly alive. Viruses infect all living things, including bacteria, and there are millions of types. Virus particles are called virions. They're made of DNA or RNA, which carry their genetic material, a protective coat of protein, and sometimes another coat of lipids. Viruses have developed a myriad number of ways to be spread from one host to another. Viruses like the one that causes measles are transmitted through coughing. Sometimes a plant or animal’s immune system will destroy an invading virus, and sometimes immunity is acquired through a vaccine. Both sorts of immunity can destroy the measles virus. Antibiotics don’t work with viruses, for antibiotics were made to defeat bacterial infections.

Viruses are classified into families and orders, much like other life forms. A paramyxovirus is a virus from the paramyxoviridae family. The paramyxoviridae family belongs to the mononegavirales order and the morbillivirus genus. 

The paramyxovirus is a single strand RNA virus. This means the genetic material of this virus is ribonucleic acid or RNA. It’s also called a ribovirus and is classified in the same group of viruses that cause diseases like Ebola and Marburg fever, rabies, varieties of rinderpest, canine distemper, Borna disease, Lassa fever, mumps, and viruses that cause various types of flu. There are about 40 viruses in the paramyxoviridae family. 

A virus of the paramyxoviridae species is spherical, with its single strand of RNA enclosed within an envelope with a diameter of about 150 nanometers. It’s surrounded by fusion proteins, hemagglutinin-neuraminidase, and matrix proteins. Attached to the RNA are phosphoproteins, which are proteins that bond to phosphoric acid and polymerases, enzymes found in RNA that helps it to replicate. The virus bonds to receptors on the host cell, fuses with the cell's membrane, invades it with its strand of RNA, and begins to replicate and form buds. These buds break off as pieces of virus, and go on to infect other cells. If the virus isn't defeated by the immune system, a case of measles will develop.