Paramyxoviridae (from Greek para- “by the side of” and myxa “mucus”) is a family of negative-strand RNA viruses in the order Mononegavirales.

After each gene is transcribed, the RNA-dependent RNA polymerase pauses to release the new mRNA when it encounters an intergenic sequence.

Evidence for a single promoter model was verified when viruses were exposed to UV light.

If the viral genome follows a multiple promoter model, the level inhibition of transcription should correlate with the length of the RNA gene.

When paramyxovirus genome was exposed to UV light, the level of inhibition of transcription was proportional to the distance from the leader sequence.

The virus takes advantage of the single promoter model by having its genes arranged in relative order of protein needed for successful infection.

The main hypothesis behind why the viruses are antigenically stable is that each protein and amino acid has an important function.

Thus, any mutation would lead to a decrease or total loss of function, which would in turn cause the new virus to be less efficient.

[11] The human parainfluenza viruses (HPIV) are the second most common causes of respiratory tract disease in infants and children.

Some paramyxoviruses, such as the henipaviruses, are zoonotic pathogens, occurring naturally in an animal host, but also able to infect humans.

Both viruses are contagious, highly virulent, and capable of infecting a number of mammalian species and causing potentially fatal disease.

[13] Novel paramyxoviruses have been discovered from terrestrial, volant, and aquatic animals, demonstrating a vast host range and great viral genetic diversity.

As molecular technology advances and viral surveillance programs are implemented, the discovery of new viruses in this group is increasing.