Paramyxoviruses

■ This family includes the genera:

■ Parmyxovirus with the parainfluenza viruses. 8| ■ Rubulavirus with the mumps virus.

^B ■ Morbillivirus with the measles virus.

■ Pneumovirus with the respiratory syncytial virus (RS).

■ Nonclassified paramyxoviruses (Hendra, Nipah).

The clinical manifestations include respiratory infections (parainfluenza, pseudocroup, mumps, RS, Nipah, Hendra), parotitis, and infections of other glandular organs (mumps), exanthem (measles), and CNS infections (mumps, measles, Nipah, Hendra).

Prevention: live vaccines are used to protect against measles and mumps; no immunoprophylactic tools are available against the other paramyxo-viruses. ■

Pathogen. The family Paramyxoviridae is a heterogeneous one, both in its biology and pathogenic properties. It is divided into two subfamilies:

■ Paramyxovirinae with the genera:

— Paramyxovirus with the human pathogen species parainfluenza virus types 1 and 3.

— Rubulavirus with the mumps virus and parainfluenza virus types 2 and 4.

— Morbillivirus with the human pathogen measles virus and several zoo-pathic species that cause severe respiratory infections in various animal species (dogs [canine distemper], cats, cattle, seals, dolphins, turtles).

— The nonclassified, closely related zoopathic and human pathogen Hendra and Nipah viruses.

■ Pneumovirinae, genus Pneumovirus, probably with several types of RS

virus (respiratory syncytial virus).

Structure of the Paramyxoviruses

All paramyxoviruses have a similar structure (Fig. 8.16). They are pleomorphic. The smallest forms are 120-150 nm in size (with the exception of the somewhat smaller RS virus). They also possess an envelope that encloses the nucleocapsid. The genome consists of a continuous, single-stranded antisense RNA. The envelope is derived from the cell membrane. Various viral proteins are integrated in the envelope, visible in the form of spikes. The generic taxons are based on these spikes: parainfluenza and mumps viruses have two types of spikes, one containing the hemagglutinin (i.e., possessing hemagglutination activity) coupled with neuraminidase (HN protein), and the other the so-called fusion (F) protein, responsible for fusion of the envelope with the cell membrane. Measles viruses contain no neuraminidase and pneumoviruses possess only the F protein.

— Parainfluenza Virus

Fig. 8.16 The envelope here is torn open, allowing the helical nucleocapsid (NC) to escape. NP: primary nucleoprotein helix (TEM).

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