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24.2 Virion properties

Paramyxoviruses are pleomorphic and about 150- 350 nm in diameter. Virions are enveloped and covered by surface glycoproteins. The genome consists of ssRNA of negative polarity and 13-19 kb in size. The RNA at 3' end is not polyadenylated and 5' end of the RNA is not capped. With the exception of family Pneumovirinae , the genome size of the viruses are the even multiples (also called as rule of six) of six. The viral N protein binds effectively with the six nucleotide of the genomic RNA for its effective replication.

 

24.3 General Concepts

• I. The Paramyxoviruses are the leading cause of respiratory disease in children; general illnesses include croup and inflammation of respiratory tract.

II. Paramyxoviruses share similar features; they contain a bilayer envelope containing spikes, have a helical symmetry and contain a negative stranded ssRNA genome. An RNA-dependent RNA polymerase (RDRP) is carried by the virus particle in order to perform the replication of the RNA genome.

III. Replication of the virus takes place in the cytoplasm and are released by the budding process.

IV. Virus antigens are confined in the lipid envelopes (spikes) and within the nucleocapsid core.

V. The viruses have a wide variety of host range that includes humans and primates.

VI. Viruses produce syncytia upon infection to susceptible cells by fusion and later cell lysis.