Properties of Orthomyxoviruses and Paramyxoviruses

Influenza virus, the causative agents of seasonal flu (and pandemic flu) is the deadly contagious virus. It is the only virus of medical importance of the family Orthomyxoviruses. Paramyxoviruses include most important agents of viral respiratory tract infections notably Respiratory syncytial virus (RSV), Measles, Mumps and Parainfluenza virus.

Some of the most important characteristics of these two families are:

Properties Orthomyxoviruses family Paramyxoviruses family
 Genera  Only one i.e. Orthomyxovirus (influenza virus)  3 genera; Paramyxovirus (parainfluenza viruses and mumps virus); Pneumovirus, (respiratory syncytial virus); and Morbillivirus (measles virus).
 Structure of the virion    
 Capsid helical helical
Envelope present  present
 Virion size  smaller ( 80 to 120 nm in diameter.)  larger (150-300 nm in diameter).
 Surface spikes

Hemagglutinin (H) and Neuraminidase (N) in different spikes.

The viruses attach to permissive cells via the hemagglutinin subunit, which binds to cell membrane glycolipids or glycoproteins containing N-acetylneuraminic acid, the receptor for virus adsorption.

Hemagglutinin (H) and Neuraminidase (N) in same spikes

Parainfluenza virus has both H and N activities, Measles lacks Neuraminidase activity and RSV lacks both H and N activities.

 Genome Single stranded (SS), negative sense, segmented RNA
(influenza A virus has 8 segemented genome)
 single stranded (SS), negative sense, non-segmented RNA
 Antigenic variation  Antigenic shift (through genetic reassortment) can occur when a host cell is infected simultaneously with viruses of two different parent strains and antigenic drift.

Antigenic drift only.

Measles and Mumps has only one serotype so confers life long immunity.

Virion polymerase

#Remember;  negative strand RNA virus has to do this.


Virally encoded RNA-dependent RNA polymerase transcribe and replicate the SS negative sense RNA.


Virally encoded RNA-dependent RNA polymerase transcribe and replicate the SS negative sense RNA.

Giant cell formation No


paramyxoviruses has the capacity to induce syncytia (multinucleated giant cells) formation .
Multinucleated giant cells originate from fusion or division of mononuclear cells.

Diseases Febrile illness of the upper and lower respiratory tract (flu); pneumonia is the most common serious complication.

RSV and parainfluenza viruses cause mild or severe upper and lower respiratory tract infections,

Mumps cause characteristics swelling of parotid glands and other inflammations (pancreatitis, meningitis, encephalitis, orchitis or oophoritis)