Influenza virus, the causative agent of seasonal flu (and pandemic flu) is a deadly contagious virus. It is the only virus of medical importance in the family Orthomyxoviruses. Paramyxoviruses include the 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) | Three genera; Paramyxovirus (parainfluenza viruses and mumps virus); Pneumovirus, (respiratory syncytial virus); and Morbillivirus (measles virus). |
| 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 the 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 segmented genomes) | 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 lifelong immunity. |
| Virion polymerase #Remember; negative-strand RNA virus has to do this. | yes Virally encoded RNA-dependent RNA polymerase transcribes and replicates the SS negative-sense RNA. | yes Virally encoded RNA-dependent RNA polymerase transcribes and replicates the SS negative-sense RNA. |
| Giant cell formation | No | yes paramyxoviruses have the capacity to induce syncytia (multinucleated giant cells) formation. Multinucleated giant cells originate from the 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) |
References
- Enders G. Paramyxoviruses. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 59. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8461/
- Couch RB. Orthomyxoviruses. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 58. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8611/