Classification and main drugs
The family Paramyxoviridae includes two major subfamilies that differ in their genera composition and surface proteins:
- Subfamily Paramyxovirinae:
- Genus Morbillivirus (measles virus).
- Genus Respirovirus (human parainfluenza viruses 1 and 3, Sendai virus).
- Genus Rubulavirus (mumps virus, parainfluenza viruses 2, 4a, 4b).
- Genus Henipavirus (zoonotic Hendra and Nipah viruses).
- Genus Avulavirus (Newcastle disease virus).
- Subfamily Pneumovirinae:
- Genus Pneumovirus (respiratory syncytial virus — RSV).
- Genus Metapneumovirus (human metapneumoviruses).
In addition to classical pathogens, new dangerous paramyxoviruses were discovered in the late 20th and early 21st centuries. For example, Hendra and Nipah viruses, whose reservoir is bats, cause severe encephalitis in humans and animals. Meanwhile, human metapneumovirus is recognized as one of the major causative agents of respiratory infections in infants.
Virion structure
Paramyxoviruses range in size from 150 to 200 nm.
Inside is a nucleocapsid with helical symmetry containing linear single-stranded negative-sense RNA. The genome is associated with three essential proteins: N (nucleoprotein — maintains structure), L (polymerase — required for replication), and P (phosphoprotein).
Externally, the virion is covered by an envelope (supercapsid). On the inner side, it is lined with a matrix protein (M) that connects the envelope to the nucleocapsid. Two types of glycoprotein spikes are located on the envelope surface:
- Fusion protein (F): mediates virus-cell membrane fusion (requires cleavage into F1 and F2 fragments).
- Attachment proteins: their type depends on the viral genus (e.g., HN — hemagglutinin-neuraminidase, H — hemagglutinin in measles virus, G — glycoprotein in RSV).
Replication cycle
The entire reproduction process of paramyxoviruses takes place exclusively in the cytoplasm of the infected cell.
- Attachment: The virus binds to cellular receptors (sialic acid) via attachment proteins (HN, H, or G).
- Penetration: The F protein fuses the viral envelope with the cell membrane. Interestingly, this same protein can cause adjacent infected cells to fuse, forming giant multinucleated structures called syncytia.
- Synthesis: The viral-encoded polymerase (brought into the cell) synthesizes mRNA to produce viral proteins, as well as a plus-strand template (antigenome). New negative-sense RNAs are then stamped out based on the antigenome.
- Release: New RNAs combine with N, L, and P proteins to form nucleocapsids, migrate to the cell membrane (to the M protein), and exit via budding.
Briefly: answers to topical questions
What specific cellular receptors do measles virus and respiratory syncytial virus use for attachment?
Measles virus and respiratory syncytial virus use different cellular molecules for adsorption onto target cells.
- Measles virus (Measles morbillivirus) — uses the complement cofactor (transmembrane protein CD46) as well as the CD150 molecule.
- Respiratory syncytial virus (Pneumovirus) — attaches via glycoprotein G to cell receptors, which are represented by sialic acid.
What laboratory diagnostic methods are used to confirm measles and mumps?
Serological and molecular genetic methods are used for laboratory confirmation of measles and mumps.
- Measles: serological detection of specific antibodies, including IgM, by ELISA; neutralization tests, complement fixation tests (CFT), hemagglutination inhibition tests (HI), and indirect hemagglutination assays (IHA) are also used. Measles virus RNA is detected by PCR, particularly in nasopharyngeal swabs.
- Mumps: ELISA, CFT, HI, paired sera testing, and PCR are used to detect viral RNA in blood, cerebrospinal fluid, or saliva. Virological diagnostics involve inoculation of cell cultures or chicken embryos followed by virus identification.
What complications of the nervous and reproductive systems are caused by the mumps virus?
Mumps virus can cause complications involving the nervous and reproductive systems.
- Nervous system: serous meningitis and meningoencephalitis.
- Reproductive system: orchitis in males and oophoritis in females. Orchitis can lead to infertility.
Class and exam questions
What is a syncytium and why does it form?
A syncytium is a multinucleated structure formed by the fusion of adjacent cells. In paramyxoviruses, this occurs due to the activity of the viral F protein (fusion protein) on the membranes of infected cells.
Where do paramyxoviruses replicate?
The reproductive cycle of paramyxoviruses occurs entirely in the cytoplasm of the host cell.
What new paramyxoviruses have been discovered recently?
In the late 1990s and early 2000s, Hendra and Nipah viruses (causing severe encephalitis) and human metapneumovirus (affecting the respiratory tract in young children) were discovered.
What else to study on this topic
- Pathogenesis of measles and features of immune response development
- Mechanism of syncytium formation and the use of Sendai virus in laboratories
- The role of reservoir animals (bats) in the spread of Hendra and Nipah viruses
- Characteristics of attachment proteins in different paramyxovirus genera (HN, H, G)
- Respiratory syncytial virus (RSV) as a pathogen of pediatric infections
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