Wild-Type Parainfluenza Virus Type 4B

Wild-type human parainfluenza virus type 4B (HPIV-4B) is a respiratory pathogen belonging to the Paramyxoviridae family that primarily infects infants, young children, and immunocompromised individuals. The virus is transmitted through direct contact with infected respiratory secretions or aerosolized droplets. Upon entry into the body, the virus attacks epithelial cells lining the upper and lower respiratory tracts, binding to sialic acid receptors via its hemagglutinin-neuraminidase (HN) glycoprotein. Viral replication leads to cytolysis and local inflammation, resulting in a range of symptoms, ranging from mild cold-like symptoms (such as runny nose, cough, and fever) to severe complications such as croup, bronchiolitis, or pneumonia. Although HPIV-4B is associated with a lower incidence of severe illness compared to HPIV-1 or HPIV-3, its role in pediatric hospitalizations is increasingly recognized. Immune responses are generally virus-type specific, but reinfection can occur due to partial cross-protection between different HPIV serotypes.

HPIV-4B has a nonsegmented, single-stranded, negative-sense RNA genome of approximately 15,000 nucleotides, encapsidated by a nucleoprotein (N) to form a helical ribonucleoprotein complex. The viral envelope is studded with two key glycoproteins: the fusion protein (F), which mediates host cell entry by inducing membrane fusion, and the HN protein, responsible for receptor binding and neuraminidase activity. The matrix protein (M), located beneath the envelope, provides structural integrity and facilitates viral assembly. The genome encodes six major proteins in the order 3′-N-P-M-F-HN-L-5′, of which the polymerase (L) and phosphoprotein form an RNA-dependent RNA polymerase complex. Notably, RNA editing of the P gene produces accessory proteins (such as V and D), which modulate the host immune response.