Croup pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Luke Rusowicz-Orazem, B.S.

Overview

Development of croup results from infiltration of white blood cells through the human parainfluenza virus (HPIV). HPIV expels its nucleocapsid into the recipient cell cytoplasm. The viral transcription then occurs through the HPIV RNA-dependent RNA polymerase. The viral mRNAs are translated into viral proteins, leading to the replication of the genome into the negative-sense RNA strand, which is then encapsidated by the nucleoprotein and used for further transcription and replication. The inflammation response to HPIV occurs from the up-regulation of cytokines and the released Immunoglobulin E inhibiting histamine. The resultant swelling of the larynx, trachea, and large bronchi obstructs the airways, which leads to croup.

Pathogenesis

Development of viral croup results from infiltration of histiocytes, lymphocytes, plasma cells, and neutrophils white blood cells primarily by human parainfluenza viruses (HPIV).^[1].
- HPIV fuses with the white blood cells through the glycoproteins hemagglutinin–neuraminidase and fusion protein.^[2]
- Upon fusion, the HPIV nucleocapsid is expelled into the recipient cell cytoplasm.^[2]
- Viral transcription occurs through virus-specific RNA-dependent RNA polymerase.^[2]
- The viral mRNAs are translated into viral proteins, leading to the replication of the genome into the following:^[2]
  - Positive-sense RNA strand
  - Negative-sense RNA strand
- The negative-sense RNA strand is encapsidated by nucleoprotein and is then used for further transcription and replication.
HPIV infection usually begins at the epithelium in the upper respiratory tract, spreading to the paranasal sinuses, larynx and bronchi.^[3]
The infiltration from HPIV causes inflammation by the up-regulated production of cytokines, localized in the trachea.^[4]
Additionally, HPIV-response Immunoglobulin E (IgE) release has been found to inhibit histamine, contributing to the inflammation that causes croup.^[5]
Of the four different serotypes, HPIV-1 and HPIV-2 are the serotypes that cause croup.^[6]

Transmission

Croup may develop after human parainfluenza virus is transmitted primarily by coughing, releasing infected secretions through respiratory droplets or contaminated surfaces or objects.^[7]

References

↑ Cherry, James D. (2008). “Croup”. New England Journal of Medicine. 358 (4): 384–391. doi:10.1056/NEJMcp072022. ISSN 0028-4793.
↑ ^2.0 ^2.1 ^2.2 ^2.3 Henrickson, K. J. (2003). “Parainfluenza Viruses”. Clinical Microbiology Reviews. 16 (2): 242–264. doi:10.1128/CMR.16.2.242-264.2003. ISSN 0893-8512.
↑ Schomacker, Henrick; Schaap-Nutt, Anne; Collins, Peter L; Schmidt, Alexander C (2012). “Pathogenesis of acute respiratory illness caused by human parainfluenza viruses”. Current Opinion in Virology. 2 (3): 294–299. doi:10.1016/j.coviro.2012.02.001. ISSN 1879-6257.
↑ Schaap-Nutt, Anne; Liesman, Rachael; Bartlett, Emmalene J.; Scull, Margaret A.; Collins, Peter L.; Pickles, Raymond J.; Schmidt, Alexander C. (2012). “Human parainfluenza virus serotypes differ in their kinetics of replication and cytokine secretion in human tracheobronchial airway epithelium”. Virology. 433 (2): 320–328. doi:10.1016/j.virol.2012.08.027. ISSN 0042-6822.
↑ Welliver RC, Sun M, Rinaldo D (1985). “Defective regulation of immune responses in croup due to parainfluenza virus”. Pediatr. Res. 19 (7): 716–20. doi:10.1203/00006450-198507000-00016. PMID 2991841.
↑ Baron, Samuel (1996). Medical microbiology. Galveston, Tex: University of Texas Medical Branch at Galveston. ISBN 0-9631172-1-1.
↑ “Human Parainfluenza Viruses | Clinical Overview of HPIVs | CDC”.

Overview