Bronchiolitis and collapse are characteristic of RS pneumonia
Case 280
【Progress】
Both infants were transported to other local hospitals near their houses where they were scheduled to get more extensive service.
【Discussion】
The term of ‘syncytial’ of respiratory syncytial (RS) virus originates from merges of infected cells by this virus, namely syncytium. RS viral infection makes infected cells make enlarge and fuse together, forming a giant cell under microscopic examination (1).
RS virus is an RNA virus including genome and mRNA with envelope. When RS virus invades a cell, genome replicate in cytoplasm and mRNA create a number of envelope protein in endoplasmic reticulum and several proteins in Golgi complex to attach cell membrane for RS virus budding from cell membrane (2).
In human, there are several defense mechanisms: first, mucin and Ig A; second, macrophages and killer cells called innate immune, inducing inflammation; third, antibody production called acquired immune, dendric cells that play a role of getting antigen information from macrophages and to convey it to helper T cells. Helper T cells stimulate killer T cell for cytocide and B cell for antibody production: cytokine storm occurs when one to three mechanisms are not successful to control pathogen attacks. In RS virus infection, immune mechanisms from first to third can work inducing its infection being left under control (3).
The symptoms are corresponded to common cold: congest at age of nose, cough, low grade fever and sore throat. RS virus infection occurs most ≤ 2 years. Most kids recover within 7 days or 10 days. People get repeated infections of RSV and acquire to produce antibody constantly via acquired immune system. But it can be severe in infants with risk factors or aged persons (4-6).
Radiologic findings of chest CT of RSV infection depict intralobular granules indicative of bronchiolitis and collapse of segmental or subsegmental indicative of bronchitis. When infant bronchus is small, it causes collapse of subsegment or segment or lobar collapse. When infant bronchus grows wide, it causes bronchitis, inducing collapse of segmental or lobar area. Histologic findings reveal that the bronchial lumen is completely or partially occupied by mucus an debris composed of necrotic epithelial cells, immune cells of macrophages, lymphocyte and neutrophils, causing bronchiolitis (1, 4-6).
Before COVID-19, RSV infection usually occurred in winter and in 2020 when COVID-19 prevailed worldwide, the number of patients with RSV infection marked decreased. But RSV resurged on spring to summer 2021 and RSV markedly resurged on summer 2022 although its reason is not clarified. Simultaneous infection of RSV and COVID-19 is unexpectedly rare, although its reason is not well-known.
In our cases, RSV and COVID-19 were infected in Case 1, an 1 year-infant whose CT showed bronchiolitis and no ground glass attenuation indicative of reflecting RSV infection but not COVID-19 and pure RSV was infected in Case 2 whose CT showed segmental collapse of S5 and S7 .
【Summary】
We presented two infants of 1 year and 4 months infected with RSV plus COVID-19 and RSV alone, respectively. Chest CT showed intralobular granules and bronchopneumonia in Case 1 and segmental collapse of right S5 and left S7 in Case 2. The symptoms of RSV infection are those of common cold. RSV infects most infants of within 6 months after birth and as growing, repeated RSV infection makes antibody reproduce, being able to tolerate RSV infection. It is borne in mind that RSV causes bronchiolitis which appears intralobular nodules or thicken broncho-vascular bundle in infants and segmental or lobar collapse in smaller infants on chest radiograph or CT.
【References】
1.Respiratory syncytial virus. From Wikipedia, the free encyclopedia
2.Battles MB, et al. "Respiratory syncytial virus entry and how to block it". Nature Reviews. Microbiology. 2019; 17 (4): 233–245.
3.Soudani N, et al. Prevalence and characteristics of acute respiratory virus infections in pediatric cancer patients. J Med Virol. 2019 Jul;91(7):1191-1201
4.Battles MB, McLellan JS. "Respiratory syncytial virus entry and how to block it". Nature Reviews. Microbiology. 2019; 17 (4): 233–245.
5.Borchers AT, et al. "Respiratory syncytial virus--a comprehensive review". Clinical Reviews in Allergy & Immunology. 2013; 45 (3): 331–379.
6.Griffiths C, et al. "Respiratory Syncytial Virus: Infection, Detection, and New Options for Prevention and Treatment". Clinical Microbiology Reviews. 2017; 30 (1): 277–319.
7.Coultas JA, et al. "Respiratory syncytial virus (RSV): a scourge from infancy to old age". Thorax. 2019; 74 (10): 986–993.
2022.10.25