Respiratory Syncytial Virus
Respiratory Syncytial Virus is a single-stranded RNA virus that has a negative sense of non-segmental RNA. It is an enveloped virus and has many proteins, which helps to perform various functions like Attachment to the host cell, the fusion of host cell membranes, ion channels, viral assembly, RNA binding, transcription, phosphorylation, immune evasion etc.
The virus may have a spherical or filamentous structure – it is pleomorphic.
RSV belongs to the mononegavirales order, paramyxoviridae family and Pneumovirinae subfamily. It is related to other common cold viruses, like human Metapneumovirus and Parainfluenzavirus..
RSV is one of the commonest causes of respiratory illness in children, especially infants. The immunity conferred is partial; hence reinfection may occur. Infection in adults tends to be milder. However, certain risk groups could be affected by severe infection.
The RSV infection is a disease of the winter. Peak is usually in December.
There are certain groups of patients who are at a higher risk of severe disease.
The transmission of RSV is mainly droplet mediated. The infectious droplets may travel approximately 1-2 metres and land on the mucous membrane of the vulnerable people, subsequently infecting them.
Those particles which land on other surfaces may remain infective for up to 24 hours but could be a much shorter duration depending on the surface. Anyone touching these surfaces may carry the virus to their nose/mouth or eye to infect themselves (unless they wash their hands before touching their face).
After the virus comes in contact with the mucous membrane, it may take 3-5 days to develop the disease. All the people who are exposed may not develop the disease. In some cases, our immunity may clear the virus. Once a person is infected, they may remain infectious for approximately 3-5 days. Some groups of patients, like children, immunocompromised or those with severe diseases, may remain infectious much longer (up to 4-6 weeks).
Aerosol generating procedures: certain medical procedures may generate smaller infective particles. In these cases virus can be transmitted more than 1-2 metres, and a higher level of protection is required (respiratory protection)
RSV may affect:
Upper respiratory tract causing – rhinorrhoea, nasal congestion, sore throat, cough.
Lower respiratory tract causing – tachypnoea, wheeze, shortness of breath, apnoea, hypoxia
Other symptoms – fever, malaise, difficulty feeding, otitis media.
It takes about 2-4 days for the sign and symptoms to progress.
RSV start replicating in the nasopharynx and eventually affect the bronchioles, causing bronchiolitis. The infection result in an inflammatory response – infiltration of the inflammatory cells, submucosal oedema, necrosis of the epithelial cells. The thickening of the wall and increased mucous with debris reduces the bronchioles’ diameter and forms mucous (+debris) plugs.
This narrowing of the bronchus may cause wheeze, air trapping or collapse of the pulmonary alveolus.
Apart from RSV, human metapneumovirus, parainfluenza virus 3 and flu are relatively common causes of bronchiolitis. Other respiratory viruses can also cause bronchiolitis. They also cause coinfection with RSV.
Diagnosis is clinical. It is not recommended to test for RSV routinely.
Direct fluorescent antibody testing and PCR can be used to test for RSV. Viral culture is the gold standard, but it is time-consuming, labour intensive and not readily available.
Treatment:
Treatment is mainly supportive.
Palivizumab
It is an RSV-specific humanized monoclonal antibody. Palivizumab is used to protect
against RSV in at-risk patients and has been shown to decrease hospitalisation in this group. It is currently part of a UK-wide immunisation schedule as per guidance issued by the Joint Committee on Vaccination and Immunisation (JCVI) in 2010. The age group and specific recommendations could be found in the
Greenbook Chapter 27a and
PHE document ( https://www.england.nhs.uk/wp-content/uploads/2020/10/C1338-palivizumab-rps-update-june-2021.pdf )
