Overview

Respiratory syncytial virus (RSV) is a common respiratory viral infection that causes mild cold-like symptoms in the winter.¹ RSV belongs to the genus Orthopenumovirus, the same family where human RSV, bovine RSV and murine pneumonia virus also belong.² RSV is a global virus that infects the lower respiratory tract of all age groups.² Patients with RSV recover from the infection within a week without any medical treatment required but there are some risk groups where RSV may cause complications.¹ In infants and younger children, initial RSV infection can cause severe bronchiolitis which can be fatal. Whereas, infection in older children and adults causes symptoms similar to those seen in mild to severe respiratory infections such as coughing, sneezing, or fever.² RSV also poses a threat to older adults, and most hospitalisations caused by RSV are in patients aged over 65 years of age.²

RSV is a viral infection that affects the respiratory system but its impact on adult fertility is not fully understood due to limited data.³ It is known that RSV, like all viral infections, causes systemic inflammation, disrupts the normal immune system and causes hormonal disruptions, which could potentially cause and impact fertility in adults. This article will discuss whether RSV has an impact on fertility in adults. 

Understanding RSV

Genetic overview

RSV is a single-stranded RNA virus containing 10 genes which encode 11 proteins.³ Protein F and protein G are two important surface proteins that play an important role in viral infection as they are directly involved in the virus attaching to host cells.³ RSV has a lipid bi-layer envelope that covers and protects a ribonucleoprotein.⁴ There is one serotype of RSV that is further classified into two strains: RSV-A and RSV-B depending on the structure of the surface proteins.⁴ RSV-A is more prevalent and is more commonly circulated within the population compared to RSV-B, but there is no clinical difference between the strains.³

Symptoms

Individuals infected with RSV usually experience symptoms 4 to 6 days after infection, and symptoms usually appear in stages rather than all at once. These can include:⁵

• Coughing and wheezing
• Sneezing
• High fever
• Appetite decreases
• Runny nose

Symptoms will depend on the age of the patient, with older children and adults experiencing milder symptoms whilst younger children and infants experience more severe symptoms. Morbidity and mortality also increase for high-risk patients including:⁴

1. Premature infants 
2. Patients who are immunocompromised such as HIV patients or cancer patients undergoing chemotherapy
3. Patients with existing medical conditions such as cardiac or pulmonary disease
4. Elderly individuals

Transmission

RSV is spread through droplets when an infected person coughs or sneezes and the droplets containing the virus enter an individual through the eyes, nose or mouth.⁵ RSV is also spread through contact, either by direct contact when touching an infected person or by indirect contact, such as touching surfaces that have come in contact with the virus and then touching your face.⁵

The first infection usually occurs during infancy, with the majority of children being infected before they are 2 years old.⁵ However, repeat infection is very common, with infections occurring at any age.⁵

RSV outbreaks occur regularly every year. Specifically in temperate climates, RSV infection peaks during the winter,¹ whilst in tropical climates there is no noticeable difference between the seasons.⁴ In the UK, RSV infection usually begins in October, and peaks in December.¹

Prevalence in adults

One study from 1975 to 1995 found an RSV prevalence rate of 7%, with the majority of patients being between 18 and 40 years of age.³ RSV infection in adults was more common in females at 65% compared to male patients.³ More than 80% of adult RSV patients show symptoms with 75% having upper-respiratory symptoms such as coughing, sneezing and a runny nose, whilst 25% showed lower respiratory symptoms like wheezing and persistent coughing.³ Additionally, more than 50% of adult patients reported high fever as a symptom.³

Outcome and complications of RSV infection

The prognosis of RSV infection is good, with the majority of patients recovering without any medical treatment within a week as the symptoms are mild to moderate.⁴ However, for individuals with weakened immune systems and those who are at high risk, RSV infection could cause complications requiring treatment.⁴ Complications in adults can include pneumonia or lung infections.³ RSV can also worsen existing medical conditions such as asthma, chronic obstructive pulmonary disease (COPD) and heart diseases such as congestive heart failure.⁵

However, there is limited data available describing RSV in the adult population.

Mechanisms of RSV impact on reproductive health

The general impact of viral infection on fertility

Viral infection causes an immune response that causes a cascade of responses that can have lasting effects on the body and can impact the reproductive system. 

Inflammation is the initial, first-line defence initiated by the immune response when a virus infection is detected. However, inflammation poses a risk to fertility.⁶ Systemic inflammation can impact reproductive organs such as the uterus, placenta, and cervix as inflammation can lead to tissue scarring.⁶ Inflammation can also directly impact ovaries and affect the health of the eggs. It can also affect testicular function in males, impacting the health of sperm.

Viral infection leads to pro-inflammatory cytokines being released by the immune system, which causes inflammation to occur around the body, including the reproductive organs. Chronic inflammation, when inflammation lasts for a prolonged period, is a response to viral infection, especially when the virus is still present in the body or when the immune system has become disrupted. This can lead to tissue damage to organs in the body, including the reproductive system, and it could lead to issues with fertility. 

The specific mechanism by which RSV may affect fertility

RSV as described above is a viral infection that mainly infects and targets the respiratory tract but like all viruses, there is a possibility that RSV can impact fertility. There is minimal data available on how RSV affects fertility, but knowledge of how other viruses impact fertility and the reproductive system can be used to infer the effects of RSV. 

RSV is spread through viral droplets and usually affects the upper respiratory system but, systemic infection, where the virus moves from its usual infection, is common.⁴ RSV is able to move from its usual infection site in the upper respiratory tract down to the lower respiratory tract⁴ and there has been evidence of RSV isolated from the liver, cerebrospinal fluid and myocardium.⁷ If RSV is found in the liver, it could also be found in the reproductive system where it can cause direct tissue damage, impairing fertility in adults. 

RSV could also affect fertility indirectly, through systemic inflammation. As described earlier, RSV can cause inflammation in the lungs and this causes direct damage to the lungs, leading to pneumonia where immediate medical treatment is required. Systemic inflammation where the entire body is affected can lead to infertility if the reproductive system is affected. 

Evidence from clinical studies

Evidence and data for RSV in the adult population are limited as most research is based on the first RSV infection in infants and young children.³ Data for how RSV affects fertility is even more limited,3 which is worrying as the lack of existing information could potentially lead to infertility in adults. Knowing if there is a direct link between RSV and fertility can improve understanding of how viral infection can impact fertility and improve the care available to patients.

The lack of evidence for understanding how RSV affects fertility is due to the limited and poor surveillance of RSV in the adult population.³ As the symptoms of RSV infection in adults are usually milder, adults may not seek medical help and health authorities are not notified. 

More data is needed to understand the disease burden and improve prevention of RSV infection. Having gaps in our knowledge of RSV makes us more vulnerable, and more research is needed to cover the gaps and to prepare for and treat RSV infection. 

Potential long-term effects

RSV infection could potentially lead to:

• Chronic health issues due to inflammation caused by a dysregulated immune system
• Direct impact on the reproductive system, impairing the fertility in adults

Conclusion

RSV is a common respiratory viral infection that causes mild cold-like symptoms in the winter. RSV is a global virus that infects the respiratory tract of all age groups. Patients with RSV recover from the infection within a week without any medical treatment required. Individuals infected with RSV usually present with symptoms, such as coughing, sneezing and fever, 4 to 6 days after infection. 

RSV, like all viral infections, causes systemic inflammation, disrupts the normal immune system, and causes hormonal disruptions, which could potentially cause and impact fertility in adults. However, the evidence and data for RSV in the adult population is limited and the data for how RSV affects fertility is even more unlimited. To better understand the role of RSV in the reproductive system and its impact on adult fertility, more research and data are needed before any conclusion can be made.