Overview of RSV

Respiratory syncytial virus (RSV) is a common respiratory virus that usually manifests as mild, cold-like symptoms. Although most people can recover within one or two weeks, RSV can have a serious impact on an individual's health. Specifically, infants and the elderly are more susceptible to the virus, with the infection leading to the need for hospitalisation. Therefore it is crucial to be informed about RSV, its symptoms, prevention, treatments, and how our genes can play a role in all of the above. This article will focus on exploring how genetics influences the susceptibility to RSV.

Epidemiology

RSV affects approximately 64 million people across the globe and causes 160,000 deaths each year. In the United States alone, according to the Centers for Disease Control and Prevention (CDC), RSV leads to an estimated: 

• 2.1 million hospital visits among children younger than 5 years old (non-hospitalisation)
• 58,000-80,000 hospitalisations among children younger than 5 years old and 60,000-160,000 hospitalisations among adults 65 years and older
• 6,000-10,000 deaths among adults 65 years and older and 100–300 deaths in children younger than 5 years old
  

Risk factors

The people most susceptible to RSV are usually those  who present one or some of the following characteristics: 

• Age (premature and very young infants, people over 65 years old)
• Chronic obstructive pulmonary disease (COPD) 
• Congenital heart disease
• Congestive heart failure
• Severe cystic fibrosis patients
• T cell immunodeficiency
• Weakened immune system
• Neuromuscular disorders (e.g. difficulty swallowing or clearing mucus secretions)
• Other underlying medical conditions
• Living in a nursing home or long-term care facility

Transmission

People commonly get RSV as an infant or toddler for the first time. Of course, repeat infections can happen throughout one's life. Most children get infected with RSV by the age of 2.

RSV can be spread between people if a person coughs or sneezes. This way, virus droplets enter your body through your eyes, nose, or mouth. Another way you can get infected is through direct contact with the virus like touching a surface with the virus on it and then touching your face. The virus can survive on hard surfaces, for example, tables for many hours, and on soft surfaces, such as tissues for shorter amounts of time. The most infectious RSV season usually starts in the autumn and peaks in the winter.

When a person is infected with RSV, they can be contagious for 3 to 8 days. They can be contagious even before they start displaying symptoms of the infection, specifically a day or two earlier. People falling in the "at risk" category can continue to spread the virus, even after they have stopped presenting symptoms, for as long as 4 weeks. This may be the case as the body has not completely eliminated the virus although it has gotten the infection under control to prevent its worsening. 

Symptoms and severity of infection

RSV infects the lungs and breathing passages, hence why its symptoms can be mistakenly taken for a cold. The symptoms of an RSV infection can take up to 4 to 6 days to manifest and might not appear all at once. These may include:

• Coughing
• Sneezing
• A congested or runny nose
• Fever
• Wheezing
• Decreased appetite
• Sore throat
• Headache
• Blush tint to your skin
• Shortness of breath

In very young infants, the symptoms can manifest as breathing difficulties, irritability, decreased activity, and even apnoea (pauses while breathing for more than 10 seconds). 

RSV can also lead to more severe lung diseases like bronchiolitis (inflammation of the small airways in the lung) and pneumonia (inflammation of the air sacs in the lung). Moreover, already present chronic health problems may worsen, such as asthma.

Prevention and treatment options

The majority of people who get infected with RSV will experience mild symptoms and most likely recover in a week or two.

Prevention

The CDC recommends the immunisation of people at risk. Immunisation can happen through vaccination, antibody doses, and personal hygiene.

Adults 60+ years old

If you are 60 years or older, consult with your doctor to see if RSV vaccinations are suitable for you -  all it takes is a single dose! The best time to get vaccinated is considered to be late summer or early autumn as that is when the peak season starts.

Infants and toddlers

For babies, there are two options to be protected from RSV.  Typically 32-36 weeks into the pregnancy, and during the RSV peak season, the mother can get vaccinated for RSV. The other option is if the baby is born during or when entering their first RSV season, and is younger than 8 months,  they can receive antibody products. If the mother gets vaccinated and the baby is born after 14 or more days after her vaccination, it is most likely that the baby will not need an RSV immunisation, unless a doctor  judges that it is needed.

In addition, it is recommended that children of 8 to 19 months, belonging to a risk group and entering their second season of RSV, should also get a dose of RSV antibody.

Everyone can help minimise the spread of RSV and protect those at risk by practising good hygiene, covering their cough or sneeze, and cleaning their hands and surfaces. Recycling or purifying indoor air, staying at home when sick, physical distancing, getting tested, and using protective equipment like masks, can also help prevent the spread of the virus. 

Treatment

Antiviral medication is not usually recommended to combat the infection. However, RSV can progress into a serious illness in some patients. Therefore, there are a few options you can follow to relieve symptoms and aid your immune system in the fight against the virus:

• You can reduce and relieve the fever and pain with over-the-counter medication such as ibuprofen. It is important to note that aspirin is not recommended for child consumption. You can also try nasal drops as they can help with congestion
• Drinking an adequate amount of fluids to prevent hydration can significantly help
• Stay away from cigarette smoking as it can aggravate the symptoms
• A humidifier or vaporiser could help by moistening the air to ease congestion and coughing
• Consult your doctor  before acquiring non-prescribed medication, especially when it concerns children, as some ingredients or the incorrect dose can be harmful to them

Healthy people do not usually get hospitalised when infected with RSV. For others, however, hospitalisation can be crucial if they have difficulty breathing or are dehydrated,where, they might require supplementation of oxygen, intravenous (IV) fluids, or intubation with mechanical ventilation. The latter is performed by inserting a breathing tube through the mouth and down to the airway. Typically, hospitalisation only lasts a few days. 

If one is on medication for another medical condition, like asthma, its use should be maintained to alleviate symptoms like breathing difficulties. 

Lastly, if secondary infections occur, like pneumonia, antibiotics might be administered. 

The role of genetics in RSV susceptibility

Basic genetics overview

We are all made up of genes. Genes are sections of the infamous DNA. If you zoom in even closer, you will see that genes are made up of sequences of molecules called bases. These bases are commonly known as adenine (A), thymine (T), guanine (G), and cytosine (C). The way bases are arranged gives rise to particular genes. Each gene carries instructions for different functions or characteristics of our body. It is almost like they are the recipe and the bases are the ingredients. Genes are inherited from one generation to the next,  so a child inherits their parents' traits, which they inherited from their parents, this is why families usually share many similar traits. Sometimes, there are errors in the sequences of the bases, resulting in the alteration of a gene, and consequently, its function too, which leads to differences in how traits appear. Such errors can be a deletion of a base, an insertion, a duplication, a translocation, or a substitution. These alterations are called mutations and can be harmless, harmful, or even beneficial. Therefore, genes are like an instruction manual for building and maintaining our bodies.

Specific genetic factors affecting RSV susceptibility

Gene mutations can heavily impact immune functions as they can limit or prevent the development of crucial immune cells and their functions, leading to increased susceptibility to certain organisms. 

Genetic variations and mutations, and innate immune response genes are influencing the risk for RSV infections. Specifically, single-nucleotide polymorphisms (SNPs) have been repeatedly associated with severe RSV infections. SNPs are alterations of a single base in a gene sequence. Several studies have linked such polymorphisms to genes involved in the immune response of the host body. 

The T helpers (Th), Th1 and Th2 type cytokines, are crucial agents of the immune response system. They activate immune cells, macrophages, and antibody-mediated responses. Many studies found RSV-associated imbalances in the Th1 and Th2 immune responses. Studies examining polymorphisms in interleukin (IL) 4 and the IL-4 receptor and IL-13, produced by Th2 cells, showed a correlation with increased severity of the infection.^1,2 Additionally, a couple of other studies suggested that the Th1 cytokines may diminish the severity of RSV since they found a lower expression of Th1 cytokine interferon (IFN)-γ in children with severe forms of the disease than in children with mild ones.^3,4 

When it comes to innate immune response genes, a study found an association between a mutation in toll-like receptor 4 (TLR4), involved in innate immunity against RSV, and an increased risk of severe RSV bronchiolitis in previously healthy infants.⁵ Moreover, another study found three alterations in the surfactant protein D (SPD) gene, involved in airway mucosal responses, in severe RSV cases.⁶ 

Consequently, the genetic susceptibility to RSV infections seems to be a complex trait as there are many plausible biological pathways through which it can be influenced. 

FAQs

Can I get tested for RSV? 

RSV is a highly contagious virus. The tests for it detect the presence of RSV genetic material or its antigens in nasal secretions to help diagnose the infection. 

There are different ways to collect that sample:

• Nasal aspirate or wash: A saline solution (salt water) gets inserted into your nose and is then removed with gentle suction
• Nasal swab test: A special swab is used to take a sample from deep inside your nose

The tests you can request are:

• Antigen (rapid) tests:  The test results are available quickly (in an hour or less) but false negatives are possible. This test searches for proteins from the virus called antigens, which trigger your immune system to attack the virus by recognizing there is an invader 
• PCR tests:  The test results take longer than the antigen tests but are more reliable. This test looks for genetic material from the virus and can detect smaller amounts than the antigen test, hence its reliability

When should I get tested for RSV?

Ideally, the RSV tests should be performed during the first few days after the symptoms have begun. This is recommended because the amount of virus present in your system is higher at the beginning of the infection, therefore it is easier to detect. The decrease in viral concentration in your system may result in less accurate test results. In addition, it is suggested to get tested during peak season, that is late fall and winter, if one belongs or comes into contact frequently with people belonging to the high-risk groups.

Summary

Respiratory syncytial virus (RSV) is a prevalent respiratory virus causing mild symptoms in most, but mainly severe infections in infants and the elderly, sometimes resulting in hospitalisation or even death. Its symptoms generally resemble cold-like symptoms like coughing, fever, and breathing difficulties. Furthermore, its transmission is usually a result of the transfer of respiratory droplets and contact with contaminated surfaces. In addition, to prevent an RSV infection, medications and vaccinations are available especially for high-risk groups, while hygiene practices are recommended for everyone. Interestingly, more and more research has established that genetic factors significantly influence susceptibility to RSV, with specific gene mutations and variations in immune response genes, such as single-nucleotide polymorphisms (SNPs) in cytokine and innate immune response genes, being linked to severe RSV infections. Genetic information can help professionals understand the mechanisms behind a certain disease and why some people suffer from it and others do not. Hence, understanding genetic susceptibility can lead to personalized prevention and treatment strategies. Lastly, always consult your healthcare provider if you have any doubts about how you should handle an RSV infection,  and do not solely rely on internet sources.