Generality
Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in children under the age of two .
In adults and older children, infection of the respiratory system usually leads to a mild disease that heals without the need for specific treatments. However, during early childhood, exposure to the viral agent often leads to pneumonia and may involve the smallest bronchial branches ( bronchiolitis) .
The respiratory syncytial virus has the characteristic of spreading in annual epidemics, which, as a rule, occur every winter .
In temperate climate countries, the period of greatest infectiousness is between November and April, with a peak in the months of January, February and March. Almost all children become infected in the first 4 years of life.
Exposure to respiratory syncytial virus does not make you completely immune, therefore reinfection is common, although it is generally less severe.
Diagnosis is based on symptoms and their occurrence at certain times of the year.
Typical manifestations of the disease induced by respiratory syncytial virus include runny nose, pharyngitis, fever, cough and wheezing; if the infection is severe, it can lead to respiratory distress.
The treatment of uncomplicated forms is mainly symptomatic, with the use of oxygen to facilitate breathing and administration of liquids to avoid dehydration.
What is RSV
RSV (an acronym that derives from the English " Respiratory Syncytial Virus ") is a viral agent capable of infecting the respiratory system of patients of any age, but mainly affects children in the first years of life.
Respiratory syncytial virus infects airway epithelia, where it causes cell necrosis.
In the tissues in culture infected with this pathogen, the cells merge together, giving rise to a conglomerate (syncytium), from which the name derives.
Causes
Respiratory syncytial virus is a very common cause of respiratory infections during early childhood .
This pathogen belongs to the Paramyxoviridae family, like the parainfluenza and measles viruses. In particular, RSV is included in the subfamily Pneumovirinae, which also includes the human metapneumovirus.
The respiratory syncytial virus is distributed worldwide and appears in annual epidemics . In temperate climates, RSV infections occur in the winter months or early spring and are prolonged, persisting in the environment for 4-5 months; during the rest of the year, on the other hand, infections are sporadic and much less common.
Respiratory syncytial virus outbreaks often overlap with influenza and human metapneumovirus. Compared to the latter, however, RSV infections are generally more constant from year to year and lead to a greater pathology, especially in infants younger than 6 months.
Anti-RSV serum antibodies (IgG immunoglobulins) transmitted by placental route from the mother to the fetus, if present at high concentrations, provide partial but incomplete protection. In other words, the possibility of getting sick depends a lot on the opportunity the child has to be exposed to the infection.
Infection is almost universal within 2 years of age.
Exposure to respiratory syncytial virus does not result in permanent absolute immunity. However, recurrences are generally less severe.
Bronchiolitis and pneumonia: causal mechanism
Bronchiolitis resulting from respiratory syncytial virus infection is caused by obstruction of the small airways during expiration and collapse of the distal lung tissue. Babies and infants are particularly susceptible to this, due to the small size of their bronchioles.
The narrowing of the airways is probably determined by the necrosis of the bronchiolar epithelium induced by the virus, with mucosal hypersecretion and edema of the surrounding submucosa.
These alterations determine the formation of mucous plugs that obstruct the bronchioles.
In pneumonia, the phenomenon is more generalized and epithelial necrosis can extend both to the bronchi and to the alveoli.
In addition to these mechanisms, elements of the host's immune response can cause inflammation and contribute to tissue damage.
Incubation period
The incubation period - from exposure to the virus until the first symptoms - is about 3-5 days.
Once contracted, the respiratory syncytial virus is eliminated from the patient in the environment for variable periods; most infants with lower airway diseases are infectious for around 5-12 days.
Transmission mode
The spread of infection occurs when large infected droplets, carried either by air or by hand, come into contact with the nasopharynx of an individual susceptible to contracting the infection.
In most families, respiratory syncytial virus is introduced by school-age children who undergo re-infection. Typically, within a few days, older brothers or sisters or one or both parents contract rhinitis, while the infant has a more severe illness with fever, otitis media, or lower airway disease.
Symptoms and complications
In most adults and older children, contact with the respiratory syncytial virus can go completely unnoticed. The most frequent symptoms are rhinitis, pharyngitis and cough, which begin 3-5 days after the infection.
However, in younger children, the infection can cause a lower respiratory illness (bronchiolitis or pneumonia). In the latter case, wheezing, wheezing, fever, anorexia and general condition are manifested.
Primary infection
In many children, the symptoms of respiratory syncytial virus infection are similar to those of a cold. These signs precede the manifestations of the lower airways by a few days and include:
- Runny nose (rhinorrhea);
- Cough (appears simultaneously with the rhinorrhea or after an interval of 1-3 days);
- Wheezing breath;
- Temperature;
- Otitis media;
- Sore throat.
Lower respiratory tract infections are characterized instead by:
- Dyspnoea;
- Cuts in the chest wall;
- Difficulty feeding.
In infants less than 6 months old, the first symptom may be the brief interruption of breathing (apnea). The symptoms can last a week or two, while the cough can last over a fortnight. If the disease is mild, it usually heals spontaneously and does not require specific treatments or special visits.
In general, the larger the child, the milder the manifestations associated with respiratory syncytial virus infection.
The croup may also follow an RSV infection, but bronchiolitis and pneumonia remain the most common manifestations.
If the disease progresses, the cough increases and air hunger appears with increased respiratory rate, intercostal and sub-rib retractions, over-expansion of the chest, restlessness and peripheral cyanosis (in particular, nail and perioral).
Symptoms of a severe infection
The infant or child under two years of age, who contracted the infection for the first time, may have a severe manifestation characterized by bronchiolitis or pneumonia.
Signs of serious and potentially fatal disease are:
- Breathing difficulties and periods of apnea;
- Increased breath rate (tachypnea with more than 70 breaths per minute);
- Wheezing (whistle);
- Poor reactivity;
- Central cyanosis;
- Insistent cough;
- Dehydration;
- Difficulty feeding (the child cannot suckle the breast or feed on the bottle).
In newborns, in ex-premature infants and in children with previous cardiac or pulmonary pathology, the event will be much more severe. Some patients, usually the youngest, develop severe respiratory distress.
Recurrent infection / infection
Respiratory syncytial virus infection can be contracted more than once. Reinfection can also occur a few weeks after recovery, but is generally observed during subsequent annual epidemics. The severity of the disease is usually minor and appears to be a function of both partial immunity and older age.
During childhood, reinfections occur mainly in situations of high promiscuity and high risk of exposure to the virus.
Children who have had bronchiolitis are more at risk of developing asthma in adulthood.
Diagnosis
Generally, tests are not necessary to make the diagnosis, unless the doctors are trying to identify an outbreak of respiratory syncytial virus infection or if hospitalization is required.
The differential diagnosis must be placed against other respiratory pathogens that frequently affect children in the first months of life (influenza virus and parainfluenza virus, human metapneumovirus and rhinovirus).
The presence of a respiratory syncytial virus infection can be suspected based on the season of the year, the age of the child and the presence of the pathogen in other family members and people in their contact.
In most cases of bronchiolitis or pneumonia caused by respiratory syncytial virus, routine laboratory investigations are of little use. The white blood cell count is not altered or high; the leukocyte formula may be normal with a neutrophil or mononuclear predominance.
The definitive diagnosis of respiratory syncytial virus infection is based on the identification of the living pathogen in respiratory secretions by cell culture. Presence can be confirmed by a molecular diagnostic test to search for genetic material, such as RT-PCR (reverse transcription PCR), or by the detection of viral antigens on mucus aspirate or nasal cavity washing.
Therapy
In most cases, respiratory syncytial virus infection heals spontaneously, without any specific treatment.
Treatment of uncomplicated bronchiolitis and pneumonia is symptomatic.
What to do
In the case of respiratory syncytial virus infection in children, in particular, it is useful:
- Let the child drink a lot, so as to keep the mucous membranes always well hydrated and correct dehydration;
- Humidify the environment with special devices, so as to reduce coughing and irritation of the mucous membranes when air passes;
- Practice nasal washes with saline solution;
- Use a mucus aspirator to free the nasal cavities;
- Never use acetylsalicylic acid (aspirin) to reduce fever.
In very young children, hospitalization may be necessary, with the possibility of oxygen supply, medicines to clear the airways and intravenous feeding or with a tube in the presence of marked tachypnea.
The use of the antiviral ribavirin is controversial; this drug is reserved for the most serious cases and is administered with specific procedures and times only in a hospital environment.
Patients who are at high risk of developing a severe respiratory syncytial virus infection may receive the palivizumab on a monthly basis. In children taking this drug - consisting of antibodies against RSV - in fact, the need for hospitalization seems reduced and the possibility of treating respiratory diseases should improve; however, doctors still do not have the certainty that this therapy is able to prevent serious complications or death.
The prognosis of this disease is more severe in very young children, in premature ones and in those who previously suffered from immunological diseases, lung problems and cardiovascular diseases.
Prevention
The most important preventive measures are aimed at blocking the spread of infection:
- Washing your hands often and well is the best way to prevent respiratory syncytial virus infection;
- Use disposable tissues and always throw them in the trash;
- If a child starts to show symptoms typical of a cold, keep it away from younger children (especially if they live in the same environment).
Vaccine
There is currently no authorized vaccine against respiratory syncytial virus. However, many lines of scientific research are directed in this direction.
