Introduction
Respiratory Syncytial Virus is an Orthopneumovirus, member of the familypneumoviridae. It is a single-stranded nonsegmented negative-sense RNA virus, class V of the Baltimore classification. There are distinguished two RSV subtypes, to know: A and B, each of which has 5 to 6 subgroups, with subtype A being the most prevalent.8
RSV is the main causative agent of respiratory tract infections in pediatric ages in Mexico and around the world.8 It is considered the main cause of hospitalizations in this age group, eliciting 3.4 million hospitalizations anually in children under 5 years old worldwide. 17 The morbidity and mortality figures for this pathology are similar, or even higher than those caused by the Influenza virus, reaching an annual mortality rate estimated at 3.1 cases per 100,000 people younger than 1 year. 17,19
RSV is responsible for almost 100% of episodes of bronchiolitis and up to 50% of viral infections of the pulmonary parenchyma in pediatric age. 8
Up to 10% of infected children with this virus can present severe forms of the disease such as pneumonia or pulmonary focus sepsis.19
Bronchiolitis is the characteristic clinical-pathological entity of RSV infection. It is defined as the first episode of wheezing in infants younger than 1 year 29, accompanied by mild symptoms such as nasal congestion, hyaline rhinorrhea, cough, tachypnea, rales, fever, irritability, or even data on respiratory failure or sepsis, all this tributary to a state of inflammation, hypersecretion of mucus, edema and necrosis of respiratory epithelial cells precipitated by the cellular infection produced by this virus. 22
Risk factors that predispose to severe RSV infection can be categorized into: maternal, environmental, and host factors. The main factors identified are, but not limited to: prematurity (due to a decrease in the number of antibodies transplacentally acquired, transmitted from the mother to the newborn), low birth weight (<2500gr according to the Mexican Clinical Practice Guidelines), genetic abnormalities, cardiopulmonary comorbidity and immunocompromises.4,29
The diagnosis is primarily clinical, however, in situations of seriousness it is necessary to determine the specific etiology of the condition, since RSV infection is clinically indistinguishable from other viral respiratory infections and the diagnosis requires laboratory tests, so it is necessary to carry out complementary studies such as real-time PCR. 4
So far, therapeutics are limited to support measures such as oxygen therapy, Ribavirin (an ineffective synthetic nucleoside with serious teratogenic effects) 3, and a humanized monoclonal antibody called Palivuzumab, which in addition to its low availability in Mexico and its high cost, is only indicated in patients with risk factors such as prematurity and with underlying comorbidities, not for those with outpatient treatment. 1
Lumicitabine also known as ALS-8176 is a new prodrug, nucleoside analogue currently in phase II of development, which selectively inhibits the activity of RNA polymerase through the termination of the classical chain. 8 This drug significantly reduced the level of contagion and the detection time of viral titers in blood without provoking any side effects.
The lack of a safe and effective treatment to cope with RSV infection requires the implementation of prophylactic measures, of which breastfeeding is considered the main one. 4
The role of breastfeeding in the contribution of humoral immunity in the newborn has been extensively described, through the passage of immunoglobulins (especially IgA type) through breast milk, likewise, it has recently been exposed that in addition to transmitting humoral-type immunity, cellular immunity such as anti-inflammatory cytokines and TGF-β, which regulates the differentiation and expansion of innate and adaptive immune cells, are also transmitted. 5
IgA represents 90% of the immunoglobulins in the breast milk (BM), with a concentration of 0.3g / ml / day. It is present in mucosa, has anti-inflammatory components, and even inactivate viruses. IgM is the second most important immunoglobulin, it is highly avid for viruses and bacteria due to its pentameric nature, having an opsonizing function. Its concentration in BM is 2.5mg / ml, it can be concentrated in mucosa when IgA levels decrease, other immunologically relevant components in breast milk are enzymes and complement, as well as lymphocytes and cytokines.
RSV infections are a serious health challenge in Mexico and in the world, which until now does not have a safe, effective and standardized treatment. Some new treatments (Lumicitabine and vaccine prototypes) seem promising as future therapeutic schemes, however, they are still in development stages II.
In our study, we determined the clinical characteristics of hospitalized RSV-infected pediatric patients, relating these characteristics to the absence or presence of exclusive breastfeeding in the first 6 postnatal months, as well as the levels of virus-specific IgA in respiratory samples.