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.