About RSV
Respiratory Syncytial Virus
(RSV) is a negative-sense, enveloped single stranded RNA virus
which belongs to the paramyxoviridae family. The virion is variable
in shape and size (average diameter of between 120 and
300nm). It is highly contagious and causes infection of the
lungs and breathing passages. Infections can range from very mild
illness to serious respiratory tract infections, including
bronchiolitis and pneumonia, which usually occur in the very young,
the very old and those with weakened immune systems.
Epidemiology of
RSV
RSV has a substantial social
impact, economically and in terms of human suffering. The
highest rates of RSV infection occur in infants 2-6 months old, and
is the major cause of serious lower respiratory disease, in
children within their first few years of life.
Each year, RSV is
responsible for estimated 125,000 paediatric hospitalisations
within the USA. RSV infections can be fatal in premature babies
less than 6 months old and in infants with chronic lung, heart or
immune deficiency diseases. It is responsible for
approximately 2,500 deaths per annum. Infections are global and
typically epidemics occur during the winter months, October through
to February. Two thirds of infants are infected with RSV during
their first year and infection is usually universal by the age of
two. The mean cost of a RSV hospital admission in the USA is
approximately $27,101.
Although RSV is primarily a
children’s virus, adults can be infected with RSV as well, the
signs and symptoms of which mimic the common cold.
Signs and
symptoms
Symptoms of RSV vary on the
severity of the infection, and where the virus is located in the
respiratory tract. Initially RSV affects the upper
respiratory tract, and symptoms may include:
- low grade fever (102°F) fever
- rhinorrhea (runny nose – clear discharge)
- nasal congestion
- cough
- decreased appetite.
As the infection travels
down to the lower respiratory tract, it can cause inflammation of
the lungs and more severe symptoms such as:
- coughing/wheezing
- difficulty breathing
- rapid breathing
- circumoral and nail bed cyanosis.
Risk factors of RSV
infection
Factors that increase the
risk of RSV infection:
- Birth within 6 months before onset of RSV season
- Low birth weight (<2500g)
- Young siblings
- Day care attendance
- Being in a multiple birth
- Passive smoke exposure
- Family history of asthma
There are also risk factors
for developing severe RSV infections. Listed below are common
risk factors for developing severe RSV that may require
hospitalisation:
- Age younger than 3 months at time of infection
- Prematurity
- Chronic lung disease
- Congenital heart disease
- Weakened immune system
- Lower socioeconomic status
- Male sex.
How RSV is
transmitted
RSV is highly
contagious. The virus is transmitted by physical contact with
infectious secretions through hand contamination and
self-inoculation of eyes, nose or mouth. The infection can also be
spread through the air, by coughing and sneezing. The virus
is unstable in the environment, surviving between 4-7 hours on
environmental surfaces, but it does not survive well at ≥ 37°C.
The spread of RSV is also
almost unavoidable due the period of viral shedding. Viral
shedding may occur one to two days before symptoms become apparent,
and can last as long as two weeks after symptom onset. For
children with defective cellular immunity, this period is
significantly greater. In most patients the incubation period
is 4-6 days.
Duration of RSV once
infected.
RSV infection usually lasts
between 7 and 14 days. Infants that are hospitalised with
lower respiratory tract illness usually spend 5 to 7 days in
hospital. The virus can infect the same person several times
during a lifetime, but re-infections are usually less severe. After
each RSV infection the body forms some immunity, but it is not
complete.
Diagnosis of
RSV
For confirmation of RSV,
testing should positively identify RSV and rule out bacterial
infection. Nasopharyngeal secretions containing epithelial cells
are necessary for positive diagnosis of severe RSV infections.
Viral isolation and
subsequent culture from respiratory secretions are considered the
gold standard of RSV diagnosis; confirmation can take several days
consequently delaying treatment time for patients that may need
immediate/aggressive treatment. Rapid diagnostic tests are
the preferred method since results are available within hours and
most clinical laboratories use antigen detection assays to diagnose
infection. Chest radiographs are sometimes used to determine the
severity of the illness.
Treatment of
RSV
No medications exist to cure
RSV and treatment is aimed at ameliorating symptoms. Patients
with severe RSV may require specialised respiratory therapy
including humidified oxygen and sometimes mechanical
ventilation.
Ribavirin aerosol
(anti-viral) has been administered to hospitalised children with
severe pneumonia (caused by RSV), and some investigators have used
a combination of immune globulin intravenous (IGIV) with high
titers of neutralising RSV antibody (RSV-IGIV) and ribavirin to
treat patients with compromised immune systems.
Causes of
RSV
RSV bronchiolitis and
pneumonia are two severe illnesses caused by RSV. RSV
bronchiolitis is associated with clinical signs and symptoms of
small airway obstruction. Airway obstruction in young infants
can be very dangerous, as they have smaller peripheral airways and
can become life-threatening if it is not manage appropriately.
During their first RSV
infection, between 25% and 40% of infants and young children have
signs of bronchiolitis or pneumonia. Of these around 2% require
hospitalisation.
Cure &
vaccinations For RSV
At present there is only one
FDA approved medication available for halting the growth of RSV
(ribavirin). No treatment currently exists that can
completely eradicate or cure RSV. Numerous clinical studies
are researching the possibility of a RSV vaccine.
Prevention of RSV in
High Risk Patients
In instances where children
are at high risk for developing RSV (e.g. when a baby has been born
prematurely, and has not received all the natural substances to
fight RSV and other viruses from the mother) medications such as
palivizumab (Synagis) or RSV immune globulin (RespiGam) may be used
to prevent infection. A new medication, Numax Anti-RSV Mab,
an antibody against RSV, similar to Synagis, but has been proposed
as being 10 times more effective.
Benefits of rapid
RSV diagnosis
The added risk of RSV
transmission, posed by the long viral shedding period in RSV, can
be reduced by early diagnosis and treatment of the infection. Other
benefits of rapid RSV diagnosis include:
- Administration of appropriate treatment
- Reduce the risk of lower tract respiratory infections
- Reduce risk of pneumonia and bronchiolitis
- Decrease morbidity associated with RSV in high-risk young
children
- Reduce the spread to others
- Reduce hospital stays
- Reduction in cost of hospital care.
Useful
links:
Centers for Diseases Control &
Prevention
The RSV Information Centre
The RSVMD Website
The RSV Prevention Information
Centre