Respiratory Syncytial Virus

Respiratory syncytial virus causes mild respiratory infections such as colds and coughs in adults and severe pulmonary diseases in children e.g. Pneumonia and bronchitis.

Family:

            Belongs to paramyxovirus family

            Prototype of pneumovirus genus of Pneumoviridae family

 Introduction:

Respiratory syncytial virus causes mild respiratory infections such as colds and coughs in adults and severe pulmonary diseases in children e.g. Pneumonia and bronchitis.

Family:

            Belongs to paramyxovirus family

            Prototype of pneumovirus genus of Pneumoviridae family

Shape of RSV

Genome:

Single RNA and helical nucleocapsid

Negative polarity

15 kb genome

Comprises of total 10 genes

Gene structure:

3̒-        NS1-NS2-N-P-M-SH-G-F-M2-L-5̒

            11 viral protein are encoded by:

N: nucleoprotein

P: phosphoprotein

L: RNA polymerase

M2: regulatory proteins:

NS1 and NS2 mediate resistance to interferon induced cellular antiviral responses.

Virus envelop contains:

M: internal matrix protein

SH: small hydrophobic protein

G: presumed attachment protein

F: fusion protein

F and G represent mahor targets for neutralizing antibodies/

Fusion proteins form surface spikes and cause the cells to fuse forming multinucleated giant cell called syncytia.

 Pathogenesis:

Incubation period: 3-6 days

Virus enters via oral and nasal pathways

Spread along epithelium of the respiratory tract, moving to lower tract may cause pneumonia or bronchitis.

In bronchitis, peribronchiolar inflammation with lymphocytes occurs.

In pneumonia, infiltration of intestinal cells with mononuclear cells is seen.

Inflammation of Bronchiole

Immunity:

Severe RSV disease develops in infants with high level of passive maternal antibodies. Maternal antibodies-RSV complex is formed.

Particular concern with premature babies who lack maturity and protective antibodies.

RSV immunity is assoctoiated to little or non-detectable interferon in nasopharyngeal secretions.

Continuous solid level of antibodies is required.

Vaccine produced was more lethal.

IgG appears in 2nd week of infection.

IgA is not found in infants.

IgM is transitory.

Respiratory Syncytial Virus

Clinical Findings:

In infants, RSV is an important cause of lower respiratory tract diseases such as bronchiolitis and Pneumonia.

RSV is also an important cause of otitis media in young children.

In older children and adults, RSV causes upper respiratory tract infections that resemble the common cold.

  Laboratory Diagnosis:

The presence of virus can be detected rapidly by:

Immunofluorescence on smears of respiratory epithelium.

Isolation in cell culture.

Rise in antibody titer of at least 4-fold is also diagnostic.

Treatment:

Aerosolized ribavirin (Virazole) is recommended for severely ill hospitalized infants, but there is uncertainty regarding its effectiveness.

A combination of ribavirin and hyper immune globulins against RSV may be more effective.

Treatment:

Aerosolized ribavirin (Virazole) is recommended for severely ill hospitalized infants, but there is uncertainty regarding its effectiveness.

A combination of ribavirin and hyperimmune globulins against RSV may be more effective.

Prevention:

There is no Vaccine.

Hyperimmune globulins are also available for prophylaxis in these infants.

Nosocomial outbreaks can be limited by hand washing and use of gloves.