Morphology Of Paramyxoviruses | Treatment |

PARAMYXOVIRUSES

Paramyxoviruses resemble orthomyxoviruses in morphology but differ from the latter in structure and other properties They belong to family Paramycoviridae. They possess single-stranded RNA genome as a single piece with helical nucleOcapsid. They are enveloped. They are spherical in shape. They are sensitive to lipid solvents.
Haemagglutination and neuraminidase activity is exhibited by some members of the family. Parainfluenza virus, mumps virus, measles virus and respiratory syncytial virus are important for human infections. Newcastle disease virus is a natural pathogen of birds but the man gets infection by handling these birds.

DIFFERENTIATION OF PARAMYXOVIRUSES

Parainfluenza virus and mumps virus have both haemagglutinin and neuraminidase, while measles virus has a haemagglutinin but no neuraminidase. Respiratory syncytial virus (RSV) does not have any of the two. The measles virus has a haemolysin while RSV has a surface glycoprotein G, which has a function similar to that of haemagglutinin.

MORPHOLOGY OF PARAMYXOVIRUSES

The paramyxoviruses are spherical enveloped particles 100-300 nm diameter in size. The envelope consists of a lipoprotein membrane and covered by projections. These projections are of two types, HN (haemagglutinin, neuraminidase) and F (fusion protein) peplomers. F glycoprotein causes fusion of cell membranes leading to the formation of syncytia.
The inner surface of the envelope is lined by matrix (M) protein. The nucleocapsid is of helical symmetry and contains a single-stranded negative-sense RNA genome as a single piece and an RNA- dependent RNA polymerase. Measles virus envelope carries only haemagglutinin but not neuraminidase.

VIRUSES OF FAMILY PARAMYXOVIRIDAE

Parainfluenza Viruses

There are four serotypes of parainfluenza
viruses, type 1, 2,3 and 4. They cause respiratory infections in children and less often in adults. They cause severe respiratory tract diseases such as laryngotracheobronchitis or group.

Laboratory Diagnosis

1. Direct Demonstration
  • Immunofluorescence: Viral antigens can be demonstrated in exfoliated cells aspirated from the respiratory tract.
  • Enzyme link Immunosorbent Assay (ELISA)
2. Isolation


Mouth washings, samples collected from posterior pharynx or nasopharynx and throat swabs are inoculated in primary human or monkey kidney cells or in continuous cell lines such as H292 derived from human lung mucoepidermoid carcinoma.
3. Serology

Detection of rising antibody titre by neutralisation, ELISA and complement fixation test is helpful in diagnosis.

Measles Virus

Measles is a highly infectious childhood disease spread by respiratory secretions. It is caused by the measles virus. The virus resembles paramyxoviruses in morphology. Infection confers life-long immunity. There is only one serotype of the measles virus.

Laboratory Diagnosis

Most cases are diagnosed clinically. In atypical cases, and for differentiation from rubella, laboratory study may be necessary
1. Direct Demonstration

Virus particles can be detected in exfoliated respiratory cells in nasal secretions by immunofluorescence.
2. Isolation

Specimens are cultured in primary embryo kidney, monkey kidney or human amnion cells.
3. Serology

Measles specific IgM antibody in the no serum can be detected by ELISA.

Prophylaxis

Live attenuated vaccine is used in children at the age of nine months. The vaccine is administered in one dose by subcutaneous route. The measles vaccine is also being used in combination with mumps and rubella (MMR vaccine). This vaccine is administered at 12-15 months of age. MMR is also given in a single dose by subcutaneous injection. it provides protection lasting for more than 20 years.

Respiratory Syncytial Virus

It is the most important cause of Respiratory Syncytial Virus (RSV)  is pleomorphic. bronchiolitis and pneumonitis in infection infants between one to six months of age. Infection in older children and adults results in rhinitis or. common cold.

Laboratory Diagnosis

1. Direct Demonstration

Rapid identification of the virus in nasopharyngeal aspirates can be done by immunofluorescence. Viral antigens can also be detected in the specimen by ELISA.
2. Isolation

The virus can be isolated from nasopharyngeal secretions by inoculating the specimen in human (HelLa, HEp-2) or monkey cell cultures. Characteristic giant cells and syncytia, formation occurs. However, definitive identification can be done by immunofluorescence.
3. Serology

It is not very helpful but CFT, neutralisation and ELISA techniques may detect rising antibody titre.
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