parvoviruses B19---52

The parvoviridae family contains, small, non-enveloped, ssDNA viruses with icosahedral capsids. Medically impotant genera are:

1.Dependovirus( e.g adeno-associated virus) is a defective virus and requires helper virus for its own replication. There is no specific disease caused by dependoviruses.

2. Erythrovirus ic capable of autonomous replication, which is independent of helper virus. Parvovirus B19 is the only member, and is the only parvovirus that is human pathogen. It is associated with several defined clinical syndromes. Human erythroid progenitor cells are the specific host cells, where the virus replicates inside the nucleus.

Pathogenesis of Parvovirus B19

Infection is transmiited by resp secretions and saliva, transplacental infection of the foetus, and blood transfusion or blood product therapy. Humans are the natural reservoir.

Most of the infections are asymptomatic. Human infection include :

1.Erythema infectiosum (slapped-cheeks syndrome, fifth disease).
2. Transient Aplastic Crisis (TAC)
3. Foetal infections leading to foetal hydrops and foetal loss.
4. Chronic B19 infections in the immunocompromised patients such as chronic anaemia, leukopenia, or thrombocytopenia.

Erythema infectiosum (EI) and transient aplastic crisis (TAC) are the commonest syndromes.

Anaemia is due to B19 infection of the red blood cell precursors. The rash associated with erythema infectiosum is due to infection of the endothelial cells as well as deposition of immune complexes. These immune complexes also contribute to the arthritis seen in adults. Infection provides lifelong immunity.

Lab Diagnosis
Cultivation of parvovirus B19 is difficult and not routinely used for diagnosis. Diagnosis is made either by direct detection of B19 antigen or DNA in clinical material, or by serologic tests.

Treatment and prevention
There is no antiviral therapy and no vaccine. Pooled immunoglobulins may be useful in chronic B19 infections in immunocompromised patients.