Parvovirus B19 (B19)

Causative Agents

Parvovirus B19 (B19) which is classified as Erythrovirus (due to its ability to invade red blood cell precursor) belongs to Parvoviridae family. It is the only human pathogenic member of Parvoviridae family. It is a non-enveloped virus containing single-stranded linear DNA genome and two proteins with icosahedral shaped viral particles which are approximately 22-24 nm in diameter. Low DNA content and lack of lipid envelope make B19 highly resistant to heat, radiation, and detergents. [1], [2]

Epidemiology

B19 is a common infection in humans that is present throughout the year. Outbreaks of infection, more commonly seen in the spring and summer, are centered by age 15 approximately 50% of cildren with detectable IgG. It occurs throughout adult life, thus 80% of the elderly are seropositive. In women of child-bearing age, annual seroconversion rate is estimated of 1.5%. While studies in different countries like USA, France, Germany, Japan show smilar patterns, higher prevalence is shown in Brazil and African continent. [3]

Modes of Transmission

B19 is mainly spread by infected respiratory droplets and blood. It can be spread transplacentally to fetus from mother. It infects and replicates in the erythrocytes. The incubation period is 4-14 days. During the first week of infection, viruses spread in the blood stream of the host. Then, symptoms of fever, malaise, arthralgia, nausea and rhinorrhea, and erythroid progenitor cell depletion in the bone marrow occur. When the symptoms disappear, red rash on the cheeks develop and immunoglobulin (IgM) appear in the serum. Transmission is high during viremia and before symptoms, and continues until the symptoms disappear. After the development of the rash, the infection is not contagious. [4]

Diagnosis

The detection of B19 is based on nucleic acid hybridization assays. Mainly ‘Dot Blot Hybridization’ and ‘In-Situ Hybridization’ have been used for detection of B19 within bone marrow and other cells. In healthy immunocompetent individuals, infection can be detected for 2-4 days by ‘Dot Blot Hybridization’ based on IgM assays ideally performed by the capture technique. In RIA or ELISA, antibody is detected by approximately 3-5 day of infection and remains detectable for 2-3 months. However, these techniques face with quite critical drawbacks even though being easy and quick techniques. Cross–reaction of antibodies or rheumatoid factor may result in false positive results and moreover, since the immunocompromised patients may not mount an immune response, these techniques based on antibody detection are not helpful and make it vital to test B19 antigens or nucleic acid (DNA).

The use of PCR both overcomes the drawbacks of antibody tests and also increases the analytical sensitivity. It is more practical, fast and reliable solution. [5]

Annotated Bibliography

1) Heegaard E D, Brown K E (2002)  Human Parvovirus B19. Clinical Microbiology Reviews 15(3): 485-505.

2) Sabella C, Goldfarb J (1999) Parvovirus B19 ınfections. American Family Physician 60:1455-60.

3) Servey JT, Reamy BV, Hodge J (February 2007). “Clinical presentations of parvovirus B19 infection”.AmFam Physician 75 (3): 373–6. PMID 17304869.Retrieved 2009-11-06. PMID 17304869

4) Pattison JR, Patou G (1996). Parvoviruses. In: Barron’s Medical Microbiology (Barron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.

5) Alfred S. Evans  Richard A. Kaslow ,Viral Infections of Humans: Epidemiology and Control, Springer; 4th edition (January 15, 1997)

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