Epidemiology and transmission
Parvovirus B19 (Parvo B19), a member of the parvovirus family, Parvoviridae, is obligatory human pathogenic. It is of worldwide distribution in both industrialized and developing countries. In regions with moderate climate infection appears to be most common between late winter and early summer time. Epidemics occur with a periodicity of about 4-5 years.
As Parvo B19 has been found in respiratory secretions at the time of viremia, respiratory spread appears to be the most common route of transmission. The virus seems to be readily horizontally transmitted through close personal contact via droplet infection but also through contaminated hands. Transmission by transfusion of blood products may be a critical event in certain patient groups.

Prevalence
The prevalence of Parvo B19 infections is age-dependent: In industrialized countries about 2-10% of children have had primary Parvo B19 infections by the age of 5 years increasing to 50% by the age of 15 years and 60% by the age of 30 years. In adults older than 60 years more than 85% have antibodies to Parvo B19. Investigations in blood donors revealed an antibody prevalence of about 60%. The immunity following Parvo B19 infections seems to be lifelong.

Parvo B19 in blood and blood products
Testing of donors or blood donations for Parvo B19 has neither been prescribed in the German Directive for Blood Typing and Blood Transfusion (hemotherapy) nor in the recommendations of the European Council and the WHO.
The risk of infection using single-donor blood products seems to be low. Reports on the frequency of Parvo B19 in donor blood vary between 1:167 (0.6%) and 1:35.000 (0.003%) depending on the epidemiological situation and the detection methods.
Conversely, a large number of blood donations (e.g. Belgium 5.000, Germany 60.000, USA >100.000) make up the plasma pools used to produce plasma derivatives such as clotting factor concentrates for the treatment of hemophilia, immunoglobulins for the treatment of an affected immunoresponse and albumin solutions for the treatment of burns, shock and trauma. Clotting-factor concentrates may very often be contaminated. Studies have detected Parvo B19 in two of three (33%) unheated batches of clotting factor preparations and in 20% to 25% of solvent- or detergent-treated batches. While the fractionation process used to obtain albumin preparations is apparently more efficient at eliminating virus, Parvo B19 was still found in 3 of 12 batches in one study. Furthermore, Parvo B19 may infrequently be transmitted by other blood-derived products such as platelets, intravenous and intramuscular immunoglobulin, and fibrin products as well as by bone marrow.
For the production of plasma derivatives and SDP (solvent-detergent preparations) nowadays only those donations are used which have <104 genome equivalents/ml plasma. Together with virus depletion methods it was achieved that, to date, plasma derivatives can be considered safe with respect to Parvo B19 infection.

Transfusion-associated Parvo B19 infections
In certain patient groups treatment with blood products in rare cases may lead to severe symptomatic courses of disease. In patients with increased erythropoesis (e.g. haemolytic anemia) and in immunocompromised individuals aplastic crises had been reported, in pregnant women fetal infections with anemia and hydrops which in certain cases may result in spontaneous abortions or intrauterine fetal death.
The same clinical pictures may result from transfusion of Parvo B19 virus positive blood. Therefore in any case it should be avoided in pregnant women, patiens with chronic-hemolytic anemia, bone marrow recipients and patients with hereditary or acquired imunnodeficiency. As the detection of Parvo B19 virus is costly, for these risk patients blood should be made available which had been tested for anti-Parvo B19 IgG antibodies. Anti-Parvo B19 IgG positive blood preservations normally don’t contain anymore Parvo B19 virus.

Diagnosis
PCR or other NATs are used for for Parvo B19 testing in connection with the production of plasma derivatives and SDPs.
The detection of anti-Parvo B19 IgG antibodies may be used for the selection of Parvo B19 IgG positive donors. The use of so-called B19 virus safe cellular blood products from such defined donors has been considered a practicable possibility to avoid possible transmission risks in particular cohorts who have no antibodies, such as pregnant women in the first trimenon, patients with congenital or acquired haemolytic anemia, or patients with cellular immunodeficiency, e.g. HIV-infected individuals or patients after high dose chemotherapy with stem cell transplantation.
Safe cellular products are those with IgG antibodies against Parvo B19 in two separate blood samples taken 6 months apart.

For information on indications for the diagnosis with the medac Parvovirus B19 serology please refer to Parvo B19 serology in this section.