Parvoviruses

This group's only human pathogen, parvovirus B19, is the causative virus in erythema infectiosum (also known as “slapped cheek syndrome” or the “fifth disease”) in children and causes aplastic crisis in anemic patients. The virus also contributes to joint diseases, embryopathies, and tissue rejec­tion following renal transplants. Diagnosis: serological (IgG and IgM) and PCR.

Pathogen. The parvoviruses are among the smallest viruses with a diameter of 19-25 mm. They are icosahedral, nonenveloped, and their genome is in the form of single-stranded DNA (ssDNA). Some parvoviruses can only replicate in the presence of a helper virus (adenovirus or herpesvirus). Parvovirus B19, the only human pathogenic parvovirus identified to date, is capable of auto­nomic replication, i.e., it requires no helper virus. Some zoopathic strains also show this capability in rodents, dogs, and pigs.

Pathogenesis and clinical picture. Parvovirus B19 replicates in the bone marrow in erythrocyte precursor cells, which are destroyed in the process. In patients already suffering from anemia (sickle-cell anemia, chronic hemo­lytic anemia), such infections result in so-called aplastic crises in which the lack of erythrocyte resupply leads to a critical shortage. In otherwise healthy persons, these infections usually run an asymptomatic course. They can, how­ever, also cause a harmless epidemic infection in children, erythema infectiosum (“slapped-cheek syndrome” or “fifth disease”). This childhood dis­ease, which used to be classified as atypical measles, is characterized by sud­den onset of exanthem on the face and extremities. Certain forms of arthritis are considered complications of a parvovirus B19 infection. The virus also ap­pears to cause spontaneous abortions in early pregnancy and fetal damage in late pregnancy (hydrops fetalis).

Diagnosis. An enzyme immunoassay reveals antibodies of the IgG and IgM classes. During the viremic phase, at the onset of clinical symptoms, the virus can also be identified in the blood by means of electron microscopy or PCR. In-vitro culturing of the pathogen is not standard procedure.

Epidemiology and prevention. The transmission route of human parvovirus B19 is not known. Droplet infection or the fecal-oral route, analogous to other parvoviruses, is suspected. Blood and blood products are infectious, so that multiple transfusion patients and drug addicts are high incidence groups. No specific prophylactic measures are recommended.