Parvovirus B19 is a single-stranded DNA virus that is the only pathogenic strain of parvovirus to man.  Infections may be asymptomatic or may manifest as an aplastic crisis, arthralgias, hemocytophagia, pure red cell aplasia or erythema infectiosum (generally seen only in pediatric cases of infection).  Fetal infection may result in either nonimmune hydrops fetalis, spontaneous abortion or both.  Infection may be transmitted via respiratory secretions or from contaminated blood or blood products.  The virus is easily transmitted to close contacts of infected persons; therefore, when the diagnosis is suspected, questioning the patient regarding contact with children with classic symptoms of erythema infectiosum may help identify parvovirus B19 as the underlying etiology.

     Erythema infectiousum (Fifth disease) is the childhood exanthem associated with parvovirus B19 infection.  The initial stage of infection usually occurs four to 14 days after infection and manifests as fever, headache and gastrointestinal irritation.  The second stage is the most well known and easily recognized stage of infection and is characterized by the development of a facial exanthem (the slapped cheek rash).  In the third stage, the patient develops an erythematous, maculopapular exanthem on the trunk and extremities.  Upon entering the third stage of infection, the patient is no longer infectious to other persons.  Therapy is symptomatic and usually requires only analgesics or antipyretics.  Another manifestation of infection during childhood may be idiopathic thrombocytopenic purpura.

     While Fifth disease is classic of childhood infection with parvovirus B19, infection in adults is usually asymptomatic or is associated with arthralgias.  The arthropathy is more common in female patients.  Pain usually occurs in the hands, wrists, knees and ankles and may be associated with joint swelling.  Symptoms usually resolve spontaneously over one to three weeks but may last months to years.  Symptomatic treatment of the joint pain is usually the only therapy required for the generally short term arthritis.

     Parvovirus B19 infection should be suspected in cases of acute worsening of anemia in patients with sickle cell anemia, thalassemia, pyruvate kinase deficiency, and iron deficiency anemia.  Bone marrow infection results in transient suppression of red blood cell production with the resultant anemia.  Because red cell production ceases, this anemia will be associated with a low reticulocyte count.  Diagnosis may be confirmed by finding parvovirus B19 DNA in the serum.  Treatment entails blood transfusions in appropriate cases, and since these patients are contagious, respiratory isolation is prudent to prevent nosocomial infection to other patients.  Chronic infection of the bone marrow may occur in immunocompromised hosts (AIDs patients, transplant recipients, and cancer patients) and results in a prolonged or recurrent anemia.

     When infection manifests as erythema infectiosum, the diagnosis may be made clinically.  However, other symptoms of infection may mimic other diseases; therefore, diagnosis with serologic testing is necessary.  A positive parvovirus B19-specific IgM antibody titer may be used to establish the diagnosis.  Since this is a common viral infection which is often asymptomatic, IgG titers are not useful to demonstrate acute infection unless serial titers demonstrating a dramatic increase are obtained.  If antibody titers are not diagnostic, viral DNA isolation from samples of blood or bone marrow using dot blot isolation or polymerase chain reaction techniques may prove diagnostic.  Pronormoblasts noted on bone marrow examination are suggestive of parvovirus B19 infection.