Parvovirus (human parvovirus B19, fifth disease)

General: There are distinct human and non-human parvoviruses, but there are no cross-infections or cross-carriers. It was discovered in 1975 by Cossart and colleagues, who found viral particles in asymptomatic patients being screened for hepatitis B infection. They demonstrated that these particles were parvoviruses and, because specimen 19 of panel B contained the unexpected virus, was designated B19. Preferentially infect rapidly dividing cells, such as erythroid progenitor cells, causing a transient cessation of erythroid production. There is an initial drop in reticulocyte count (occasionally accompanied by thrombocytopenia and leukopenia), then anemia, followed by reticulocytosis as the marrow recovers.

Clinical: A single-stranded DNA virus which causes fifth disease, typically in children, consisting of a "slapped-cheek" facial and lacey truncal and limb rash (erythema infectiosum) with self-limiting mild cold-like symptoms lasting 7-10 days. Occasionally there is joint pain and swelling (usually hands, wrists, knees). There is a 4~14 day incubation. IgM appears in the second week, IgG after the third; may also do PCR for viral DNA, which is more sensitive. Causes a rapid drop in May rarely cause an acute severe anemia (Hg drop by <=1g/mL in the otherwise healthy, but may be much more), especially in those with a chronic anemia (sickle cell anemia, iron deficiency anemia, thalassemia, etc.), or may cause a chronic anemia due to persistent infection in the immunocompromised. Hydrops fetalis and fetal death are complications of intrauterine parvovirus B19 infection.

• DDx:
  • Of similar rash: Rubella, enteroviruses, arboviruses, streptococcal infection, allergy.
  • Of acute aplastic anemia: Bacterial infections (eg. pneumococcal septicaemia) or marrow suppressive drugs (chloramphenicol).

Growth characteristics: