Review Question - QID 101469

Erythema infectiosum is caused by parvovirus B19, a non-enveloped, single-stranded DNA virus.

Erythema infectiosum is a "slapped face" rash that most commonly presents in children aged 4-12 with fever and flu like symptoms. It has a 7-10 day incubation period. Infected adults may also present with arthralgias. Parvovirus B19 can result in aplastic crisis in sickle cell patients and hydrops fetalis in pregnant women, and thus, is important to recognize early. Parvoviridae (from the Latin, parvum = small) are the only single-stranded DNA viruses tested on the USMLE Step 1.

Servey et al. review the presentation and treatment of parvovirus B19 infection: Fifth disease is highly infectious and is caused by parvovirus B19 which is spread by respiratory droplet. The "slapped cheek" rash of fifth disease, however, presents after the child is no longer contagious and treatment is supportive. While most patients completely recover without intervention, some with underlying conditions may require transfusions or intravenous immunoglobulin therapy.

Lamont et al. highlight the danger of parvovirus infection in pregnancy, noting that 30-50% of pregnant women are nonimmune. Normal outcomes without consequence can be seen with fetal infection but fetal demise is also possible, even without infectious sequelae seen on ultrasound, and parvovirus B19 should always be considered when hydrops fetalis is present without an obvious immune mechanism.

Illustration A demonstrates the physical exam finding of "slapped cheeks" that is often seen with children infected with Parvovirus B19.

Incorrect answers:
Answer 1: Enveloped viruses with double-stranded DNA include herpes, hepadna, and pox viruses.
Answer 2: No viruses tested on the USMLE Step 1 are enveloped with single-stranded DNA.
Answer 3: Most RNA viruses tested on the USMLE Step 1 are single-stranded and enveloped. Exceptions include reoviruses (double-stranded and non-enveloped) and picorna and calciviruses (single-stranded, non-enveloped).
Answer 4: Non-enveloped viruses with double-stranded DNA include adeno, and papova (papilloma + polyoma) viruses.