Which of the following statements is most accurate regarding human infection with parvovirus B19?

Introduction / Context:
Parvovirus B19 is a small DNA virus that infects humans and causes a range of clinical syndromes. It is best known for causing erythema infectiosum in children but also has important effects on red blood cell production. Many exam questions test detailed knowledge about its pathogenesis and diagnostic features. This question asks you to select the most accurate statement from a set of closely related options, so careful reading and recall of virology concepts are required.

Given Data / Assumptions:

• The virus under discussion is parvovirus B19, a human pathogen.
• Options mention severe anemia, hydrops fetalis, RNA detection, and replication mechanisms.
• We assume familiarity with the fact that parvovirus B19 is a single stranded DNA virus with a tropism for erythroid precursors.

Concept / Approach:
Parvovirus B19 has a strong tropism for erythroid precursor cells in the bone marrow. It binds to the P antigen on these cells, infects them, and halts red blood cell production. In healthy individuals, this temporary shut down may cause only mild symptoms, but in patients with chronic hemolytic anemias such as sickle cell disease, it can lead to a transient aplastic crisis with severe anemia. In pregnancy, infection of a seronegative mother can spread to the fetus and cause hydrops fetalis because of severe fetal anemia, but this is less likely in a mother who is already seropositive and immune. Parvovirus B19 is a single stranded DNA virus, and diagnostic tests rely on detection of viral DNA or specific IgM and IgG antibodies, not RNA. The virus uses host cell enzymes for DNA replication in the nucleus; it does not carry its own DNA polymerase.

Step-by-Step Solution:
Step 1: Recall that parvovirus B19 infects and destroys erythroid precursor cells in the bone marrow. Step 2: Recognise that this can cause severe anemia, particularly in individuals with increased red cell turnover. Step 3: Evaluate option A, which correctly links parvovirus B19 with infection of erythrocyte precursors and severe anemia. Step 4: Consider option B, which mentions hydrops fetalis in a seropositive mother. A mother who is already immune is less likely to transmit the virus, so this statement is inaccurate. Step 5: Assess option C, which refers to detection of viral RNA. Parvovirus B19 is a DNA virus, so tests target viral DNA or antibodies, making this statement incorrect. Step 6: Analyse option D, which claims that the virus uses a virally encoded DNA polymerase. In reality, parvoviruses rely on host DNA polymerase, so this statement is also incorrect.

Verification / Alternative check:
Virology and hematology references describe parvovirus B19 as a cause of acute aplastic crises in patients with hemolytic anemias, confirming its preference for erythroid precursors. They explain that the virus uses the host DNA replication machinery and that diagnostic tests frequently include PCR for viral DNA and serology for IgM and IgG antibodies. Obstetric texts note that primary infection in pregnancy, particularly in a non immune woman, can lead to fetal hydrops due to severe anemia, but prior immunity reduces this risk. These sources support option A as the most accurate statement.

Why Other Options Are Wrong:

• Parvovirus B19 commonly causes hydrops fetalis by transplacental infection of a fetus in an already immune seropositive mother: Primary infection in a non immune mother is the main concern; prior immunity generally protects the fetus.
• Parvovirus B19 is usually diagnosed by direct detection of viral RNA using standard PCR tests: The virus is a DNA virus, so PCR targets viral DNA, not RNA.
• Parvovirus B19 replicates in the host cell nucleus using a virally encoded DNA polymerase to create a double stranded DNA intermediate: The virus uses host cell DNA polymerase and does not encode its own polymerase.

Common Pitfalls:
Students frequently confuse DNA and RNA viruses when recalling diagnostic techniques. It is crucial to remember that parvovirus B19 is a single stranded DNA virus. Another common error is assuming that any mention of hydrops fetalis must be correct, without considering the detail about maternal serostatus. Misremembering whether a virus carries its own polymerase is also common. A good revision strategy is to group viruses by nucleic acid type and replication strategy, noting which rely heavily on host enzymes and which carry their own polymerases.

Final Answer:
The most accurate statement about infection with parvovirus B19 is that it can cause severe anemia because it preferentially infects and destroys erythrocyte precursor cells in the bone marrow.