Chapter 15. Congenital Fetal Infections

Essentials of Diagnosis

• Caused by parvovirus B19, a single-stranded DNA virus
• Clinical manifestations: commonly asymptomatic, erythema infectiosum, systemic symptoms (fever, arthropathy, malaise), or aplastic crises
• Complications in pregnancy: fetal demise, fetal anemia, hydrops fetalis
• Diagnosis: serologic tests (immunoglobulin [Ig] G and IgM antibodies); serum viral DNA polymerase chain reaction
• Antenatal sonographic findings: fetal anemia, hydrops, elevated middle cerebral artery peak systolic velocity
• Fetal diagnosis: cordocentesis
• Fetal treatment: intrauterine blood transfusion

Pathogenesis

Parvovirus B19 infection, a common childhood infection, tends to be more frequent in late winter or early spring. The infection is caused by a single-stranded DNA virus, the B19 parvovirus, which is transmitted through respiratory secretions and hand-to-mouth contact. The virus has a predilection for rapidly dividing cells such as erythroid progenitor cells.

Prevalence of seropositivity increases with age, and about 50–60% of reproductive-aged women have documented antibodies to parvovirus B19 consistent with prior infection. Immunity is considered lifelong, although reinfection has been documented. The incidence of acute parvovirus infection during pregnancy is 3.3–3.8%. Schoolteachers, day care workers, and homemakers are most susceptible. Nonimmune individuals exposed in a classroom have a 20–30% risk of infection. The secondary attack rate for household members is up to 50%.

During pregnancy, the virus can cross the placenta and infect red cell progenitors in the fetal bone marrow. The virus suppresses erythropoiesis by attaching to the “P” antigen on red cell stem cells. This results in severe anemia and high-output congestive heart failure. In addition to the reduced survival of fetal red blood cells, anemia is further complicated by the increased demands of an expanding intravascular volume and the inability of the immature immune system to control the infection. Additionally, the virus can attack fetal myocardiocytes via the same “P” antigen and cause a cardiomyopathy, further exacerbating the congestive heart failure.

Prevention

Pregnant women who are susceptible to parvovirus B19 should avoid contact with known infected individuals. However, since 20% of infections are subclinical, exposure cannot be eliminated by identifying and excluding individuals with acute parvovirus B19 infection. Additionally, those with infection are infectious prior to the onset of symptoms. Therefore, a policy to routinely remove women from occupations considered high risk, such as day care attendants, is not recommended. On the other hand, patients should be counseled on careful hand washing and avoidance of sharing food and drink.

Clinical Findings

Symptoms & Signs (Table 15–1)

Parvovirus B19 causes ...