Parvovirus

Question 1

Parvovirus B19 structure

Answer 1

Single-stranded DNA virus

Question 2

What percent of women of reproductive age are Parvovirus immune?

Answer 2

50-75% of women are IgG+ (immune)

Question 3

When is Parvovirus infection more common?

Answer 3

Winter and spring

Question 4

Among which group does Parvovirus infection occur the most?

Answer 4

Schoolteachers, day care workers, and women with nursery or school-aged children in the home. Around 50% to 80% of susceptible household members and 20% to 30% of individuals exposed in a classroom acquire acute infection from an infected child.

Question 5

Parvovirus - adverse prognostic factors

Answer 5

Older maternal age
Maternal immunity and seroconversion
Raised maternal serum alpha-fetoprotein
Ultrasound findings

Question 6

How common are symptoms in adults with Parvovirus? What are the symptoms?

Answer 6

In adults at least half of the infections are asymptomatic.

About 30% may have flulike symptoms, arthralgias, and adenopathy.

Question 7

What are symptoms of Parvovirus in children?

Answer 7

Parvovirus B19 causes a common exanthematous disease in children 5 to 14 years old, called fifth disease or erythema infectiosum. Children have symptoms such as low- grade fever and “slapped-cheeks” rash, and are usually diagnosed just based on these symptoms.

Question 8

Transmission of Parvovirus

Answer 8

Respiratory droplets

Question 9

Parvovirus incubation period? When is infectivity greatest?

Answer 9

Incubation period 13-18 days

Infectivity greatest 7-10 days before the onset of symptoms

Question 10

What are the target cells for Parvovirus infection?

Answer 10

• The major target cells for parvovirus B19 are erythroid progenitors bearing the main cellular parvovirus B19 receptor P blood group antigen globoside on their surface.
• The virus causes infection and lysis of erythroid progenitor cells by apoptosis, leading to hemolysis and transient aplastic crisis.
• Cells in the S-phase of DNA mitosis are particularly vulnerable to parvovirus B19 and the fetus is at risk because of the vast number of cells in active mitosis, shorter half-life of RBCs, and immature immune system.

Question 11

Fetal complications of Parvovirus infection

Answer 11

• Fetal anemia is thought to be responsible for the development of skin edema and effusions.
• Hepatitis, placentitis, and myocarditis leading to heart failure may contribute to the development of fetal hydrops.

Question 12

What percentage of fetuses of mothers with primary Parvovirus infection will become infected themselves?

Answer 12

25-30% of fetuses of mothers with primary parvovirus B19 infection become infected themselves by vertical transmission.

Question 13

What percentage of Parvovirus-infected fetuses will develop complications?

Answer 13

10%

Question 14

What percentage of Parvovirus-infected fetuses will develop complications?

Answer 14

10%

Question 15

Of fetuses infected with Parvovirus, what percentage will develop anemia?

Answer 15

5-20%

Question 16

Of fetuses that develop anemia from Parvovirus, what percentage will develop hydrops fetalis?

Answer 16

30-50 (2-6% of all infected fetuses)

Question 17

What is the risk of fetal death from Parvovirus?

Answer 17

1-6%. Fetal death occurs almost exclusively in hydropic cases diagnosed at 20 weeks are treated with timely transfusion (90% survival).

Question 18

US findings in fetal parvovirus infection

Answer 18

Pericardial or pleural effusion
Ascites
Abdominal wall/skin edema
Bilateral hydroceles
Oligohydramnios or hydramnios
Increased (>95th percentile) cardiac biventricular outer diameter
Rare:
Hydrocephalus
Microcephaly
Intracranial and hepatic calcifications

Question 19

Treatment of Parvovirus exposure

Answer 19

Intravenous immunoglobulin (IVIG) prophylaxis is reasonable to consider for documented exposures in immunocompromised patients, although it is not currently recommended for prophylaxis in pregnancy.

Question 20

Diagnosis of maternal Parvovirus infection

Answer 20

Maternal infection is usually diagnosed by IgM+ or by IgG seroconversion. IgM appears by 3 days of an acute infection, peaks at 25 to 30 days, and disappears by 4 months. Serum IgG appears a few days after IgM, and coincides with resolution of maternal symptoms. The detection of viral DNA by PCR is another means of diagnosis.

Question 21

After maternal Parvovirus infection has been diagnosed, how do you screen for fetal anemia?

Answer 21

• Anemia can be detected by increased PSV of the MCA prior to the appearance hydrops
• With fetal anemia there is an increase of fetal cardiac output to maintain adequate oxygen delivery to tissues, leading to increased blood flow velocities
• MCA PSV using a threshold of >/=1.50 MoM has a high sensitivity (100%) and specificity (100%) for detecting fetal anemia

Question 22

Surveillance of fetuses after maternal Parvovirus infection

Answer 22

• If MCA PSV values are <1.50 MoM, it is suggested to continue weekly ultrasound scans for 10 to 12 weeks after the expo- sure
• The peak incidence of hydrops is at about four to six weeks after maternal infection
• Fetal surveillance should be initiated no later than four weeks after the onset of illness or estimate of seroconversion
• In cases of elevated MCA PSV but no hydrops, surveillance should be increased with US two to three per week to detect any sign of hydrops, or umbilical cord sampling performed.

Question 23

How is fetal Parvovirus infection confirmed

Answer 23

Amniotic fluid PCR

Question 24

Is there antiviral therapy available for Parvovirus?

Answer 24

There are no trials evaluating therapeutic interventions. No antiviral therapy is available.

Question 25

Can fetal anemia caused by Parvovirus resolve spontaneously?

Answer 25

Yes. Anemia and even hydrops can resolve spontaneously over four to six weeks (about 30% spontaneous resolution for hydrops) Resolution is more common in older (>20 weeks) fetuses because of a more mature immune system.

Question 26

Treatment of anemia in the fetus affected by Parvovirus between 24 and 33 6/7w

Answer 26

- Between 24 and 33 6/7 weeks, steroids for fetal lung maturity should be given - Fetal cordocentesis to document anemia and transfusion as necessary improve outcome in anemic and/or hydropic fetuses. - Frequently, one transfusion is sufficient.

Question 27

Treatment of anemia in the fetus affected by Parvovirus before 24w

Answer 27

-Before 24 weeks, with severe hydrops, termination may be offered, but transfusion can be beneficial, with apparently minimal to no significant sequelae if successful

Question 28

Treatment of anemia in the fetus affected by Parvovirus after 34w

Answer 28

After 34 weeks, delivery should be considered.

Question 29

In addition to fetal RBC transfusion for Parvovirus, what else should be considered?

Answer 29

Platelets should also be ready at the time of PUBS, as multiple series have demonstrated a concomitantly high incidence of fetal thrombocytopenia at the time of transfusion.

Question 30

Long-term prognosis for infants born to mothers infected by Parvovirus

Answer 30

- Infants born to IgM+ mothers are born IgG+ (mostly maternal), and 25% stay IgG+ at one year, as they were infected and have become immune. - General health status of survivors is no different compared with the general population - Some trials illustrate an incidence of developmental delay similar to the general population even in cases of fetuses transfused in utero for hydrops - More recent data of survivors aged six months to eight years demonstrated a 32% incidence of psychomotor developmental delay, independent of pretransfusion hemoglobin, platelet, or blood pH values. - Patients need to be counseled regarding the overall uncertainty regarding long-term neurodevelopmental outcome among survivors