Parvovirus Flashcards
Ref: EB MFM
Parvovirus B19 structure
Single-stranded DNA virus
What percent of women of reproductive age are Parvovirus immune?
50-75% of women are IgG+ (immune)
When is Parvovirus infection more common?
Winter and spring
Among which group does Parvovirus infection occur the most?
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.
Parvovirus - adverse prognostic factors
Older maternal age
Maternal immunity and seroconversion
Raised maternal serum alpha-fetoprotein
Ultrasound findings
How common are symptoms in adults with Parvovirus? What are the symptoms?
In adults at least half of the infections are asymptomatic.
About 30% may have flulike symptoms, arthralgias, and adenopathy.
What are symptoms of Parvovirus in children?
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.
Transmission of Parvovirus
Respiratory droplets
Parvovirus incubation period? When is infectivity greatest?
Incubation period 13-18 days
Infectivity greatest 7-10 days before the onset of symptoms
What are the target cells for Parvovirus infection?
- 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.
Fetal complications of Parvovirus infection
- 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.
What percentage of fetuses of mothers with primary Parvovirus infection will become infected themselves?
25-30% of fetuses of mothers with primary parvovirus B19 infection become infected themselves by vertical transmission.
What percentage of Parvovirus-infected fetuses will develop complications?
10%
What percentage of Parvovirus-infected fetuses will develop complications?
10%
Of fetuses infected with Parvovirus, what percentage will develop anemia?
5-20%
Of fetuses that develop anemia from Parvovirus, what percentage will develop hydrops fetalis?
30-50 (2-6% of all infected fetuses)
What is the risk of fetal death from Parvovirus?
1-6%. Fetal death occurs almost exclusively in hydropic cases diagnosed at 20 weeks are treated with timely transfusion (90% survival).
US findings in fetal parvovirus infection
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
Treatment of Parvovirus exposure
Intravenous immunoglobulin (IVIG) prophylaxis is reasonable to consider for documented exposures in immunocompromised patients, although it is not currently recommended for prophylaxis in pregnancy.
Diagnosis of maternal Parvovirus infection
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.
After maternal Parvovirus infection has been diagnosed, how do you screen for fetal anemia?
- 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
Surveillance of fetuses after maternal Parvovirus infection
- 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.
How is fetal Parvovirus infection confirmed
Amniotic fluid PCR
Is there antiviral therapy available for Parvovirus?
There are no trials evaluating therapeutic interventions. No antiviral therapy is available.
Can fetal anemia caused by Parvovirus resolve spontaneously?
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.
Treatment of anemia in the fetus affected by Parvovirus between 24 and 33 6/7w
- 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.
Treatment of anemia in the fetus affected by Parvovirus before 24w
-Before 24 weeks, with severe hydrops, termination may be offered, but transfusion can be beneficial, with apparently minimal to no significant sequelae if successful
Treatment of anemia in the fetus affected by Parvovirus after 34w
After 34 weeks, delivery should be considered.
In addition to fetal RBC transfusion for Parvovirus, what else should be considered?
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.
Long-term prognosis for infants born to mothers infected by Parvovirus
- 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
