The Flemish Association for Obstetrics and Gynaecology is concerned about the alarming rise in parvovirus infections this year. An increasing number of pregnant women are seeking medical help. The association issued a call for vigilance to colleagues earlier this month.
“We see more and more pregnant women with parvoviral infections,” said Isabelle Dehaene, a gynaecologist at UZ Gent on VRT NWS. “These women don’t always have symptoms, but we discover the infection when they come in because their baby is moving less.”
Common childhood illness
Parvovirus B19, often simply referred to as parvovirus, causes a common childhood illness known as slapped cheek syndrome or fifth disease, which is usually mild. However, when contracted during pregnancy, this virus can lead to serious complications such as miscarriage, fetal death, or severe anemia in the unborn baby. The virus can also cause joint pain in adults, serious blood problems in people with sickle-cell disease, and long-term anemia in those with weakened immune systems. It spreads mainly through coughing and sneezing, but can also be transmitted through blood and in hospitals.
While we know that parvoviral infections are common in children and that the virus continues to infect people at a lower rate into adulthood, there hasn’t been much research on how widespread the infection is overall. Most studies focus specifically on the risks to pregnant women.
Currently, there’s no vaccine for parvovirus B19. However, after infection, people usually have antibodies for life, which can help us understand how many people have been exposed to the virus and map the risk of getting infected at different ages.
Multi-country study
We previously explored how many people in five European countries (Belgium, England & Wales, Finland, Italy, Poland) have antibodies against parvovirus, to compare the spread of the virus and assess the risk to pregnant women using population data. The study represents the first comprehensive analysis of parvovirus B19 infections using large serum banks across several European countries with a standardized laboratory assay and it allowed us to uncover several novel insights about parvovirus B19.
While the age-specific seroprevalence profiles in the five countries showed similar patterns, including a rapid increase during childhood, a plateau in young adults, and another increase later, we observed differences in the force of infection during childhood and adolescence, and in the risk of infection during pregnancy. These differences might be influenced by cultural and behavioral factors that affect contact rates among key transmission groups.
Waning immunity?
The unexpected plateau we observed in seroprevalence among adults aged 20-40 challenges the assumption of lifelong immunity, and could potentially be related to the waning of antibodies for parvovirus B19.
We evaluated several immunological scenarios by fitting different compartmental dynamic transmission models to serological data using data on social contact patterns. Our results show that for four countries (all studied except for Finland), model selection criteria favor the scenarios allowing for waning immunity at an age-specific rate over the assumption of lifelong immunity, assuming that the transmission rates are directly proportional to the contact rates. Different views on the evolution of the immune response to PVB19 infection lead to altered estimates of the age-specific force of infection and the basic reproduction number. The scenarios which allow for multiple infections during one lifetime predict a higher frequency of parvovirus infection in pregnant women and of associated fetal deaths.
Niel Hens: “There is a limit to what can be inferred from serological surveys, and our findings highlight the need for improved surveillance and routine epidemiological data collection to better understand the public health impact of parvovirus B19.”
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