Medical Matters: Almost everyone has heard about a disease of dogs caused by a "parvovirus". Although this virus is not transmitted to people, there is another type of parvovirus, called parvovirus B19, which can infect humans and which can have significant consequences for some individuals.
In a Check-up column earlier this year, reference was made to viral infections in children, one of which is caused by parvovirus B19. The piece correctly concluded that "Fifth disease", also called "erythema infectiousum" or "slapped-cheek syndrome" (other names for parvovirus B19 infection), is generally a mild viral infection. Its symptoms includes rash, malaise, mild fever, runny nose and sore throat, and it leaves no lasting ill effects in infected healthy people. Most individuals (65-70 per cent) will have been exposed to the virus by adulthood and will be essentially immune from any subsequent parvovirus B19 infection.
Parvovirus B19 is transmitted by respiratory secretions and close contact with infected, and often non-symptomatic, individuals. It can also be transmitted by blood, but thanks to the implementation of screening tests by blood-product manufacturers, this source of transmission is negligible.
Importantly, two groups of individuals need to be particularly aware of parvovirus B19 infection: pregnant women, the focus of this piece, and immuno-compromised patients (eg, bone marrow and solid organ transplant patients).
Children tend to be the greatest source of parvovirus B19 infection. Most health promotion agencies, while advising that women working with children should be aware of the effects of the infection, do not recommend avoidance of such workplaces.
About one in three pregnant women are susceptible to parvovirus B19 infection, although infection occurs only in about one in 500 pregnancies. If a woman becomes infected with parvovirus B19 during the first 26 weeks of pregnancy, there is a 10 per cent chance that the infection will be transmitted to the foetus, resulting in foetal anaemia, hydrops foetalis (fluid retention) and, on occasion, spontaneous abortion.
There is no significant evidence that parvovirus B19 infection causes any congenital defects. Although precise numbers are difficult to establish, in part due to a general lack of awareness of the effects of parvovirus B19 infection in pregnancy and the cyclical nature of the infection, it is estimated that between 2,500 and 5,000 cases of parvovirus B19-induced foetal loss occur each year in the EU, which equates to about 100-200 cases per annum in Ireland.
Although the symptoms of parvovirus B19 infection may not always be apparent during pregnancy, blood tests developed by an Irish company, Biotrin, can establish the susceptibility of a pregnant woman to the infection and if infection has occurred during pregnancy. In addition, ultrasound scanning can detect symptoms of foetal parvovirus B19 infection, and recent evidence from the scientific literature strongly indicates that foetal blood transfusions may increase the survival rate of parvovirus B19-infected foetuses.
Thus, all relevant healthcare workers, pregnant women and their partners should be aware of this infection, its diagnosis and the emerging treatments. If possible, pregnant women should attempt to minimise contact with potentially infected individuals and discuss the issue immediately with their GP if they suspect exposure may have occurred.
In conclusion, parvovirus B19 can cause foetal loss in pregnancy. Only about 30 per cent of pregnant women are susceptible to parvovirus B19 infection; the disease is easily diagnosed; and advances in the treatment of parvovirus B19-infected pregnant women increase the rate of foetal survival, even if infection has occurred.
Dr Sean Doyle, Department of Biology and National Institute for Cellular Biotechnology, National University of Ireland Maynooth. His parvovirus B19 research programme was funded by the EU, Health Research Board and Enterprise Ireland. Website: www.euparvo.com. He was previously head of research and development with Biotrin (Ireland).
Muiris Houston is on leave.