Parvoviruses are small round viruses with a single stranded DNA genome that lack a lipid envelope. Fairly widespread, they are noted as significant pathogens in veterinary medicine, causing a range of diseases that includes reproductive failure.
Parvovirus B19 (also known as Erythrovirus B19) causes a common childhood illness called erythema infectiosum or fifth disease. The disease is characterised by fever and a rash with erythematous cheeks, from which it derives its common name ‘slapped cheek' disease. Parvovirus B19 infection generally results in a mild febrile illness, but can have more severe manifestations in patients at risk. In patients with increased red blood cell turnover (underlying haemolytic haemoglobulinopathies), infection can lead to a transient aplastic crises, and to pure red cell aplasia in immunocompromised. Infection in the first 20 weeks of pregnancy is associated with increase risk of intrauterine death and hydrops fetalis. For this reason, an observed increase in parvovirus B19 activity in Scotland warrants increased vigilance by clinicians and awareness of the relevant information and guidance on diagnosis and management of infection (1-4).
A common infection, parvovirus is usually spread by the respiratory route although it may also be transmitted by blood components or blood products.
Surveillance in Scotland
As for other non-notifiable conditions, surveillance information on Parvovirus B19 infections is based on the numbers of laboratory reports to HPS, which come for the most part from hospitalised patients. Information on laboratory confirmed cases of this infection are currently routinely reported electronically to HPS through ECOSS (Electronic Communication of Surveillance in Scotland).
Trends in Scotland (1988-2013)
In temperate countries like the UK a seasonal pattern in transmission can be observed, with increased numbers of cases reported in spring and early summer. A three to four year epidemic cycle of increasing case reports has been observed for parvovirus B19 in the UK.2
Historically, we have seen cyclical increases in laboratory reports of Parvovirus B19 infections every three to four years. In recent years, there have been years where this cyclical time period has extended to more than four years. An increase in laboratory detections of Parvovirus B19 in Spring 2013 was described in an article in the HPS weekly report, the details of which are also described below.
This increase is in keeping with a 4-year cycle as the last peak in Parvovirus B19 activity seen was in 2009. Prior to 2009, peaks in activity were seen in 1994, 1998, 2003 and 2007.
The number of laboratory confirmed reports of Parvovirus B19 infections submitted to HPS since January 1988 to date are shown in Figure 1. Infection is most common in young children, but testing is largely focused on pregnant women (see Figure 1), because of the potentially serious consequences, as well as the demonstration that complications of in-utero infection can be successfully treated with foetal transfusion. Despite this recognised ascertainment bias, the number of laboratory confirmed reports shown below suggests an increase in parvovirus B19 activity in Scotland in the first quarter of 2013.
An increase in parvovirus B19 activity was already noted in England and Wales in the first two quarters of last year (2012).(2) Figure 1 shows that whilst the number of laboratory confirmed cases reported in the first three months (weeks 1-12) of 2012 was within expected levels in Scotland, the number of cases reported increased in the summer and autumn of 2012. The number of reports received in the first three months of 2013, indicate a further increase in parvovirus B19 activity in Scotland, to levels which are higher than at the same time in previous years. The increase in laboratory confirmed infections can be seen across most health boards in Scotland, without apparent geographical focus.
The recent increase seen in 2013 may in part be related to increased numbers of tests performed due to increased awareness of the infection. However as negative test results for Parvovirus B19 are not reported through the ECOSS laboratory reporting system (ECOSS), changes in testing strategy can not be quantified.
Figure 1: Number of laboratory confirmed Parvovirus B19 cases in Scotland from January 1988 to March 2013 (Click on image below to view a larger version of this figure)
Footnote: Please note the following caveats regarding the data presented in Figure 1:
- The method for submitting reports of laboratory confirmed Parvovirus B19 infections over time has changed. Prior to the implementation of an electronic laboratory reporting system called ECOSS in 2008, reports of these infections were submitted through a different laboratory reporting scheme which was predominantly paper-based.
- Data on Parvovirus B19 infections before the first week of 2008 is not directly comparable to current data due to key differences on how this data was processed and how episodes of infection were defined. More than one laboratory test result may be reported for the same individual (multiple testing). For the data on cases prior to 2008, laboratory reports received within the same week were de-duplicated manually. For data on cases from 2008 onwards, episode length is defined as 8 weeks, so that in the rare event that further laboratory results are received for the same infected individual in this time span, this is only recorded as one case. The data from before 2008 gives a good indication of the trend of Parvovirus B19 activity over time, however it is not possible to directly compare the absolute numbers of cases recorded from week 1 2008 onwards, with the number of cases recorded before this date.
Incidence and Risk
Parvovirus B19 is a common infection, with approximately 50-60% of individuals having been infected by the time they reach adulthood. Infection is most common in young children, but testing is largely focused on pregnant women (see Figure 2 below), because of the potentially serious consequences, as well as the demonstration that complications of in-utero infection can be successfully treated with foetal transfusion.
The exact time in which an increase in Parvovirus B19 activity occurs each year may vary from year to year and infection can occur at any time throughout the year. However, peaks in infections being reported are seen usually in the spring or summer months.
In adults, especially women, B19 infection can be complicated by acute polyarthritis, which may persist in some cases. Infection during pregnancy is of special concern since B19 can cross the placenta, with potentially serious complications (although most women infected during pregnancy deliver a healthy infant). There is also a high risk of complications in patients who are immunocompromised or who have chronic haemolytic anaemia.
In the first quarter of 2013, the numbers of laboratory reports received increased, both for women of child-bearing age as well as the overall population (Figure 2).
Figure 2: Number of laboratory confirmed Parvovirus B19 cases in Scotland from January 2008 to March 2013, reported through the electronic reporting system (ECOSS)
There is currently no licensed vaccine for Parvovirus B19. Guidance on the management of Parvovirus B19 infection in health care settings, the community and in pregnant women is available from Public Health England.
1. HPA Rash Guidance Group (2011). Guidance on Viral Rash in Pregnancy: Investigation, Diagnosis and Management of Viral Rash Illness, or Exposure to Viral Rash Illness in Pregnancy.
2. PHE website: Infectious Diseases › Infections A-Z › Parvovirus B19 (slapped cheek syndrome, fifth disease or erythema infectiosum) › Parvovirus - general information.
3. Crowcroft NS, Roth CE, Cohen BJ, Miller E. (1999). Guidance for control of Parvovirus B19 infection in healthcare settings and the community. J Public Health 21(4): 439-446.
4. NHS Clinical Knowledge Summaries, http://www.cks.nhs.uk/parvovirus_b19_infection.
5. HPA (2012) Increased parvovirus B19 activity in England and Wales. Health Protection Report 6(11)