Human parvovirus B19 in clotting factor concentrates: B19 DNA detection by the nested polymerase chain reaction

Secondary structure of DNA released from purified capsids of human parvovirus B19 under moderate denaturing conditions

Parvovirus B19 (B19V) possesses a linear single-stranded DNA genome of either positive or negative polarity. Due to intramolecular sequence homologies, either strand may theoretically be folded in several alternative ways. Viral DNA, when extracted from virions by several procedures, presents as linear single-stranded and/or linear double-stranded molecules, except when one particular commercial kit is used. This protocol yields DNA with an aberrant electrophoretic mobility in addition to linear double-stranded molecules, but never any single-stranded molecules. This peculiar kind of DNA was found in all plasma or serum samples tested and so we decided to analyse its secondary structure. In line with our results for one- and two-dimensional electrophoresis, mobility shift assays, DNA preparation by an in-house extraction method with moderate denaturing conditions, density gradient ultracentrifugation, DNA digestion experiments and competition hybridization assays, we conclude that (i) the unique internal portions of this distinctive single-stranded molecules are folded into tight tangles and (ii) the two terminal redundant regions are associated with each other, yielding non-covalently closed pseudo-circular molecules stabilized by a short (18 nucleotides) intramolecular stem, whereas the extreme 3'- and 5'-ends are folded back on themselves, forming a structure resembling a twin hairpin. The question arises as to whether this fairly unstable structure represents the encapsidated genome structure. The answer to this question remains quite relevant in terms of comprehending the initiation and end of B19V genome replication.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

Parvovirus B19V DNA contamination in Chinese plasma and plasma derivatives

Background

To ensure the safety of plasma derivatives, screening for human parvovirus B19V genomic DNA in donated plasma using a pooling strategy is performed in some countries. We investigated the prevalence of B19V DNA and anti-B19V antibodies in Chinese plasma pools, plasma derivatives and plasma donations to evaluate the risk posed by B19V.

Methods

Using a Q-PCR assay developed in-house, we tested for B19V genomic DNA in 142 plasma pools collected between January 2009 and June 2011 from two Chinese blood products manufacturers. Plasma derivatives collected between 1993–1995 (10 batches of albumin, 155 batches of intravenous immunoglobulin, IVIG) and 2009–2011 (50 batches of albumin, 54 batches of IVIG, 35 batches of factor VIII, 7 batches of fibrinogen, and 17 batches of prothrombin complex concentrate, PCC) were also tested for B19V contamination. In addition, B19V genome prevalence in minipools(including 90 individual donations) of 49680 individual plasma samples collected between August 2011 and March 2012 by a single Chinese manufacturer was investigated. IgM/IgG was also investigated in plasma pools/derivatives and in minipools with B19V-DNA titers above 1x10⁴ and 1x10⁶ geq/mL using B19 ELISA IgM/IgG assay(Virion-Serion, Würzburg, Germany), respectively.

Results

B19V-DNA was detected in 54.2% of plasma pools from two Chinese blood product manufacturers; among recently produced blood products, B19V was detected in 21/54 IVIG samples, 19/35 factor VIII samples, 6/7 fibrinogen samples, and 12/17 PCC samples, but not in albumin samples. The levels of B19V-DNA in these samples varied from 10²-10⁷ geq/mL. In samples with >10⁴ geq/mL genome DNA, B19V-specific IgG was also found in all corresponding plasma pools and IVIG, whereas none was detected in the majority of other plasma derivatives. Screening of plasma donations indicated that most minipools were contaminated with B19V-DNA (10²-10⁸ geq/mL) and one donation had 1.09 × 10¹⁰ geq/mL B19V genomic DNA along with a non-classical IgG/IgM profile.

Conclusions

Despite the implementation of some inactivation/removal methods designed to prevent viral contamination, B19V DNA was detectable in Chinese plasma pools and plasma derivatives. Thus, the introduction of B19V screening and discard donation with high viramic concentration for Chinese plasma donors would be desirable.

Human erythrovirus B19 and blood transfusion ? an update

Erythrovirus (parvovirus) B19 (B19) is a common human pathogen. It is a non-enveloped single-strand DNA virus packaging its genome in small tight capsids consisting of viral VP1 and VP2 proteins. It is now accepted that B19 is a relatively quickly evolving virus having diverged in several genetic variants recently identified. The main route of B19 transmission is respiratory, with a majority of infections occurring during childhood and manifesting as erythema infectiousum. B19 can also be transmitted vertically and via blood transfusion and organ transplantation. The majority of adult populations show immunological evidence of previous exposure to B19. Although the immune response is able to clear infection and provide life-long protection against B19, recent data suggest that in some, if not the majority, of individuals the acute phase of infection is followed by viral persistence in the blood or other tissues regardless of the host's immunocompetence. Transmission of B19 by blood and blood products and its resistance to common viral inactivation methods raises several blood safety questions, still unanswered. The diversity of B19 strains and the ability of the virus to persist in the presence of specific antibodies raise the issue of transmissibility by transfusion not so much to immunocompetent recipients but rather to the large proportion of recipients in whom there is some degree of immunodeficiency. The ability of the virus to reactivate in immunodeficient recipients may create difficulties in differentiating between transfusion transmission and reactivation.

B19 virus infection in renal transplant recipients

BACKGROUND

B19 virus infection with persistent anaemia has been reported in organ transplant recipients. Detection of B19 virus DNA in serum is the best direct marker of active infection.

OBJECTIVE

The present study evaluated the incidence and clinical role of active B19 virus infection in renal transplant recipients presenting with anaemia.

STUDY DESIGN

Forty-eight such recipients were investigated by nested PCR on serum samples. The controls were 21 recipients without anaemia. Active HCMV infection was also investigated as a marker of high immunosuppression.

RESULTS AND CONCLUSIONS

In 11/48 (23%) patients B19 virus DNA was demonstrated in serum versus only 1/21 (5%) of the controls. Ten of these 11 patients had already been seropositive at transplantation and active infection occurred in eight of them during the first 3 months after transplantation. The remaining patient experienced a primary infection 9 months after transplantation. Eight (73%) of these 11 patients displayed a concomitant HCMV infection and four (36%) showed increasing serum creatinine levels but none developed glomerulopathy; 3/11 (27%) recovered spontaneously from anaemia whereas 8/11 (73%) needed therapy. In conclusion, the relatively high occurrence (23%) of B19 virus infection in patients presenting with anaemia, suggests that it should be considered in the differential diagnosis of persistent anaemia in renal transplant recipients. Presence of the viral DNA should be assessed early from transplantation and the viral load should be monitored to follow persistent infection and better understand the relation between active infection and occurrence of anaemia, and to assess the efficacy of IVIG therapy and/or immunosuppression reduction in clearing the virus.

Analysis of B19 virus contamination in plasma pools for manufacturing, by using a competitive polymerase chain reaction assay

BACKGROUND AND OBJECTIVES

The presence of B19 virus in blood poses a risk of transmission of the virus via blood or blood products. Screening processes for manufacturing should be aimed at achieving production plasma pools with B19 virus contamination levels below 104 genome equivalents/ml (geq/ml) in order to prevent transmission of infection through plasma derivatives.

MATERIALS AND METHODS

The suitability of a competitor plasmid as an internal analytical standard for the detection of B19 virus in plasma pools was assessed by using a competitive polymerase chain reaction (PCR) assay. Seventy-five plasma pools, each consisting of 960 single donations, were analysed for B19 virus contamination following a lysis treatment.

RESULTS

The amount of competitor plasmid in the competitive PCR assay established, with good accuracy, a threshold value for discrimination of the viral load in plasma pools. Analysis of samples from plasma pools showed that 12% of pools were contaminated with B19 virus at levels above the set threshold value.

CONCLUSIONS

The competitive PCR assay developed proved to be effective for discrimination of the B19 virus contamination level in screening of plasma pools for manufacturing.

Persistent parvovirus B19 infections with different clinical outcomes in renal transplant recipients: diagnostic relevance of polymerase chain reaction (PCR) and of quantification of B19 DNA in sera

OBJECTIVE: To study parvovirus B19 infection in immunocompromised subjects such as renal transplantation recipients. METHODS: Two cases of B19 infection in renal transplant recipients have been included in the study. The outcome of the infection has been studied by both serologic and virologic methods. A monitoring of the DNAemia was done by a nested PCR in endpoint titration assays. RESULTS: In one patient with severe anemia an acute B19 infection was diagnosed by PCR 26 days after the transplant; a high level of DNAemia persisted until an intravenous immunoglobulin treatment. Then a sharp decrease of the DNAemia was shown, without full clearance of B19 virus. In a lymphocyte suspension from the organ donor, B19 DNA was detected. In the other patient, who recovered spontaneously from anemia, a persistent B19 infection was demonstrated at day 106 after transplantation and was still demonstrable after 470 days. CONCLUSIONS: A high level of B19 DNAemia was associated with symptomatic infection, with severe anemia, whereas low-level DNAemia was long-lasting in asymptomatic subjects with impaired immunologic responses. The endpoint titration assay by nested PCR was very useful for the monitoring of B19 infection, particularly following the therapeutic intravenous immunoglobulin administration.

Parvovirus B19 DNA in plasma pools and plasma derivatives

BACKGROUND AND OBJECTIVES

Human parvovirus B19 (B19) has been transmitted by various plasma-derived medicinal products. The aim of this study was to determine the frequency and the level of B19 DNA contamination in plasma pools destined for fractionation and in a broad range of plasma derivatives. In addition, removal of B19 DNA by the manufacturing process was investigated in cases where corresponding samples from plasma pool and product were available.

MATERIALS AND METHODS

Plasma pool samples and blood products were tested for B19 DNA by nested polymerase chain reaction (PCR), and the viral DNA content was determined by TaqMan quantitative PCR.

RESULTS

Two-hundred and twenty two of 372 plasma pools for fractionation contained B19 DNA at concentrations of 10(2)-10(8) genome equivalents/ml (geq/ml). While approximately 65% of the DNA-positive plasma pools were only moderately contaminated (< 10(5) geq/ml), 35% contained > 10(6) geq/ml. High frequencies of contamination were detected in Factor VIII (79 of 91), prothrombin complex concentrates (38 of 43) and Factor IX (41 of 62), where the concentration of B19 DNA ranged between 102 and 107 geq/ml. A lower level of B19 DNA contamination was found in antithrombin III (five of 26 samples), in anti-D immunoglobulins (three of 37 samples) and in albumin (four of 51 samples), with levels ranging between 10(2) and 10(3) geq/ml. Furthermore, investigation of plasma pools for solvent/detergent plasma (S/D plasma), from two manufacturers, revealed B19 DNA in 15 of 66 batches at concentrations of 10(2)-10(8) geq/ml. Similar concentrations were detected in the corresponding final S/D plasma products. Anti-B19 immunoglobulin G (IgG) was found in plasma pools and S/D plasma at concentrations of approximately 40 IU/ml.

CONCLUSION

Although positive PCR results do not necessarily reflect infectivity, these data show that B19 is a common contaminant in plasma pools and in plasma-derived medicinal products. Considering the resistance of animal parvoviruses to inactivation by heat and chemical agents, and the absence of specific information for B19, the risk of B19 transmission by plasma products should be considered. Physicians should be aware of this problem when treating patients of B19-related risk groups. The plasma fractionation industry should continue their efforts to avoid B19 contamination of plasma derivatives and develop methods which are effective in removing/inactivating parvovirus B19.

Clinical illness due to parvovirus B19 infection after infusion of solvent/detergent-treated pooled plasma

BACKGROUND

Lipid-enveloped viruses such as HIV, HBV, and HCV can be inactivated by treatment with solvents and detergents. HAV and human parvovirus B19 lack lipid envelopes and are not inactivated. Solvent/detergent-treated pooled plasma (S/D plasma) contains neutralizing antibodies, but it is not known whether the parvovirus B19 antibody content is sufficient to prevent transmission of the disease. A patient is described who developed a clinical illness due to parvovirus B19 infection after the infusion of S/D plasma.

CASE REPORT

A 36-year-old woman with myasthenia gravis underwent five plasma exchange procedures from January 15 to January 25, 1999, using albumin, except for 5 units of SD plasma given because of a low fibrinogen level. Four of the 5 units were implicated in a recall after high levels of parvovirus B19 DNA were found in several lots. Two weeks after the infusion, the patient developed fatigue, a rash, and severe polyarthralgias. Parvovirus B19 IgG and IgM antibody titers were consistent with an acute infection.

CONCLUSION

Clinically apparent parvovirus B19 infection can follow the use of S/D plasma that contains high levels of parvovirus B19 DNA.

Viral safety of haemophilia treatment products

The epidemics of HIV and hepatitis C in treated haemophiliacs spurred rapid technological advances in the viral safety of clotting factor concentrates produced from large donor pools. Sequential steps are now employed to minimize infectious risks. The initial viral burden is reduced by screening donors and by testing individual donations and plasma pools for antivirus antibodies, viral antigens, and nucleic acid. These techniques are supplemented by nonspecific viral reduction steps based on physical partitioning and inactivation of pathogens by physical (eg, heat) or chemical (eg, solvent-detergent) means. Although these processes have virtually eliminated the transmission of HIV and hepatitis B and C, there is still evidence that concentrates can transmit small nonenveloped viruses, such as parvovirus B19 and hepatitis A virus. Furthermore, new agents which may not be susceptible to current viral inactivation procedures continue to be identified. Concerns such as these have also given impetus to the development of recombinant clotting factor proteins. Recombinant factor IX concentrate is now produced without the use of human plasma proteins at any step in the manufacturing or formulation process. In practice, the risk of viral transmission by clotting factor concentrates is now so remote that any manipulations to further reduce this risk may be counter-productive, by enhancing cost (hence compromising availability) and potentially promoting other adverse effects such as immunogenicity.

Prevalence of human parvovirus B19 and TT virus in a group of young haemophiliacs in South Africa

A well recognized hazard of transfusion with blood or blood products is the acquisition of a viral infection. Parvovirus B19 and transfusion transmitted virus (TTV) are two of several non-enveloped viruses that may on rare occasions be present in coagulation factor concentrates. The prevalence of these viruses in the South African Haemophilia population has not previously been studied. Thirty-nine Haemophiliac children were investigated for evidence of parvovirus and TTV infection. 26 boys with Haemophilia A had been treated with cryoprecipitate or intermediate purity factor VIII, and 13 boys with Haemophilia B had received prothrombin complex concentrates. All the plasma products were prepared from South African donors and were virally inactivated by heat or solvent/detergent since 1992. A control group of 32 children who had not been transfused were also studied. IgG antibodies to B19 were present in 29 of the 39 patients (74%), 18/26 (69%) with Haemophilia A and 12 of the 13 (85%) with Haemophilia B. None of the patients was IgM antibody positive but two children were PCR positive for B19 DNA. Of the control children, 47% had IgG antibodies to B19, but none were IgM antibody or B19 DNA positive. TTV viral DNA was found in 10.2% of patients and in 9% of the control group. The results indicate that our locally produced plasma products are not a significant source of TTV transmitted infection but may contribute to infection by B19 parvovirus.

Transmission of symptomatic parvovirus B19 infection by fibrin sealant used during surgery

Human parvovirus B19 infection has been shown to be transmissible by blood and blood products and to result in transient aplastic crisis in patients with rapid red cell turnover. We report three cases of iatrogenic parvovirus B19 infection resulting from the use of the same batch of fibrin sealant under operation. Fibrin sealant, which is a typical haemostatic agent produced from blood, has been used during surgery. Human parvovirus is resistant to existing virus-inactivating techniques, suggesting that infection may occur from blood products contaminated with it. Use of recombinant products for these proteins may thus be necessary.

Safety issues for plasma derivatives and benefit from NAT testing

Manufacturing processes for plasma derivatives are in general highly effective for removal or inactivation of enveloped viruses and the products are safe with regard to the clinically important viruses HIV, HCV and HBV. They are not so effective for the elimination for non-enveloped viruses, especially Parvovirus B19 (B19). A certain risk remains of B19 contamination for some plasma derivatives that is caused, firstly, by the occurrence of highly contaminated donations (up to 10(14)genomes/ml) and secondly, by the extreme heat resistance and small size of B19 which makes it difficult to remove or inactivate. NAT is a beneficial tool for detection of virus contamination. It is routinely used for the detection of HCV-RNA in plasma pools, thereby preventing the processing of HCV-RNA positive material. NAT assays may also be valuable for testing the removal of viruses during manufacturing. This may be especially important if a virus cannot be tested by infectivity assays.

Efficacy of viral clearance methods used in the manufacture of activated prothrombin complex concentrates: focus on AUTOPLEX T

Various methods are described for the elimination of infectious viruses from activated prothrombin complex concentrates (aPCCs) and for the analysis of the final products (AUTOPLEX T and FEIBA VH). Viruses of concern in human plasma-derived products are enveloped (hepatitis B and C, cytomegalovirus, Epstein-Barr virus, and human immunodeficiency virus [HIV]) and nonenveloped (hepatitis A and parvovirus B19). Donated blood used for AUTOPLEX T is screened for antihepatitis C, HBsAg, anti-HIV types 1 and 2, and p24 antigen. Plasma pools utilized for raw materials are also tested by PCR for HIV and hepatitis C virus. Partial virus inactivation and partitioning are achieved by purification of the aPCC. Further reduction of virus infectivity is accomplished by lyophilization and dry-heat treatment. Each step undergoes virus elimination validation studies in which a relevant sample is 'spiked' with the appropriate virus or model virus. The total reduction in virus from raw material to final product can then be calculated. For AUTOPLEX T the cumulative log10 reduction factors for several viruses vary from 4.2 to 14.3. This ensures an exceptionally high margin of safety. Definitive evidence for product safety was obtained by clinical observation of treated patients. The viral inactivation process of AUTOPLEX T involves a four-tier viral safety program, including Cohn alcohol fractionation and dry-heat treatment, in place of the two-stage vapour-heating process for FEIBA.

A randomized trial of solvent/detergent and standard fresh frozen plasma in the treatment of the coagulopathy seen during Orthotopic Liver Transplantation

BACKGROUND

Viral transmission remains a residual risk in single unit blood component therapy. Virus inactivation of pooled fresh frozen plasma (FFP) by the solvent/detergent (SD) method can be used to reduce this risk but results in some loss of factor activity including factor VIII and (2-antiplasmin. This study was aimed at assessing the clinical effectiveness solvent/detergent treated pooled fresh frozen plasma (SDFFP) in the correction of the coagulopathy seen during Orthotopic Liver Transplantation (OLT) as compared with standard FFP.

METHOD

Twenty eight patients with an underlying derangement of coagulation and who were due to undergo OLT were randomized to receive either FFP or SDFFP. They were assessed for side effects, correction of coagulopathy, and seroconversion for viral markers.

RESULTS

Patients undergoing OLT showed equal correction of clotting factors and partial thromboplastin time (PTT) when treated with FFP or SDFFP. There was also a similar time course to return to baseline values in each group. There was no significant difference in correction of INR in either group. Usage of other blood components during the operation was identical in the two groups. No seroconversions were seen for HIV, HBC or HCV but only 12 patients were available for long term follow-up.

CONCLUSION

SDFFP is an efficacious and safe source of coagulation factors for patients with liver disease undergoing Orthotopic Liver Transplantation. No adverse effects were seen during its administration. Further work is required to ascertain long term possibilities of seroconversion.

Long-term follow up of patients treated with intermediate FVIII concentrate BPL 8Y

Long-term surveillance studies of clotting factor concentrates are important to detect infrequent or delayed complications and to provide data against which newer products can be compared. We have assessed the long-term use of BPL 8Y factor VIII (FVIII) concentrate (Bio Products Limited, Elstree, UK) in a cohort of 33 patients. These patients have been treated for a median of 96 months. They have received between one batch (in total) and 10 batches per year and between 1020 units (in total) and 116,700 units per year of BPL 8Y concentrate. No patient has developed a clinically significant FVIII inhibitor. There has been no evidence of transmission of hepatitis C, hepatitis B or HIV 1 or 2. Parvovirus B19 IgG antibody was present in 100% of the patients screened. Analysis of CD4 and CD8 lymphocyte subsets, using age-related normal ranges, showed persistently depressed values in five patients, one of whom had a consistently low CD4/CD8 ratio.

Human parvovirus B19 and blood products

BACKGROUND AND OBJECTIVES

Human B19 parvovirus (B19), identified in 1975, was only recognised as the causative agent of fifth disease in 1983. The incidence of viraemia is low, around 1 in 1,000, but is sufficient to ensure that most plasma pools for fractionation contain some virus. While infection usually occurs in childhood and is benign, chronic infection sometimes occurs and may be of concern in certain patient groups.

MATERIALS AND METHODS

This review is based on a meeting held in March 1995, and addresses recent concerns regarding the potential transmission of B19 infection by pooled plasma products.

RESULTS

Recent data on the pathophysiology and assay of this virus are summarised along with possible approaches to donor screening, product screening, and virus removal. Only five cases of symptomatic infection have been reported in persons with haemophilia, but no technology for virus removal is established, and infection may be of concern in pregnant women, and in patients with enhanced red cell turnover or who are immunosuppressed, including those infected with human immunodeficiency virus, but only rarely in immunocompetent patients.

CONCLUSIONS

For the future, well-validated assays relevant to virus infectivity are required if blood donations, plasma pools, or plasma products are to be screened, and an in-process virus inactivation step for B19 would be highly desirable. In the interim, non-plasma or recombinant products or a selective transfusion policy might be used in patient groups in which B19 infection is of particular concern. Further clinical data on the prognosis and impact of B19 infection are needed to justify both such policies and the future adoption of new technologies designed to reduce any excess B19 infectivity arising from transfused products.

Human parvovirus B19 infection within a family and risk for pregnant women

During an outbreak of parvovirus B19 infection among four related families at least 70% of the household contacts, including a woman at the 33rd week of pregnancy, became infected. Twins were born at the 39th week of pregnancy, both with B19 infection. B19 DNA was detected in their sera by a nested PCR, anti-B19 IgM was detectable only by an immunofluorescence assay, and low levels of maternal anti-B19 IgG were demonstrable by an immunoenzymatic test in the serum of both children. All the haematological parameters were normal at birth and 6 months later, when B19 DNA and anti-B19 antibody were no longer detectable in serum samples. This observation emphasizes the high risk of B19 infection among household contacts and the possibility of a favourable outcome of the foetal infection, possibly related to infection late in the pregnancy.

The prevalence of antibody to parvovirus B19 in hemophiliacs and in the general population

The prevalence of antibodies to parvovirus B19 (B19) was measured in the sera of 566 hemophiliacs and 524 individuals of the general population by immunofluorescence assays, using antigen expressed by the baculovirus system. In the general population, anti-B19 IgG seroprevalence was found to continuously decline from 64 percent at birth to 0 percent in the age of 9-11 months and thereupon to increase to 61 percent in the age of 12 years. In younger adults and older people, IgG seroprevalence only slowly increased with age, reaching 77 percent in people aged 60 and above. In contrast, in hemophilic children treated exclusively with virally inactivated clotting factor concentrates, neither decrease nor increase of B19 IgG antibody was detectable and the overall seroprevalence was 92 percent. In the group of hemophiliacs older than 12 years and treated before 1984 with non-inactivated clotting factor concentrates, 98 percent showed antibody to B19. Anti-B19 IgM seroprevalence was significantly higher in hemophilic than in non-hemophilic individuals older than 12 years. Since it seems to be unlikely that the high seroprevalence in hemophiliacs is acquired by immunization with inactivated viral antigen, the results suggest that infection with B19 is transmitted by clotting factor concentrates, even if subjected to virucidal methods.

Parvovirus B19 infection

Human parvovirus B19, discovered in 1974, is a single-stranded DNA virus which causes erythema infectiosum, arthralgia, aplastic crisis in patients with red cell defects, chronic anaemia in immunocompromised patients, and fetal hydrops. Seroprevalence in developed countries is 2-10% in children less than 5 years, 40-60% in adults more than 20 years, and 85% or more in those over 70 years. The virus may be transmitted by the respiratory route and by transfusion of infected blood and blood products. After an incubation period of six to eight days, viraemia occurs, during which reticulocyte numbers fall dramatically resulting in a temporary drop in haemoglobin of 1 g/dl in a normal person. Clearance of viraemia is dependent on development of specific antibody to the B19 structural proteins, VP1 and VP2. The red cell receptor for the virus is blood group P antigen. Diagnosis in immunocompetent persons depends on detection of specific IgM in serum. Diagnosis in immunocompromised persons depends on detection of B19 antigen or DNA in serum. There is no specific treatment for B19 infection; however, human normal immunoglobulin may be used as a source of specific antibody in chronically infected persons. A recombinant parvovirus B19 vaccine is under development.

Incidence of human parvovirus B19 DNA detection in blood donors

1000 serum samples from blood donors were tested for human parvovirus B19 (B19) DNA by a nested PCR assay: six samples were positive for B19 DNA. The frequency was 1/167 (0.6%), considerably higher than previous surveys (0.004-0.03%). Five of the six samples were also positive for anti-B19 IgM, indicating an acute phase of infection. It is recommended to screen for B19 DNA in blood products to prevent transfusion mediated viral infection for those susceptible such as immunocompromised patients and pregnant women.

Persistent B19 parvovirus infections in haemophilic HIV-1 infected patients

B19 infection can be acquired by transmission with blood factors in patients with congenital bleeding disorders, requiring clotting factor concentrates. In immunodeficient patients, the failure of immunity to clear B19 virus may produce persistent infections. The presence of B19 DNA in blood samples from seven haemophilic patients with concomitant HIV-1 infection was studied over a period of three-to-four years. Dot blot hybridization assays with DNA and RNA probes were used to detect medium high viremias, and polymerase chain reaction (PCR) to detect very low viremic titres. Three patients were negative for B19 DNA in all the blood samples, while four patients were persistently positive for B19 DNA. Viral persistence, which in one patient was detected throughout the study period (40 months), occurred at low titre in all four positive patients with some recurrent increases in viral titre. In the four patients persistently positive for B19 DNA, acute or chronic clinical symptoms and signs that could be associated with B19 were not noted when virus was present at low titre (B19 DNA detectable only by PCR). When patients had a higher viral titre (B19 DNA detectable by dot blot hybridization) acute manifestations (aplastic crisis, Fifth disease, fevers, pneumonitis) were found.

Detection of human parvovirus B19 DNA PCR products by RNA probe hybridization enzyme immunoassay

We have developed an RNA probe hybridization enzyme immunoassay for detection of human parvovirus B19 PCR-amplified DNA. The assay is easy to perform and increases assay sensitivity without the added inconvenience and risk of false-positive results associated with nested PCR.

A recombinant immunoblot and ELISA for detection of acute parvovirus B19 infection

Laboratory diagnosis of parvovirus B19 (B19) infection has been hampered by the limited availability of B19 virus. Recombinant viral proteins are now available for use as antigen in serological assays. We compared detection of anti-B19 IgM by "mu-capture assay" using viral B19 particles to a recombinant (rec.) immunoblot and a rec. enzyme-immunoassay (ELISA) using viral structural proteins as antigens expressed in E. coli. The rec. immunoblot was 94.3% sensitive and 96.4% specific for anti-B19 IgM, and the sensitivity of the rec. ELISA was 94.3% and the specificity, only 72.7%. There was an agreement between the "mu-capture assay" and the rec. immunoblot in 87.8% and the rec. ELISA in only 74.4%. For detection of anti-B19 IgG in patients with acute B19 infection, the rec. immunoblot was 94.3% and the rec. ELISA 85.7% sensitive. The rec. immunoblot is more reliable for detection of acute B19 infection than the rec. ELISA.

B19 parvovirus DNA in solvent/detergent-treated anti-haemophilia concentrates

A transfusional B19 parvovirus infection may have severe consequences in immunocompromised hosts. The presence of B19 DNA was investigated with a polymerase chain reaction (PCR) assay in 30 batches of solvent/detergent-treated clotting factor concentrates (12 batches of factor VIII, 16 batches of factor IX, 1 batch of factor VII, and 1 batch of PPSB). B19 DNA was detected in 6 (20%) batches, including 3 factor VIII and 3 factor IX concentrates. Because of the frequency of B19 DNA in batches of clotting factors, measures to prevent transfusional risk of B19 infection via these blood products are justified, especially in recipients immunocompromised by HIV infection.

Human parvovirus B19 infection in bone marrow transplantation patients

We report the results of a survey of parvovirus B19 infection carried out with the aim to evaluate the frequency and the role of this infection in bone marrow transplant (BMT) recipients, as it is known that B19 virus can persist in clinical circumstances of immunodeficiency. Fifty-one patients subjected to BMT in the Bone Marrow Transplantation Center of Florence were enrolled in this study. Immunological and virological indications of B19 infection were tested weekly during the stay in hospital. A high rate of seroconversion or B19 antibody rise was observed, but, in absence of B19 IgM or B19 DNA presence, this result seems to be attributable to a passive immunization, rather than to a recent viral infection. In these 51 patients, as well as in 59 others not included in this study, clinical manifestations imputable to B19 infection have never been observed. It is possible that the isolation measures and the intravenous immunoglobulins (IVIG) administration may contribute in preventing B19 infection in the BMT recipients at least until the hospital discharge.

Human parvovirus B19 infections: routine diagnosis by a new nested polymerase chain reaction assay

A nested primer PCR assay was developed to detect human parvovirus B19 in various clinical specimens in a routine diagnostic laboratory. Under optimized conditions the highly specific assay had a sensitivity of less than 10 genome units. For practical reasons, however, this sensitivity was adjusted to 10-100 virus genomes in diagnostic applications. Using clinical specimens from 200 patients with suspected B19 infection, nested PCR was shown to have important diagnostic advantages over the detection of B19 specific antibodies. The data suggest that on the basis of serological data as obtained with currently available test systems a considerable proportion of B19 infections would be misdiagnosed. Examples for the usefulness of the PCR assay in routine diagnosis are given.

Nested polymerase chain reaction assay for the detection of B19 parvovirus DNA in human immunodeficiency virus patients

Persistent B19 parvovirus infection has been recognized in immunocompromised patients, often occurring with a low-titer viremia. In this study, nested polymerase chain reaction (PCR) for the detection of B19 parvovirus DNA was carried out on the sera of 49 human immunodeficiency virus (HIV)-1-seropositive patients, negative for the detection of B19 DNA at dot blot hybridization assay and with different values of serum anti-B19 IgM (27 patients proved positive and 22 negative). Of the 49 HIV-seropositive samples tested by nested PCR, seven were positive for the detection of B19 DNA. All seven belonged to the group of subjects seropositive for specific anti-B19 IgM. The study shows that, in the presence of specific B19 IgM, circulating virus may still be present but can be detected only by PCR. In that B19 infection can occur with low-titer viremia in immunocompromised patients, PCR may be the only method for virus detection.