High frequencies of exposure to the novel human parvovirus PARV4 in hemophiliacs and injection drug users, as detected by a serological assay for PARV4 antibodies

Abstract

Background: PARV4 is a human parvovirus that was first detected in and cloned from an individual with a human immunodeficiency virus (HIV) seroconversion-like illness and that subsequently persisted in the lymphoid tissue and bone marrow. In contrast to human parvovirus B19 infections, PARV4 infections are most frequently detected in injection drug users (IDUs), particularly those who are coinfected with HIV type 1 (HIV-1). To investigate the routes of transmission of PARV4 and to ascertain whether infections are acquired through plasma-derived blood products, we developed a novel anti-PARV4 enzyme-linked immunosorbent assay (ELISA) to determine its seroprevalence in subjects with parenteral exposure.

Methods: PARV4 viral protein 2 (VP2) was expressed and used as antigen in an indirect ELISA, to detect anti-PARV4 immunoglobulin G.

Results: All 50 adult control subjects who were nonparenterally exposed to PARV4 were anti-PARV4 negative, in contrast to HIV-infected and HIV-uninfected IDUs, who had antibody frequencies of 67% and 33%, respectively. Predominantly parenteral transmission was confirmed by the finding of similar frequencies of infection among HIV-coinfected and HIV-uninfected hemophiliacs (11 of 20 individuals and 4 of 15 individuals, respectively) who were treated with nonvirally inactivated factor VIII/factor IX, whereas all but 1 of the 35 nonhemophiliac siblings of these siblings were found to be seronegative (despite having close household contact).

Conclusions: The present study provides convincing evidence that PARV4 is primarily transmitted parenterally. Evidence for widespread infection of hemophiliacs treated with nonvirally inactivated clotting factor creates fresh safety concerns for plasma-derived blood products, particularly because parvoviruses are relatively resistant to virus inactivation.

Figure 1. Expression of PARV4 VP1 and VP2 proteins and immunodetection by Western blot

(A, B) Detection of VP1 and VP2 expression by Coomassie Blue staining in VP1-Bac and VP2-Bac infected cell extracts (lane 1, arrowed) and mock-infected control Sf9 cells (lane 2). (C, D) Partially purified preparations of expressed proteins from VP1-Bac, VP2-Bac and mock-infected cells (lanes 1, 2, 3) analysed by SDS-PAGE and Coomassie Blue staining (C) and by Western blot (D) using a plasma sample from a high-risk individual (an HIV-infected IDU).

Figure 2. Visualisation of virus-like particles in purified recombinant VP2

Low (upper panel) and high (lower panel) magnification images by transmission EM of virus-like particles spontaneously formed in baculovirus-derived VP2 antigen negatively stained with uranyl acetate. Samples were viewed on a Philips CM120 transmission electron microscope and images captured on a Gatan Orius 1000 Digital Camera.

Figure 3. Immunoreactivity of plasma samples from different risk groups in the VP2-based ELISA

Distribution of serological reactivity of individual plasma samples from different study subject categories referred to Table 1. The y-axis records net OD (OD for VP2 preparations - mock-infected control preparations). The designated cut-off of 0.113 is depicted as a dashed line.