One hypervirulent clone, sequence type 283, accounts for a large proportion of invasive Streptococcus agalactiae isolated from humans and diseased tilapia in Southeast Asia

Background

In 2015, Singapore had the first and only reported foodborne outbreak of invasive disease caused by the group B Streptococcus (GBS; Streptococcus agalactiae). Disease, predominantly septic arthritis and meningitis, was associated with sequence type (ST)283, acquired from eating raw farmed freshwater fish. Although GBS sepsis is well-described in neonates and older adults with co-morbidities, this outbreak affected non-pregnant and younger adults with fewer co-morbidities, suggesting greater virulence. Before 2015 ST283 had only been reported from twenty humans in Hong Kong and two in France, and from one fish in Thailand. We hypothesised that ST283 was causing region-wide infection in Southeast Asia.

Methodology/Principal findings

We performed a literature review, whole genome sequencing on 145 GBS isolates collected from six Southeast Asian countries, and phylogenetic analysis on 7,468 GBS sequences including 227 variants of ST283 from humans and animals. Although almost absent outside Asia, ST283 was found in all invasive Asian collections analysed, from 1995 to 2017. It accounted for 29/38 (76%) human isolates in Lao PDR, 102/139 (73%) in Thailand, 4/13 (31%) in Vietnam, and 167/739 (23%) in Singapore. ST283 and its variants were found in 62/62 (100%) tilapia from 14 outbreak sites in Malaysia and Vietnam, in seven fish species in Singapore markets, and a diseased frog in China.

Conclusions

GBS ST283 is widespread in Southeast Asia, where it accounts for a large proportion of bacteraemic GBS, and causes disease and economic loss in aquaculture. If human ST283 is fishborne, as in the Singapore outbreak, then GBS sepsis in Thailand and Lao PDR is predominantly a foodborne disease. However, whether transmission is from aquaculture to humans, or vice versa, or involves an unidentified reservoir remains unknown. Creation of cross-border collaborations in human and animal health are needed to complete the epidemiological picture.

An outbreak due to a bacterium called Streptococccus agalactiae in Singapore in 2015 was caused by a clone called ST283, and was associated with consumption of raw freshwater-fish. It was considered unique as it was the only reported foodborne outbreak of this bacterium. Our new data show that invasive ST283 disease is far from unique. ST283 has been causing disease in humans and farmed fish in SE Asian countries for decades. Reports of ST283 are almost absent outside Asia. We suspect that human ST283 is fishborne in other Asian countries, as it was in Singapore, but we haven’t looked at this yet. We don’t know where ST283 originally came from; it may have been transmitted from humans to fish, or come from another animal. More studies are needed to determine ST283’s geographical extent and burden of disease, as well as its origin, how it is transmitted, and what enables it to be so aggressive. We may then be able to interrupt transmission, to the benefit of fish, farmers, and the general public.

A chemiluminescent, magnetic particle-based immunoassay for the detection of hepatitis C virus core antigen in human serum or plasma

Hepatitis C virus (HCV) exposure in blood donors is determined serologically by the detection of anti-HCV antibodies in serum or plasma. However, a "window" period of 30-70 days after exposure exists where specific antibodies to HCV antigens are not detected. The use of nucleic acid testing for the detection of HCV RNA or antigen testing for the detection of HCV core protein have resulted in dramatic reductions in the pre-seroconversion window period. In this study, an automated HCV core antigen detection test was developed. This magnetic microparticle-based assay utilizes anti-HCV core monoclonal antibody to capture antigen present in human serum or plasma. Captured antigen is then detected using an anti-HCV core monoclonal antibody conjugated with a chemiluminescent compound. The specificity of this assay was established at 99% upon testing a population of normal volunteer blood donors. Sensitivity was determined by testing 16 commercially available HCV seroconversion panels representing genotypes 1a, 1b, 2b, and 3a. In each panel tested, HCV core antigen was detected prior to anti-HCV antibody, resulting in a reduction of the window period by greater than 23 days on average, and greater than 34 days on panels initially NAT negative. In addition, HCV core antigen was detected in >97% of HCV RNA positive/antibody negative specimens, exhibiting sensitivity nearly equivalent to nucleic acid testing in the pre-seroconversion window period for the panels examined.

Brief report: no evidence for parvovirus B19 or hepatitis E virus as a cause of acute liver failure

Viral hepatitis A and B are known to cause acute liver failure. While nearly 20% of acute liver failure cases are of indeterminate etiology, screening for other viruses has not been uniformly performed. We looked for evidence for parvovirus B19 and hepatitis E virus in sera from U.S. acute liver failure patients. For B19, 78 patients' sera, including 34 with indeterminate etiology, were evaluated by DNA dot-blot hybridization, reverse transcription polymerase chain reaction, and enzyme-linked immunosorbent assay for immunoglobin G and M antibodies; none showed evidence for infection.

ELISA for detection of antibody to the E2 protein of GB virus C

An enzyme linked immunosorbent assay (ELISA) for detection of antibodies to mammalian cell-expressed E2 protein of GB virus C (GBV-C E2) is described. Antibodies to GBV-C E2 are captured on a solid phase coated with affinity purified E2 protein. Bound antibody is detected in an indirect assay format using horseradish peroxidase (HRPO) labeled goat anti-human IgG as the secondary antibody. Following a color development step, absorbance at 492 nm is measured. A population of 100 volunteer blood donors was tested to assess the specificity of this assay. Individuals reactive for antibody to GBV-C E2 can be considered to have been exposed to GB virus C.

Seroprevalence of GB virus C and persistence of RNA and antibody

Exposure to GB virus C (GBV-C) was determined in several U.S. populations by both reverse-transcription-polymerase chain reaction (RT-PCR) and by an enzyme linked immunosorbent assay (ELISA) for antibodies to mammalian cell-expressed GBV-C envelope protein, E2 (GBV-C E2). Most individuals exposed to GBV-C were either RNA positive/ELISA negative or ELISA positive/RNA negative. Exposure, therefore, was measured as the sum of GBV-C RNA positive and GBV-C E2 antibody positive specimens, and was higher in commercial plasmapheresis donors (40.5%) than in volunteer blood donors (5.5%). In intravenous drug users (IVDUs), GBV-C exposure was 89.2%. Serial bleed specimens tested for GBV-C RNA indicate that some patients remain viremic for at least 3 years and fail to produce detectable antibodies to GBV-C E2. In other exposed individuals who tested negative for GBV-C RNA, antibodies to E2 appear to be similarly long-lived (greater than 3 years) with a fairly constant titer (ranging in reciprocal endpoint dilution from 336 to 21,504). Since the detection of GBV-C RNA and GBV-C E2 antibody are mutually exclusive in most exposed individuals, studies pertaining to incidence and prevalence of GBV-C infection require both antibody and nucleic acid detection.

GB virus C E2 glycoprotein: expression in CHO cells, purification and characterization

A 315 amino acid recombinant segment of the GB virus C (GBV-C) E2 envelope glycoprotein (E2-315) was expressed and secreted from CHO cells. E2-315 was purified by affinity chromatography using a monoclonal antibody directed to a FLAG sequence genetically engineered onto the C terminus of the recombinant protein. The secreted protein had a molecular mass of 48-56 kDa and was shown to be N-glycosylated. Amino acid sequencing confirmed the expected N-terminal sequence. Purified E2-315 was used to develop an ELISA for detection of E2 antibodies in human sera. Antibodies to GBV-C E2 appeared to be directed toward conformational epitopes since human sera reactivity was detected in ELISA using native E2-315, but it was extremely weak or non-existent with denatured E2 protein. The use of an ELISA which can detect human GBV-C E2 antibodies will be important in further understanding of the clinical significance and epidemiology of GBV-C.

An ELISA for detection of antibodies to the E2 protein of GB virus C

An ELISA was developed for detection of antibodies to GB virus C (GBV-C) using a recombinant E2 protein expressed in CHO cells. Seroconversion to anti-E2 positivity was noted among several persons infected with GBV-C RNA-positive blood through transfusion. Of 6 blood recipients infected by GBV-C RNA-positive donors, 4 (67%) became anti-E2 positive and cleared their viremia. Thus, anti-E2 seroconversion is associated with viral clearance. The prevalence of antibodies to E2 was relatively low (3.0%-8.1%) in volunteer blood donors but was higher in several other groups, including plasmapheresis donors (34.0%), intravenous drug users (85.2%), and West African subjects (13.3%), all of whom tested negative by GBV-C reverse-transcription polymerase chain reaction (RT-PCR). These data demonstrate that testing for anti-E2 should greatly extend the ability of RT-PCR to define the epidemiology and clinical significance of GBV-C.

Prevalence studies of GB virus-C infection using reverse transcriptase-polymerase chain reaction

Among the three recently described GB viruses (GBV-A, GBV-B, and GBV-C), only GBV-C has been linked to cryptogenic hepatitis in man. Because of the limited utility of currently available research tests to determine antibody response to GBV-C proteins, the prevalence of GBV-C RNA in human sera was studied using reverse transcription-polymerase chain reaction (RT-PCR). The prevalence of GBV-C is higher among volunteer blood donors with elevated serum alanine aminotransferase (ALT) levels (3.9%) than among volunteer blood donors with normal ALT levels (0.8%). Higher rates were also noted among commercial blood donors (12.9%) and intravenous drug users (16.0%). GBV-C was frequently detected in residents of West Africa, where the prevalence was > 10% in most age groups. Approximately 20% of patients diagnosed with either acute or chronic hepatitis C virus (HCV) were found to be positive for GBV-C RNA. In addition, GBV-C RNA sequences were detected in individuals diagnosed with non-A-E hepatitis, with clinical courses ranging from mild disease to fulminant hepatitis. Fourteen of sixteen subjects with or without clinically apparent hepatitis were positive for GBV-C RNA more than 1 year after the initial positive result.

Molecular and serologic analysis in the transmission of the GB hepatitis agents

Two flavivirus-like genomes have recently been cloned from infectious tamarin (Saguinus labiatus) serum, derived from the human viral hepatitis GB strain, which is known to induce hepatitis in tamarins. In order to study the natural history of GB infections, further transmission studies were carried out in tamarins. Reverse-transcription-polymerase chain reaction and enzyme-linked immunosorbant assays were developed for the detection of RNA and antibodies associated with the two agents, GB virus-A and GB virus-B. The infectivity of both of these agents was demonstrated in tamarins to be filterable through a 0.1 micron filter. Two distinct genomes were identified in the serum of eight of the infected tamarins, while in four tamarins, the genomes were detected independently of each other. Although specific antibodies to the GB virus-B epitopes were detected in the serum of animals inoculated with both agents or GB virus-B alone, antibodies to putative epitopes specific to GB virus-A were not detected in any of the animals. All tamarins inoculated with serum containing GB virus-B exhibited an elevation in liver enzyme levels after inoculation. Elevations of serum liver enzyme levels did not occur when GB virus-A was the only agent detected in the serum. Infection with the original infectious tamarin inoculum conferred protection from reinfection with GB virus-B but not with GB virus-A.

Antibodies to recombinant and synthetic peptides derived from the hepatitis C virus genome in long-term-studied patients with posttransfusion hepatitis C

Eight of 13 Swedish patients (62%), studied prospectively, who developed posttransfusion non-A, non-B hepatitis (PT-NANBH) had earlier been found to seroconvert for antibodies to hepatitis C virus (anti-HCV) c100-3 in the first-generation anti-HCV enzyme-linked immunosorbent assay 1-18 (mean, 8) weeks after onset of hepatitis. By using a second-generation test utilizing antigens encoded by the core NS3 and NS4 region of HCV, a further four patients non-reactive to c100-3 (NS4) were found to seroconvert. Thus 12 of 13 (92%) Swedish patients with PT-NANBH were shown to have HCV infection. In addition, the serologic reactivity for several individual synthetic peptides and/or recombinant HCV proteins was studied in seven anti-HCV c100-3 seroconverts studied long-term after onset of acute PT-HCV infection. No special patterns were found that could differentiate patients who recovered from those who developed chronic HCV infection. It was concluded that the addition of new recombinant antigens derived from the core and NS3 region to c100-3 (NS4) both improved the sensitivity of the anti-HCV test and shortened the window phase to seroconversion.

IgM-antibody response to hepatitis C virus antigens in acute and chronic post-transfusion non-A, non-B hepatitis

A specific IgM solid-phase enzyme-linked immunoassay for the diagnosis of a recent infection by hepatitis C virus (HCV) was developed. The assay utilizes a structural antigen encoded by sequences at the 5' end of HCV (core region) and non-structural (NS) antigens encoded by the NS-3 (33c) and NS-4 (c100-3) regions of the HCV genome. Serial serum samples from several clinically diagnosed post-transfusion non-A, non-B hepatitis patients were analyzed for anti-HCV IgM. This antibody was frequently but transiently detected. Anti-HCV core IgM was more frequently detected than anti-c100-3 or anti-33c IgM. In individuals who resolved their HCV infection or progressed to chronicity, anti-HCV IgM was produced transiently at or near the onset of clinically diagnosed acute hepatitis.

Detection of antibodies to hepatitis C virus in U.S. blood donors

An enzyme immunoassay (EIA) which utilizes a solid phase coated with a recombinant antigen (c100-3) derived from the hepatitis C virus (HCV) genome was evaluated for efficacy in the detection of antibodies to HCV (anti-HCV). The sensitivity of the antibody test was demonstrated by the detection of anti-HCV in a well-characterized panel of human specimens known to contain the infectious agent of non-A, non-B hepatitis. The specificity of the anti-HCV test was evaluated by testing 6,118 serum specimens from volunteer blood donors considered to be at low risk for exposure to HCV. The specificity of the anti-HCV EIA was demonstrated to be 99.56%, since 6,069 of 6,096 specimens from this low-risk group were nonreactive. A total of 49 (0.80%) of the 6,118 specimens were repeatedly reactive in the test, and 22 (46.81%) of the 47 specimens available for additional testing were confirmed as positive for antibodies to HCV c100-3. Among commercial plasma donors, 390 (10.49%) of 3,718 specimens were repeatedly reactive in the EIA. A total of 375 (97.40%) of the 385 specimens available for further testing were confirmed as positive. These limited data indicate that the prevalence of antibodies to HCV is 0.36% (22 confirmed positives among 6,118 specimens) among volunteer blood donors and 10.08% (375 confirmed positives among 3,718 specimens) among commercial plasma donors. The importance of confirmatory testing is discussed.

Reliable detection of individuals seropositive for the human immunodeficiency virus (HIV) by competitive immunoassays using Escherichia coli-expressed HIV structural proteins

We molecularly cloned the gag and env genes of the human immunodeficiency virus (HIV) and expressed fragments of these genes in Escherichia coli. Using the recombinant core and envelope proteins, we developed two competitive immunoassays (CIAs). Samples that recognized either the envelope or core proteins were considered positive for antibodies to HIV. This test system was comparable with western blot in detecting antibodies in patients with AIDS or AIDS-related complex that were repeatably reactive in the HIV screening test. All 360 individuals who were positive by western blot were positive by the CIA. A total of 844 samples repeatably reactive by an ELISA screening test were negative both by western blot and by the CIA; 48 samples positive by ELISA, but negative or indeterminate by western blot, were positive by the CIA. Alternate research procedures verified the positivity of these individuals. These data indicate that the CIA described here may be useful as an adjunct or alternative to the western blot.