F-Specific RNA Bacteriophages, Especially Members of Subgroup II, Should Be Reconsidered as Good Indicators of Viral Pollution of Oysters.

Norovirus (NoV) is the leading cause of gastroenteritis outbreaks linked to oyster consumption. In this study, we investigated the potential of F-specific RNA bacteriophages (FRNAPH) as indicators of viral contamination in oysters by focusing especially on FRNAPH subgroup II (FRNAPH-II). These viral indicators have been neglected because their behavior is sometimes different from that of NoV in shellfish, especially during the depuration processes usually performed before marketing. However, a significant bias needs to be taken into account. This bias is that, in the absence of routine culture methods, NoV is targeted by genome detection, while the presence of FRNAPH is usually investigated by isolation of infectious particles. In this study, by targeting both viruses using genome detection, a significant correlation between the presence of FRNAPH-II and that of NoV in shellfish collected from various European harvesting areas impacted by fecal pollution was observed. Moreover, during their depuration, while the long period of persistence of NoV was confirmed, a similar or even longer period of persistence of the FRNAPH-II genome, which was over 30 days, was observed. Such a striking genome persistence calls into question the relevance of molecular methods for assessing viral hazards. Targeting the same virus (i.e., FRNAPH-II) by culture and genome detection in specimens from harvesting areas as well as during depuration, we concluded that the presence of genomes in shellfish does not provide any information on the presence of the corresponding infectious particles. In view of these results, infectious FRNAPH detection should be reconsidered as a valuable indicator in oysters, and its potential for use in assessing viral hazard needs to be investigated.IMPORTANCE This work brings new data about the behavior of viruses in shellfish, as well as about the relevance of molecular methods for their detection and evaluation of the viral hazard. First, a strong correlation between the presence of F-specific RNA bacteriophages of subgroup II (FRNAPH-II) and that of norovirus (NoV) in shellfish impacted by fecal contamination has been observed when both viruses are detected using molecular approaches. Second, when reverse transcription-PCR and culture are used to detect FRNAPH-II in shellfish, it appears that the genomes of the viruses present a longer period of persistence than infectious virus, and thus, virus genome detection fails to give information about the concomitant presence of infectious viruses. Finally, this study shows that FRNAPH persist at least as long as NoV does. These data are major arguments to reconsider the potential of FRNAPH as indicators of shellfish viral quality.

Serum rotavirus neutralizing-antibody titers compared by plaque reduction and enzyme-linked immunosorbent assay-based neutralization assays.

Comparisons in rotavirus neutralizing-antibody responses were made with sera collected from vaccinated infants. The methods were a plaque reduction assay and a new enzyme-linked immunosorbent assay-based neutralization assay. Agreement of 94% was found in detecting at least fourfold seroresponses, and correlation coefficients between titers obtained by the two methods showed excellent agreement, indicating that either could be used reliably.

Comparison of commercial enzyme immunoassay kits with plaque reduction neutralization test for detection of measles virus antibody.

Four commercially available enzyme immunoassay (EIA) kits were evaluated in comparison with the plaque reduction neutralization (PRN) test for detection of measles virus antibody. The EIA kits, Enzygnost (Behring), Diamedix, Vidas (bioMerieux Vitek), and Measlestat (Biowhittaker), were assessed with two PRN cutoff titers: a PRN titer of 8, the lowest detectable antibody level by the PRN test under the test conditions, and a titer of 120, which has been shown to be the minimum protective antibody titer. At a PRN cutoff titer of 8, the sensitivity was 88.2, 91.1, 74.6, and 69.8% for Behring, Diamedix, Vidas, and Biowhittaker EIA tests, respectively, with negative predictive values ranging from 22.7 to 45.5%. The specificity was 93.8% for Diamedix and 100% for the rest. At a PRN cutoff titer of 120, the sensitivity and specificity, respectively, were 100 and 90.7% (Behring), 98.2 and 58.8% (Diamedix), 90.6 and 94.5% (Vidas), and 85.7 and 96.4% (Biowhittaker). At this PRN cutoff titer, the negative predictive values of all EIA tests improved considerably, ranging from 70.7 to 100%. The EIA results showed an excellent association with PRN results when the PRN titers of the test samples were either < 8 or > 1,052. Discrepancies occurred especially when testing samples having PRN titers in the range of 8 to 120, indicating lack of sensitivity of the EIA tests in detecting measles virus antibody at low levels. Maternally derived measles virus antibody at this level has been shown to interfere with measles vaccine response in children and hence has implications from the standpoint of measles immunization. The ready availability, ease of operation, and rapid turnaround time are strong plus points of the EIA kits, and they could be useful in a clinical laboratory setting for routine application, but they may have limited use in vaccine-related studies and seroepidemiological surveys.

New HIV plaque titration; application to the assay of neutralizing antibody.

A simple, sensitive and accurate plaque assay was developed using HPB-Ma, a variant of the human T-cell line HPB-ALL, which becomes adherent to the substratum after infection with an amphotropic murine sarcoma virus (MSVa). The simplicity of this novel plaque assay allowed us to examine a large number of serum samples from patients with HIV infection for neutralizing antibody activity against two human immunodeficiency virus type-1 (HIV-1) strains. During the progression of clinical disease, the neutralizing activity in the sera from two individual patients remained unchanged or increased. A patient with a known time of HIV infection produced cross-neutralizing antibody at 25-34 weeks. The neutralizing activity in the sera from 17 asymptomatic carriers, four patients with AIDS-related complex and four AIDS patients was also examined and was found to be unrelated to the clinical stage.

A collaborative study to assess the proficiency of laboratory estimates of potency of live measles vaccines.

A collaborative study was undertaken to assess the variability in estimates of the potency of measles vaccines. Overall a median variation of 2.0 log10 between estimates was observed. This was reduced to a median of 1.0 log10 when the potencies were expressed relative to a reference vaccine. A difference in the sensitivity between plaque assays and TCID50 assays was also reduced when relative potencies were used. The benefit of including a common reference preparation in vaccine assays was therefore demonstrated. For the vaccines assayed in this study, it was not necessary to use a measles reference of the same strain as the vaccines tested. We therefore recommend that measles vaccines be assayed against a single international reference preparation.