Rapid detection of human rotavirus strains in stools by single-sandwich enzyme-linked immunosorbent assay systems using monoclonal antibodies

Enhancement of detection and quantification of rotavirus in stool using a modified real-time RT-PCR assay

A sensitive and specific real-time RT-PCR assay to detect rotavirus in stool samples was optimized and validated using a wide range of rotavirus genotypes. The target of the original TaqMan(R) assay is an 87 bp fragment of the highly conserved non-structural protein 3 (NSP3) gene. Here we modified the original assay by introducing degeneracy into the forward primer to account for sequence variation between rotavirus genotypes, added four nucleotides at the 3' end of the reverse primer to reduce its stability, and modified the probe label. Amplification and detection conditions were optimized using purified dsRNA from two cultivated strains. The limit of detection of the modified assay was calculated to be approximately 44 genome copies per reaction. To validate the reactivity of the assay, 103 archived RNAs that had been extracted from stools and genotyped during routine U.S. surveillance were tested. Samples were selected to represent both rare and common genotypes that have been detected in U.S. children. Nine genotypes known to be circulating in the United States were detected by the real-time assay demonstrating broad reactivity. In addition, other enteric viruses were not detected demonstrating that the assay is specific for rotavirus and does not cross-react with other viruses potentially present in stool samples. This real-time assay is an important addition to the arsenal of molecular tools available to quickly identify rotavirus in stool samples during routine surveillance.

Characterization of VP6 genes from rotavirus strains collected in the United States from 1996–2002

We sequenced 22 VP6 genes from common rotavirus strains P[8], G1; P[4], G2; P[8], G3; P[8], G4 and P[8], G9 and uncommon type P[6], G9 collected in the US over a 6-year period. All strains defined as members of VP6 antigenic subgroup (SG) I according to reactivity patterns with monoclonal antibodies formed a genetic cluster (Genogroup I) with SG I reference strains. Similarly, all strains in antigenic SGII formed a group (Genogroup II) with corresponding standard strains of the same SG. Most US strains of each genogroup had diverged by 10-15% from the VP6 gene sequence of reference strains collected >20 years earlier and some recent isolates from other countries. Evolutionary analysis demonstrated that recently isolated US strains of both genogroups have diverged into 2-3 related clusters consistent with other recent findings. Unexpectedly, some recent isolates from other countries have diverged greatly from both older reference isolates and from the recent US isolates characterized here. This finding suggests that genetic diversity in human rotavirus VP6 genes may be greater than previously recognized. These sequences will help in the construction of a VP6 gene database to aid in the development of broadly reactive molecular assays and permit identification of regions where primers and probes for existing assays may need to be redesigned.

Comparison of different immunostaining techniques and monoclonal antibodies to the lower matrix phosphoprotein (pp65) for optimal quantitation of human cytomegalovirus antigenemia

The main parameters of immunostaining techniques, i.e., the type of fixative, immunocytochemical reaction, and quality of monoclonal antibodies (MAbs), for quantitation of human cytomegalovirus (HCMV) antigenemia in peripheral blood polymorphonuclear leukocytes (currently performed by the indirect immunofluorescence or immunoperoxidase reaction by using MAbs to HCMV pp65) were investigated in order to optimize procedural steps and reagents. Significantly better results (in terms of the number of positive cells) were obtained on multiple cytospin preparations from heart transplant recipients with HCMV viremia when we used (i) formalin instead of methanol-acetone fixation and (ii) the indirect immunofluorescence reaction instead of the immunoperoxidase reaction, the avidin-biotin complex method, or the alkaline phosphatase antialkaline phosphatase procedure. In addition, comparison of the staining capabilities of three MAbs to pp65, which were developed in the laboratory and which were reactive to different epitopes of the protein, with a commercially available MAb (Clonab CMV) for determination of HCMV antigenemia showed that, while individual MAbs did not provide better results, the pool of MAbs detected a significantly higher number of positive peripheral blood polymorphonuclear leukocytes than Clonab CMV did. In addition, the sensitivity of the pool in detecting patients with low levels of viremia (less than 5/2 x 10(5) cells inoculated) as antigenemia positive was 100%, whereas the sensitivity of Clonab CMV was 47%. No differences in the specificities between the two MAb preparations were observed.

Isolation of an avianlike group A rotavirus from a calf with diarrhea

An atypical group A rotavirus (993/83) was isolated from a 3-day-old German calf with diarrhea. It differed from 35 conventional German bovine rotavirus isolates analyzed previously with respect to subgroup (strain 993/83 was non-subgroup I and non-subgroup II), serotype (strain 993/83 showed a two-way cross-reaction with serotype 7 and a one-way cross-reaction with serotype 3), and electropherotype (strain 993/83 showed comigrating gene segments 10 and 11). Isolate 993/83 reacted with only one of four monoclonal antibodies that recognized a common VP6 epitope(s). In addition, VP6 and VP2 of isolate 993/83 showed one-dimensional peptide maps that differed substantially from the peptide maps of VP6 and VP2 from all bovine rotavirus isolates. By RNA-RNA hybridization, the 993/83 probe failed to react with a panel of mammalian rotavirus strains, including bovine rotaviruses. It hybridized, however, to genomic RNA of an avian rotavirus strain. Isolate 993/83 could thus represent a candidate for a natural interspecies transmission of rotavirus between different classes of vertebrates.

Isolation and characterization of two distinct human rotavirus strains with G6 specificity

Two new human rotavirus (HRV) strains, PA151 and PA169, with subgroup I specificity and a long RNA pattern, yet with a serotype G (VP7) specificity different from those of any of the six well-established HRV serotypes (G1 to G4, G8, and G9), were isolated 3 months apart from two children with acute gastroenteritis in Sicily, southern Italy, in the winter season of 1987 and 1988. The HRV isolates were adapted to growth in cell cultures and were then characterized by neutralization and RNA-RNA (Northern blot) hybridization. Cross-neutralization studies with type-specific immune sera to RV serotypes 1 to 10 showed the antigenic relatedness of the two strains with serotype 6 bovine strains UK and NCDV. Monoclonal antibodies to VP7 of UK were able to recognize UK and NCDV strains as well as both HRV isolates. Cross-hybridization studies showed a genetic relatedness of PA151 and PA169 to bovine strains for all genes except gene 4. Gene 4 of PA151 appeared to be genetically related to that of AU228 (a human strain of subgroup I and with serotype G3 specificity that belongs to a feline genogroup), whereas gene 4 of PA169 appeared to be unique, yet it was related to gene 4 of two recently reported subgroup I HRV strains, one (PA710) with serotype G3 specificity and the other (HAL1271) with serotype G8 specificity. The new HRV strains must be taken into consideration when deciding strategies for the development of an effective RV vaccine.

Nosocomial outbreak of neonatal gastroenteritis caused by a new serotype 4, subtype 4B human rotavirus

A nosocomial outbreak of rotavirus gastroenteritis involving 52 newborns occurred between June and September 1988 at the University Children's Hospital of Freiburg, Federal Republic of Germany. Stools from 27 representative patients were examined for rotavirus serotypes, using a monoclonal antibody-based enzyme-linked immunosorbent assay. The electropherotype was also examined by polyacrylamide gel electrophoresis of genomic RNA. As many as 18 patients were found to be infected by serotype 4, subtype 4B strain, and in all of them the same electropherotype was detected. Although rotavirus from the remaining nine patients could not be typed, the electropherotype in four was identical to that of the serotype 4, subtype 4B strain. Thus, most of the patients in the outbreak were infected by the same rotavirus strain. Retrospective epidemiological studies showed that the 4B strain began to circulate at the hospital in January 1988, whereas only rotavirus serotypes 1, 3, and 4A were detected in 1985-1987. The primary case of the outbreak was presumably a newborn with acute gastroenteritis, admitted to the hospital from a small maternity unit in the same urban area. During the outbreak, 12 of 44 healthy newborns in the nurseries of the Children's Hospital and other maternity hospitals were found to be asymptomatic rotavirus carriers, and in three of the newborns the same 4B strain was detected. This is the first reported outbreak caused by a serotype 4, subtype 4B strain.

Serotype 3 human rotavirus strains with subgroup I specificity

During an epidemiological study on human rotavirus (HRV) infections in Italy, three subgroup I strains not associated with serotype 2 reactivity were detected. All three strains were serotype 3, each with a distinct RNA pattern showing fast-moving tenth and eleventh segments (long electropherotype). Following successful adaptation to growth in cell cultures, the serotype 3 strains (MZ58, PCP5, and PA710) were further characterized by neutralization and by RNA-RNA (Northern blot) hybridization. Antiserum to reference HRV strain YO (subgroup II, serotype 3), as well as a monoclonal antibody to VP7 of YO neutralized, at comparable titers, the homologous virus, the three unusual HRV strains, and two reference simian strains (SA11 and RRV-2, both subgroup I, serotype 3), whereas SA11 antiserum and a monoclonal antibody to VP7 of SA11 neutralized simian strains more efficiently. However, antiserum to PCP5 neutralized the three unusual isolates and the simian strains at significantly higher titers than it did with reference strain YO. With 32P-labeled RNA from MZ58 as a probe, a high degree of homology was detected by Northern blot hybridization with strains PCP5, PA710, SA11, and UK (bovine rotavirus) at the level of several segments and with strain YO only at the level of genes 7 to 9. Conversely, labeled RNA of strain YO hybridized extensively with Wa (subgroup II, serotype 1 HRV strain) but only at the level of genes 7 to 9 with MZ58, PCP5, PA710, SA11, and UK. Finally, the labeled SA11 probe hybridized at the level of RNA segments 1 to 3 and 6 to 11 to the three unusual strains. These findings suggest that the unusual subgroup I, serotype 3, strains isolated from humans are more likely to be animal rotaviruses rather than natural reassortants between different HRV strains.

Isolation in Europe of 69 M-like (serotype 8) human rotavirus strains with either subgroup I or II specificity and a long RNA electropherotype

During an epidemiological study on the prevalence of human rotavirus (HRV) serotypes 1-4 in Europe, we found that some strains could not be typed. However, when a monoclonal antibody directed to serotype 8 HRV was included in the typing assay, we detected seven 69 M-like (serotype 8) strains, six from Finland and one from Italy. The previously reported serotype 8 HRV strains, 69 M, B 37, and B 38 isolated in Indonesia, were of subgroup I specificity and presented a peculiar "super short" RNA electropherotype. In contrast, all the seven European strains possessed a long RNA pattern, and one of them had subgroup II specificity. Three of these strains were adapted to growth in cell cultures and were further characterized by neutralization and by Northern blot hybridization. They appeared to be closely related to serotype 8 HRV strain 69 M by neutralization, but showed partial homology with several human and animal strains by hybridization. The epidemiological importance of these serotype 8 strains circulating in Europe should be investigated, in view of their possible inclusion in a rotavirus vaccine.

Prevalence of human rotavirus serotypes in some European countries 1981-1988

An extended epidemiological survey on the circulation of the 4 established human rotavirus (HRV) serotypes in some European countries was carried out on 831 fecal strains collected from infants and young children with acute non-bacterial gastroenteritis during 1981-88. Typing was done by enzyme-linked immunosorbent assay and/or solid-phase immune electron microscopy using VP7 type-specific neutralizing monoclonal antibodies. Serotype 1 HRV strains were found to be largely predominant in this period both in Italy and other countries, whereas serotype 4 strains were less common. The number of strains of serotypes 1 and 4 circulating in Europe was equivalent only in 1983-84. Serotype 2 strains were significantly represented only in 1981-84, while strains of serotype 3 were nearly absent, since only 8 strains (2 of which belonged to subgroup I) were found during the entire study period. About 10% of strains could not be typed, while 9 strains exhibited dual VP7 reactivity and 6 were non-group A HRVs. These epidemiological findings must be taken into consideration when deciding strategies for preparing vaccines to be used in Europe.