Baculovirus expression and antigenic characterization of the capsid proteins of three Norwalk-like viruses

Human caliciviruses (HuCVs) are antigenically diverse. The antigenic relationships among different HuCVs have been difficult to study because HuCVs cannot be passaged in the laboratory. In this study, we describe cloning, sequencing and expression of the viral capsid proteins of three HuCVs that were identified in outbreaks of acute gastroenteritis in Virginia in 1997-1998. Yields of the capsid proteins similar to previously expressed recombinant Norwalk virus were obtained using the baculovirus expression system. Recombinant VA97207 capsid protein (rVA97207) and rVA98387, but not rVA98115, formed virus-like particles (VLPs). All three recombinant capsid antigens detected seroresponses in patients involved in outbreaks of acute gastroenteritis associated with genetically homologous or related HuCVs. The antigenic relationships of the three strains were further characterized using hyperimmune antisera against the three capsid antigens as well as four previously characterized recombinant capsid antigens of Norwalk (rNV), Mexico (rMxV), Hawaii (rHV), and Grimsby viruses (rGrV). VA98387 shared 98% aa identity with GrV; rVA98387 was detected by antisera to GrV. VA98115 shared 87% aa identity with Desert Storm virus and 65% aa identity with prototype Norwalk virus (NV); rVA98115 reacted weakly with NV antisera. VA97207 shared 80% aa identity with Amsterdam and 75% aa identity with Leeds strains and rVA97207 was not detected by any of the heterologous antibodies. In conclusion, VA97207 and VA98115 may belong to CV antigenic types not previously expressed, while VA98387 is a GrV-like virus. Low levels of cross-reactive antibodies were detected between types. Further studies to characterize these antigens and to develop enzyme immune assays (EIAs) for these strains are in progress.

Prevalence and genetic diversity of human caliciviruses (HuCVs) in Mexican children

Human caliciviruses (HuCVs) contain two genera: "Norwalk-like viruses" (NLVs) and "Sapporo-like viruses" (SLVs). The importance of the two genera as a cause of acute gastroenteritis of infants and children remains unknown. Beginning in 1989, a birth cohort of children in Mexico was enrolled and monitored for acute gastroenteritis. A subset of 115 diarrhea stool specimens from 76 children and 66 non-diarrhea stool specimens from 64 children was examined for HuCVs by RT-PCR by using a primer pair (p289/290) that detects both NLVs and SLVs. Twenty-two (19%) of the 115 diarrhea stool specimens and 5 (7%) of 66 non-diarrhea stool specimens produced RT-PCR products of expected size (319 bp for NLVs and 331 bp for SLVs). Twenty of the twenty-seven strains were cloned and sequenced. Pairwise sequence analysis showed that 9 (60%) and 6 (40%) of the 15 strains from the diarrhea stools were NLVs and SLVs, respectively. The same proportions of NLVs (60%) and SLVs (40%) were observed in the non-diarrhea stools. Strains in the NLV genus could be further divided into four clusters: Lordsdale, MxV, and HV and one potentially new cluster. Strains in the SLV genus could be divided into three clusters: Sapporo/82, Lon/92, and a potentially new cluster. Strains from the Lordsdale cluster were the most common among these children. The findings of both genera and multiple clusters of HuCVs co-circulating and the identification of new strains of HuCVs in the population justify the need for future studies of HuCVs in infants and children.

Diagnosis of human caliciviruses by use of enzyme immunoassays

The application of molecular technologies, such as the expression of viral proteins in baculovirus, has provided a powerful approach to the diagnosis of human calicivirus (HuCV) infections. The baculovirus-expressed HuCV capsid protein self-assembles into virus-like particles, providing excellent reagents for immunologic assays, such as enzyme immunoassays (EIAs). Following the expression of the capsid protein of Norwalk virus, the capsid proteins of 8 other HuCV strains have been expressed in baculovirus. The unlimited supply of baculovirus-produced reagents for HuCVs allows these EIAs to be applied in large-scale clinical and epidemiological studies. Both the antigen and antibody-detection EIAs are highly sensitive. The antigen-detection EIAs are highly specific, but the antibody-detection EIAs are more broadly reactive. This article reviews baculovirus expression techniques used to produce HuCV capsid antigens, development of EIAs using these antigens, and application of these EIAs in studies of HuCV infection and illness.

The influence of trimethaphan (Arfonad)-induced hypotension with and without spine distraction on canine spinal cord blood flow

Controlled hypotension is used in scoliosis surgery to reduce the need for transfusion and to improve operating conditions, but there is concern that deliberate hypotension may decrease spinal cord blood flow (SCBF) and predispose the spinal cord to injury, particularly when it is distracted during Harrington instrumentation. To study the effect of deliberate hypotension on SCBF, the mean arterial pressure (MAP) was reduced to 50% of its normotensive value with trimethaphan (Arfonad) in dogs and the SCBF measured using the hydrogen washout technique with and without spine distraction. The SCBF was significantly reduced to half its normotensive value of 23.2 ml/min/100 gm to 11.4 ml/min/100 gm after hypotension was established. The SCBF remained significantly decreased compared with controls when measured at 30, 45, and 60 minutes following the induction of hypotension and also when hypotension was terminated. SCBF was not further reduced when 2 cm of spine distraction was added. These results show that induction of hypotension with trimethaphan is associated with a similar decrease in SCBF, which is maintained as long as the drug is used and that this effect continues after the drug is terminated and the MAP increases. Cautiously extrapolating these findings clinically would suggest that trimethaphan may not be the drug of choice for controlled hypotension during scoliosis surgery, despite its apparently favorable hemodynamic and hormonal responses.

The diagnosis and treatment of functional disorders of the biliary tract

An approach to the diagnosis and treatment of patients with presumed functional disorders of the biliary tract (biliary dyskinesia) is described. The current diagnostic criteria are pain compatible with biliary pain in the absence of gallstones and other organic gastrointestinal disease, or other disorders which might produce abdominal pain, together with reproduction of the patient's symptoms by cholecystokinin, or morphine, or both. Other diagnostic methods are described together with their limitations. The results of operation in 38 of 45 patients seen in this Unit during the past six years are presented. The results were poor in 20% of patients, but two-thirds of the group have had good results in the short term.

Hyperkinesis and diet: a double-blind crossover trial with a tartrazine challenge

A pilot study was conducted on 22 children (19 boys and three girls) aged between four and eight years, who were selected as hyperactive on the basis of developmental history and clinical judgement. Conners' parent-teacher ratings, objective tests of attention, standard perceptualmotor tests and subtests from the Wechsler Intelligence Scale for Children (WISC), were used as response variables. The children were tested before and after four weeks on the elimination diet, after a tartrazine and placebo challenge, and, finally, after a four-week washout period on the diet. Results showed a statistically significant improvement in the mothers' ratings of the children's behaviour after the first four weeks of the diet. The improvement was maintained in a combined analysis of the initial four-week diet period and four-week washout period. This result was not substantiated by the statistical analysis of the results from objective tests. The rating scales and objective tests for the full sample did not show a statistically significant deterioration in the children's behaviour when they were challenged under double-blind test conditions with the Yellow Dye No. 5, tartrazine, and the tests were conducted the day after a two-week challenge period. A comparison of mother ratings of behaviour during challenge and placebo double-blind trial and in the 24 hours preceding tests, in a subgroup of the children who, while on the diet, showed a 25% reduction of symptoms on the Conner's rating scale, indicated a significant challenge effect (P less than 0.025), with mothers reporting more symptoms during the challenge period. Dietary infringements with suspected trigger substances occurred throughout the trial.