The electron microscopical and physical characteristics of small round human fecal viruses: an interim scheme for classification

Outbreaks of food-borne and waterborne viral gastroenteritis

Norwalk virus infection is the epidemiologic prototype for outbreaks of food-borne and waterborne gastroenteritis. Around the world, Norwalk virus and Norwalk-like viruses appear to be major causes of food-borne and waterborne illness. Assessment of the overall significance of viral agents to the epidemiology of food-borne and waterborne illness is hampered by the lack of surveillance throughout much of the world. In areas where food-borne and waterborne illness surveillance is conducted, outbreaks of viral gastroenteritis are underreported because of the lack of availability of routine laboratory services to confirm the viral etiology. Routine use of epidemiologic criteria as an alternative to laboratory confirmation will allow better assessments of the importance of viral gastroenteritis until effective laboratory methods can be widely implemented. Outbreaks of viral gastroenteritis have been propagated by contamination of water supplies, raw foods, and ill food handlers. Controlling an outbreak depends on identifying and removing the source of contamination. The demonstrated occurrence of person-to-person transmission and the likely occurrence of transmission of Norwalk-like viruses by aerosol make it necessary to evaluate the potential for transmission by food handlers and servers in every outbreak, regardless of primary source.

Generation and characterization of murine monoclonal antibodies reactive against N-terminal and other regions of HIV-1 reverse transcriptase

We produced a series of monoclonal antibodies against the human immunodeficiency virus (HIV-1) reverse transcriptase by immunizing mice with either purified recombinant HIV-1 p66 protein or with recombinant vaccinia virus which expresses HIV-1 pol sequences. The antibodies generated were specific for the reverse transcriptase protein, and recognized only the p51 and p66 subunits of the enzyme in each of the HIV-1 viral lysates and lysates of HIV-1 infected cells. The antibodies did not cross-react with HIV-2 reverse transcriptase. Most important, several of the antibodies are unique, in that they are the first that can bind to sites close to the N-terminal. This latter region has been suggested to form part of the polymerase domain of the reverse transcriptase. None of the antibodies could neutralize either the RNA-dependent DNA polymerase or RNase H activities of either p66 or p51/66 proteins. The binding patterns of these various antibodies to p66 and p51/66 were dependent on each of three independent variables: the source of antigen amployed, the individual specificity of the antibody, and the method employed to detect reactivity. These monoclonal antibodies provide useful reagents for the study of reverse transcriptase native structure-function relationships.

Sequence and genome organization of a human small round-structured (Norwalk-like) virus

Small round-structured viruses (SRSVs), also known as Norwalk or Norwalk-like viruses, are the major worldwide cause of acute, epidemic nonbacterial gastroenteritis in humans. These viruses, which contain a single-stranded RNA genome, have remained refractory to molecular characterization because of the small amounts of virus in clinical samples and the absence of an animal model and an in vitro culture system. The complete genomic nucleotide sequence of an SRSV, Southampton virus, was determined. The 7696-nucleotide RNA genome encodes three open reading frames whose sequences and organization strongly support proposals that SRVSs are members of the Caliciviridae.

Demonstration of low molecular weight polypeptides associated with small, round-structured viruses by western immunoblot analysis

Small, round-structured viruses (SRSV) were detected in 14 of 300 fecal specimens obtained from patients with acute gastroenteritis by electron microscopy. These SRSV strains were morphologically indistinguishable from one another. While 11 of these strains had a single usual major structural protein with molecular weight of 63,000 (63K) daltons (p63), interestingly, three strains possessed a single major structural protein with molecular weight of 33K daltons (p33). Treatments of p63-SRSV with proteolytic enzymes or denaturating reagents did not affect the molecular weight of p63, and the p33 was not detectable by Western immunoblot in the ultracentrifugal supernatant of the p63-SRSV suspension. These results suggest that the p33 is neither a definitive subunit of p63 nor disintegrated component derived from the p63-SRSV but a novel polypeptide of SRSV. Immune electron microscopy and Western immunoblot analyses indicated that p63- and p33-SRSVs may share an antigenic determinant(s).

3' terminal nucleotide sequence of human astrovirus type 1 and routine detection of astrovirus nucleic acid and antigens

Human astrovirus type 1 was purified by caesium chloride density-gradient centrifugation and the virus was located using an immunodot blot technique with polyclonal rabbit serum, which reacted with all five serotypes. The virus banded with a density of 1.33 g/ml. RNA was extracted from the purified virus, converted into double-stranded cDNA, using an oligo(dT) primer, and cloned into plasmid and M13 vectors. The sequence of the 3' end of astrovirus RNA adjacent to the poly(A) tract was determined. This sequence showed no significant homology with the equivalent region of other positive-sense RNA viruses. Synthetic oligonucleotide primers were designed to amplify specifically astrovirus type 1 RNA in a polymerase chain reaction.

Detection of Norwalk-like virus and specific antibody by immune-electron microscopy with colloidal gold immune complexes

Direct electron-microscopy (DEM), immune electron microscopy (IEM) and four different procedures of immune electron microscopy with colloidal gold immune complexes were evaluated for the detection of Norwalk-like virus and specific antibody. A solid-phase immune electron microscopy with colloidal gold immune complexes-triple layer method (SPIEMGIC-TLM) is developed for screening patients' specimens for the detection of Norwalk-like virus and its specific antibody. The method demonstrates low non-specific background labelling and is simple, sensitive and easy to perform. A quadruple layer method (SPIEMGIC-QLM), which is a modification of the triple layer method, has been established by adding a cross-linking anti-IgG layer to amplify the reaction and to provide a more sensitive test which is suitable for screening monoclonal antibodies prepared against 32-34-nm Norwalk-like virus isolated in our laboratory.

Application of two RNA extraction methods prior to amplification of hepatitis E virus nucleic acid by the polymerase chain reaction

Amplification of the enterically-transmitted non-A, non-B hepatitis virus (HEV) RNA using conventional reverse transcriptase reactions followed by the polymerase chain reaction (PCR) of the cDNA has not been successful. However, after application of two different RNA capture/extraction methods we were able to amplify HEV nucleic acid from clinical samples and specimens from experimentally infected animals. The first procedure, adapted from an immune electron microscopy (IEM) technique, incorporated an immunocapture step with concentration of the virus-antibody complexes by pelleting in a Beckman airfuge. In the second method, glass powder (or size-fractionated silicon dioxide) was used to capture the RNA from its surrounding milieu by adsorption of the nucleic acid to the silicate particles. Since conventional immunoassays for HEV antigen or antibody are not currently available, the use of these RNA extraction methods, coupled with PCR techniques, will be valuable in screening clinical specimens and in further defining the course of disease using animal infectivity studies.

A dot-blot hybridization procedure for the detection of astrovirus in stool samples

We have developed a nucleic acid dot-blot hybridization test for the detection of astroviruses in stool samples. The test was not as sensitive as electron microscopy for the detection of low numbers of well preserved astrovirus particles, but was able to identify astroviruses in stools containing particles of indistinct morphology. In total, this procedure identified astroviruses in more samples than did electron microscopy, and the data indicate that the incidence of astroviruses may be substantially underestimated.

Electron microscopic reporting of gastrointestinal viruses in the United Kingdom, 1985-1987

We examined some epidemiological features of the viruses associated with gastrointestinal illness, using national data reported by electron microscopists in the United Kingdom. During the 3 years analyzed (1985-1987), a total of 1,993 positive detections of astroviruses, caliciviruses, coronaviruses, and small round structured viruses (SRSVs) were reported. In 1 year of this period, 8,210 rotaviruses were reported. More than 90% of the astroviruses and caliciviruses were detected in children under 5 years of age, while coronaviruses and SRSVs were detected in adults as well as children. Detections of astroviruses increased in the winter and were infrequent during the summer, a seasonal pattern similar to that observed for rotaviruses. There was some variability between reporting regions in rates of detection of fecal viruses. We have attempted to identify the reasons for this. We make suggestions for improving the detection of human fecal viruses, and we recognize the need for continued surveillance of these agents.

Pattern of shedding of small, round-structured virus particles in stools of patients of outbreaks of food-poisoning from raw oysters

The pattern of shedding of the small, round-structured virus (SRSV) particles in the stools of patients who suffered from food-poisoning due to raw oysters was investigated. The duration and concentration of fecal shedding of the SRSV particles were studied by electron microscopic examinations of stool specimens obtained during the course of illness to see a relation of viral shedding to day of illness. It was found that the fecal shedding of the SRSV particles occurred within five days of illness; thereafter, the concentration of the SRSV particles in feces rapidly decreased within a few days during the course of illness.

Antigenic relatedness among the Norwalk-like agents by serum antibody rises

The Norwalk, Snow Mountain (SMA), and Hawaii agents are etiologically associated with separate outbreaks of acute viral gastroenteritis. Previous cross-challenge of volunteers, immune electron microscopy, and/or enzyme-immunoassay analysis suggested that these agents are antigenically distinct. We examined paired sera from human volunteers challenged with these agents for the presence of homologous and heterologous serum antibody titer rises to the agents. Two-way cross-reactions occurred between Hawaii agent and SMA. A one-way cross-reaction occurred between Norwalk agent and SMA, as volunteers challenged with Norwalk agent had heterologous serum antibody titer rises to SMA, but the reverse did not occur. The Norwalk and Hawaii agents had minimal cross-reaction, with only one volunteer challenged with Hawaii agents having a heterologous rise to Norwalk agent. These observations indicate varying degrees of antigenic relatedness among these agents.

Antigenic characterization of small, round-structured viruses by immune electron microscopy

Small, round-structured viruses (SRSVs) detected from nonbacterial gastroenteritis outbreaks in Tokyo and Saitama Prefecture, Japan, during the period from 1977 to 1988 were tentatively classified into nine antigenic patterns from SRSV-1 (S-1) to SRSV-9 (S-9) by cross-immune electron microscopy (IEM). S-1 and S-2 appeared pattern specific, while S-3 to S-9, distinguishable from each other in their reactivity, appeared somewhat antigenically related. Their antigenic relatedness to the Norwal, Hawaii, and Otofuke agents was also examined by IEM by using antisera to these agents. S-3 appeared most closely related to the Norwalk agent. S-4 and S-5 were related to the Norwalk agent and, presumably, were distantly related to the Hawaii and Otofuke agents. S-6 and S-7 were related to the Hawaii and Otofuke agents. S-8 and S-9 were related to the Otofuke agent and, presumably, were distantly related to the Hawaii agent. The prevalence of each antigenic pattern in 38 outbreaks was examined: S-8 was implicated in 24% of the outbreaks S-5 in 16%, S-4 in 13%, S-9 in 13%, S-6 in 11%, and others in 5%.

Three serotypes of Norwalk-like virus demonstrated by solid-phase immune electron microscopy

Solid phase immune electron microscopy (SPIEM) was used to investigate the serological differences between Norwalk-like virus (NLV) strains from five different outbreaks within the United Kingdom. The existence of two previously demonstrated serotypes, Lewis et al. (Journal of Clinical Microbiology 26:938-942, 1988), was confirmed by the use of whole convalescent sera and purified IgM. A third serotype was found to be the agent of two recent hospital outbreaks and could similarly be typed by use of whole sera or pure IgM. Paired sera were available for two of the three serotypes and demonstrated rising antibody levels. These antibody rises were also specific for the infecting serotype. However, two serum pairs from a later outbreak gave antibody rises to all three serotypes, although much higher counts were produced with the infecting serotype. SPIEM is a useful method for distinguishing NLV serotypes and can also be used to detect specific IgM and to demonstrate seroconversion. Cross-reacting antibodies, possibly anamnestic in origin, can occur after natural infection and could cause confusion in typing virus unless further evidence of the identity of the infecting agent is obtained.

Electron microscopy of stool-shed viruses: retention of characteristic morphologies after long-term storage at ultralow temperatures

Storage of stool specimens at -70 degrees C has been reported to destroy the characteristic morphology of calicivirus. To determine if other stool-shed viruses are similarly affected, stool specimens previously examined by electron microscopy and observed to contain virus particles were reexamined after 6-10 years of storage at -70 degrees C to -85 degrees C. The stools contained virus particles of different morphological types, including astrovirus, small round structured virus, adenovirus, and rotavirus as well as calicivirus. Also reexamined were stools containing coronavirus-like particles and T = 19 virus-like particles. Characteristic virus particles, including calicivirus particles, were recognized in all the stools reexamined. The results indicate that long-term storage of stools at ultralow temperatures does not present a significant problem for the morphological identification of stool-shed viruses.

Western blot (immunoblot) assay of small, round-structured virus associated with an acute gastroenteritis outbreak in Tokyo

Small, round-structured virus (SRSV) was detected in a stool specimen of a patient during an acute gastroenteritis outbreak in Tokyo and was tentatively named SRSV-9. SRSV-9 was purified by sucrose velocity gradient centrifugation after CsCl density gradient centrifugation. The buoyant density of SRSV-9 appeared to be 1.36 g/ml in CsCl. A Western blot (immunoblot) assay using the biotin-avidin system revealed that SRSV-9 was antigenically related to the Hawaii agent but distinct from the Norwalk agent and contained a single major structural protein with a molecular size of 63.0 +/- 0.6 kilodaltons. The prevalence of SRSV-9 infection in Tokyo was surveyed by the Western blot antibody assay by using a crude virus preparation as the antigen. Seroconversion was observed in 56.5% of the patients involved in the outbreaks from which SRSV was detected by electron microscopy.

Prevalence of small round structured virus infections in acute gastroenteritis outbreaks in Tokyo

During the three-year period from 1984 to 1987, 506 acute gastroenteritis outbreaks involving 14,383 patients were reported to the Bureau of Public Health, Tokyo Metropolitan Government. Eighty (4,324 patients) of 150 outbreaks (4,860 patients) from which etiologic agents were not identified were subjected to virological investigation. Spherical particles of 28-32 nm in diameter with capsomere-like structures on the surface were detected in patients' stool specimens. Buoyant density of the particles appeared to be 1.36 to 1.40 g/ml in CsCl. Seroconversion to the particles was observed in patients by immune electron microscopy. From these observations, we concluded that the detected particles were members of small round structured virus (SRSV), and that they were implicated in the etiologically ill-defined outbreaks encountered. Prevalence of SRSV infections in these outbreaks was examined by electron microscopy. SRSV was positive in 83.8% of the outbreaks, and 96.4% of the cases. SRSV-positive outbreaks usually occurred during winter in contrast to bacterial outbreaks which often occurred in the summer season. Of 80 outbreaks examined, 53 were associated with the ingestion of oysters, and the remaining 27 mostly with food other than oysters. Oyster-associated outbreaks usually occurred on a small scale, while unassociated ones on diverse scales ranged from family clusters to large outbreaks.

Human viral gastroenteritis

During the last 15 years, several different groups of fastidious viruses that are responsible for a large proportion of acute viral gastroenteritis cases have been discovered by the electron microscopic examination of stool specimens. This disease is one of the most prevalent and serious clinical syndromes seen around the world, especially in children. Rotaviruses, in the family Reoviridae, and fastidious fecal adenoviruses account for much of the viral gastroenteritis in infants and young children, whereas the small caliciviruses and unclassified astroviruses, and possibly enteric coronaviruses, are responsible for significantly fewer cases overall. In addition to electron microscopy, enzyme immunoassays and other rapid antigen detection systems have been developed to detect rotaviruses and fastidious fecal adenoviruses in the stool specimens of both nonhospitalized patients and those hospitalized for dehydration and electrolyte imbalance. Experimental rotavirus vaccines have also been developed, due to the prevalence and seriousness of rotavirus infection. The small, unclassified Norwalk virus and morphologically similar viruses are responsible for large and small outbreaks of acute gastroenteritis in older children, adolescents, and adults. Hospitalization of older patients infected with these viruses is usually not required, and their laboratory diagnoses have been limited primarily to research laboratories.

Solid-phase immune electron microscopy with human immunoglobulin M for serotyping of Norwalk-like viruses

A solid-phase immune electron microscopy method that uses protein A, goat anti-human immunoglobulin M (IgM), and human serum is described. Evaluation of the method with different immunoglobulin fractions showed that human IgM constituted the major virus capture antibody. The method appeared to distinguish between two Norwalk-like virus serotypes and demonstrated specific IgM responses to these serotypes in infected individuals. Further work is being carried out to define the relationship of these two serotypes to the previously described Norwalk agent (A. Z. Kapikian, R. G. Wyatt, R. Dolin, T. S. Thornhill, A. R. Kalica, and R. M. Chanock, J. Virol. 10:1075-1081, 1972), and four subsequent hospital outbreaks are being studied.

Viral enteritis

Rotavirus has emerged as the major enteric pathogen causing acute diarrhea in young children throughout the world. Other viral pathogens have been recognized and additional candidate agents are suspected but none approaches rotavirus in its global impact. A strong appropriate emphasis has been placed on preventive therapy. Although vaccines are not yet available, it is clear that improved hygienic practices, particularly in pediatric institutions, and breast feeding can do much to prevent serious illness during the early months when babies are so vulnerable. During the past decade, from clinical studies and animal models, much has been learned about the pathogenesis of rotavirus diarrhea. These findings provide a sound basis for the use of rational oral fluid therapy, early feeding, and avoidance of drugs during active management. Among the many challenges that remain are the elucidation of the full spectrum of enteric viral pathogens, their impact on man, and their prevention and active therapy.

An electron microscopical investigation of faecal small round viruses

A retrospective study of small round featureless viruses (SRVs) initially identified by negative-staining electron microscopy of stool samples was performed. A variety of technique, including immunoelectron microscopy and caesium chloride gradient centrifugation, was applied in an attempt to classify further these viruses. Over a four-year period, 64 SRV-positive samples were reported (1.8% of the stool samples sent for electron microscopy and 6.2% of the total number of positive samples), of which 53 were available for further study. A significant degree of misclassification was found. Viruses previously identified as SRVs were shown to be astrovirus (n = 14), calicivirus (n = 2), and "Norwalk-like" virus (n = 1). The majority of the 36 remaining samples were identified as parvovirus-like (n = 27) (75%), 14 of which were associated with the presence of adenovirus particles. Enteroviruses (n = 3) and hepatitis A virus (n = 1) were infrequently detected. The remaining viruses (n = 5) could not be adequately classified. Parvovirus may be the predominant SRV associated with acute diarrhoeal disease in childhood.

Norwalk like viruses: study of an outbreak

An outbreak of acute non-bacterial gastroenteritis is reported, during which a ward had to be closed, and stool samples from 15 patients showed a virus structurally similar to the Norwalk agent.

Waterborne Viral Gastroenteritis

In studying the causes of human gastroenteritis, electron microscopy and related techniques have led to the identification of new viral agents that had previously escaped detection by routine cell culture procedures. Efforts to characterize and study these agents further are currently being made by researchers in many areas of the world. Two of the best‐known agents, rotavirus and Norwalk virus, have been implicated in waterborne outbreaks of this illness. Another virus, the Snow Mountain agent, was first identified from the investigation of one waterborne gastroenteritis outbreak.

The detection of rotaviruses in products of wastewater treatment

Rotaviruses present in products of wastewater treatment were assayed in MA104 cells by indirect immunofluorescence. Levels in settled sewage, activated sludge and effluent were greater than 10(3) per litre in March and April but virus was not detected during later months. This pattern correlated with the decline in laboratory reports of human rotavirus infection.

A centenary of academic and less learned food microbiology. Pitfalls of the past and promises for the future

A review is presented of the development of Food Microbiology from its roots in different disciplines - including human and animal medicine, general microbiology, agricultural science and food chemistry - to an autonomous science with the main vocation to provide the knowledge allowing providing food that is wholesome, of high quality and acceptable in the microbiological sense. This evolution entailed a change in approach from mere, and often rather primitive inspection of end-products to intervention by (i) identification of hazard points ("critical points" or CPs) by ecological studies; (ii) elimination of CPs by elaboration of Good Manufacturing and Distribution Practices (GMPs); (iii) validation of GMPs by monitoring production lines and final products at point of sale and gauging the results by Risk Analysis. It is emphasized, that although advanced and ecologically sound techniques have become available, it will still require extensive education and training at all levels before the scientific advances outlined in this review will have been fully integrated in day-to-day food production and catering in developed as well developing areas of the world. Interdisciplinary instruction and co-operation cannot be missed in attempts to reach this goal.

Micro-organisms in gastroenteritis

We present bacteriological and virological findings together with salient clinical features from a prospective study of 447 children aged under 2 years admitted to hospital with infectious gastroenteritis. Putative pathogenic micro-organisms were identified in the stools of 75% of these children. Eight identifiably distinct groups of viruses, found on electron microscopy and tissue culture were present in 67% of patients--rotavirus was detected most frequently. Pathogenic bacteria (salmonellas, shigellas, Escherichia coli, and Campylobacter jejuni--but excluding Clostridium difficile) were found in 16% only. Altogether 4 X 9% of 390 patients had gastroenteritis associated with Cl difficile toxin. The mean duration of diarrhoea was shortest in patients with identifiable virus, with rotavirus having a mean of 5 X 01 days, and was longest in patients with pathogenic bacteria in the stools (11 X 14 days). The finding of more than one type of virus did not seem to be associated with a significantly increased duration of diarrhoea. There are few clinical features which can be associated specifically with any particular micro-organism or groups of these. Multiple organism isolation was common, but the severity of the illness in those patients with at least two types of organism was not greater. Certain viruses, including the norwalk-like virus, known to be associated with outbreaks of gastroenteritis were found as frequently in a group of patients who did not have diarrhoea studied for comparison. Virus was still detectable in the stools of up to 40% of asymptomatic children on the day of discharge.

Food borne infection by a Norwalk like virus (small round structured virus)

Two outbreaks of gastrointestinal illness with identical symptoms occurred in parties attending banquets on consecutive evenings at a large hotel. The illness was typical of epidemic winter vomiting disease. Small round structured viruses resembling those seen in the Norwalk Ohio outbreak were identified by electron microscopy in stools of victims from one episode. One food handler was found to be excreting the virus, and there was evidence of a poor standard of hygiene in the kitchen. A food history analysis showed the illness to be significantly associated with eating cold cooked ham.

An outbreak of food-borne gastroenteritis in two hospitals associated with a Norwalk-like virus

Two connected outbreaks of gastroenteritis in separate hospitals associated with a small round structured virus morphologically indistinguishable from the Norwalk virus are described. The virus was most probably introduced on chicken sandwiches prepared by a member of the kitchen staff who was incubating the disease.

Haemolytic uraemic syndrome: evidence of multiple viral infections in a cluster of ten cases

During July 1979, ten patients were admitted to the hospital with bloody diarrhoea followed by manifestations of haemolytic uraemic syndrome (HUS): acute microangiopathic haemolytic anaemia, intravascular coagulopathy, and impaired renal function. Ages ranged from 13 months to 58 yr, with only two patients more than 5 yr old. In a household that included seven children born to three sisters who married three brothers, six children required hospitalization for bloody diarrhoea and four developed HUS; the father of one case and the maternal grandmother also developed bloody diarrhoea. Echovirus type 11 was isolated from the pharyngeal secretions or faeces of all members of the household with bloody diarrhoea, with the exception of the grandmother. Picornavirus-like particles were seen by direct electron microscopy (E/M) in faeces from four other HUS patients and an adenovirus in one, but these viruses failed to replicate in cell cultures. Parvovirus-like particles were seen by E/M in faeces from six patients. Serological examination indicated recent infection with one or more enteroviruses (echovirus 11, coxsackieviruses A4, B2, B4) in nine cases. Combined viral studies revealed presumptive evidence of recent infection with two or more viruses in all of the patients with HUS. Stools were negative for bacterial pathogens including campylobacter, salmonella, shigella, and yersinia organisms. Only one of nine patients tested had circulating immune complexes. Our data support the concept that the pathology seen in HUS may be due to a Shwartzman-type reaction provoked by concurrent infection with two or more viral agents.