Nosocomial infantile gastroenteritis associated with minirotavirus and calicivirus

Neuroinvasion and Inflammation in Viral Central Nervous System Infections

Neurotropic viruses can cause devastating central nervous system (CNS) infections, especially in young children and the elderly. The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) have been described as relevant sites of entry for specific viruses as well as for leukocytes, which are recruited during the proinflammatory response in the course of CNS infection. In this review, we illustrate examples of established brain barrier models, in which the specific reaction patterns of different viral families can be analyzed. Furthermore, we highlight the pathogen specific array of cytokines and chemokines involved in immunological responses in viral CNS infections. We discuss in detail the link between specific cytokines and chemokines and leukocyte migration profiles. The thorough understanding of the complex and interrelated inflammatory mechanisms as well as identifying universal mediators promoting CNS inflammation is essential for the development of new diagnostic and treatment strategies.

Comprehensive review of human sapoviruses

Sapoviruses cause acute gastroenteritis in humans and animals. They belong to the genus Sapovirus within the family Caliciviridae. They infect and cause disease in humans of all ages, in both sporadic cases and outbreaks. The clinical symptoms of sapovirus gastroenteritis are indistinguishable from those caused by noroviruses, so laboratory diagnosis is essential to identify the pathogen. Sapoviruses are highly diverse genetically and antigenically. Currently, reverse transcription-PCR (RT-PCR) assays are widely used for sapovirus detection from clinical specimens due to their high sensitivity and broad reactivity as well as the lack of sensitive assays for antigen detection or cell culture systems for the detection of infectious viruses. Sapoviruses were first discovered in 1976 by electron microscopy in diarrheic samples of humans. To date, sapoviruses have also been detected from several animals: pigs, mink, dogs, sea lions, and bats. In this review, we focus on genomic and antigenic features, molecular typing/classification, detection methods, and clinical and epidemiological profiles of human sapoviruses.

Small round viruses: classification and role in food-borne infections

Since the first observation of Norwalk virus in the electron microscope in 1972, many different small virus particles in the size range 20-40 nm have been described world-wide in association with outbreaks of gastroenteritis. Progress characterizing these agents has been hampered by the relatively small numbers of particles present in clinical material and the lack of success in culturing them. Although the relationship between some of these viruses remains confusing, a number of distinct groups has emerged, based on morphological features and limited physical data. Immuno-electron microscopy has proved valuable in detecting viruses but the addition of antibody can mask surface morphological features. Examination of viruses in negatively stained preparations without added antibody has revealed distinct morphological differences and viruses previously thought to be simply antigenic variants within the Norwalk group of viruses clearly belong to other groups. Preliminary evidence suggests that one human virus unrelated to Norwalk has a single-stranded DNA genome and is a parvovirus. Some groups have been implicated in outbreaks of food-borne gastroenteritis, particularly after the consumption of shellfish, and their role in other food-borne and water-borne outbreaks is being increasingly recognized.

Health risks of enteric viral infections in children

Children are at a greater risk of infections from serious enteric viral illness than adults for a number of reasons. Most important is the immune system, which is needed to control the infection processes. This difference can lead to more serious infections than in adults, who have fully developed immune systems. There are a number of significant physiological and behavioral differences between adults and children that place children at a greater risk of exposure and a greater risk of serious infection from enteric viruses. Although most enteric viruses cause mild or asymptomatic infections, they can cause a wide range of serious and life-threatening illnesses in children. The peak incidence of most enteric viral illnesses is in children <2yr of age, although all age groups of children are affected. Most of these infections are more serious and result in higher mortality in children than adults. The fetus is also affected by enterovirus and infectious hepatitis resulting in significant risk of fetal death or serious illness. In addition to the poliovirus vaccine, the only vaccine available is for hepatitis A virus (HAV). A vaccine for rotavirus has currently been withdrawn, pending review because of potential adverse effects in infants. No specific treatment is available for the other enteric viruses. Enteric viral infections are very common in childhood. Most children are infected with rotavirus during the first 2yr of life. The incidence of enteroviruses and the viral enteric viruses ranges from 10% to 40% in children and is largely dependent on age. On average, half or more of the infections are asymptomatic. The incidence of hepatitis A virus is much lower than the enteric diarrheal viruses. There is no current evidence for hepatitis E virus (HEV) acquisition in children in the U.S. Enteric viral diseases have a major impact on direct and indirect health care costs (i.e., lost wages) and amount to several billion dollars a year in the U.S. Total direct and indirect costs for nonhospitalized cases may run from $88/case for Norwalk virus to $1,193/case for enterovirus aseptic meningitis. Direct costs of hospitalization ran from $887/case for Norwalk virus to $86,899/case for hepatitis A. These costs are based on 1997-1999 data. Generally, attack rates during drinking water outbreaks are greater for children than adults. The exception appears to be hepatitis E virus where young adults are more affected. However, pregnant women suffer a high mortality, resulting in concurrent fetal death. Also, secondary attack rates are much higher among children, probably because of fewer sanitary habits among this age group. Overall, waterborne outbreaks of viral disease have a greater impact among children than adults. To better quantify the impact on children, the literature hould be further reviewed for case studies of waterborne outbreaks where data are available on the resulting illness by age group. The EPA and/or Centers for Disease Control should attempt to collect these data as future outbreaks are documented.

Sapporo virus: history and recent findings

Morphologically distinct caliciviruses of human origin were first found in stools of children with gastroenteritis in 1976. Sapporo virus, or human calicivirus Sapporo, with typical surface morphology was first detected during a gastroenteritis outbreak in a home for infants in Sapporo, Japan, in 1977. Since then, morphologically and antigenically identical virus has been detected frequently in the same institution in association with outbreaks of gastroenteritis. Sapporo virus is widely distributed worldwide, as evidenced by the appearance of antigenically or genetically similar viruses and seroepidemiologic findings. Sapporo virus plays an important role in outbreaks of infantile gastroenteritis and is less important in foodborne outbreaks. Sapporo virus has been approved as the type species of the genus "Sapporo-like viruses in the family Caliciviridae. The history of and recent findings, as obtained by newly developed techniques, about Sapporo viruses are presented.

Identification of minireovirus as a Norwalk-like virus in pediatric patients with gastroenteritis

In 1977, 30- to 32-nm virus-like particles, named minireovirus because of their unique morphologic appearance, were detected by electron microscopy in the stools of infants and young children with gastroenteritis. Sequence analysis of approximately 2,800 consecutive bases derived from overlapping PCR clones of a recent minireovirus clinical isolate showed 52% nucleotide sequence identity with the Norwalk virus sequence and, in addition, demonstrated that the genomic organizations of these two viruses were similar. Our data show that minireovirus is a Norwalk-like virus and should now also be included in the Caliciviridae family.

Prevalence of nosocomial rotavirus infection in hospitalized children in Benin City, Nigeria

A total of 1496 stool samples from 445 children admitted into the paediatric wards of the University of Benin Teaching Hospital, Benin City between November 1989 and April 1990 were examined for the presence of rotavirus antigen. The total prevalence of rotavirus infection in this study was 28.1% (125 in 445). Fifty-four (12.1%) of the 445 children had nosocomial rotavirus infection: 22 (9.6%) of the 230 children (neonates, infants and young children) who had diarrhoea and 32 (14.9%) of the 215 children (neonates, infants and young children) who had no diarrhoea. The importance of maintaining strict hygiene in hospital wards cannot be overemphasized.

Human, small round structured viruses, caliciviruses and astroviruses

Epidemiological studies on SRSVs, human calicivirus and astroviruses have been limited by the problems of establishing them in cell culture and the inability to transmit them to animals or to use strains from animals as a source of antigen for diagnostic tests. The use of EM and the subsequent development of RIAs and EIAs in a few research centres has shown that they are a cause of outbreaks and sporadic cases of diarrhoea and vomiting. SRSVs have increasingly been recognized as a major cause of outbreaks of gastroenteritis in the community and in hospital wards. The symptoms of illness are generally mild and of short duration and patients seldom require medical attention. However, because of the high attack rates and large numbers of persons of all age groups involved, there is often considerable economic loss and disruption of services. Evidence is accumulating that polluted water, molluscan shellfish, and contaminated cold foods are major sources of infection. Recently a SRSV has been shown to be the cause of epidemics and sporadic cases of waterborne enterically transmitted non-A, non-B hepatitis (hepatitis E virus) which have occurred in the USSR, India, Mexico and Africa. Astroviruses and human caliciviruses are occasional causes of outbreaks of vomiting and diarrhoea in infants and the elderly which can necessitate the closure of hospital wards and cause considerable disruption. Symptoms are generally mild and of short duration and therefore the majority of cases are unlikely to be investigated by laboratories. Diagnosis of infections is at present limited to the few laboratories that have developed their own assays or have access to electronmicroscopy facilities.

Uncontrolled nosocomial rotavirus transmission during a community outbreak

Between Jan. 11 and March 31, 1983, 60 pediatric patients were diagnosed with rotavirus gastroenteritis. Of these cases 24 were community acquired, 29 were nosocomial, and 7 were of undetermined origin. Despite intensive infection control efforts, nosocomial transmission continued as long as patients with community-acquired cases were admitted. The use of disinfectants and germicides that were ineffective against rotavirus may have contributed to the continued nosocomial spread during a community outbreak.

Prospective study of nosocomial rotavirus infection in a paediatric hospital

Hospital-acquired enteric infections, particularly those due to rotavirus, were investigated by studying 220 patients under 3 years of age who were admitted without gastroenteritis to two paediatric general medical wards during a 10 month period. Faecal specimens were collected within 48 h of admission and then daily until the patients were discharged. Samples were also collected after discharge if patients developed enteric symptoms within 2 days of discharge. Fourteen per cent (31 of 220) of patients acquired rotavirus infections while in hospital, 23% (seven of 30) excreted rotavirus only after discharge; 29% of patients infected with rotavirus were asymptomatic (nine of 31). Acquisition of rotavirus infection was most prevalent during the months May-August, with a prevalence of 34% (12 of 35) in May. Hospitalization was prolonged in those patients who acquired rotavirus (11.1 days compared with 8.0 days, P less than 0.05). This study highlights the importance of rotavirus as a cause of hospital cross-infection, particularly in the very young patient, and emphasizes the need for further assessment of factors involved in its acquisition. In order to determine correctly the incidence of hospital-acquired illness, it is essential to follow patients after discharge from hospital. This study reinforces the importance of developing preventive measures in order to reduce the frequency of this illness.

An outbreak of acute infectious nonbacterial gastroenteritis in a high school in Maryland

An outbreak of acute infectious nonbacterial gastroenteritis (AING) occurred in a high school in Maryland in 1984. Thirty-six percent of students surveyed met the case definition of gastroenteritis, as did 24 percent of school employees. Eating lunch in the cafeteria on January 30 was significantly associated with illness. After controlling for other food items consumed during the January 30 lunch, only the sandwiches were significantly associated with illness, but the source of the contamination was not identified. Four of 17 serum pairs from sick students and none of the 8 serum pairs from exposed controls (a nonsignificant difference) showed at least a 4-fold rise in antibody titre to Norwalk virus between acute- and convalescent-phase specimens. This outbreak of AING is believed to be the first to implicate epidemiologically sandwiches as vehicles of transmission. The outbreak highlights the need for investigators to look for a viral etiology in gastroenteritis 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.

Antibodies to the Giardia lamblia double-stranded RNA virus major protein can block the viral infection

The double-stranded RNA virus-like particles, found among several independent isolates and cloned strains of Giardia lamblia, have previously been reported to be spheres of 35 nm with a genome of 7 kilobase pairs and a major protein of 100 kDa. The virus is capable of infecting certain virus-free isolates of G. lamblia. Antisera raised in mice against the intact virus did not react with the double-stranded RNA, but reacted strongly with the 100 kDa protein in Western blots. Preincubation of the virus with antisera abolished viral infectivity, whereas the antisera against double-stranded RNA showed only a weak blocking effect. Inclusion of the antiviral sera in the cultures of virus-infected G. lamblia at 10(3)-fold dilution resulted in elimination of the virus from the protozoa. Apparently, the 100 kDa protein is necessary for the initiation of viral infection and possibly subsequent assembly or replication of viral progeny particles.

Electron microscopy procedure influences detection of rotaviruses

Technical parameters of electron microscope staining procedures (type of stain, pH of stain, and time of staining) influence particle integrity for three groups of rotaviruses. Simian rotavirus SA11 (group A), Chinese adult diarrhea rotavirus and porcine rotavirus-like agent (group B), and porcine pararotavirus (group C) were tested. All rotavirus strains were quite stable in uranyl acetate and phosphotungstic acid at pH 4.5 and relatively stable in ammonium molybdate. However, staining with phosphotungstic acid at higher pH values with increased staining time yielded a reduction in the number of particles and particles that were broken or degraded to single-shelled particles or core particles. The different staining procedures were also tested in immunoelectron microscopy experiments. Antibody molecules bound to rotavirus particles were observed clearly only with phosphotungstic acid staining and not with uranyl acetate. We therefore recommend that uranyl acetate and phosphotungstic acid at pH 4.5 be used for negative staining of rotaviruses; phosphotungstic acid at pH 4.5 is optimal for immunoelectron microscopy. These technical points may be critical for rotavirus detection and are important for studies pertaining to the epidemiology and clinical importance of the non-group A rotaviruses.

Rapid diagnosis of rotavirus gastroenteritis by a commercial latex agglutination test

The Rotalex test, a commercial latex agglutination test for rotavirus, was compared with direct electron microscopy (EM) and the Rotazyme test I, a commercial enzyme immunoassay, for detection of rotavirus in stools of children and neonates. For initial stool specimens from 265 children (less than 3 years old) with diarrhea, the Rotalex test had a sensitivity of 81.7% and specificity of 99.5% compared with EM results. Positive and negative predictive values were 98 and 94.9%, respectively. The Rotalex test was slightly more sensitive and specific than the Rotazyme test. When daily stool specimens from patients with rotavirus gastroenteritis were examined, the sensitivity of the Rotalex test varied depending on the time of stool collection relative to the onset of symptoms. Sensitivity was 100 (20/20), 96 (23/24), and 54% (7/13) during 1 to 4, 5 to 7, and 8 to 18 days, respectively, after the onset of symptoms. The sensitivity of the Rotazyme test varied similarly with days from onset. We also examined 214 EM-negative stool specimens from asymptomatic newborns. False positivity by the Rotalex test was only 3.3% (7/214) compared with 4.2% (9/215) for the Rotazyme test. The Rotalex test was as sensitive and specific as EM for detection of rotavirus during the acute stage of illness and much faster and cheaper than EM or the Rotazyme test. The test appears to be suitable for routine use in small hospitals, emergency wards, or even the physician's office for rapid diagnosis of rotavirus gastroenteritis.

Prevalence of antibody to human calicivirus in Japan and Southeast Asia determined by radioimmunoassay

Three hundred ninety single sera from adults in Japan, Indonesia, Singapore, and Papua New Guinea were tested for antibodies to human calicivirus (HCV) by a radioimmunoassay blocking test. A high prevalence of antibodies was observed in samples collected in Japan and Southeast Asia. Of 240 serum specimens collected from five districts in Japan, 209 (87.1%) were positive for HCV antibodies. No striking difference in the prevalence of the antibody was seen among those districts. In sera collected in Southeast Asia, 84.0% (126 of 150) had antibodies to HCV (70% [35 of 50] in Singapore, 88% [44 of 50] in Indonesia, and 94% [47 of 50] in Papua New Guinea). These results indicate that HCV is a common infectious agent in Japan and Southeast Asia.

Interventions for the control of diarrhoeal diseases among young children: chemoprophylaxis

A number of situations place young children at increased risk of diarrhoea. Among these, the best documented in developing countries is contact with a diarrhoea case in a family or household. The most common application of chemoprophylaxis in developing countries is to prevent cholera or shigellosis among household contacts of known cases. There is little evidence that chemoprophylaxis is effective in reducing diarrhoea morbidity and mortality, except perhaps in travellers. Theoretical calculations in this paper (based on optimistic assumptions) suggest that chemoprophylaxis of household contacts of known cholera cases in Bangladesh might reduce overall diarrhoea incidence rates in children under 5 years of age by 0.02-0.06% and diarrhoea mortality rates by 0.4-1.2%. Chemoprophylaxis of household contacts of known shigellosis cases might reduce overall diarrhoea incidence rates by 0.15-0.35% and diarrhoea mortality rates by 0.3-0.7% in the same age group. The correct identification of index cases of cholera and shigellosis, followed by the rapid distribution of drugs to their household contacts, requires skills and resources that are scarce in the developing countries. Chemoprophylaxis can contribute to the widespread emergence and dissemination of antimicrobial resistance. The available evidence suggests that chemoprophylaxis is not feasible in many settings and that, even if successfully implemented, it is not a cost-effective intervention for national diarrhoeal diseases control programmes.

Nosocomial infections in the pediatric intensive care unit

Nosocomial (hospital-acquired) infections are a major complication of serious illnesses. Severely ill patients have a greater risk of acquiring nosocomial infections, so this problem is greatest in intensive care units. Studies have demonstrated that nosocomial infections are largely preventable. Adherence to recommended techniques for patient care will have the greatest benefit in the intensive care unit. In this paper the background epidemiology of nosocomial infections is reviewed and related to pediatrics and intensive care units. Types of diseases, assistance equipment, and monitoring devices which are associated with a high risk of nosocomial infections are emphasized and specific steps for lowering this risk are listed.

Hospital acquired rotaviral gastroenteritis in a general paediatric unit

Between 1 October 1981 and 30 September 1982, 74 children with acute gastroenteritis were admitted to the paediatric wards at St Thomas' Hospital, and a further 37 patients acquired gastroenteritis while in hospital. Rotaviruses were detected in the stools of 29 of 74 (39 per cent) of patients with community-acquired and 22 of 37 (59 per cent) of patients with hospital-acquired infection. Although patients were also admitted with bacterial stool pathogens, barrier nursing techniques were apparently successful in preventing spread of these. The use of a virucidal agent for handwashing might be effective in preventing hospital-acquired rotaviral infections.

The polypeptide of a human calicivirus

Viral particles morphologically resembling animals caliciviruses in the faeces of a patient with acute gastroenteritis were purified, radiolabeled with [125I], and analyzed by SDS-PAGE. A single major structural protein with a mol. mass 62,000 daltons was identified by immunoprecipitation technique. The finding is consistent with human calicivirus-like particles associated with gastroenteritis being a member of the family Caliciviridae.

Potential spectrum of etiological agents of viral enteritis in hospitalized infants

Fecal specimens were obtained from 1,160 infants and young children with acute nonbacterial gastroenteritis over a period of 2 years. A total of 100 specimens were obtained from age-matched asymptomatic controls. The specimens were examined for the presence of viruses by electron microscopy. Viruses or virus-like particles frequently associated with enteritis were detected in 27% (314 of 1,160) of the symptomatic patients. No viruses or virus-like particles were detected in the 100 control subjects. Rotavirus was detected in 73% (230 of 314) of the virus-positive samples. The mean age of rotavirus-positive patients was 11.5 months, although the patients ranged in age from 2 weeks to 5 years. Of the symptomatic patients, 45 (14%) exhibited small virus-like particles (15 to 40 nm) in the feces in the absence of any other detectable pathogen. Some of the virus-like particles observed in these patients appeared to be similar to astrovirus, and some appeared to be similar to the Otofuke agent or possibly minireovirus. Significantly, however, the mean age of infants with enteritis from whom these small virus-like particles were recovered was 4.5 months (range, 10 days to 19 months). Our findings confirmed the already-known fact that rotaviruses constitute the most important cause of viral enteritis in young children. In addition, small viruses may be an important cause of gastroenteritis in infants under 5 months of age.

Microtiter solid-phase radioimmunoassay for detection of human calicivirus in stools

A microtiter solid-phase radioimmunoassay (RIA) was developed for detection of human calicivirus in stool specimens. Seventy-eight stool specimens were tested by RIA. All 17 specimens positive for human calicivirus by electron microscopy (EM) were also positive by RIA. In addition, of 21 specimens obtained from an outbreak of caliciviral gastroenteritis, 11 were positive by RIA but negative by EM. Of 20 specimens positive for rotavirus by EM and 20 nondiarrheic specimens with no virus, 2 and 1, respectively, were positive by RIA but were subsequently shown to be falsely positive by a blocking test. There was no cross-reaction between human and feline caliciviruses. Thus, the test was more sensitive than EM and, with an appropriate blocking test, was specific for human calicivirus. It might be especially useful for screening large numbers of stool specimens.

Calicivirus gastroenteritis in North West London

During a thirty-month study of gastroenteritis in North West London, 592 cases were found to be associated with excretion of viruses. 39 (6·6%) of these patients, most of whom were admitted to hospital because of gastroenteritis, were shedding caliciviruses. The cases occurred throughout the year with a peak incidence in the winter. The 39 patients ranged in age from 6 weeks to 13 years, the peak incidence beig among infants aged 1-6 months. The clinical features of calcivirus infection are not distinguishable from those of rotavirus infection.

Comparison of three electron microscopy techniques for the detection of human rotaviruses

Rotavirus detection by direct electron microscopy was compared with direct and indirect immune electron microscopy techniques. The latter two approaches permitted the enumeration of 25 and 103 times more rotaviruses respectively, than direct electron microscopy. Also, 70% and 90% of the virus particles were aggregated by direct and indirect immune electron microscopy techniques respectively, thus facilitating their detection.

Prevalence of antibody to human calicivirus in general population of northern Japan

Serum specimens from children and adults living in Saporo, Japan, were tested for antibody against human calicivirus by immune electron microscopy (IEM), using virus-rich faecal extracts as the source of antigen. Of 83 serum specimens tested, 49 (59%) were positive for calicivirus antibody. Age-related prevalence of antibody to calicivirus was as follows: 23% (3/13) in the 0-5-month-old group, 30% (6/20) in the 6-23-month-old group, 65% (13/20) in the 2-5-year-old group, and 90% in school children (18/20) and adults (9/10). As for IEM antibody ratings scored from 0 to 4, almost all positive sera from older infants and preschool children scored 3 to 4. Antibody scores were rather more scattered in school children. The results indicated that caliciviral infection is prevalent in younger children in this part of Japan.

The 30- to 54-nm rotavirus-like particles in gastroenteritis: incidence and antigenic relationship to rotavirus

The 30- to 54-nm rotavirus-like particles were observed in the stool specimens of 17 children with gastroenteritis. These small rotavirus-like particles were shown to be antigenically related to the commonly described 68-nm rotavirus using the techniques of immune electron microscopy and ELISA (enzyme-linked immunosorbent assay). Four specimens containing the small rotavirus-like particles were shown to contain an antigen of a common human rotavirus serotype (type 2). The findings of small rotavirus-like particles of different diameters sharing a common antigen with rotavirus type 2 cautions against the naming of new candidate viruses based on morphology alone. In addition, the shedding of pure populations of single-shelled rotaviruses, herein described, could be an unusual phenomenon which may occur only sporadically. The relationship of the smaller rotavirus-like particles to rotavirus morphogenesis is discussed.

The 33- to 39-nm virus-like particles, tentatively designed as Sapporo agent, associated with an outbreak of acute gastroenteritis

An outbreak of nonbacterial gastroenteritis occurred in an orphanage in December 1979. Of 54 residents, 43 were affected with acute gastroenteritis. Diarrhea was the commonest symptom. The 33- to 39-nm virus-like particles, tentatively designated as Sapporo agent, were detected in 17 (48.6%) of the patients' 35 fecal specimens. Morphologically, it was difficult to distinguish the Sapporo agent from other agents without geometrical pattern of the surface. Antigenically, the Sapporo agent related to the Otofuke agent detected in an outbreak of the institution for mentally retarded adults and also to the SRV ;76 detected in familial cases of infectious gastroenteritis. The Sapporo agent might belong to a new group of those gastroenteritis viruses which were larger in size than the Norwalk virus group.

40-43-nm viruslike particles associated with gastroenteritis

By electron microscopy, 40-43-nm spherical viruslike particles were demonstrated in stools from gastroenteritis patients. The particles have 6-7-nm projections on the periphery and some of them show ringlike structures on their surface. Immune electron microscopy on paired sera and feces from one of the patients demonstrated preexisting antibody to the particles in acute-phase serum and an increase in antibody during illness.

Astrovirus-like, coronavirus-like, and parvovirus-like particles detected in the diarrheal stools of beagle pups

Astrovirus-like, coronavirus-like, and parvovirus-like particles were detected through electron microscopic (EM) examination of loose and diarrheal stools from a litter of beagle pups. Banding patterns obtained from equilibrium centrifugations in CsCl supported the EM identification. Densities associated with the identified particles were: 1.34 g/ml for astrovirus, 1.39 g/ml for "full" parvovirus and 1.24-1.26 g/ml for "typical" coronavirus. Convalescent sera from the pups aggregated these three particle types as observed by immunoelectron microscopy (IEM). Only coronavirus-like particles were later detected in formed stools from these same pups. Coronavirus and parvo-like viruses are recognized agents of canine viral enteritis, however, astrovirus has not been previously reported in dogs.

New concepts in viral gastroenteritis

The use of negative contrast electronmicroscopy of stool suspension in the investigation of the aetiology of childhood gastroenteritis has led to the recognition of a number of candidate viral agents. There is convincing evidence that rotavirus is the single most important cause of community acquired gastroenteritis, and is responsible for some nosocomial outbreaks. The epidemiology of rotavirus acqusition, differential clinical susceptibilities of young and older infants, pathogenesis of disease, mechanisms of immunity and breast milk protection, and the role of different viral serotypes are aspects as yet poorly understood; and attempts to propagate human rotavirus in tissue culture have met with only limited success. Moreover, the aetiologically unaccountable one third of cases of infantile diarrhoea, and the association of enteritis with up to six other virus-like particles add to the complexity of the problem. This review considers the available data from human and animal studies, and based on the experience of ourselves and others comments on the present state of knowledge and trends in continuing research.

An outbreak of gastroenteritis associated with calicivirus in an infant home

In October 1977 an outbreak of acute infectious diarrhea occurred in an infant home in the city of Sapporo, Japan. Of 34 residents aged two to 20 months, 26 (77%) suffered from diarrhea. In ten of these patients the diarrhea was accompanied by vomiting. Electron microscopic examinations revealed typical calicivirus particles in eight faecal specimens, seven of which were from the group of 26 affected patients (28%) and one of which was from the group of eight infants without symptoms (13%). Immune electron microscopy tests for antibody responses against one of the isolated strains of calicivirus were carried out on 27 paired pre- and post-outbreak sera. Seroconversions were demonstrated in 18 of 19 (95%) affected infants and in six of eight (75%) unaffected infants. One patient with lack of antibody response was the youngest child--two months old. Periodic surveys on enteric viruses circulating in the home revealed that calicivirus was specifically associated with the outbreak of gastroenteritis. These observations provide further evidence for the causative role of calicivirus in acute gastroenteritis in children.