Viruses in bathing waters

The Association of Helicobacter pylori Biofilm with Enterovirus 71 Prolongs Viral Viability and Survival

The transition time during which a virus leaves its host and infects the next susceptible host is critical for virus survival. Enterovirus 71 (EV71) is stable in aqueous environments, but its molecular interactions with bacteria and their biofilms are not well-established. Helicobacter pylori is a highly successful gut bacterial pathogen, with its capacity to form biofilms being linked to its transmission. Given that both are gut-associated microbes, we hypothesized that biofilms formed by H. pylori may play a significant role in the survival of EV71 in the external environment. In this study, we examine the interactions of EV71 with the preformed biofilm of H. pylori to mimic its natural state in the environment. Immunofluorescence confocal microscopy and scanning electron microscopy revealed that EV71 particles persisted for up to 10 days when incubated with the H. pylori biofilm. Furthermore, the presence of the H. pylori biofilm significantly augmented viral viability, as verified through virus plaque assays. Interestingly, the viability of EV71 was dependent on the quantity of H. pylori biofilm formation. Thus, two H. pylori strains able to generate large amounts of biofilm could facilitate EV71 viability for up to 17 days, whereas two other H. pylori strains that produced moderate or low quantities of biofilm could not prolong virus viability. It is interesting that biofilm contains N-acetyl-glucosamine and glycosaminoglycan, and that EV71 has binding affinity to cell-surface heparan sulfate glycosaminoglycan, which acts as an EV71 attachment receptor. The synergistic ability of H. pylori biofilm to promote EV71 viability for extended periods implies that H. pylori biofilm may serve as an additional pathway of EV71 transmission.

Epidemiology of Classic and Novel Human Astrovirus: Gastroenteritis and Beyond

Since they were identified in 1975, human astroviruses have been considered one of the most important agents of viral acute gastroenteritis in children. However, highly divergent astroviruses infecting humans have been recently discovered and associated with extra-intestinal infections. The report of cases of fatal meningitis and encephalitis, especially in immunocompromised individuals, has broadened their disease spectrum. Although zoonotic transmission among animal and human astroviruses has not been clearly recognized, the genetic similarity between some human and animal viruses makes it likely to occur. This review provides an update on the epidemiology of both classic and novel human astroviruses, and a comprehensive view on confirmed or potential association between astrovirus and human disease.

Human astroviruses

Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses that were discovered in 1975. Astroviruses infecting other species, particularly mammalian and avian, were identified and classified into the genera Mamastrovirus and Avastrovirus. Through next-generation sequencing, many new astroviruses infecting different species, including humans, have been described, and the Astroviridae family shows a high diversity and zoonotic potential. Three divergent groups of HAstVs are recognized: the classic (MAstV 1), HAstV-MLB (MAstV 6), and HAstV-VA/HMO (MAstV 8 and MAstV 9) groups. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The other groups have also been identified in children with gastroenteritis, but extraintestinal pathologies have been suggested for them as well. Classic HAstVs may be grown in cells, allowing the study of their cell cycle, which is similar to that of caliciviruses. The continuous emergence of new astroviruses with a potential zoonotic transmission highlights the need to gain insights on their biology in order to prevent future health threats. This review focuses on the basic virology, pathogenesis, host response, epidemiology, diagnostic assays, and prevention strategies for HAstVs.

Waterborne human pathogenic viruses of public health concern

In recent years, the impending impact of waterborne pathogens on human health has become a growing concern. Drinking water and recreational exposure to polluted water have shown to be linked to viral infections, since viruses are shed in extremely high numbers in the faeces and vomit of infected individuals and are routinely introduced into the water environment. All of the identified pathogenic viruses that pose a significant public health threat in the water environment are transmitted via the faecal-oral route. This group, are collectively known as enteric viruses, and their possible health effects include gastroenteritis, paralysis, meningitis, hepatitis, respiratory illness and diarrhoea. This review addresses both past and recent investigations into viral contamination of surface waters, with emphasis on six types of potential waterborne human pathogenic viruses. In addition, the viral associated illnesses are outlined with reference to their pathogenesis and routes of transmission.

Molecular characterization of astroviruses by reverse transcriptase PCR and sequence analysis: comparison of clinical and environmental isolates from South Africa

A comparative analysis was performed with 25 isolates of astroviruses (AstVs) detected in sewage sources and 22 concurrently identified clinical AstV isolates from the Tshwane (Pretoria) Metropolitan Area in South Africa. The samples and specimens were screened for AstVs by using an enzyme immunoassay and/or a reverse transcriptase PCR (RT-PCR) for the highly conserved untranslated region (3' end) of the genome. The RT-PCR results were confirmed by oligonucleotide probe dot blot hybridization. Viable viruses were propagated in cell cultures for amplification when a minimal specimen was available or indeterminate sequences were obtained. AstV strains were characterized by RT-PCR and partial sequence analysis of the capsid region. The presence of multiple human AstV (HAstV) types in a single sewage sample complicated identification of individual strains, and additional type-specific RT-PCR and sequence analyses of the capsid region were required for characterization. Amplification and characterization of one genotype from a sample, therefore, did not preclude the possibility that a sample harbored additional different genotypes. Genotype and sequence information obtained from AstVs in wastewater samples were compared to information obtained from AstV strains from human stools. HAstV type 1 (HAstV-1), as well as HAstV-3, -5, -6, and -8, were identified among the clinical isolates, and HAstV-1, -2, -3, -4, -5, -7, and -8 were identified among the environmental samples. Phylogenetic analysis demonstrated that HAstV-1, -3, -5, and -8, which were present in human stool and sewage samples, clustered together, indicating that these viruses are closely related. The concurrent presence of identical HAstV strains in wastewater samples and in hospitalized patients suggests that AstVs present in the environment pose a potential risk to communities in which fecally contaminated water is used for recreational and domestic purposes.

The occurrence of hepatitis A and astroviruses in selected river and dam waters in South Africa

Over a period of one year (June 1997-May 1998) samples of surface waters, used for domestic and recreational purposes, were collected weekly from the same sites on the Klip River and Vaal Dam, Gauteng, South Africa. Sensitive and specific reverse transcriptase-polymerase chain reaction-oligonucleotide probe assays were used to detect HAV and HAstV RNA in concentrates of the water and infectious virus in cell cultures infected with the water concentrates. HAV was detected in 18 (35.3%) of the river and 19 (37.3%) of the dam water samples, often in association with the RNA from other enteric viruses. HAstV was detected less frequently and was present in 11 (21.6%) of the river and 3 (5.9%) of the dam water samples. A seasonal pattern was noted for HAV but not for HAstV. Cell culture amplification in a variety of carefully selected cell culture systems enhanced the detection of both viruses. Infectious viruses were detected in dam water samples where microbiological indicators of faecal pollution were absent or within acceptable limits. The presence of these viruses in the dam and river water could pose a potential health risk for people using these waters for domestic or recreational purposes.

Description of a DNA amplification procedure for the detection of bacteriophages of Bacteroides fragilis HSP40 in environmental samples

A molecular test based on DNA amplification by PCR was developed for the detection of bacteriophages of Bacteroides fragilis strain HSP40 in the environment. These specific phages are associated with faecal contamination of human origin. A homologous DNA region of 1.5 kb, identified previously by hybridisation, was used to design primers for the detection of B. fragilis HSP40 phages. A nested-PCR procedure for the DNA amplification of those phages was developed. The sensitivity of the nested-PCR was between 10(-1) and 10(-2) PFU for purified HSP40 phage solutions, sewage and seawater samples, and between 1 and 10 PFU for river water samples. Specific amplification of HSP40 phages was observed when viral suspensions of 10(3) PFU/ml or lower were used. Common levels of B. fragilis phages found in sewage are 10(1)-10(2) PFU/ml. A total of 24 water samples (sewage, river water and seawater) were tested both by PCR and by plaque assay, to evaluate the efficiency of the molecular method in field samples. The data obtained by PCR in environmental samples showed good concordance with the PFU counts and a higher sensitivity.

Genomic characterization of human astrovirus type 6 Katano virus and the establishment of a rapid and effective reverse transcription-polymerase chain reaction to detect all serotypes of human astrovirus

We previously reported that human astrovirus type 6 (HAstV T6) was the etiologic agent of a large-scale outbreak of acute gastroenteritis that occurred in 1991 in Katano City, Osaka, Japan [Oishi et al., 1994]. The two representative strains, Katano virus K23 and K24, have been analyzed by sequencing the open reading frame 2 (ORF2) region after amplification by reverse transcription-polymerase chain reaction (RT-PCR). The ORF2 region of HAstV T6 strains, including K23, was found to be about 20 bp smaller than those of other types. There was 94% nucleotide sequence identity and 95% amino acid sequence identity between K23 and K24, with the Oxford strains belonging to HAstV T6. The high homology of the ORF2 region between the Katano and Oxford strains shows intratype genomic stability, irrespective of time and place of virus isolation. Comparing sequences of ORF2 of different HAstV serotypes, we established a rapid and highly sensitive detection system for HAstV types using RT-PCR with the AC230/AC1' primer set designed from the 5'-terminal end region of ORF2. This RT-PCR system seems very useful in detecting at least two different viruses in a single PCR test tube using AC230/AC1' in addition to the NV81/82, SM82 primer sets. Thus, our rapid and effective detection system may contribute to the epidemiologic characterization of astrovirus infections as well as Norwalk-like viruses.

Absence of human astrovirus RNA in sewage and environmental samples

Over a period of several weeks during the summer of 1996, samples of sewage, sea water, river water, sand and silt were collected from a sewage works at Weston-super-Mare, England and from coastal areas nearby. A sensitive reverse-transcriptase polymerase chain reaction (RT-PCR) was used to search for human astrovirus (HAstV) RNA in concentrates of the samples. No evidence of astrovirus was found in any sample, which suggests that contamination with these viruses is not a problem in this area during the summer holiday season. Furthermore, the single case of astrovirus diarrhoea diagnosed in this laboratory in the summer occurred at the end of the sampling period, and not in the survey area. The primers used sometimes yielded a product two-thirds the expected size but bearing no sequence homology with HAstV. The confirmation that poliovirus adsorbs to sand and silt shows that these materials might be able to concentrate other enteric viruses in water to a level which could be a threat to the health of people coming into contact with it.

Prevalence of antibodies to astrovirus types 1 and 3 in children and adolescents in Norfolk, Virginia

OBJECTIVE

To determine the prevalence of antibody to human astrovirus types 1 (HAstV-1) and 3 (HAstV-3) in children.

METHODS

Sera from children hospitalized in Norfolk, VA, for noninfectious conditions were collected for a 1-month period every 6 months from 1993 to 1996 and tested by enzyme immunoassay for antibody to HAstV-1 and HAstV-3 with the use of baculovirus-expressed recombinant capsid proteins as antigens.

RESULTS

The seroprevalence of 393 infants and children to HAstV-1 decreased from 67% in infants <3 months of age to 7% by 6 to 8 months of age, consistent with loss of transplacental antibodies. Children acquired HAstV-1 antibody with a peak prevalence of 94% at 6 to 9 years of age (P < 0.001). Antibodies to HAstV-3 exhibited a lower prevalence, with 26% positive at <3 months, 0% at 6 to 11 months and 42% by 6 to 9 years of age. HAstV-1 seroprevalence in children O to 2 months of age decreased from 89% in November, 1993, to 40% in November, 1996 (P = 0.009).

CONCLUSIONS

Astrovirus type-specific antibody prevalence can be measured by baculovirus-expressed capsid antigens in an enzyme immunoassay. Children developed antibody to HAstV-1 (94%) and to HAstV-3 (42%) by 6 to 9 years of age indicating frequent exposure to these enteric viruses in infancy and early childhood.

Prevalence of human astrovirus serotype 4: capsid protein sequence and comparison with other strains

Astrovirus serotype 4 has increased in relative prevalence in the Oxford, UK area in 1993. The structural gene of human astrovirus serotype 4 has been sequenced and the results indicate that this protein differs substantially from serotypes 1 and 2. In particular, conservation at the C terminus is greatly reduced. However, amino acid substitutions in this region show a strong conservation in character suggesting that structural or functional constraints operate in this region.