Prevalence of vaccine-derived polioviruses in the environment

Contextualizing Wastewater-Based surveillance in the COVID-19 vaccination era

SARS-CoV-2 wastewater-based surveillance (WBS) offers a tool for cost-effective oversight of a population's infections. In the past two years, WBS has proven to be crucial for managing the pandemic across different geographical regions. However, the changing context of the pandemic due to high levels of COVID-19 vaccination warrants a closer examination of its implication towards SARS-CoV-2 WBS. Two main questions were raised: 1) Does vaccination cause shedding of viral signatures without infection? 2) Does vaccination affect the relationship between wastewater and clinical data? To answer, we review historical reports of shedding from viral vaccines in use prior to the COVID-19 pandemic including for polio, rotavirus, influenza and measles infection and provide a perspective on the implications of different COVID-19 vaccination strategies with regard to the potential shedding of viral signatures into the sewershed. Additionally, we reviewed studies that looked into the relationship between wastewater and clinical data and how vaccination campaigns could have affected the relationship. Finally, analyzing wastewater and clinical data from the Netherlands, we observed changes in the relationship concomitant with increasing vaccination coverage and switches in dominant variants of concern. First, that no vaccine-derived shedding is expected from the current commercial pipeline of COVID-19 vaccines that may confound interpretation of WBS data. Secondly, that breakthrough infections from vaccinated individuals contribute significantly to wastewater signals and must be interpreted in light of the changing dynamics of shedding from new variants of concern.

Outbreaks of Circulating Vaccine-derived Poliovirus in the World Health Organization Western Pacific Region, 2000-2021

The World Health Organization Western Pacific Region (WPR) has maintained the polio-free status for more than two decades. At the global level, there were only 6 confirmed polio cases due to wild type 1 poliovirus in Pakistan, Afghanistan, and Malawi in 2021, therefore, the risk of the importation of wild poliovirus from the endemic countries to the WPR is considerably lower than ever before. On the other hand, the risk of polio outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) still cannot be ignored even in the WPR. Since late 2010s, cVDPV outbreaks in the WPR have appeared to be more extensive in frequency and magnitude. Moreover, the emergence of concomitant polio outbreaks of type 1 and type 2 cVDPVs in the Philippines and Malaysia during 2019-2020 has highlighted the remaining risk of cVDPV outbreaks in high-risk areas and/or communities in the WPR. The previous cVDPV outbreaks in the WPR have been rapidly and effectively controlled, however, the future risk of polio outbreaks associated with cVDPVs needs to be reconsidered and polio immunization and surveillance strategies should be updated accordingly.

Wastewater surveillance for SARS-CoV-2: Lessons learnt from recent studies to define future applications

Wastewater-based epidemiology (WBE) is successful in the detection of the spread of SARS-CoV-2. This review examines the methods used and results of recent studies on the quantification of SARS-CoV-2 in wastewater. WBE becomes essential, especially with virus transmission path uncertainty, limitations on the number of clinical tests that could be conducted, and a relatively long period for infected people to show symptoms. Wastewater surveillance was used to show the effect of lockdown on the virus spread. A WBE framework tailored for SARS-CoV-2 that incorporates lessons learnt from the reviewed studies was developed. Results of the review helped outline challenges facing the detection of SARS-CoV-2 in wastewater samples. A comparison between the various studies with regards to sample concentration and virus quantification was conducted. Five different primers sets were used for qPCR quantification; however, due to limited data availability, there is no consensus on the most sensitive primer. Correlating the slope of the relationship between the number of gene copies vs. the cumulative number of infections normalized to the total population served with the average new cases, suggests that qPCR results could help estimating the number of new infections. The correlation is improved when a lag period was introduced to account for asymptomatic infections. Based on lessons learnt from recent studies, it is recommended that future applications should consider the following: 1) ensuring occupational safety in managing sewage collection and processing, 2) evaluating the effectiveness of greywater disinfection, 3) measuring viral RNA decay due to biological and chemical activities during collection and treatment, 4) assessing the effectiveness of digital PCR, and 5) conducting large scale international studies that follow standardized protocols.

Bacteriophage T4 nanoparticles for vaccine delivery against infectious diseases

Subunit vaccines containing one or more target antigens from pathogenic organisms represent safer alternatives to whole pathogen vaccines. However, the antigens by themselves are not sufficiently immunogenic and require additives known as adjuvants to enhance immunogenicity and protective efficacy. Assembly of the antigens into virus-like nanoparticles (VLPs) is a better approach as it allows presentation of the epitopes in a more native context. The repetitive, symmetrical, and high density display of antigens on the VLPs mimic pathogen-associated molecular patterns seen on bacteria and viruses. The antigens, thus, might be better presented to stimulate host's innate as well as adaptive immune systems thereby eliciting both humoral and cellular immune responses. Bacteriophages such as phage T4 provide excellent platforms to generate the nanoparticle vaccines. The T4 capsid containing two non-essential outer proteins Soc and Hoc allow high density array of antigen epitopes in the form of peptides, domains, full-length proteins, or even multi-subunit complexes. Co-delivery of DNAs, targeting molecules, and/or molecular adjuvants provides additional advantages. Recent studies demonstrate that the phage T4 VLPs are highly immunogenic, do not need an adjuvant, and provide complete protection against bacterial and viral pathogens. Thus, phage T4 could potentially be developed as a "universal" VLP platform to design future multivalent vaccines against complex and emerging pathogens.

Insights from a Systematic Search for Information on Designs, Costs, and Effectiveness of Poliovirus Environmental Surveillance Systems

Poliovirus surveillance plays a critical role in achieving and certifying eradication and will play a key role in the polio endgame. Environmental surveillance can provide an opportunity to detect circulating polioviruses prior to the observation of any acute flaccid paralysis cases. We completed a systematic review of peer-reviewed publications on environmental surveillance for polio including the search terms "environmental surveillance" or "sewage," and "polio," "poliovirus," or "poliomyelitis," and compared characteristics of the resulting studies. The review included 146 studies representing 101 environmental surveillance activities from 48 countries published between 1975 and 2016. Studies reported taking samples from sewage treatment facilities, surface waters, and various other environmental sources, although they generally did not present sufficient details to thoroughly evaluate the sewage systems and catchment areas. When reported, catchment areas varied from 50 to over 7.3 million people (median of 500,000 for the 25% of activities that reported catchment areas, notably with 60% of the studies not reporting this information and 16% reporting insufficient information to estimate the catchment area population size). While numerous studies reported the ability of environmental surveillance to detect polioviruses in the absence of clinical cases, the review revealed very limited information about the costs and limited information to support quantitative population effectiveness of conducting environmental surveillance. This review motivates future studies to better characterize poliovirus environmental surveillance systems and the potential value of information that they may provide in the polio endgame.

One-year Survey of human enteroviruses from sewage and the factors affecting virus adsorption to the suspended solids

This study described the results of environmental enterovirus surveillance conducted in Shandong Province of China in 2013. Altogether 39 sewage samples were collected and 873 enterovirus isolates (including 334 polioviruses) belonging to 22 serotypes were obtained. Echovirus (E) -7, coxsackievirus (CV) -B5, E-11, E-6, and E-3 were the most commonly detected non-polio enterovirus serotypes, and phylogeny of E-7 and CV-B5 was described. The numbers of isolates of different serotypes from sewage supernatant were compared with those from the solids. Interestingly, dramatic divergence was observed between the supernatant and solids origin for the serotypes of E-3 and E-6, which were prone to the solids and supernatant, respectively. A following adsorption test with E-3 and E-6 added sewage specimens confirmed the different preference. Furthermore, the adsorption of Sabin poliovirus type 1 to the solids under different conditions was investigated, and the results showed that acid medium, cold temperature, and high solids concentration facilitated the viral adsorption to the solids, whereas change of virus titer did not influence the proportion of adsorption. These results highlighted the importance of combining the enterovirus isolates from the supernatant and solids together in environmental surveillance so as to better understand the local circulation of different serotypes.

Molecular and Phenotypic Characterization of a Highly Evolved Type 2 Vaccine-Derived Poliovirus Isolated from Seawater in Brazil, 2014

A type 2 vaccine-derived poliovirus (VDPV), differing from the Sabin 2 strain at 8.6% (78/903) of VP1 nucleotide positions, was isolated from seawater collected from a seaport in São Paulo State, Brazil. The P1/capsid region is related to the Sabin 2 strain, but sequences within the 5'-untranslated region and downstream of the P1 region were derived from recombination with other members of Human Enterovirus Species C (HEV-C). The two known attenuating mutations had reverted to wild-type (A481G in the 5'-UTR and Ile143Thr in VP1). The VDPV isolate had lost the temperature sensitive phenotype and had accumulated amino acid substitutions in neutralizing antigenic (NAg) sites 3a and 3b. The date of the initiating OPV dose, estimated from the number of synonymous substitutions in the capsid region, was approximately 8.5 years before seawater sampling, a finding consistent with a long time of virus replication and possible transmission among several individuals. Although no closely related type 2 VDPVs were detected in Brazil or elsewhere, this VDPV was found in an area with a mobile population, where conditions may favor both viral infection and spread. Environmental surveillance serves as an important tool for sensitive and early detection of circulating poliovirus in the final stages of global polio eradication.

Environmental surveillance of human enteroviruses in Shandong Province, China, 2008 to 2012: serotypes, temporal fluctuation, and molecular epidemiology

Environmental surveillance is an effective approach in investigating the circulation of polioviruses (PVs) and other human enteroviruses (EVs) in the population. The present report describes the results of environmental surveillance conducted in Shandong Province, China, from 2008 to 2012. A total of 129 sewage samples were collected, and 168 PVs and 1,007 nonpolio enteroviruses (NPEVs) were isolated. VP1 sequencing and typing were performed on all isolates. All PV strains were Sabin-like, with the numbers of VP1 substitutions ranging from 0 to 7. The NPEVs belonged to 19 serotypes, and echovirus 6 (E6), E11, coxsackievirus B3 (CVB3), E3, E12, and E7 were the six main serotypes, which accounted for 18.3%, 14.8%, 14.5%, 12.9%, 9.0%, and 5.7% of NPEVs isolated, respectively. Typical summer-fall peaks of NPEV were observed in the monthly distribution of isolation, and an epidemic pattern of annual circulation was revealed for the common serotypes. Phylogenetic analysis was performed on environmental CVB3 and E3 strains with global reference strains and local strains from aseptic meningitis patients. Shandong strains formed distinct clusters, and a close relationship was observed between local environmental and clinical strains. As an EV-specific case surveillance system is absent in China and many other countries, continuous environmental surveillance should be encouraged to investigate the temporal circulation and phylogeny of EVs in the population.

Environmental surveillance of poliovirus in sewage water around the introduction period for inactivated polio vaccine in Japan

Environmental virus surveillance was conducted at two independent sewage plants from urban and rural areas in the northern prefecture of the Kyushu district, Japan, to trace polioviruses (PVs) within communities. Consequently, 83 PVs were isolated over a 34-month period from April 2010 to January 2013. The frequency of PV isolation at the urban plant was 1.5 times higher than that at the rural plant. Molecular sequence analysis of the viral VP1 gene identified all three serotypes among the PV isolates, with the most prevalent serotype being type 2 (46%). Nearly all poliovirus isolates exhibited more than one nucleotide mutation from the Sabin vaccine strains. During this study, inactivated poliovirus vaccine (IPV) was introduced for routine immunization on 1 September 2012, replacing the live oral poliovirus vaccine (OPV). Interestingly, the frequency of PV isolation from sewage waters declined before OPV cessation at both sites. Our study highlights the importance of environmental surveillance for the detection of the excretion of PVs from an OPV-immunized population in a highly sensitive manner, during the OPV-to-IPV transition period.

An outbreak of type π vaccine-derived poliovirus in Sichuan province, China: emergence and circulation in an under-immunized population

BACKGROUND

During August 2011-February 2012, an outbreak of type Π circulating vaccine-derived poliovirus (cVDPVs) occurred in Sichuan Province, China.

METHODS

A field investigation of the outbreak was conducted to characterize outbreak isolates and to guide emergency response. Sequence analysis of poliovirus capsid protein VP1 was performed to determine the viral propagation, and a coverage survey was carried out for risk assessment.

RESULTS

One clinical compatible polio case and three VDPV cases were determined in Ngawa County, Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan Province. Case patients were unimmunized children, 0.8-1 years old. Genetic sequencing showed that the isolates diverged from the VP1 region of the type Π Sabin strain by 5-12 nucleotides (nt) and shared the same 5 nt VP1 substitutions, which indicate single lineage of cVDPVs. Of the 7 acute flaccid paralysis cases (all>6 months) reported in Ngawa Prefecture in 2011, 4 (57.1%) cases (including 2 polio cases) did not receive oral attenuated poliovirus vaccine. Supplementary immunization activities (SIAs) were conducted in February-May, 2012, and the strain has not been isolated since.

CONCLUSION

High coverage of routine immunization should be maintained among children until WPV transmission is globally eradicated. Risk assessments should be conducted regularly to pinpoint high risk areas or subpopulations, with SIAs developed if necessary.

Development and introduction of inactivated poliovirus vaccines derived from Sabin strains in Japan

During the endgame of global polio eradication, the universal introduction of inactivated poliovirus vaccines is urgently required to reduce the risk of vaccine-associated paralytic poliomyelitis and polio outbreaks due to wild and vaccine-derived polioviruses. In particular, the development of inactivated poliovirus vaccines (IPVs) derived from the attenuated Sabin strains is considered to be a highly favorable option for the production of novel IPV that reduce the risk of facility-acquired transmission of poliovirus to the communities. In Japan, Sabin-derived IPVs (sIPVs) have been developed and introduced for routine immunization in November 2012. They are the first licensed sIPVs in the world. Consequently, trivalent oral poliovirus vaccine was used for polio control in Japan for more than half a century but has now been removed from the list of vaccines licensed for routine immunization. This paper reviews the development, introduction, characterization, and global status of IPV derived from attenuated Sabin strains.

Estimation of contamination sources of human enteroviruses in a wastewater treatment and reclamation system by PCR-DGGE

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was employed to estimate the contamination sources of human enteroviruses and understand how their dominant strains vary in a wastewater treatment and reclamation system consisting of sewage collection, wastewater treatment with membrane bioreactor and open lakes for reclaimed water storage and reuse. After PCR-DGGE using a selected primer set targeting enteroviruses, phylogenetic analysis of acquired enterovirus gene sequences was performed. Enteroviruses identified from the septic tank were much more diverse than those from grey water and kitchen wastewater. Several unique types of enterovirus different from those in wastewater samples were dominant in a biological wastewater treatment unit. Membrane filtration followed by chlorination was proved effective for physically eliminating enteroviruses; however, secondary contamination likely occurred as the reclaimed water was stored in artificial lakes. Enterovirus 71 (EV71), a hand-foot-and-mouth disease (HFMD) viral pathogen, was detected mainly from the artificial lakes, implying that wastewater effluent was not the contamination source of EV71 and that there were unidentified non-point sources of the contamination with the HFMD viral pathogen in the reclaimed water stored in the artificial lakes. The PCR-DGGE targeting enteroviruses provided robust evidence about viral contamination sources in the wastewater treatment and reclamation system.

Isolation and characterization of a type 2 vaccine-derived poliovirus from environmental surveillance in China, 2012

Environmental surveillance of poliovirus on sewage has been conducted in Shandong Province, China since 2008. A type 2 vaccine-derived poliovirus (VDPV) with 7 mutations in VP1 coding region was isolated from the sewage collected in the city of Jinan in December 2012. The complete genome sequencing analysis of this isolate revealed 25 nucleotide substitutions, 7 of which resulted in amino acid alteration. No evidence of recombination with other poliovirus serotypes was observed. The virus did not lose temperature sensitive phenotype at 40°C. An estimation based on the evolution rate of the P1 coding region suggested that evolution time of this strain might be 160–176 days. VP1 sequence analysis revealed that this VDPV strain is of no close relationship with other local type 2 polioviruses (n = 66) from sewage collected between May 2012 and June 2013, suggesting the lack of its circulation in the local population. The person who excreted the virus was not known and no closely related virus was isolated in local population via acute flaccid paralysis surveillance. By far this is the first report of VDPV isolated from sewage in China, and these results underscore the value of environmental surveillance in the polio surveillance system even in countries with high rates of OPV coverage.

Environmental surveillance of human parechoviruses in sewage in The Netherlands

The circulation of human parechoviruses (HPeVs) in the population was studied by environmental surveillance comprising of molecular analyses of sewage samples (n = 89) that were collected from 15 different locations in The Netherlands. Samples were taken from sewage originating from schools (n = 9) or from parts of municipalities (n = 6) during the Dutch school year 2010-2011. At 13/15 locations HPeV1, HPeV3, or HPeV6 RNA was detected at least once; however, sequence diversity did not reflect associations in time or place. A higher percentage of positives was observed in the samples originating from the municipalities. It was demonstrated that HPeV circulated in the studied population to a higher extent than would be expected from the current knowledge on infections predominating in young children.

Environmental surveillance of enterovirus in Northern India using an integrated shell vial culture with a semi-nested RT PCR and partial sequencing of the VP1 gene

Enteroviruses have been reported in epidemic form during last 10 years in northern India. Environmental surveillance of sewage is the method of choice in limited resources countries for detection of enterovirus serotypes circulating in the community. Twenty-four sewage samples collected between January, 2009 and December, 2010 were tested for enterovirus by using a new modified integrated shell vial culture (ISVC) with a semi-nested RT-PCR of a partial VP1 gene and virus isolation integrated with semi-nested RT-PCR of a partial VP1 gene. Twenty-one (87.5%) out of 24 samples were positive for enterovirus by the conventional method and all samples (100%) by the ISVC-RT-PCR. The additional positive samples detected by ISVC-RT-PCR was typed as six different enterovirus serotypes (Sabin poliovirus 3, Coxsackievirus B3, Coxsackievirus A13, Coxsackievirus A17, Echovirus 33, and Enterovirus 75). Phylogenetic analysis of a partial VP1 gene of Echovirus 19 showed that one genetic lineage clustered with isolates from Georgia suggesting their importation into northern India. Detection of wild poliovirus in the absence of clinical cases with 16 different co-circulating enterovirus serotypes supports the need of increased molecular surveillance of sewage. Rapid identification and characterization of enterovirus serotypes is necessary to study their transmission and evolution in different geographical regions to prevent future outbreak.

Oral poliovirus vaccine evolution and insights relevant to modeling the risks of circulating vaccine-derived polioviruses (cVDPVs)

The live, attenuated oral poliovirus vaccine (OPV) provides a powerful tool for controlling and stopping the transmission of wild polioviruses (WPVs), although the risks of vaccine-associated paralytic polio (VAPP) and circulating vaccine-derived poliovirus (cVDPV) outbreaks exist as long as OPV remains in use. Understanding the dynamics of cVDPV emergence and outbreaks as a function of population immunity and other risk factors may help to improve risk management and the development of strategies to respond to possible outbreaks. We performed a comprehensive review of the literature related to the process of OPV evolution and information available from actual experiences with cVDPV outbreaks. Only a relatively small fraction of poliovirus infections cause symptoms, which makes direct observation of the trajectory of OPV evolution within a population impractical and leads to significant uncertainty. Despite a large global surveillance system, the existing genetic sequence data largely provide information about transmitted virulent polioviruses that caused acute flaccid paralysis, and essentially no data track the changes that occur in OPV sequences as the viruses transmit largely asymptomatically through real populations with suboptimal immunity. We updated estimates of cVDPV risks based on actual experiences and identified the many limitations in the existing data on poliovirus transmission and immunity and OPV virus evolution that complicate modeling. Modelers should explore the space of potential model formulations and inputs consistent with the available evidence and future studies should seek to improve our understanding of the OPV virus evolution process to provide better information for policymakers working to manage cVDPV risks.

Polio eradication in India: progress, but environmental surveillance and vigilance still needed

Poliomyelitis has appeared in epidemic form, become endemic on a global scale, and has been reduced to near elimination, all within the span of documented medical history. Nevertheless, effective vaccinations, global surveillance network, development of accurate viral diagnosis prompted the historical challenge, global polio eradication initiative (GPEI). Environmental surveillance of poliovirus means monitoring of wild polio virus (WPV) and vaccine derived polio virus (cVDPV) circulation in human populations by examining environmental specimens supposedly contaminated by human feces. The rationale for surveillance is based on the fact that PV-infected individuals, whether presenting with disease symptoms or not, shed large amounts of PV in the feces for several weeks. As the morbidity: infection ratio of PV infection is very low, and therefore this fact contributes to the sensitivity of poliovirus surveillance, which under optimal conditions can be better than that of the standard acute flaccid paralysis (AFP) surveillance. The World Health Organization (WHO) has included environmental surveillance of poliovirus in the new Strategic Plan of the Global Polio Eradication Initiative for years 2010-2012 to be increasingly used in PV surveillance, supplementing AFP surveillance and the strategic advisory group of experts on immunization (SAGE) recommended a switch from tOPV-bOPV to remove the threat of cVDPV2 and to accelerate the elimination of WPV type 1 and 3 as bOPV is a more immunogenic vaccine and to introduce one dose of IPV in their vaccination schedule prior to OPV cessation.

Risks associated with the use of live-attenuated vaccine poliovirus strains and the strategies for control and eradication of paralytic poliomyelitis

The Global Polio Eradication Initiative was launched in 1988 with the aim to eliminate paralytic poliomyelitis. Two effective vaccines are available: inactivated polio vaccine (IPV) and oral polio vaccine (OPV). Since 1964, OPV has been used instead of IPV in most countries due to several economic and biological advantages. However, in rare cases, the live-attenuated Sabin strains of OPV revert to neurovirulence and cause vaccine-associated paralytic poliomyelitis in vaccinees or lead to emergence of vaccine-derived poliovirus strains. Attenuating mutations and recombination events have been associated with the reversion of vaccine strains to neurovirulence. The substitution of OPV with an improved new-generation IPV and the availability of new specific drugs against polioviruses are considered as future strategies for outbreak control and the eradication of paralytic poliomyelitis worldwide.

Intercity spread of echovirus 6 in Shandong Province, China: application of environmental surveillance in tracing circulating enteroviruses

Environmental surveillance is an effective approach in investigating circulating enteroviruses and had been conducted in the cities of Jinan and Linyi since February 2008 and April 2010, respectively. This study analyzed 46 sewage samples collected in the two cities in 2011 and found that echovirus 6 (E6) was the predominant serotype, with 134 isolates (65 in Jinan and 69 in Linyi) from 23 (50%) samples. This differs from the 2010 data that found 29 E6 isolates in Jinan and only 3 in Linyi. Phylogenetic analysis of the VP1 coding region showed that all environmental E6 samples from 2008 to 2011 (n = 167) segregated into two lineages and revealed an increase in VP1 gene diversity in 2011, suggesting that the increased number of E6 detections reflects a real epidemic in the two cities. Most Linyi isolates (n = 61, or 88%) in 2011 segregated into sublineage 1a, together with 18 Jinan isolates in 2011. Interestingly, the ancestral VP1 sequence of sublineage 1a inferred using the maximum-likelihood method had 100% identity with the sequence of one environmental isolate from Jinan in August 2010, suggesting an intercity spread from Jinan to Linyi. By Bayesian phylodynamic methods, the most recent common ancestor of Linyi isolates in sublineage 1a dated back to 24 December 2010, revealing that this sublineage was likely imported into Linyi from August to December in 2010. This study demonstrates that environmental surveillance is a sensitive method in tracing transmission pathways of circulating enteroviruses among different regions and reveals that E6-associated aseptic meningitis is an emerging concern in China.

Feasibility of quantitative environmental surveillance in poliovirus eradication strategies

The progress of the Global Polio Eradication Initiative is monitored by acute flaccid paralysis (AFP) surveillance supplemented with environmental surveillance in selected areas. To assess the sensitivity of environmental surveillance, stools from (re)vaccinated elderly persons with a low seroprevalence and from wastewater were concurrently collected and analyzed in the Netherlands over a prolonged period of time. A total number of 228 healthy individuals with different levels of immunity were challenged with monovalent oral polio vaccine serotype 1 or 3. Poliovirus concentrations were determined by the titration of fecal suspensions on poliovirus-sensitive L20B cells and of sewage concentrates by L20B monolayer plaque assay. Almost half of the individuals (45%) shed poliovirus on day 3 after challenge, which peaked (57%) on day 8 with an average poliovirus excretion of 1.3 × 10(5) TCID(50) per g of feces and gradually decreased to less than 5% on day 42. The virus concentrations in sewage peaked on days 6 to 8 at approximately 100 PFU per liter, remained high until day 14, and subsequently decreased to less than 10 PFU per liter on day 29. The estimated poliovirus concentration in sewage approximated the measured initial virus excretion in feces, within 1 log(10) variation, resulting in a sensitivity of detection of 100 infected but mostly asymptomatic individuals in tens of thousands of individuals. An additional second peak observed in sewage may indicate secondary transmission missed by enterovirus or AFP surveillance in patients. This enables the detection of circulating poliovirus by environmental surveillance, supporting its feasibility as an early warning system.

Cocirculation of two transmission lineages of echovirus 6 in jinan, china, as revealed by environmental surveillance and sequence analysis

Enterovirus environmental surveillance on sewage from the city of Jinan, Shandong Province, China, was initiated in 2008. Thirty echovirus 6 (E6) strains-1 in 2008 and 29 in 2010-were isolated and identified. Most E6 isolates (n = 21) came from the sewage collected on August 2010, revealing high local E6 activity at that time. Interestingly, the VP1 sequences of most isolates, even from the same sewage, were not identical. Phylogenetic analysis of VP1 sequences revealed two lineages for these isolates, with 78.0 to 80.0% nucleotide identities with one another, 94.8 to 100.0% identity within the major lineage, and 92.7 to 98.5% identity within the minor one. The VP1 sequences of environmental isolates, clinical isolates from 1998 to 2010, and global E6 were subjected to evolutionary analysis using Bayesian phylodynamic methods. The inferred E6 VP1 ancestral sequence dated back to 1901 (range, 1873 to 1928) and evolved with 7.047 × 10(-3) substitutions per site per year. Shandong E6 segregated into three clusters, and the two environmental lineages belonged to clusters A and C, which originated in 2003 and 1992, respectively. The antigenicity analysis via neutralization assay confirmed great antigenic differences between Shandong isolates and a prototype strain. These findings underscore the value of continuous environmental surveillance and genetic analysis to monitor circulating enteroviruses in the population and give further insight into E6 evolution.

Mechanisms of genetic variation in polioviruses

Polioviruses, as with all RNA viruses, are in a constant process of evolution driven by different mechanisms. With multiple mechanisms for genetic variability, they are successful conformists, adapting to changes in their habitat. The evolution of polioviruses may occur with generation of point mutations followed by genetic drift and selection. The mutation rate of polioviruses based on several studies is approximately 3 × 10(-2) mutations/synonymous site/year in the gene encoding viral protein 1. Genetic variation in polioviruses may also be increased by sharing of genetic data of two different poliovirus lineages by means of homologous recombination. According to the current view, recombination is considered usually to occur by strand-switching, but a non-replicative model has also been described. In recombination, polioviruses may either gain a set of advantageous mutations selected and fixed in previous generations of the parental viruses or get rid of deleterious ones. The prerequisites and constraints of the evolution mechanisms will be discussed. Furthermore, consequences of poliovirus evolution will be reviewed in the light of observations made on currently circulating polioviruses. We will also describe how polioviruses strike back: as wild type polioviruses approach eradication, vaccine derived strains increase their occurrence and genetic variability.

Isolation of a recombinant type 3/type 2 poliovirus with a chimeric capsid VP1 from sewage in Shandong, China

The genetic and phenotypic characterization of poliovirus strain P3/Jinan/1/09, isolated from sewage sample in Jinan city, Shandong province, China, was described. The strain had a Sabin type 3/type 2/type 3 recombinant genome, with the first crossover site located in capsid VP1 coding region between nucleotide positions 3293 and 3294 (numbering according to Sabin 3), and the second crossover site in 3D region between positions 6374 and 6378. The recombinant had introduced six Sabin 2-derived amino acids into the carboxyl terminus of Sabin 3 VP1 capsid protein. The complete genome of the isolate revealed eight nucleotide substitutions in Sabin 3 region with two substitutions resulting in amino acid alteration, and two missense substitutions in the Sabin 2 region. An estimation based on the evolution rate of the P1 coding region of Sabin 3 background suggested that evolution time of strain P3/Jinan/1/09 might be 76-80 days. The person who excreted the recombinant was not known and no evidence was obtained for its circulation in population via acute flaccid paralysis surveillance. The virus showed Sabin 3 serological characterization in neutralization test, and it did not lose temperature sensitivity phenotype at 40 degrees C. The significance of environmental surveillance and the presence of natural capsid recombinant poliovirus strain in the context of the global polio eradication initiative are discussed.

A Sabin 2-related poliovirus recombinant contains a homologous sequence of human enterovirus species C in the viral polymerase coding region

A type 2 vaccine-related poliovirus (strain CHN3024), differing from the Sabin 2 strain by 0.44% in the VP1 coding region was isolated from a patient with vaccine-associated paralytic poliomyelitis. Sequences downstream of nucleotide position 6735 (3D(pol) coding region) were derived from an unidentified sequence; no close match for a potential parent was found, but it could be classified into a non-polio human enteroviruses species C (HEV-C) phylogeny. The virus differed antigenically from the parental Sabin strain, having an amino acid substitution in the neutralizing antigenic site 1. The similarity between CHN3024 and Sabin 2 sequences suggests that the recombination was recent; this is supported by the estimation that the initiating OPV dose was given only 36-75 days before sampling. The patient's clinical manifestations, intratypic differentiation examination, and whole-genome sequencing showed that this recombinant exhibited characteristics of neurovirulent vaccine-derived polioviruses (VDPV), which may, thus, pose a potential threat to a polio-free world.

Comparative study of enteric viruses, coliphages and indicator bacteria for evaluating water quality in a tropical high-altitude system

BACKGROUND

Bacteria used as indicators for pathogenic microorganisms in water are not considered adequate as enteric virus indicators. Surface water from a tropical high-altitude system located in Mexico City that receives rainwater, treated and non-treated wastewater used for irrigation, and groundwater used for drinking, was studied.

METHODS

The presence of enterovirus, rotavirus, astrovirus, coliphage, coliform bacteria, and enterococci was determined during annual cycles in 2001 and 2002. Enteric viruses in concentrated water samples were detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Coliphages were detected using the double agar layer method. Bacteria analyses of the water samples were carried out by membrane filtration.

RESULTS

The presence of viruses and bacteria in the water used for irrigation showed no relationship between current bacterial indicator detection and viral presence. Coliphages showed strong association with indicator bacteria and enterovirus, but weak association with other enteric viruses. Enterovirus and rotavirus showed significant seasonal differences in water used for irrigation, although this was not clear for astrovirus.

CONCLUSION

Coliphages proved to be adequate faecal pollution indicators for the irrigation water studied. Viral presence in this tropical high-altitude system showed a similar trend to data previously reported for temperate zones.

Evaluation of a two-dose administration of live oral poliovirus vaccine for wild and virulent vaccine-derived poliovirus type 1, 2, 3 strains in Japan

We evaluated the efficacy of Japan's vaccination policy, a 2-dose administration of live oral poliovirus vaccine (OPV) against wild and virulent vaccine-derived poliovirus (VDPV) type 1, 2, 3 strains, by investigating the neutralizing antibody titers of residents in Toyama Prefecture, Japan. Seropositivities against the virulent type 1 and 2 strains were more than 90%, but the values against the virulent type 3 strains were approximately 60%. Also, while geometric mean antibody titers against virulent type 1 and 2 strains were more than 180, those against the virulent type 3 strains were 58-59, and 9-12, in particular, at 10 to 19 y of age. A booster dose of the vaccine for the type 3 virus is recommended for adolescents. However, high herd immunity against type 1, 2 and 3 viruses has been maintained for these 22 y, although the seropositivity against type 3 virus was always lower than other types. Our results suggest that Japan's vaccination policy might be enough to prevent an epidemic of poliomyelitis caused by wild and virulent VDPV type 1, 2, 3 strains, even though the titers against type 3 viruses were the lowest.

Recombinant Sabin environmental isolates in Greece and Cyprus

AIMS

Twenty-one polioviruses (PVs) Sabin strains were isolated from sewage treatment plants from Metamorphosis, Athens, Greece during the time period from May to October 1996, and from two other sites located at Nicosia and Limassol in Cyprus between April and December 2003 were retrospectively investigated for the detection of recombinant PVs.

METHODS AND RESULTS

Three PVs isolates were found as tripartite recombinants, S3/S2/S1 in the 2C genomic viral region. The first recombination site S3/S2 was located close to the 5' end of 2C while the second recombination site S2/S1 was located towards the 3' end of 2C. Such recombination is a rare event producing a tripartite hybrid 2C protein. Three more PVs isolates were characterized as bipartite S2/S1 recombinants and one as S2/S3 bipartite recombinant.

CONCLUSIONS

Detection of recombinant circulating vaccine-derived PVs (cVDPVs) is crucial, since increased transmissibility over that of the parental Sabin strains has been proposed to be the result of recombination events.

SIGNIFICANCE AND IMPACT OF THE STUDY

Importation of recombinant cVDPVs evolved derivatives pose a serious threat to public health and environmental surveillance should be implemented during and after PVs eradication.

Isolation of recombinant type 2 vaccine-derived poliovirus (VDPV) from a Nigerian child

A type 2 vaccine-derived poliovirus (VDPV), differing from Sabin 2 at 2.5% (22/903) of VP1 nucleotide (nt) positions, was isolated from an incompletely immunized 21-month-old Nigerian child who developed acute flaccid paralysis in 2002. Sequences upstream of nt position 620 (within the 5'-untranslated region [5'-UTR]) and downstream of nt position 5840 (in the 3C(pro) region) were derived from species C enteroviruses unrelated to the oral poliovirus vaccine (OPV) strains. The two substitutions associated with the attenuated phenotype had either recombined out (A(481)-->G in the 5'-UTR) or reverted (Ile(143)-->Thr in VP1). The VDPV isolate had lost the temperature sensitive phenotype of Sabin 2 and it was antigenically distinct from the parental OPV strain, having amino acid substitutions in or near neutralizing antigenic sites 1 and 3. The date of the initiating OPV dose, calculated from the number of synonymous substitutions in the capsid region, was estimated to be approximately 16 to 18 months before onset of paralysis, a finding inconsistent with the most recent mass OPV campaign (conducted 12 days before onset of paralysis) as being the source of infection. Although no related type 2 VDPVs were detected in Nigeria or elsewhere, the VDPV was found in an area where conditions favor VDPV emergence and spread.

Risks of paralytic disease due to wild or vaccine-derived poliovirus after eradication

After the global eradication of wild polioviruses, the risk of paralytic poliomyelitis from polioviruses will still exist and require active management. Possible reintroductions of poliovirus that can spread rapidly in unprotected populations present challenges to policymakers. For example, at least one outbreak will likely occur due to circulation of a neurovirulent vaccine-derived poliovirus after discontinuation of oral poliovirus vaccine and also could possibly result from the escape of poliovirus from a laboratory or vaccine production facility or from an intentional act. In addition, continued vaccination with oral poliovirus vaccines would result in the continued occurrence of vaccine-associated paralytic poliomyelitis. The likelihood and impacts of reintroductions in the form of poliomyelitis outbreaks depend on the policy decisions and on the size and characteristics of the vulnerable population, which change over time. A plan for managing these risks must begin with an attempt to characterize and quantify them as a function of time. This article attempts to comprehensively characterize the risks, synthesize the existing data available for modeling them, and present quantitative risk estimates that can provide a starting point for informing policy decisions.

Poliovirus vaccine strains in sewage and river water in South Africa

Since the initiation of the global poliomyelitis eradication program in 1988, the number of wild-type polio cases decreased from 350,000 to fewer than 500, and the number of polio endemic countries declined from more than 125 to 10. The last case of polio in South Africa caused by a wild-type poliovirus (PV) occurred in 1989. The live attenuated oral poliovirus vaccine (OPV) has been effectively used in the reduction and control of poliomyelitis. However, as OPV strains are excreted in stools after vaccination, this vaccine could become a source of dissemination of PVs in the environment and the potential cause of poliomyelitis. Therefore, the aim of the study was to determine the occurrence of OPV strains in selected sewage and river water samples. During the period between 2001 and 2003, 138 samples of river water and 213 samples of settled sewage were collected from selected areas of South Africa. A total of 860 plaques were analysed, which consisted of 703 plaques from the sewage and 157 plaques from the river water samples. Using a reverse transcriptase (RT)-multiplex PCR, 49 PVs were successfully distinguished from 176 non-polio enteroviruses (NPEVs). The 176 NPEVs consisted of 50 coxsackie B2 viruses (CBV2), followed by 39 echoviruses 11 (ECV11), 25 CBV5, 21 CBV3, 15 CBV4, 14 coxsackie A6 viruses (CAV6), 7 CBV6, 2 CAV5, 2 CBV1, and 1 ECV19, which was in agreement with the prevalence of these EVs in other parts of the world. The Sabin-specific RT-triplex PCR revealed the presence of 29 Sabin PV type 1, 8 Sabin PV type 2, and 12 Sabin PV type 3 isolates. Buffalo green monkey kidney and primary liver carcinoma cell cultures allowed the amplification of a broad spectrum of EVs, whereas human epidermoid carcinoma cells were more selective for PVs. This study addressed some of the issues regarding the prevalence of OPV strains in the environment. The identification of 49 viable OPV isolates confirmed the presence and circulation of PV vaccine strains in sewage and river water. The extent of the potential health risk constituted by these OPV isolates remains to be investigated.

Molecular epidemiology of echoviruses 11 and 13, based on an environmental surveillance conducted in Toyama Prefecture, 2002-2003

Nineteen echovirus 11 (E11) and 12 E13 isolates were isolated from three rivers in Toyama Prefecture, Japan, during an environmental surveillance conducted from April 2002 to March 2003. The nucleotide sequences of E13 isolates were closely related to those from patients with aseptic meningitis, with less than 1.3% divergence in the VP1 region of the viral capsid gene, and belonged to the same clade responsible for a worldwide outbreak that started in 2000. In contrast, E11 isolates were clustered into three genomic groups and were not closely related to echovirus strains isolated from patients. These results suggest that the combination of both virus isolation from environmental sources and phylogenetic analysis could be complementary assessment approaches to trace prevalent and minor circulating enteroviruses in the human population.

Modulation of poliovirus replicative fitness in HeLa cells by deoptimization of synonymous codon usage in the capsid region

We replaced degenerate codons for nine amino acids within the capsid region of the Sabin type 2 oral poliovirus vaccine strain with corresponding nonpreferred synonymous codons. Codon replacements were introduced into four contiguous intervals spanning 97% of the capsid region. In the capsid region of the most highly modified virus construct, the effective number of codons used (N(C)) fell from 56.2 to 29.8, the number of CG dinucleotides rose from 97 to 302, and the G+C content increased from 48.4% to 56.4%. Replicative fitness in HeLa cells, measured by plaque areas and virus yields in single-step growth experiments, decreased in proportion to the number of replacement codons. Plaque areas decreased over an approximately 10-fold range, and virus yields decreased over an approximately 65-fold range. Perhaps unexpectedly, the synthesis and processing of viral proteins appeared to be largely unaltered by the restriction in codon usage. In contrast, total yields of viral RNA in infected cells were reduced approximately 3-fold and specific infectivities of purified virions (measured by particle/PFU ratios) decreased approximately 18-fold in the most highly modified virus. The replicative fitness of both codon replacement viruses and unmodified viruses increased with the passage number in HeLa cells. After 25 serial passages (approximately 50 replication cycles), most codon replacements were retained, and the relative fitness of the modified viruses remained well below that of the unmodified virus. The increased replicative fitness of high-passage modified virus was associated with the elimination of several CG dinucleotides. Potential applications for the systematic modulation of poliovirus replicative fitness by deoptimization of codon usage are discussed.

VACCINE-DERIVED POLIOVIRUSES AND THE ENDGAME STRATEGY FOR GLOBAL POLIO ERADICATION

As the global eradication of wild poliovirus nears, the World Health Organization (WHO) is addressing challenges unprecedented in public health. The live, attenuated oral poliovirus vaccine (OPV), used for more than four decades to interrupt poliovirus transmission, and the vaccine of choice for developing countries, is genetically unstable. Reversion of the small number of substitutions conferring the attenuated phenotype frequently occurs during OPV replication in humans and is the underlying cause of the rare cases of vaccine-associated paralytic poliomyelitis (VAPP) in OPV recipients and their close contacts. Whereas VAPP has long been recognized, two other adverse events have been identified more recently: (a) long-term excretion of highly evolved vaccine-derived polioviruses (VDPVs) in persons with primary immunodeficiencies, and (b) polio outbreaks associated with circulating VDPVs in areas with low rates of OPV coverage. Developing a posteradication strategy to minimize the risks of VDPV emergence and spread has become an urgent WHO priority.

Some ethical issues arising from polio eradication programmes in India

The World Health Organisation's programme for the eradication of poliomyelitis as currently practised in India raises many ethical issues. In this paper we concentrate on just two. The first is the balance to be struck between the risks and benefits generated by the eradication programme itself. The issue of risks and benefits arises in relation to the choice between two different vaccine types available for polio programmes: oral polio vaccine (OPV) and inactivated polio vaccine (IPV). OPV is the vaccine currently used in the eradication campaign in India. We argue that given the current risks/benefits profile of this vaccine, there is an urgent need to review the programme and take remedial action to address existing problems (at least in India). The second issue we discuss is the fact that there is little effort to gain the informed consent of the parents of vaccinated children, as they are not currently told about the potential limitations of OPV or the possibility of vaccine-induced harm. We suggest that such a policy might be justifiable, given the importance of polio eradication, but only if there is a system of compensation for vaccine-induced harm as part of the eradication programme itself. There is a real danger that if these issues are not addressed then public trust in the eradication programme and vaccination programmes as a whole will be lost.

Polio eradication: the OPV paradox

Routine and mass administration of oral polio vaccine (OPV) since 1961 has prevented many millions of cases of paralytic poliomyelitis. The public health value of this inexpensive and easily administered product has been extraordinary. Progress of the Global Polio Eradication Initiative has further defined the value of OPV as well as its risk through vaccine-associated paralytic poliomyelitis (VAPP) and vaccine-derived polioviruses (VDPV). Although both are rare, once wild poliovirus transmission has been interrupted by OPV, the only poliomyelitis due to poliovirus will be caused by OPV. Poliovirus will be eradicated only when OPV use is discontinued. This paradox provides a major incentive for eventually stopping polio immunization or replacing OPV, but it also introduces complexity into the process of identifying safe and scientifically sound strategies for doing so. The core post eradication immunization issues include the risk/benefits of continued OPV use, the extent of OPV replacement with IPV, possible strategies for discontinuing OPV, and the potential for development and licensure of a safe and effective replacement for OPV. Formulation of an informed post eradication immunization policy requires careful evaluation of polio epidemiology, surveillance capability, vaccine availability, laboratory containment, and the risks posed by the very tool responsible for successful interruption of wild poliovirus transmission.

Circulation of endemic type 2 vaccine-derived poliovirus in Egypt from 1983 to 1993

From 1988 to 1993, 30 cases of poliomyelitis associated with poliovirus type 2 were found in seven governorates of Egypt. Because many of the cases were geographically and temporally clustered and because the case isolates differed antigenically from the vaccine strain, it was initially assumed that the cases signaled the continued circulation of wild type 2 poliovirus. However, comparison of sequences encoding the major capsid protein, VP1 (903 nucleotides), revealed that the isolates were related (93 to 97% nucleotide sequence identity) to the Sabin type 2 oral poliovirus vaccine (OPV) strain and unrelated (<82% nucleotide sequence identity) to the wild type 2 polioviruses previously indigenous to Egypt (last known isolate: 1979) or to any contemporary wild type 2 polioviruses found elsewhere. The rate and pattern of VP1 divergence among the circulating vaccine-derived poliovirus (cVDPV) isolates suggested that all lineages were derived from a single OPV infection that occurred around 1983 and that progeny from the initiating infection circulated for approximately a decade within Egypt along several independent chains of transmission. Complete genomic sequences of an early (1988) and a late (1993) cVDPV isolate revealed that their 5' untranslated region (5' UTR) and noncapsid- 3' UTR sequences were derived from other species C enteroviruses. Circulation of type 2 cVDPVs occurred at a time of low OPV coverage in the affected communities and ceased when OPV coverage rates increased. The potential for cVDPVs to circulate in populations with low immunity to poliovirus has important implications for current and future strategies to eradicate polio worldwide.

Isolation of vaccine-derived type 1 polioviruses displaying similar properties to virulent wild strain Mahoney from sewage in Japan

Type 1, 2, and 3 vaccine-derived polioviruses were isolated from a sewage disposal plant located downstream of the Oyabe River in Toyama Prefecture, Japan, between October 1993 and September 1995. Neurovirulence was analyzed in 13 type 1 vaccine-derived strains, using mutant analysis by polymerase chain reaction and restriction enzyme cleavage (MAPREC). Nine strains (69%) were estimated to have marked neurovirulence. Some of the neutralizing antigenic sites, temperature sensitivity, and plaque-forming ability of two virulent vaccine-derived poliovirus strains were similar to Mahoney strain. The neutralizing activity of human sera obtained after oral poliomyelitis vaccine (OPV) administration against one of the virulent vaccine-derived polioviruses was examined. Although all human sera showed sufficient neutralizing activity for the prevention of poliomyelitis by vaccine-derived poliovirus strains, a lower titer than that against Sabin type 1 strain was observed. Vaccination against virulent vaccine-derived poliovirus will be effective. However, the environmental presence of viruses that have properties similar to those Mahoney strain is a threat. The introduction of inactivated poliovirus vaccine (IPV), and well-maintained herd immunity, together with reinforced environmental surveillance is important for the final phase of the polio eradication program by the World Health Organization (WHO).

[Contribution to knowledge about the permanence and circulation of poliovirus vaccine in the environment]

The erradication of poliomyelitis in the world is a goal that requires the adoption of effective and safe strategies for its attainment. Knowing how long the strains of poliovirus derived from the oral attenuated virus vaccine may circulate and remain in the environment was essential to define the measures to be taken and was also the objective of our paper. Specimens of stools and sewage water, which were weekly obtained at the end of the National Polio Vaccination Campaign, in 1998, were analyzed. Viruses were isolated and identified by culture and neutralization tests for the identification of poliovirus. In the particular case of the sewage water, it was also used the polymerase chain reaction. The curves of elimination in both media were drawn and it was concluded that the permanence of viruses in the environment did not exceed the 12 weeks after the immunization with the oral attenuated virus vaccine.