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Excretion of attenuated polioviruses in children vaccinated with live oral poliovirus vaccine.

The excretion of attenuated polioviruses was studied in a group of nursery children vaccinated with 105TCD50 of each type of virus. The primovaccinated children were found to excrete type 1 poliovirus for 8 weeks, type 2 for 11 weeks after the vaccination with the type 1 + 2 bivaccine. Poliovirus type 1 as eliminated by 78% and type 2 by 98% of the vaccinees. The separately administered type 3 was detectable for 6 weeks and was isolated from 100% of the vaccinees. The highest per cent of children with type 1 excretion positivity was recorded at week 5, with type 2 positivity at week 1 and with type 3 positivity at week 2. The poliovirus excretion peaked early after the vaccination, the titres of the poliovirus type 2 were the highest. The children revaccinated next year with the type 1 + 2 bivaccine eliminated the respective types of virus 1 - 2 weeks; type 3 poliovirus was detectable for 6 weeks after revaccination and was excreted by the highest per cent of vaccines. The contact infections caused by the attenuated polioviruses developed in 9 from 22 children vaccinated previously. The excretion of polioviruses did not last longer than 1 week. The contact infections were most frequently caused by the poliovirus type 2. The examined children, particularly those vaccinated previously, turned out to excrete also other enteroviruses identified as Coxsakieviruses B 4 and B 5 and Echovirus 21. In the primovaccinated these viruses were isolated only from those with the negative excretion of polioviruses.

Child, Preschool↗

Canyon rim residues, including antigenic determinants, modulate serotype-specific binding of polioviruses to mutants of the poliovirus receptor.

Several mouse cell lines expressing hybrid human poliovirus receptors (hPVRs) bearing mutations in the first immunoglobulin-like domain were previously characterized for their defective binding and replication of poliovirus type 1 Mahoney (G. Bernhardt, J. Harber, A. Zibert, M. DeCrombrugghe, and E. Wimmer, Virology, 203, 344-356, 1994). Here we report that these mutant hPVRs were utilized to explore differences in the binding behavior of the three serotypes of poliovirus. Type 3 polioviruses (both Sabin and the neurovirulent Leon strain) clearly bound to the hPVR mutant Q130G/GD, but were incapable of initiating infection. Also, binding at 25 degrees of poliovirus types 2 and 3 to cell lines expressing the hPVR mutants P84SYS/HPGA, L99GAE/AAAA, and D117F was greater than type 1 poliovirus. Further study of the serotype-specific interaction with mutant hPVRs was accomplished with antigenic hybrid viruses. Improved binding by antigenic hybrid viruses demonstrated that serotype-specific binding to mutant hPVRs is, in part, determined by the amino acid sequence of neutralization antigenic sites (NAgs) and the probable conformational rearrangement of amino acids adjacent to the NAg sites. Finally, site-directed mutants of poliovirus were utilized to determine the relative contributions, to hPVR interactions, of individual amino acids with solvent accessible side chains in the viral canyon. Of the 18 viable virus mutants produced, 3 (D1226A, I1089A, and VPEK1166HPGA) expressed impaired replication phenotypes on the mutant hPVR cell lines P84SYS/HYSA and D117F. A location at the rim of the poliovirus canyon was implicated for the interaction of the amino terminal domain of the poliovirus receptor with conserved and serotype-specific viral surface amino acids. The possible involvement of elements of neutralization antigenic sites in receptor binding may explain, in part, why poliovirus exists in only three serotypes.

Animals↗

Expression of the poliovirus receptor in intestinal epithelial cells is not sufficient to permit poliovirus replication in the mouse gut.

Although the initial site of poliovirus replication in humans is the intestine, previously isolated transgenic mice which carry the human poliovirus receptor (PVR) gene (TgPVR mice), which develop poliomyelitis after intracerebral inoculation, are not susceptible to infection by the oral route. The low levels of PVR expressed in the TgPVR mouse intestine might explain the absence of poliovirus replication at that site. To ascertain whether PVR is the sole determinant of poliovirus susceptibility of the mouse intestine, we have generated transgenic mice by using the promoter for rat intestine fatty acid binding protein to direct PVR expression in mouse gut. Pvr was detected by immunohistochemistry in the enterocytes and M cells of transgenic mouse (TgFABP-PVR) small intestine. Upon oral inoculation with poliovirus, no increase in virus titer was detected in the feces of TgFABP-PVR mice, and no virus replication was observed in the small intestine, although poliovirus replicated in the brain after intracerebral inoculation. The failure of poliovirus to replicate in the TgFABP-PVR mouse small intestine was not due to lack of virus binding sites, because poliovirus could attach to fragments of small intestine from these mice. These results indicate that the inability of poliovirus to replicate in the mouse alimentary tract is not solely due to the absence of virus receptor, and other factors are involved in determining the ability of poliovirus to replicate in the mouse gut.

Animals↗

Sequential use of inactivated poliovirus vaccine followed by oral poliovirus vaccine in Oman.

Seroprevalence and geometric mean titers (GMTs) were compared at 6 and 10 months after vaccination with monovalent type 1 oral poliovirus vaccine (OPV) at 6 months and trivalent OPV at 7 and 9 months. Group 1 had received 4 doses of OPV, group 2 OPV at birth and 3 doses of OPV and inactivated poliovirus vaccine (IPV), and group 3 placebo at birth and 3 doses of IPV. A total of 547 infants completed the study. At 10 months, seroprevalence to poliovirus type 1 was 98%, 99%, and 98% in groups 1, 2, and 3; 100%, 100%, and 98% to poliovirus type 2; and 80%, 96%, and 91% to poliovirus type 3. Differences in seroprevalence among the groups were significant for poliovirus type 3 (P < .001). Between 6 and 10 months, significant increases in seroprevalence and GMTs occurred for poliovirus type 1 but not for types 2 and 3. Two OPV doses following 3 IPV doses did not significantly increase seroprevalence or raise GMTs for poliovirus types 2 and 3; however, significant increases were found for poliovirus type 1, which may have benefitted from monovalent type 1 administration.

Antibodies, Viral↗

Analysis of antigenic profiles of inactivated poliovirus vaccine and vaccine-derived polioviruses by block-ELISA method.

A new block-ELISA test for quantitative evaluation of relative reactivity of antigenic sites was developed and used to reveal the detailed epitope structure of inactivated poliovirus vaccines (IPV) and live poliovirus strains. Poliovirus was captured on ELISA plates coated with rabbit anti-poliovirus IgG and blocked by monoclonal antibodies (Mabs) specific to individual epitopes before the remaining reactive antigenic sites were quantified by polyclonal anti-poliovirus IgG conjugate. The decrease of conjugate binding by the pre-treatment with a Mab reflects its contribution to the overall reactivity of poliovirus antigen. The level of block activity of Mabs for a given antigen can be expressed as a percent of reduction of antigenic reactivity as determined by ELISA test. It can be normalized by expressing this value as a ratio to the block activity of a reference sample. The data on the blocking-activity of a panel of monoclonal antibodies specific to different antigenic sites represents the epitope composition (antigenic profile) of a sample. Quantitative differences in epitope composition were determined for nine samples of inactivated poliovirus vaccine (IPV) and compared with the International Reference Reagent. This method could be used for monitoring consistency of IPV production, comparison of vaccines made by different manufacturers, and for the analysis of antigenically modified strains of attenuated poliovirus. Antigenic structures of two isolates of type 1 vaccine-derived poliovirus (VDPV) were compared with the structures of parental Sabin 1 and wild-type Mahoney strains using 17 monoclonal antibodies and revealed significant differences, suggesting that the method can be used for screening of field isolates and rapid identification of antigenically divergent VDPV strains.

Animals↗

Monospecific antisera against capsid polypeptides of poliovirus type 1 distinguish antigenic structures of poliovirus proteins.

Pure poliovirus polypeptides, namely VP1, VP2, VP3 and VP4, have been isolated by isoelectric focusing after dissociation of poliovirus by urea. When injected into rabbits, all four polypeptides produced monospecific antisera which were used for the characterization of poliovirus particles and poliovirus-infected cells. The specificity of these antisera was determined by immunoprecipitation of polypeptides obtained by dissociation of poliovirus with SDS, followed by characterization by polyacrylamide gel electrophoresis. The antisera revealed differences in the antigenic sites of native poliovirus particles, heated poliovirus particles and naturally occurring empty capsids. Only VP3 antiserum reacted with native poliovirus and showed some neutralization, whereas all antisera precipitated heated virus and empty capsids. These antisera reacted also with the appropriate precursors of the capsid polypeptides demonstrating their usefulness for an analysis of the cleavage pathway by monospecific antibodies and revealed a second protomer (90 kilodalton) polypeptide for the capsid proteins of poliovirus particles.

Antibodies, Viral↗

Interaction of poliovirus with its receptor affords a high level of infectivity to the virion in poliovirus infections mediated by the Fc receptor.

Poliovirus infects susceptible cells through the poliovirus receptor (PVR), which functions to bind virus and to change its conformation. These two activities are thought to be necessary for efficient poliovirus infection. How binding and conformation conversion activities contribute to the establishment of poliovirus infection was investigated. Mouse L cells expressing mouse high-affinity Fcgamma receptor molecules were established and used to study poliovirus infection mediated by mouse antipoliovirus monoclonal antibodies (MAbs) (immunoglobulin G2a [IgG2a] subtypes) or PVR-IgG2a, a chimeric molecule consisting of the extracellular moiety of PVR and the hinge and Fc portion of mouse IgG2a. The antibodies and PVR-IgG2a showed the same degree of affinity for poliovirus, but the infectivities mediated by these molecules were different. Among the molecules tested, PVR-IgG2a mediated the infection most efficiently, showing 50- to 100-fold-higher efficiency than that attained with the different MAbs. A conformational change of poliovirus was induced only by PVR-IgG2a. These results strongly suggested that some specific interaction(s) between poliovirus and the PVR is required for high-level infectivity of poliovirus in this system.

Animals↗

Rapid RT-PCR amplification of full-length poliovirus genomes allows rapid discrimination between wild-type and recombinant vaccine-derived polioviruses.

Poliomyelitis outbreaks in areas that were free for a long time of wild-type polioviruses have been reported. Characterization at nucleotide level of the causative agents showed that the isolated viruses were recombinant oral polio vaccine (OPV)-derived polioviruses. To allow rapid identification and detailed analysis of such recombinant polioviruses, a robust full-length reverse transcriptase-PCR (RT-PCR) was developed using SuperScript II (RT) and expand (PCR). Without extensive purification, it was possible to amplify and characterize the full-length genomes of all selected vaccine, wild-type, and recombinant vaccine-derived polioviruses within a week. Endonuclease nuclease analysis (SpeI) of the full-length amplicons allowed easy discrimination between recombinant and non-recombinant polioviruses. Furthermore, sequence analysis of cloned full-length amplicons of a recombinant vaccine-derived poliovirus strain showed that the quasi-species nature of a viral stock is preserved during the RT-PCR procedure. This robust and rapid RT-PCR method will allow rapid characterization of (recombinant) poliovirus strains in case of a local poliomyelitis outbreak, and will help to assess the risk of the appearance of such strains after wild-type poliovirus has been eradicated globally.

Genes, Viral↗

Preexisting immunity to poliovirus does not impair the efficacy of recombinant poliovirus vaccine vectors.

Recombinant viruses are attractive candidates for the development of novel vaccines. A number of viruses have been engineered as vaccine vectors to express antigens from other pathogens or tumors. Inoculation of susceptible animals with this type of recombinant virus results in the induction of both humoral and cellular immune responses directed against the foreign antigens. A general problem to this approach is that existing immunity to the vector can diminish or completely abolish the efficacy of the viral vector. In this study, we investigated whether poliovirus recombinants are capable of inducing effective immunity to the foreign antigen in previously vaccinated animals. Antipoliovirus immunity was induced in susceptible mice by intraperitoneal immunization with live poliovirus. Immunized mice developed antibodies directed against capsid proteins that effectively neutralized poliovirus in vitro and protected animals from a lethal challenge with a high dose of pathogenic poliovirus. To test whether preexisting immunity reduces the efficacy of vaccination with recombinant poliovirus, immunized mice were inoculated with a recombinant poliovirus expressing the C-terminal half of chicken ovalbumin (Polio-Ova). Animals developed ovalbumin-specific antibodies and cytotoxic T lymphocytes (CTL). While the antibody titers observed in preimmune and naive mice were similar, the overall CTL response appeared to be reduced in preimmune mice. Importantly, vaccination with Polio-Ova was able to effectively protect preimmune mice against lethal challenge with a tumor expressing the antigen. Thus, preexisting immunity to poliovirus does not compromise seriously the efficacy of replication-competent poliovirus vaccine vectors. These results contrast with those observed for other viral vaccine vectors and suggest that preexisting immunity does not equally affect the vaccine potential of individual viral vectors.

Animals↗

Molecular evolution of oral poliovirus vaccine strains during multiplication in humans and possible implications for global eradication of poliovirus.

The oral poliovirus vaccine (OPV) has been effectively used in the control of poliomyelitis and in the eradication of wild polioviruses. Although there are many advantages in using attenuated OPV strains in the campaign to eradicate poliomyelitis, several studies have demonstrated that there are some disadvantages such as (a) excretion by vaccines of OPV-derived polioviruses with genomic modifications known to increase the neurovirulence, (b) appearance of vaccine-associated paralytic poliomyelitis (VAPP) and other adverse effects in vaccinees, (c) occurrence of persistent infections caused by OPV-derived strains in immunodeficient patients with VAPP, (d) transmission of OPV-derived polioviruses to susceptible individuals which develop VAPP, and (e) detection of OPV-derived polioviruses in the environment, which could be a source of infection for humans in the future. Different studies indicate that it is important to consider the possibility of persistent infections and excretion of OPV-derived polioviruses for long periods by humans, and also the survival in the environment of OPV-derived polioviruses excreted by humans, which could be transmitted and circulate in a non-immune population after stopping poliovirus vaccination. The findings reported here may have important implications for global poliomyelitis eradication initiative and indicate that surveillance of OPV-derived strains will also be important in the final step of eradication of poliomyelitis from the planet.

Animals↗

Intratypic differentiation of poliovirus strains by enzyme-linked immunosorbent assay (ELISA): poliovirus type 1.

A double antibody sandwich-ELISA has been developed for the detection of antigenic differences between wild and vaccine derived strains of Poliovirus type 1. Poliovirus strains antibodies were prepared in rabbits by immunization with virus suspensions of: Sabin LSc2ab (vaccine derived) and Brunhilde and Mahoney (wild types). IgG fractions were purified from antiserum by precipitation with ammonium sulphate and DEAE-Sephadex A50 chromatography. Purified IgG antibodies were used for coating of microtest plates (catching antibodies). The same reagents labeled with horseradish peroxidase were used as conjugates (detecting antibodies). Detecting antibodies were made strain specific by cross-absorption with the heterologous virus strain. Absorbed and non-absorbed detecting antibodies were subsequently used for detection and quantitation of the poliovirus antigen(s) bound to IgG-coated surfaces. Poliovirus laboratory strains and isolates from sixty-six individuals were differentiated intratypically as vaccine derived or wild types when the ELISA was performed using absorbed conjugates. No intermediate strains were found, and all clinical samples tested fell in two distinct categories. Conversely, when detecting antibodies were used before absorption a high degree of homology between wild and vaccine strains was demonstrated and the differentiation between the two groups was poorly achieved. The ELISA has been optimized in terms of specificity and sensitivity. Less than 10 ng of poliovirus antigens could be detected by non-absorbed detecting antibodies whereas 18 ng was the minimal amount detected by the same antibodies after absorption. Preparation of strain specific antibodies did not require a previous concentration of the poliovirus suspension used for the absorption. It is proposed that the developed ELISA is capable of: 1) detection of low amounts of poliovirus antigens in clinical samples, and 2) intratypic differentiation of poliovirus antigens as either vaccine derived or wild types.

Antibodies, Viral↗

Differences in the UV-crosslinking patterns of the poliovirus 5'-untranslated region with cell proteins from poliovirus-susceptible and -resistant tissues.

The restricted tissue tropism observed in poliovirus infection is not governed solely by the expression of the poliovirus receptor (PVR) gene, but might be controlled at stages beyond virus entry, such as translation, replication, or assembly. Translation of poliovirus RNA by a cap-independent mechanism requires interactions of the 5'-untranslated region (5'UTR) with cell proteins. To determine whether the patterns of these interacting proteins differ in HeLa cells and permissive and nonpermissive tissues, UV-crosslinking assays using the poliovirus 5'UTR and tissue extracts from PVR transgenic mice were performed. The results indicate a correlation between the presence of a 97-kDa UV-crosslinked protein and permissivity to poliovirus infection. Acquired poliovirus susceptibility in in vitro-cultured kidney cells also correlates with the presence of a 97-kDa crosslinked band. The interaction of the 97-kDa protein from HeLa cells and mouse brain with the poliovirus 5'UTR is stable and specific. Whether the 97-kDa protein plays a role in poliovirus translation and tissue susceptibility remains to be determined.

Animals↗

Amino acid residues on human poliovirus receptor involved in interaction with poliovirus.

We have previously demonstrated that the N-terminal immunoglobulin-like domain (domain 1; 115 amino acids) of human poliovirus receptor (hPVR) is essential for poliovirus binding and infection to cells. To identify amino acids involved in the interaction with poliovirus, we constructed a number of cDNAs encoding mutant hPVRs whose domain 1 was partially derived from mouse PVR (mPVR) homolog, which does not serve as a binding site for poliovirus. Poliovirus binding and infection assays were performed on mouse L cells that express these chimera cDNAs. Anti-hPVR monoclonal antibodies were employed to confirm the presence of mutant PVRs on the surface of mouse cells and to know conformational alteration of these PVRs. A significant decrease in efficiency of both poliovirus binding and infection to the cells was observed when one or a few amino acids of hPVR at Gly73, Ser74, Gln82, Leu99-Glu102, or Gln130-Ser132 were substituted by the corresponding amino acids of mPVR. Similar results were obtained when a 2-amino acid insertion of mPVR, which was missing in hPVR, was introduced at the corresponding site (between Arg98 and Leu99) of hPVR. These amino acids were highly conserved in functional PVRs of primates but not in unfunctional PVRs of rodents. These results indicate that the amino acids identified may have important roles in interaction of PVR with poliovirus that leads to the establishment of the virus infection. In the three-dimensional model of the domain 1 of hPVR, these amino acids are located on one side of the molecule. This suggests that the interaction with poliovirus occurs on this side of the domain 1.

Amino Acid Sequence↗

Immunoglobulin a as a serological marker for the (silent) circulation of poliovirus in an inactivated poliovirus-vaccinated population.

Poliovirus-specific immunoglobulin A (IgA) is detected after infection with wild-type virus or vaccination with live attenuated oral poliovirus (OPV) but not after vaccination with inactivated poliovirus (IPV). We examined whether the presence of IgA in serum can be used as a marker for poliovirus circulation in IPV-vaccinated populations in The Netherlands. In seronegative persons challenged with OPV, the sensitivity of this marker was 76%-86%. Results from a serosurvey showed a high seroprevalence (63%-73%) of IgA in the population born before vaccination was introduced in The Netherlands, which reflects natural exposure. The start of the vaccination program in 1957 corresponded to a reduction in the IgA seroprevalence in both vaccinated (2.1%-4.5%) and nonvaccinated groups (8.3%-11.7%). The presence of IgA-positive persons in the population could largely be explained by the occurrence of episodes of proven poliovirus circulation. We propose to use the detection of poliovirus-specific IgA as a tool to monitor virus circulation in IPV-vaccinated and nonvaccinated populations, to aid the poliovirus eradication process.

Biomarkers↗

Excretion of wild-type and vaccine-derived poliovirus in the feces of poliovirus receptor-transgenic mice.

The emergence of circulating vaccine-derived poliovirus (cVDPV) strains in suboptimally vaccinated populations is a serious threat to the global poliovirus eradication. The genetic determinants for the transmissibility phenotype of polioviruses, and in particularly of cVDPV strains, are currently unknown. Here we describe the fecal excretion of wild-type poliovirus, oral polio vaccine, and cVDPV (Hispaniola) strains after intraperitoneal injection in poliovirus receptor-transgenic mice. Both the pattern and the level of fecal excretion of the cVDPV strains resemble those of wild-type poliovirus type 1. In contrast, very little poliovirus was present in the feces after oral polio vaccine administration. This mouse model will be helpful in elucidating the genetic determinants for the high fecal-oral transmission phenotype of cVDPV strains.

Animals↗

Comparison of enhanced potency inactivated poliovirus vaccine (EIPV) versus standard oral poliovirus vaccine (OPV) in Thai infants.

Enhanced potency inactivated poliovirus vaccine (EIPV), combined with diphtheria-tetanus-pertussis (DTP) vaccine, was compared with oral poliovirus vaccine (OPV) regarding immunogenicity in Thai infants, vaccinated at 2, 4 and 6 months of age. EIPV induced significantly higher seroconversion rates than OPV to all 3 poliovirus types after the second and third immunization. After 3 doses of each vaccine, at 7 months of age, all infants receiving EIPV proved seropositive for poliovirus type 1, type 2 and type 3 neutralizing antibodies, whereas of those receiving OPV, 9% remained seronegative (titre < 1:4) for type 1 (p = 0.0042) and 11% for type 3 (p = 0.0013). All participating children were given an additional dose of OPV at the age of 9 months and tested again at 12 months of age. At that point, virtually all infants had poliovirus neutralizing antibodies, but the geometric mean titres to each poliovirus type were significantly higher in the vaccinees who had received EIPV. It is concluded that the greater immunogenicity of EIPV vis-à-vis 3 doses of OPV may be biologically significant for protection against poliovirus types 1 and 3 in countries where cases of poliomyelitis occur in young children. These findings warrant considering EIPV, alone or in combination with OPV, for an immunization programme in Thailand and similar countries in the future.

Antibodies, Viral↗

Absence of wild poliovirus circulation among healthy children in a rural area with high oral poliovirus vaccination coverage.

Poliovirus circulation in a rural community was studied by a stool sample survey. No acute paralytic poliomyelitis case had been reported from the study area during the previous 5 months. Immunization coverage in age groups 7 to 12 months and 12 to 60 months was 95.8 and 94 per cent, respectively. Of the 257 children from whom stool samples were collected (about 6% of the child population), 161 (62.6%) were positive for virus isolation. Poliovirus was isolated from 60 (23.3%) children. All three poliovirus types were detected (41 type 1, 16 type 2 and 3 type 3). Intratypic differentiation tests classified these isolates as vaccine-like. Among the children excreting poliovirus, the proportion of those who did not receive polio vaccine within 30 days prior to the sample collection was 46.3, and 68.7 per cent for poliovirus type 1 and 2, respectively. It was concluded that these poliovirus excreting children were infected by the vaccine strains circulating in the environment. The survey showed that wild poliovirus was not detectable within five months after the last case of acute poliomyelitis. Displacement of the wild virus from the environment and circulation of vaccine virus was achieved by high vaccination coverage in this area.

Child Welfare↗

Efficient delivery of circulating poliovirus to the central nervous system independently of poliovirus receptor.

The transgenic (Tg) mice carrying the human gene for poliovirus receptor (PVR) are susceptible to poliovirus intravenously (i.v.) inoculated as well as intracerebrally or intraspinally inoculated. Thus, i.v.-inoculated poliovirus may invade the central nervous system (CNS) through the blood-brain barrier (BBB). To know the contribution of PVR to tissue distribution and BBB permeability of i.v.-inoculated polioviruses, these dissemination processes were investigated and compared between the Tg mice and non-Tg mice. Distribution profile of i.v.-inoculated poliovirus in various tissues of the Tg mice is similar to that in non-Tg mice. The data suggest that tissue distribution of the virus occurs independently of the transgene for PVR. The amount of poliovirus delivered to the CNS suggested the existence of a specific delivery system of the virus to the CNS. Virus accumulation in the CNS of the Tg mice was measured up to 7.5 hr after the i.v. inoculation. The viruses, regardless of whether the virulent or attenuated strain, seem to accumulate at a constant rate of approximately 0.2 microliter/min/g tissue. Similar phenomena were observed when the viruses were inoculated into non-Tg mice. The rates of the virus accumulation in the CNS are more than 100 times higher than that of albumin, which is considered not to permeate through the BBB via a specific transport system, and only three times lower than that of monoclonal antibody against transferrin receptor (OX-26), which is a potential candidate as a drug delivery vehicle specific to the CNS. These data suggest that polioviruses permeate through the BBB at a fairly high rate, independently of PVR and virus strains.

Animals↗