Molecular epidemiology of poliovirus infection in Tunisia.
(17/2233)
This report is an overview of poliomyelitis surveillance in Tunisia from 1991 to 1996. In all, 2088 stool specimens, collected from 152 acute flaccid paralysis (AFP) cases and from 1747 of their healthy contacts were investigated. Virus isolation was done systematically in RD and HEp-2C cell lines and isolated viruses were typed by sero-neutralisation as polioviruses or non-polio enteroviruses. Poliovirus isolates were analysed systematically for their wild or vaccine-related origin by two methods--one based on antigenic differences and one on genetic differences between strains. All type 2 polioviruses were vaccine-related and most wild viruses belonged to polio serotype 3. Wild polio type 3 viruses were detected in 1991 and 1992 in six cases of paralytic polio. A silent circulation of wild polio 1 and wild polio 3 was detected in 1994. No wild virus was detected in Tunisia from 1995 onwards. Wild polioviruses were sequenced and compared with Tunisian wild strains isolated during the 1980s, as well as other genotypes from the international database. These investigations revealed a single Tunisian polio 3 genotype that has been circulating from 1985 to 1994 and two different polio 1 genotypes. These results reflect effective control strategies within the country and contribute to the improvement of the polio eradication programme effectiveness at national and global levels. (+info)
Isolation and molecular characterization of a poliovirus type 1 mutant that replicates in the spinal cords of mice.
(18/2233)
The Mahoney strain of poliovirus type 1 (OM) is generally unable to cause paralysis in mice. We isolated a mouse-adapted mutant, PV1/OM-SA (SA), from the spinal cord of a mouse that had been intracerebrally inoculated with OM. SA showed mouse neurovirulence only with intraspinal inoculation, and the infected mice developed a flaccid paralysis, which was indistinguishable from that observed in poliovirus-sensitive transgenic mice inoculated with OM. SA antigens were detected in neurons of the spinal cords of the infected mice. Nucleotide (nt) sequence analysis revealed 9 nt changes on the SA genome, resulting in three amino acid (a.a.) substitutions, i.e., one each in the capsid proteins VP4 and VP1 and in the noncapsid protein 2C. To identify the key mutation site(s) for the mouse neurovirulence, virus recombinants between OM and SA were constructed by using infectious cDNA clones of these two viruses and tested for their mouse neurovirulence after inoculation via an intraspinal route. The results indicated that a mutation at nt 928 (replacement of A with G), resulting in a substitution of Met for Ile at a.a. 62 within VP4, was responsible for conferring the mouse neurovirulence phenotype of the mutant SA. The mutation in VP4 may render the virus accessible to a molecule that acts as a virus receptor and is located on the surfaces of neurons of the mouse spinal cord. This molecule appears not to be expressed in the mouse brain. (+info)
Poliovirus induces apoptosis in the mouse central nervous system.
(19/2233)
Poliovirus (PV) is the etiological agent of human paralytic poliomyelitis. Paralysis results from the destruction of motoneurons, a consequence of PV replication. However, the PV-induced process leading to the death of motoneurons is not well known. We investigated whether PV-induced central nervous system (CNS) injury is associated with apoptosis by using mice as animal models. Transgenic mice expressing the human PV receptor were infected intracerebrally with either the neurovirulent PV-1 Mahoney strain or a paralytogenic dose of the attenuated PV-1 Sabin strain. Nontransgenic mice were infected with a mouse-adapted PV-1 Mahoney mutant. DNA fragmentation was demonstrated in CNS tissue from paralyzed mice by visualization of DNA oligonucleosomal laddering and by enzyme-linked immunosorbent assay. Viral antigens and DNA fragmentation detected by the in situ terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling technique were colocalized in neurons of spinal cords from paralyzed mice. In addition, morphological changes characteristic of cells undergoing apoptosis were observed in motoneurons by electron microscopy. Thus, we show that PV multiplication and CNS injury during paralytic poliomyelitis are associated with apoptosis. (+info)
The properties of chimeric picornavirus IRESes show that discrimination between internal translation initiation sites is influenced by the identity of the IRES and not just the context of the AUG codon.
(20/2233)
The internal ribosome entry segment (IRES) of picornaviruses consists of approximately 450 nt of 5'-untranslated region, terminating at the 3' end with an approximately 25 nt element consisting of an absolutely conserved UUUC motif followed by a more variable pyrimidine-rich tract and G-poor spacer, and finally an AUG triplet, which is considered to be the actual ribosome entry site. Events following entry at this site differ among picornaviruses: in encephalomyocarditis virus (EMCV) virtually all ribosomes initiate translation at this site (AUG-11); in foot-and-mouth-disease virus (FMDV), one-third of the ribosomes initiate at this AUG (the Lab site), and the rest at the next AUG 84 nt downstream (Lb site); and in poliovirus (PV), the AUG at the 3' end of the IRES (at nt 586 in PV type 1) is considered to be a silent entry site, with all ribosomes initiating translation at the next AUG downstream (nt 743). To investigate what determines this different behavior, chimeras were constructed with a crossover at the conserved UUUC motif: the body of the IRES, the sequences upstream of this UUUC motif, was derived from one species, and the downstream sequences from another. When the body of the FMDV or PV IRESes was replaced by that of EMCV, there was a marked increase in the absolute and relative frequency of initiation at the upstream AUG, the Lab site of FMDV and 586AUG of PV, respectively. In contrast, when the body of the EMCV IRES was replaced by that of PV, initiation occurred with no preference at three AUGs: the normal site (AUG-11), AUG-10 situated 8 nt upstream, and AUG-12, which is 12 nt downstream. Thus although the context of the AUG at the 3' end of the IRES may influence initiation frequency at this site, as was shown by improving the context of 586AUG of PV, the behavior of the ribosome is also highly dependent on the nature of the upstream IRES. Delivery of the ribosome to this AUG in an initiation-competent manner is particularly efficient and accurate with the EMCV IRES. (+info)
Resistance of ribosomal protein mRNA translation to protein synthesis shutoff induced by poliovirus.
(21/2233)
Poliovirus infection induces an overall inhibition of host protein synthesis, although some mRNAs continue to be translated, suggesting different translation requirements for cellular mRNAs. It is known that ribosomal protein mRNAs are translationally regulated and that the phosphorylation of ribosomal protein S6 is involved in the regulation. Here, we report that the translation of ribosomal protein mRNAs resists poliovirus infection and correlates with an increase in p70(s6k) activity and phosphorylation of ribosomal protein S6. (+info)
Comparison of enterovirus-specific cellular immunity in two populations of young children vaccinated with inactivated or live poliovirus vaccines.
(22/2233)
Enterovirus-specific cellular immunity was studied in Estonian and in Finnish children at the age of 9 months. The aim was to evaluate the level of responsiveness in two neighbouring countries with different poliovirus immunization practices and striking differences in the incidence of insulin-dependent diabetes mellitus (IDDM), a disease in which early enterovirus infections are an aetiological risk factor. The Estonian children immunized with live attenuated polio vaccine had stronger T cell responses to coxsackievirus B4 and poliovirus type 1 when compared with Finnish children immunized with inactivated polio vaccine (median stimulation indices 10.4 and 6.3 in Estonian children and 1.9 and 2.9 in Finnish children, respectively; P < 0.05). Lymphocytes stimulated by poliovirus type 1 antigen expressed interferon-gamma (IFN-gamma) mRNAs, which strongly correlated with the level of proliferation responses. Lymphocytes of Estonian children had a tendency towards stronger expression of IFN-gamma upon poliovirus challenge when compared with Finnish children. The number of children who had experienced coxsackievirus B infections, as determined by the presence of neutralizing antibodies, did not differ between Estonian and Finnish children. The results show that Finnish children have weaker cellular immunity against enteroviruses at the age of 9 months compared with Estonian children at the same age. This is most probably due to the difference in polio vaccination schedules; in Estonia live poliovirus vaccine is used and given at earlier ages than the inactivated vaccines in Finland. This leads to stronger T cell immunity which cross-reacts with other enterovirus serotypes. This may explain the lower incidence of IDDM in Estonia by providing effective protection against diabetogenic enterovirus strains in Estonian children. (+info)
Genetic basis for immunological aberrations in poliovirus Sabin serotype 3 strains imported in the netherlands.
(23/2233)
During the characterization of poliovirus type 3 strains imported in The Netherlands, Sabin serotype 3 strains that reacted with both specific antisera against Sabin-like (vaccine) and non-Sabin-like (wild-type) strains by the intratypic strain differentiation assay have been found. The present study was done to determine the pathogenic potential of these virus strains for humans. Characterization of these so-called double-reactive strains with neutralizing monoclonal antibodies (MAbs) against the major antigenic sites of serotype 3 Sabin virus led to the identification of two groups with different antigenic properties. Six of the seven strains were resistant to neutralization with MAbs against sites 2B and 3B and one strain was neutralized by all the MAbs in a manner similar to that for the Sabin serotype 3 virus. Partial sequencing of the coding regions confirmed the antigenic changes for all six antigenically distinct strains. By inoculation of these viruses into transgenic mice which express the human poliovirus receptor, one strain was identified as highly neurovirulent, three were identified as intermediate, and three were identified as attenuated. Sera from vaccinated persons efficiently neutralized the mutants. Our data suggest that some double-reactive strains are a potential risk to the unvaccinated community but not to the vaccinated population. (+info)
Genomic characterization of human and environmental polioviruses isolated in Albania.
(24/2233)
Between April and December 1996, a serious outbreak of poliomyelitis occurred in Albania; almost 140 subjects were involved, and the episode presented an unusually high mortality rate (12%). During the outbreak, water samples from the Lana River in Tirana, Albania, and stool samples from two cases of paralytic poliomyelitis were collected and analyzed for the presence of polioviruses. Six polioviruses were isolated from the environmental and human samples, according to standard methods. All the samples were characterized by partial genomic sequencing of 330 bases across the 5' untranslated region (5'-UTR) (nucleotide positions 200 to 530) and of 300 bases across the VP1 region (nucleotide positions 2474 to 2774). Comparison of these sequences with those present in data banks permitted the identification of environmental isolates Lana A and Lana B as, respectively, a Sabin-like type 2 poliovirus and an intertypic recombinant poliovirus (Sabin-like type 2/wild type 1), both bearing a G instead of an A at nucleotide position 481. The two other environmental polioviruses were similar to the isolates from the paralytic cases. They were characterized by a peculiar 5'-UTR and by a VP1 region showing 98% homology with the Albanian epidemic type 1 isolates reported by other authors. This study confirms the environmental circulation in Albania of recombinant poliovirus strains, likely sustained by a massive vaccination effort and by the presence in the environment of a type 1 poliovirus, as isolated from the Lana River in Tirana about 2 months before the first case of symptomatic acute flaccid paralysis was reported in this town. (+info)