Persistence of vaccine-derived poliovirus following a mass vaccination campaign in Cuba: implications for stopping polio vaccination after global eradication.

BACKGROUND: With substantial progress made toward polio eradication, developing the appropriate strategy for discontinuing global oral poliovirus vaccine (OPV) after global eradication becomes increasingly important. At issue is the theoretical risk of independent circulation of potentially virulent OPV-derived strains. Because Cuba uses OPV only in mass campaigns, it represents an ideal site to assess vaccine-derived poliovirus persistence. METHODS: Infants born after the 1997 biannual mass campaigns were evaluated for past (neutralizing antibody) or current (virus excretion) evidence of vaccine-derived poliovirus exposure. We obtained sera and/or stool specimens from 861 infants; a second serum from 218 infants. RESULTS: All stool specimens were poliovirus negative. Of 762 infants, 113 (14.8%) had initially detectable poliovirus type 1 antibody, 193 (25.3%) type 2, and 94 (12.3%) type 3. A precipitous antibody decline occurred in initially positive sera. CONCLUSIONS: Our results suggest that in a country with high population immunity, vaccine-derived virus is unlikely to establish ongoing circulation.

Genotype-specific RNA probes for direct identification of wild polioviruses by blot hybridization.

We have developed RNA probes for the direct identification of wild poliovirus isolates by blot hybridization. The probes are complementary to sequences of the first 30 to 32 codons of VP1, which evolve more extensively (approximately 1.5-fold) than the rest of VP1. To illustrate our general approach, we describe the design of probes specific to each of four major genotypes recently endemic (1981 to 1991) to the Americas: Andean type 1, Brazil type 1, Brazil type 3, and Central America-Mexico type 3. A wild isolate of each genotype was selected according to molecular and epidemiologic criteria to be representative of the principal lineages in circulation. Variable VP1 sequences of the representative isolates were amplified by the reverse transcriptase PCR and were inserted into a plasmid vector containing a T7 promoter. The in vitro transcripts, labeled with digoxigenin, served as probes. These formed stable hybrids only with RNAs of isolates of the corresponding genotypes. Hybrids were detected by a sensitive chemiluminescence assay, capable under normal diagnostic conditions of detecting specific wild poliovirus sequences in samples containing up to a 100-fold excess of Sabin vaccine strain-related sequences of the same serotype.

Direct detection of wild poliovirus circulation by stool surveys of healthy children and analysis of community wastewater.

Cartagena, Colombia, was one of the last cities in the Americas known to have endemic poliomyelitis. After 3 cases were identified in 1991, two approaches for detecting continued silent transmission of wild polioviruses within a high-risk community were used: stool surveys of healthy children and virologic analysis of community sewage. Wild type 1 polioviruses were isolated from 8% of the children studied and from 21% of sewage samples. The proportions of wild polioviruses, vaccine-related polioviruses, and nonpolio enteric viruses were similar for both approaches. Wild poliovirus sequences were also amplified directly from processed sewage samples by the polymerase chain reaction using primer pairs specific for the indigenous type 1 genotype. The last reported cases associated with wild polioviruses in the Americas occurred in Colombia (8 April 1991) and Peru (23 August 1991). Direct sampling for wild polioviruses in high-risk communities can provide further evidence that eradication of the indigenous wild polioviruses has been achieved in the Americas.

Genotype-specific in vitro amplification of sequences of the wild type 3 polioviruses from Mexico and Guatemala.

The extensive nucleotide sequence heterogeneity among independent genotypes of wild polioviruses permits the systematic design of genotype-specific molecular reagents. We have prepared two sets of polymerase chain reaction (PCR) primer pairs specific for the genotype of wild poliovirus type 3 recently endemic to Mexico and Guatemala. Nucleotide sequences of a representative wild type 3 virus isolated in Mexico in 1989 differed from the corresponding Sabin 3 (Leon 12 a1b) sequences at 167 of 900 positions within the VP1 region. From the sequence data, wild virus-specific primer pairs were designed to complement regions of high mismatch (greater than 33%) with Sabin 3 templates. Primer binding sites were spaced along the genome so that the predicted amplification products (142 bp and 163 bp) could be easily resolved electrophoretically from the products generated with our Sabin strain-specific primers (Sabin 1: 97 bp; Sabin 2: 71 bp; Sabin 3: 53 bp). RNAs of all wild type 3 poliovirus isolates from Mexico and Guatemala obtained over a 13-year period (1977-1990) served as efficient templates for amplification of the 142-bp and 163-bp products. Genomic templates derived from vaccine-related polioviruses and most heterologous wild polioviruses were inactive under equivalent reaction conditions. Amplifications generating a 114-bp product with a broadly reacting primer pair, matching highly conserved sequences in the 5'-noncoding region, provided a positive control for the presence in samples of poliovirus (or enterovirus) RNAs. Selective amplification of wild Mexico-Guatemala type 3 poliovirus sequences was obtained with either primer set in reactions containing large stoichiometric excesses (up to 10(6)-fold) of vaccine-related RNAs. We have used wild genotype-specific PCR primer sets to facilitate identification of wild polioviruses present in both clinical and environmental samples.

[Epidemic outbreak of viral meningitis caused by type 30 ECHO virus]. / Brote epidémico de meningitis viral causado por virus ECHO tipo 30.

The clinical records of 15 children admitted to Hospital Infantile de México Federico Gómez with diagnosis of viral meningitis were reviewed. They were part of 19 patients admitted with this diagnosis during a 5 week period (March 22 to April 30, 1992) and represent a significant increase of aseptic meningitis compared with the same periods of previous years at Hospital Infantile de Mexico and in Mexico City where there is an ongoing epidemic outbreak of this entity. All the patients studied had spinal fluid findings consistent with viral meningitis and in 4 of them on ECHO virus type 30 was isolated at the Enterovirus Section of the CDC, Atlanta Georgia USA.

Oligonucleotide probes for the specific detection of the wild poliovirus types 1 and 3 endemic to Brazil.

Synthetic oligodeoxynucleotide probes, 21-23 nucleotides in length, were prepared which specifically hybridize to the genomes of the wild type 1 and 3 polioviruses currently endemic to the northeastern region of Brazil. The probes are complementary to sequences near the 5'-terminus of the VP1 gene that differ substantially among genetically distant polioviruses but are largely conserved among related isolates. The probes have been routinely used in the laboratory surveillance of poliomyelitis cases in Brazil, permitting direct, rapid identification of the indigenous wild polioviruses by dot-blot hybridization.

Outbreak of poliomyelitis-like paralysis associated with enterovirus 71.

In the summer of 1987 five children were seen at The Children's Hospital of Philadelphia because of acute onset of flaccid paralysis of an arm or leg(s). Although there were documented exposures to oral poliovirus vaccine and coxsackievirus B3 in some of the cases, the clinical, epidemiologic and laboratory findings indicate that enterovirus 71 was the common etiologic agent for this unusual outbreak of poliomyelitis-like paralysis. Of the five children three recovered completely; the other two had residual paralysis with weakness and muscle wasting. Imaging studies of the spinal cord in the two children with residual paralysis revealed defects in the ventral aspect of the spinal cord. This series of paralytic cases attributed to enterovirus 71 is the largest reported in the United States.