Identification and control of a poliomyelitis outbreak in Xinjiang, China

Progress toward global interruption of wild poliovirus transmission, 2010-2013, and tackling the challenges to complete eradication

Despite substantial progress, global polio eradication has remained elusive. Indigenous wild poliovirus (WPV) transmission in 4 endemic countries (Afghanistan, India, Nigeria, and Pakistan) persisted into 2010 and outbreaks from imported WPV continued. By 2013, most outbreaks in the interim were promptly controlled. The number of polio-affected districts globally has declined by 74% (from 481 in 2009 to 126 in 2013), including a 79% decrease in the number of affected districts in endemic countries (from 304 to 63). India is now polio-free. The challenges to success in the remaining polio-endemic countries include (1) threats to the security of vaccinators in each country and a ban on polio vaccination in areas of Afghanistan and Pakistan; (2) a risk of decreased government commitment; and (3) remaining surveillance gaps. Coordinated efforts under the International Health Regulations and efforts to mitigate the challenges provide a clear opportunity to soon secure global eradication.

Challenges of maintaining polio-free status of the European Region

BACKGROUND

The European region, certified as polio free in 2002, had recent wild poliovirus (WPV) introductions, resulting in a major outbreak in Central Asian countries and Russia in 2010 and in current widespread WPV type 1 circulation in Israel, which endangered the polio-free status of the region.

METHODS

We assessed the data on the major determinants of poliovirus transmission risk (population immunity, surveillance, and outbreak preparedness) and reviewed current threats and measures implemented in response to recent WPV introductions.

RESULTS

Despite high regional vaccination coverage and functioning surveillance, several countries in the region are at high or intermediate risk of poliovirus transmission. Coverage remains suboptimal in some countries, subnational geographic areas, and population groups, and surveillance (acute flaccid paralysis, enterovirus, and environmental) needs further strengthening. Supplementary immunization activities, which were instrumental in the rapid interruption of WPV1 circulation in 2010, should be implemented in high-risk countries to close population immunity gaps. National polio outbreak preparedness plans need strengthening. Immunization efforts to interrupt WPV transmission in Israel should continue.

CONCLUSIONS

The European region has successfully maintained its polio-free status since 2002, but numerous challenges remain. Staying polio free will require continued coordinated efforts, political commitment and financial support from all countries.

Phylogeny of imported and reestablished wild polioviruses in theDemocratic Republic of the Congo from 2006 to 2011

BACKGROUND

The last case of polio associated with wild poliovirus (WPV) indigenous to the Democratic Republic of the Congo (DRC) was reported in 2001, marking a major milestone toward polio eradication in Africa. However, during 2006-2011, outbreaks associated with WPV type 1 (WPV1) were widespread in the DRC, with >250 reported cases.

METHODS

WPV1 isolates obtained from patients with acute flaccid paralysis (AFP) were compared by nucleotide sequencing of the VP1 capsid region (906 nucleotides). VP1 sequence relationships among isolates from the DRC and other countries were visualized in phylogenetic trees, and isolates representing distinct lineage groups were mapped.

RESULTS

Phylogenetic analysis indicated that WPV1 was imported twice in 2004-2005 and once in approximately 2006 from Uttar Pradesh, India (a major reservoir of endemicity for WPV1 and WPV3 until 2010-2011), into Angola. WPV1 from the first importation spread to the DRC in 2006, sparking a series of outbreaks that continued into 2011. WPV1 from the second importation was widely disseminated in the DRC and spread to the Congo in 2010-2011. VP1 sequence relationships revealed frequent transmission of WPV1 across the borders of Angola, the DRC, and the Congo. Long branches on the phylogenetic tree signaled prolonged gaps in AFP surveillance and a likely underreporting of polio cases.

CONCLUSIONS

The reestablishment of widespread and protracted WPV1 transmission in the DRC and Angola following long-range importations highlights the continuing risks of WPV spread until global eradication is achieved, and it further underscores the need for all countries to maintain high levels of poliovirus vaccine coverage and sensitive surveillance to protect their polio-free status.

Poliomyelitis: historical facts, epidemiology, and current challenges in eradication

Poliomyelitis is a highly infectious disease caused by a virus belonging to the Picornaviridae family. It finds a mention even in ancient Egyptian paintings and carvings. The clinical features are varied ranging from mild cases of respiratory illness, gastroenteritis, and malaise to severe forms of paralysis. These have been categorized into inapparent infection without symptoms, mild illness (abortive poliomyelitis), aseptic meningitis (nonparalytic poliomyelitis), and paralytic poliomyelitis. This disease has been associated with crippling deformities affecting thousands of lives throughout the world. Only due to the perseverance and determination of great scientists in 1900s, the genomic structure of the virus and its pathogenesis could be elucidated. Contribution of Salk and Sabin in the form of vaccines-oral polio vaccine (OPV) and the inactivated polio vaccine-heralded a scientific revolution. In 1994, the World Health Organization (WHO) Region of The Americas was certified polio free followed by the WHO Western Pacific Region in 2000 and the WHO European Region in June 2002 of the 3 types of wild poliovirus (types 1, 2, and 3). In 2013, only 3 countries remained polio endemic-Nigeria, Pakistan, and Afghanistan. Global eradication of polio is imperative else the threat of an outbreak will hover forever. Today, all the governments of the world in collaboration with WHO stand unified in their fight against poliomyelitis and the task when achieved will pave the way for eliminating other infections in future.

Molecular characterization of enteroviruses including a new type EV-C99 isolated from Xinjiang students in Shandong, China in 2011

The last case of infection with wild-type poliovirus indigenous to China was reported in 1994. In 2011, a poliomyelitis outbreak caused by imported wide-type poliovirus occurred in Xinjiang Uighur Autonomous Region. Here, we report the results of enterovirus (EV) isolation from Xinjiang students that returned to school in Shandong after summer vacation during this outbreak. Stool specimens from 376 students were collected and 10 EV strains were isolated including 4 polioviruses (All Sabin strains), 1 coxsackievirus (CV) A13, 3 CVA17 and 2 EV-C99. VP1 sequence analysis revealed these CVA13, CVA17 and EV-C99 strains had 71.3–81.8%, 76.5–84.6% and 74.2–82.9% nucleotide similarity with strains from other countries within a serotype, respectively. EV-C99 strains had 82.7–92.8% VP1 similarity with two previously reported Xinjiang strains. Complete genome analysis on EV-C99 strains revealed intra-serotypic genetic recombination events. These findings reflect great genetic divergence between Chinese strains and strains from other countries of the three types, and provide valuable information on monitoring EV transmission over long distance.

Bioinformatics analysis and genetic diversity of the poliovirus

Poliomyelitis, a disease which can manifest as muscle paralysis, is caused by the poliovirus, which is a human enterovirus and member of the family Picornaviridae that usually transmits by the faecal-oral route. The viruses of the OPV (oral poliovirus attenuated-live vaccine) strains can mutate in the human intestine during replication and some of these mutations can lead to the recovery of serious neurovirulence. Informatics research of the poliovirus genome can be used to explain further the characteristics of this virus. In this study, sequences from 100 poliovirus isolates were acquired from GenBank. To determine the evolutionary relationship between the strains, we compared and analysed the sequences of the complete poliovirus genome and the VP1 region. The reconstructed phylogenetic trees for the complete sequences and the VP1 sequences were both divided into two branches, indicating that the genetic relationships of the whole poliovirus genome and the VP1 sequences are very similar. This branching indicates that the virulence and pathogenicity of poliomyelitis may be associated with the VP1 region. Sequence alignment of the VP1 region revealed numerous mutation sites in which mutation rates of >30 % were detected. In a group of strains recorded in the USA, mutation sites and mutation types were the same and this may be associated with their distribution in the evolutionary tree and their genetic relationship. In conclusion, the genetic evolutionary relationships of poliovirus isolate sequences are determined to a great extent by the VP1 protein, and poliovirus strains located on the same branch of the phylogenetic tree contain the same mutation spots and mutation types. Hence, the genetic characteristics of the VP1 region in the poliovirus genome should be analysed to identify the transmission route of poliovirus and provide the basis of viral immunity development.

Robustness against serum neutralization of a poliovirus type 1 from a lethal epidemic of poliomyelitis in the Republic of Congo in 2010

In 2010, a large outbreak of poliomyelitis with unusual 47% lethality occurred in Pointe Noire, Republic of Congo. Vaccine-mediated immunity against the outbreak virus was never investigated. A wild poliovirus 1 (WPV1) isolated from a fatal case (termed PV1-RC2010) showed a previously unknown combination of amino acid exchanges in critical antigenic site 2 (AgS2, VP1 capsid protein positions 221SAAL → 221PADL). These exchanges were also detected in an additional 11 WPV1 strains from fatal cases. PV1-RC2010 escaped neutralization by three different mAbs relevant for AgS2. Virus neutralization was tested in sera from fatal cases, who died before supplementary immunization (n = 24), Gabonese recipients of recent oral polio vaccination (n = 12), routinely vaccinated German medical students (n = 34), and German outpatients tested for antipoliovirus immunity (n = 17) on Vero, human rhabdomyosarcoma, and human epidermoid carcinoma 2 cells. Fatal poliomyelitis cases gave laboratory evidence of previous trivalent vaccination. Neutralizing antibody titers against PV1-RC2010 were significantly lower than those against the vaccine strain Sabin-1, two genetically distinct WPV1s isolated in 1965 and 2010 and two genetically distinct vaccine-derived PV strains. Of German vaccinees tested according to World Health Organization protocols, 15-29% were unprotected according to their neutralization titers (<1:8 serum dilution), even though all were protected against Sabin-1. Phylogenetic analysis of the WPV1 outbreak strains suggested a recent introduction of virus progenitors from Asia with formation of separate Angolan and Congolese lineages. Only the latter carried both critical AgS2 mutations. Antigenetically variant PVs may become relevant during the final phase of poliomyelitis eradication in populations with predominantly vaccine-derived immunity. Sustained vaccination coverage and clinical and environmental surveillance will be necessary.

Sero-survey of polio antibodies during wild poliovirus outbreak in southern Xinjiang Uygur Autonomous Region, China

Background

After being polio free for more than 10 years, an outbreak following importation of wild poliovirus (WPV) was confirmed in Xinjiang Uygur Autonomous Region, China, in 2011.

Methods

A cross-sectional study was conducted prior to supplementary immunization activities (SIAs), immediately after the confirmation of the WPV outbreak. In selected prefectures, participants aged ≤60 years old who visited hospitals at county-level or above to have their blood drawn for reasons not related to the study, were invited to participate in our study. Antibody titers ≥8 were considered positive.

Results

Among the 2,611 participants enrolled, 2,253 (86.3%), 2,283 (87.4%), and 1,989 (76.2%) were seropositive to P1, P2 and P3 respectively, and 1744 (66.8%) participants were seropositive to all the three serotypes. Lower antibody seropositivities and geometric mean titers were observed in children <1 year of age and in adults aged 15–39 years.

Conclusion

Serosurveys to estimate population immunity in districts at high risk of polio importation might be useful to gauge underlying population immunity gaps to polio and possibly to guide preparedness and response planning. Consideration should be given to older children and adults during polio risk assessment planning and outbreak response.

A barcode of organellar genome polymorphisms identifies the geographic origin of Plasmodium falciparum strains

Malaria is a major public health problem that is actively being addressed in a global eradication campaign. Increased population mobility through international air travel has elevated the risk of re-introducing parasites to elimination areas and dispersing drug-resistant parasites to new regions. A simple genetic marker that quickly and accurately identifies the geographic origin of infections would be a valuable public health tool for locating the source of imported outbreaks. Here we analyse the mitochondrion and apicoplast genomes of 711 Plasmodium falciparum isolates from 14 countries, and find evidence that they are non-recombining and co-inherited. The high degree of linkage produces a panel of relatively few single-nucleotide polymorphisms (SNPs) that is geographically informative. We design a 23-SNP barcode that is highly predictive (~92%) and easily adapted to aid case management in the field and survey parasite migration worldwide.

Tracing the source of malarial infections is an important step towards monitoring and controlling the disease. Here, Preston et al. analyse sequence data from 711 isolates and design a genetic barcode based on combined mitochondrial and apicoplast genomes that is able to distinguish between malaria parasites isolated from different geographical regions.

Public health workers and vaccination coverage in Eastern China: a health economic analysis

Background: Vaccine-preventable diseases cause more than one million deaths among children under 5 years of age every year. Public Health Workers (PHWs) are needed to provide immunization services, but the role of human resources for public health as a determinant of vaccination coverage at the population level has not been assessed in China. The objective of this study was to test whether PHW density was positively associated with childhood vaccination coverage in Zhejiang Province, East China. Methods: The vaccination coverage rates of Measles Containing Vaccine (MCV), Diphtheria, Tetanus and Pertussis combined vaccine (DTP), and Poliomyelitis Vaccine (PV) were chosen as the dependent variables. Vaccination coverage data of children aged 13–24 months for each county in Zhejiang Province were taken from the Zhejiang Immunization Information System (ZJIIS). Aggregate PHW density was an independent variable in one set of regressions, and Vaccine Personnel (VP) and other PHW densities were used separately in another set. Data on densities of PHW and VP were taken from a national investigation on EPI launched by Ministry of Health of China in 2013. We controlled other determinants that may influence the vaccination coverage like Gross Domestic Product (GDP) per person, proportion of migrant children aged <7 years, and land area. These data were taken from Zhejiang Provincial Bureau of Statistics and ZJIIS. Results: PHW density was significantly influence the coverage rates of MCV [Adjusted Odds Ratio(AOR) = 4.29], DTP₃(AOR = 2.16), and PV₃ (AOR = 3.30). However, when the effects of VPs and other PHWs were assessed separately, we found that VP density was significantly associated with coverage of all three vaccinations (MCV AOR = 7.05; DTP₃ AOR = 1.82; PV₃ AOR = 4.83), while other PHW density was not. Proportion of migrant children < 7 years and Land area were found as negative and significant determinants for vaccination coverage, while GDP per person had no effect on vaccination coverage. Conclusions: A higher density of PHWs (VP) would improve the availability of immunization services over time and space, which may increase the possibility of achieving a higher childhood vaccination coverage rate. It was indicated that the level of GDP per person had no association with the improved vaccination coverage after controlling for other potential factors. Our findings implicated that PHW density was a major constraint on immunization coverage in Zhejiang Province.

Limited and localized outbreak of newly emergent type 2 vaccine-derived poliovirus in Sichuan, China

From August 2011 to February 2012, an outbreak caused by type 2 circulating vaccine-derived poliovirus (cVDPV) occurred in Aba County, Sichuan, China. During the outbreak, four type 2 VDPVs (≥0.6% nucleotide divergence in the VP1 region relative to the Sabin 2 strain) were isolated from 3 patients with acute flaccid paralysis (AFP) and one close contact. In addition, a type 2 pre-VDPV (0.3% to 0.5% divergence from Sabin 2) that was genetically related to these type 2 VDPVs was isolated from another AFP patient. These 4 patients were all unimmunized children 0.7 to 1.1 years old. Nucleotide sequencing revealed that the 4 VDPV isolates differed from Sabin 2 by 0.7% to 1.2% in nucleotides in the VP1 region and shared 5 nucleotide substitutions with the pre-VDPV. All 5 isolates were closely related, and all were S2/S3/S2/S3 recombinants sharing common recombination crossover sites. Although the two major determinants of attenuation and temperature sensitivity phenotype of Sabin 2 (A481 in the 5' untranslated region and Ile143 in the VP1 protein) had reverted in all 5 isolates, one VDPV (strain CHN16017) still retained the temperature sensitivity phenotype. Phylogenetic analysis of the third coding position of the complete P1 coding region suggested that the cVDPVs circulated locally for about 7 months following the initiating oral poliovirus vaccine (OPV) dose. Our findings reinforce the point that cVDPVs can emerge and spread in isolated communities with immunity gaps and highlight the emergence risks of type 2 cVDPVs accompanying the trivalent OPV used. To solve this issue, it is recommended that type 2 OPV be removed from the trivalent OPV or that inactivated polio vaccine (IPV) be used instead.

Enhanced surveillance of acute flaccid paralysis following importation of wild poliovirus in Xinjiang Uygur Autonomous Region, China

Background

After being polio free for more than 10 years, an outbreak occurred in China in 2011 in Xinjiang Uygur Autonomous Region (Xinjiang) following the importation of wild poliovirus (WPV) originating from neighboring Pakistan.

Methods

To strengthen acute flaccid paralysis (AFP) surveillance in Xinjiang, “zero case daily reporting” and retrospective searching of AFP cases were initiated after the confirmation of the WPV outbreak. To pinpoint all the polio cases in time, AFP surveillance system was expanded to include persons of all ages in the entire population in Xinjiang.

Results

Totally, 578 AFP cases were reported in 2011 in Xinjiang, including 21 WPV cases, 23 clinical compatible polio cases and 534 non-polio AFP cases. Of the 44 polio cases, 27 (61.4%) cases were reported among adults aged 15–53 years. Strengthening AFP surveillance resulted in an increase in the number of non-polio AFP cases in 2011 (148 children < 15 years) compared with 76 cases < 15 years in 2010. The AFP surveillance system in Xinjiang was sensitive enough to detect polio cases, with the AFP incidence of 3.28/100,000 among children < 15 years of age.

Conclusions

Incorporating adult cases into the AFP surveillance system is of potential value to understand the overall characteristics of the epidemic and to guide emergency responses, especially in countries facing WPV outbreak following long-term polio free status. The AFP surveillance system in Xinjiang was satisfactory despite limitations in biological sample collection.