High Serotype Diversity of Non-polio Enteroviruses Isolated in Ghana during Acute Flaccid Paralysis Surveillance, 2010-2014

Abstract

Aim: Sabin-like polioviruses and non-polio enteroviruses (NPEVs) isolated from acute flaccid paralysis cases have continued to circulate in the country. However, no wild poliovirus has been detected in Ghana since the last case of poliomyelitis in 2008. This decline has been attributed to active surveillance and intensive oral polio vaccine immunization. As we approach polio-free world, surveillance of NPEVs implicated in acute flaccid paralysis (AFP) is useful for establishing temporal and geographical patterns of circulation and diversity. Study Design: This was a retrospective study using stool samples store at -20°C. Place and Duration: The investigation was carried out at the WHO-accredited Regional Reference  Polio Laboratory, Noguchi Memorial Institute for Medical Research, Legon, Ghana from January 2010 to December 2014. Methods: We investigated stool samples collected from 1422 patients with AFP from 2010-2014 across the country. We tested the samples for human enterovirus infection using standard cell culture methods. Serological identification of NPEV was done using RIVM-specific antisera pools A-G and H-R (The Netherlands). Untyped (UT)-NPEVs were sequenced directly using reverse transcription–polymerase chain reaction (RT-PCR). The pan-enterovirus (Pan-EV) primer (CDC, Atlanta, GA) used in the PCR assay targeted a highly conserved VP1 region of the enterovirus. Results: Two hundred and thirty-five cases were confirmed as positive on RD cells indicating a NPEV isolation rate of 16.5%. Of these RD positive isolates, 110 (46.8%) were further analyzed using sero-neutralization and 28 different NPEVs serotypes were identified. Two additional sero-types E71 and EV A76 were identified by sequencing. All the 30 serotypes belong to four species group: 5 belong to HEV-A, 23 HEV-B, 1 HEV-C and 1 HEV-D. The mean age of the children was 3 years with a range of 8 months to 21 years and standard deviation of 3. Most infections occurred in children within the age group of 2-6 years with no statistical difference p>0.975. The NPEVs were found to circulate throughout the 5-year period and across the country, with the highest prevalence (24%) in the Brong Ahafo region.  Conclusion: The study provided definitive evidence on the circulation of NPEV serotypes implicated in AFP in a polio-free country, and highlights the importance of monitoring NPEVs that mimic polio as we approach polio-free world and continuous vaccination for interruption of transmission.