Importation and Circulation of Vaccine-Derived Poliovirus Serotype 2, Senegal, 2020-2021

Abstract

Environmental surveillance for poliovirus is increasingly used in poliovirus eradication efforts as a supplement to acute flaccid paralysis (AFP) surveillance. Environmental surveillance was officially established in 2017 in Senegal, where no poliovirus had been detected since 2010. We tested sewage samples from 2 sites in Dakar monthly for polioviruses. We identified a vaccine-derived poliovirus serotype 2 on January 19, 2021, from a sample collected on December 24, 2020; by December 31, 2021, we had detected 70 vaccine-derived poliovirus serotype 2 isolates circulating in 7 of 14 regions in Senegal. Sources included 18 AFP cases, 20 direct contacts, 17 contacts in the community, and 15 sewage samples. Phylogenetic analysis revealed the circulation of 2 clusters and provided evidence on the virus introduction from Guinea. Because novel oral polio vaccine serotype 2 was used for response activities throughout Senegal, we recommend expanding environmental surveillance into other regions.

Keywords: Senegal; acute flaccid paralysis; environmental surveillance; polio; vaccine-derived poliovirus serotype 2; viruses.

Figure 1

Temporal distribution of enterovirus isolates detected in Senegal during 2015–2021. A) Enteroviruses detected from acute flaccid paralysis surveillance, including all human specimens (cases, close contacts, and community contacts). B) Enteroviruses detected from environmental surveillance. cVDPV2, circulating vaccine-derived poliovirus serotype 2; NPEV, nonpolio enterovirus; PV-SL, Sabin-like poliovirus.

Figure 2

Maximum-likelihood tree based on complete viral protein 1 sequences of cVDPV2 isolates circulating in Senegal during 2020–2021. The tree is midpoint-rooted; nodes are labeled with local support values computed using the Shimodaira-Hasegawa test for 5,000 bootstrap replications. Strain identifiers are designated as follows: SEN-XXX-XXX-21-xxx indicates an isolate from an acute flaccid paralysis (AFP) cases; SEN-XXX-XXX-21-xxx-Cx, close contact of an AFP case; SEN-XXX-XXX-21-xxx-CCxx, community contact of an AFP case; ENV-XXX-XXX-XXX-XXX-21-xxx, isolate from a sewage sample; SEN-ENV-XXX-XXX-XXX-21-Cx-XXX, community contact around a positive environmental site. Isolate names are color-coded as follows: dark blue, new characterized isolates from the Diourbel region (SEN-DIO); green, the Thiès region (SEN-THI); red, the Dakar region (SEN-DAK); pink, the Louga region (SEN-LOU); purple, the Matam region (SEN-MAT); gray, the Fatick region (SEN-FAK); brown, the Kaolack region (SEN-KAO); black, Guinea (GUI), Mauritania (MAU), and The Gambia (GAM), and previous sequences of cVDPV2 from West Africa countries. Asterisk * indicates the first sequence isolated from sewage in Senegal in December 2020. cVDPV2, circulating vaccine-derived poliovirus serotype 2.