Environmental Surveillance for Poliovirus in Polio High Risk States of Nigeria, 2011- 2012

Abstract

Introduction: Nigeria is one of the three polio endemic countries in the world along Pakistan and Afghanistan. The detection of persons with Acute Flaccid Paralysis (AFP) and testing of stool specimens from these patients is the surveillance standard for detection of poliovirus. World Health Organization recommends complementary surveillance by testing sewage samples and stool of healthy children. Kano is the epi-center of polio in Nigeria. Environmental surveillance was introduced in June 2011 in Kano State and in April 2012 in Sokoto State. Methods: Grab method was used to collect sewage samples by trained environmental health workers. The samples were tested in Ibadan Polio Laboratory which is part of the Global Polio Laboratory Network. The Samples were concentrated using the two-phase separation method. Isolation of Poliovirus was carried out in RD and L20B cell lines. Poliovirus identification was done using the micro neutralization techniques. Results: In Kano State, from week 28 of 2011 to week 52 of 2012, a total of 60 samples were collected. In Sokoto State, from week 13 – 52 of 2012, a total of 80 sewage samples were collected from four sewage sites. In Kano and Sokoto, 62 and 93 single or mixed isolates were detected from the samples. In Kano, 39 (63%) of the isolates were Sabin viruses, 16 (26%) were circulating vaccine derived polio viruses type 2 (cVDPV2), 2 (3%) were wild polio virus type 1 (WPV1), 4 (6%) were non polio enteroviruses (NPENT) and 1 (3%) were wild polio virus type 3 (WPV3). In Sokoto, 33 (35%) of the isolates were cVDPV2, 27 (29%) were Sabin viruses, 16 (17%) were wild virus type 1 and 17 (18%) were non polio enteroviruses. No wild virus type 3 was detected from AFP cases and environmental samples in Sokoto State in 2012. Conclusion: The results confirm the prevailing immunity gap in polio high risk areas of Nigeria and pronounced immunity gap against type 2 polio virus in Sokoto. Long distance travelers such as nomads play important role in disseminating poliovirus. Special focus should be given to reach and vaccinate such underserved and migrant communities. In addition to the national campaigns with bivalent oral polio vaccine (bOPV) and trivalent oral polio vaccine (tOPV), an aggressive strategy should be adopted to mop up any detection of cVDPV in cases, contacts, or the environment.