Distribution of phage types of Vibrio cholerae 01 biotype El Tor in Nigeria (2007-2013): Implication in cholera mortality

Abstract

Nigeria has been plagued with seasonal epidemics of cholera with high mortality impact since 2007. Data to understand the molecular epidemiology of strains for developing country-specific control measures are either not available or incomplete in most of the epidemic states. To bridge this information gap, this study determined the phage type profiles of some selected Vibrio cholerae 01 biotype El Tor strains involved in epidemic between 2007 and 2013 in nine states of the country. A total of 52 epidemic strains of V. cholerae from nine states: Abia, Bauchi, Borno, Kano, Gombe, Ilorin, Lagos, Ogun and Osun based on viability and positive serogrouping of 122 stock cultures were phage typed using both the old (two groups) and new (10 groups) typing schemes according to World health Organization (WHO) guidelines. Data were descriptively analyzed for variation and predominance of phage types using STATA 8.0. The proportions of strains belonging to the T2 and T4 phage types were 55.7 and 44.3%, respectively (P>0.05). With the new typing scheme, epidemic strains of phage types ranging from 4 to 8 were found per state. Further analysis revealed phage predominance in the following decreasing order: T-27>T-24>T-23. Other phage types seen were T-7, T-10, T-12, T-14, T-16 and T-17. Phage variation analysis further revealed involvement of strains from multiple phage types ≥3 during the 2010 cholera epidemics versus ≤2 in other cholera epidemics since 2007. Findings from this study indicate that multiple phage types of V. cholerae 01 biotype El Tor with the predominance of T-27 are common in Nigerian cholera epidemic situation since 2007. This study also revealed phage multiplicity to play a role in the documented higher case fatality of 2010 cholera epidemics compared to recent outbreaks in the country.   Key words: Vibrio cholerae 01 biotype El Tor, phage typing, cholera, Nigeria.