MICROEVOLUTION AND ETHNIC-RELATED PATTERNS OF TRANSMISSION WITHIN CYCLIC OUTBREAKS OF S. SONNEI SHIGELLOSIS IN ISRAEL

Adi Behar ^1,2 Kate Baker ^3,4 Ravit Bassal ⁵ Analia Ezernitchi ⁶ Lea Valinsky ⁶ Nicolas Thomson ³ Daniel Cohen ¹

¹Department of Epidemiology and Preventive Medicine, School of Public Health, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv
²Division of Parasitology, Kimron Veterinary Institute, Beit-Dagan
³Pathogen Genomics, The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge
⁴Functional and comparative Genomics, University of Liverpool, Liverpool
⁵Israel Center for Disease Control, Ministry of Health, Tel Hashomer
⁶Ministry of Health, Central Laboratories, Jerusalem

We analyzed whole genome sequences (WGS) of 281 S. sonnei isolates of Israeli children to appraise the microevolution and patterns of S. sonnei transmission within countrywide biennial epidemics occurring in Israel in 2000-2012. The phylogenetic analysis revealed two distinct sub-clades: one containing 264 isolates (~94%) (i.e. major sub clade), more prevalent among Jewish children and a second containing 16 isolates (~5.7%) (i.e. minor sub clade), more prevalent among Israeli Arab children and especially among Bedouin children of Southern Israel. The majority of clones within the sub-clades can be found throughout the years with certain replacements, becoming epidemic when the level of population natural immunity to S. sonnei decreases significantly.

WGS analysis also suggested that plasmid spA is going under degradation with the loss of tetracycline resistance genes over time corroborating the trend of decrease in resistance to tetracycline detected in S. sonnei isolates observed over the same period. pINVB, which encodes in S. sonnei for the O-antigen, the protective Shigella antigen, seems to be under very little immune selection which is of much relevance for Shigella vaccine development.

Adi Behar

Kimron Veterinary Institute