Exploring Salmonella’s deadly sub-Saharan adaptation

I contributed to a literature review article that was published in The Lancet in May 2012 that we hope will produce a wider appreciation of the severity and distinct causes of a disease that is an important cause of death in African adults and children.

Invasive non-typhoidal Salmonella (iNTS) is a blood-borne infection that kills approximately one in four of people in sub-Saharan Africa who catch it. Yet, in the rest of the word, NTS is simply an unpleasant disease: it is a leading cause of acute inflammatory diarrhoea that is self-limiting and tends to be fatal in less than 1 per cent of people.

This difference in the severity of the disease in sub-Saharan Africa when compared with the rest of the world is due, in large part, to synergy with other factors including young age of the person, malnutrition, or coinfection with malaria or HIV. However, our collaborative research with laboratories in Kenya, Malawi and Liverpool using whole-genome sequence analysis has also uncovered an additional complicating factor; the bacterium responsible for the severe disease is distinct from that found in the rest of the world.

In 2009, we announced that a distinct genotype of Salmonella Typhimurium, designated ST313, had emerged as a new pathogenic group in sub-Saharan Africa, and might have adapted to the susceptible population in these regions. While Salmonella Typhimurium genotypes associated with inflammatory diarrhoea have spread globally, the ST313 genotype is specifically associated with susceptible populations in sub-Saharan Africa. The genetic make-up of the pathogen may therefore contribute to the severity and/or epidemiology of this disease. The molecular basis of this association is now the subject of intense interest in laboratories across the world.

I work as part of research consortium that includes the Wellcome Trust Sanger Institute, laboratories in the UK and US, and – most importantly – collaborators from several sub-Sahara African countries, which has contributed significantly to understanding this disease. The collaboration combines local field studies in Malawi, Kenya, Uganda, Democratic Republic of Congo, Mali and Nigeria with molecular and genome sequencing efforts in laboratories around the world.

Despite the significant steps we have taken in understanding this disease in recent years, advocacy for further field studies and the development of effective intervention strategies is lacking. By developing a complete understanding of the epidemiology of this neglected disease, we hope that new avenues will open for development and implementation of vaccine and public health strategies to prevent infections and interrupt transmission.

Review article: Feasey et al. Invasive non-typhoidal salmonella disease: an emerging and neglected tropical disease in Africa. Lancet 2012 (Epub ahead of print). doi: http://dx.doi.org/10.1016/S0140-6736(11)61752-2

Related Links

• Microbial Pathogenesis team
• Salmonella research at the Wellcome Trust Sanger Institute