Global Genetic Study of S. Enteritidis Reveals Lethal Infections in Africa

It is estimated that 680,000 deaths occur every year worldwide from invasive non-typhoidal Salmonella (iNTS) disease. In high income settings, distinct Salmonella Enteritidis lineages are associated with enterocolitis. In low income settings infections are becoming an invasive and deadly disease. More than half of the deaths associated with iNTS were in Africa.

In the first global-scale genetic study, scientists sequenced 675 isolates of S. Enteritidis from 45 countries and six continents. Three separate types were revealed. A common global type and two novel African Types.

According to a recent press release, “Scientists at the Wellcome Trust Sanger Institute, Liverpool School of Tropical Medicine and University of Liverpool found two novel African types, which looked the same, but were genetically different from the Western type.” African S. Enteritidis types have developed resistance to many antibiotics, such as amoxicillin and chloramphenicol. It may only be a matter of time before resistance to the last line antibiotic cephalosporin spreads. Finding strategies to eradicate iNTS is a priority.

The more common global type is linked to poultry and predominantly infects the intestine, causing diarrhea. In Africa, however, the newly identified types are a major cause of blood poisoning in those with weakened immune systems. In these cases, Salmonellae are able to pass, with greater ease, from the gut into the blood stream. The environmental reservoir from which these African bacteria are transmitted to people is still not clear. In Africa, iNTS is a serious challenge to identify due to a lack of laboratory capacity.

It has been concluded that further investigation, into where these types reside in the environment, is necessary and urgently needed to help prevent further deaths. Professor Melita Gordon, joint lead author from the University of Liverpool’s Institute of Infection and Global health said, “It is possible that Salmonella lives in standing water, so improving access to sanitation and clean water is extremely important.” A human vaccine is also under development.

The study highlighted a very important issue; under certain circumstances a mild version of a bacterium can evolve into a more dangerous pathogen.

According to Professor Nick Thomson, joint lead author from the Sanger Institute, “A combination of HIV, antibiotic resistance, lack of health care and sanitation has facilitated the emergence of Salmonellae as a deadly disease in Africa and its importance was not originally recognized.”