30 October 2012

Africa: Lethal Salmonella Strain Targets HIV Positive Africans

Nairobi — Fears are growing over an emerging form of intestinal disease in Africa, to which HIV positive people are particularly vulnerable. Medical experts have expressed concerns that health infrastructures across the continent lack the capacity to detect or cope with the dangerous bacterium.

The scientists say that invasive non-Typhoidal Salmonella (iNTS) thrives in the blood systems of people in Sub-Saharan Africa whose body immunity is weakened by HIV/AIDS. This revelation adds yet another dangerous disease to the list of opportunistic infections plaguing HIV positive people in Africa.

According to a study by the Wellcome Trust Sanger Institute, a genomics research centre in the United Kingdom, the relatively new disease causes death in up to 45 per cent of those infected. It has spread from two focal points in Southern and Central Africa to the rest of the continent, reports the study, published in Nature Genetics last month (30 September).

The study found that iNTS also targets people whose immunity is weakened by other conditions such as malaria and malnutrition, both common in Sub-Saharan Africa.

The iNTS-causing bacteria, Salmonella typhimurium, has become resistant to the frontline antibiotics used to treat related blood-borne intestinal diseases.

"In many places in Africa, the basic microbiological facilities are not available, which makes diagnosis of iNTS difficult, as blood culture is the only definitive diagnostic for the disease," the Sanger Institute's Robert Kingsley, one of the authors of the study, told SciDev.Net.

Francis Nyamiobo, a research physician at the Kenya Aids Control Project, said that iNTS could be a major cause of death in HIV positive patients, but could go unrecognised due to "diagnosis challenges".

"Our greatest problem is making the diagnosis," Nyamiobo told SciDev.Net.

Scientists used whole genome sequencing to define a novel lineage of Salmonella Typhimurium, which is causing a previously unidentified epidemic across the region. They discovered that its genetic makeup was evolving into a more typhoid-like bacterium, able to spread efficiently around the human body.

From sequenced samples, the team created a phylogenetic or 'family tree', depicting the pathogen's evolution. This enabled them to date when each sample first emerged and overlay this with geographical information about where samples came from.

The scientists found that this invasive disease comprises two very closely related waves: the first wave originating 52 years ago from a possible south-eastern hub; and the second around 35 years ago, possibly from the Congo Basin.

Kingsley recommended further studies to establish whether the pathogen was being transmitted exclusively through humans or whether a zoonotic (animal) reservoir existed as well.

"We need to understand the transmission routes to address the hypothesis that this pathogen is behaving in a different mode from that we normally associate with NTS," he explained.

Link to full study

This article has been produced by SciDev.Net's Sub-Saharan Africa desk.


Nature doi:10.1038/ng.2423 (2012)

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