Salmonella Strain Spreads Alongside HIV

Researchers find that a deadly bacterial disease hitchhikes in people infected with the virus that causes AIDS to spread throughout sub-Saharan Africa.

By | October 1, 2012

Scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cellsCredit: Rocky Mountain Laboratories, NIAID, NIH

A lethal form of Salmonella prevalent in sub-Saharan Africa may have evolved to take advantage of weaknesses in the immune system created by the emergence of HIV, according to a report in Nature Genetics released this week (September 30).

A relative of the Salmonella commonly linked to cases of food poisoning, this strain—known as invasive nontyphoidal Salmonella (iNTS)—is spread from person to person and kills up to half the adults it infects. But little is known about how it became so widespread throughout sub-Saharan Africa in the past 50 years.

So researchers at the Wellcome Trust Sanger Institute in Cambridge, UK, sequenced the genomes of 129 isolates of Salmonella typhimurium—the most common cause of the disease—collected from seven African countries between 1988 and 2010. Organizing them into family trees, they found two distinct lineages that emerged and spread in ways that overlapped the spread of HIV. And when compared to strains that cause gastroenteritis or typhoid, the iNTSs were less genetically diverse, which suggests they were introduced only a few times and spread through human populations. “It's remarkable that these are such tightly grouped sets of organisms, and it's quite clear that it's an epidemic,” molecular microbiologist and leader of the research team Gordon Dougan told ScienceNOW.

Many scientists had thought that iNTSs jumped from animals to humans and then died off, as did other nontyphoidal strains. But this study suggests that these two lineages underwent genetic changes that allowed them to jump between people. It also indicates that their spread followed a similar geographic and temporal pathway as that of HIV.

The authors suggest that these deadly strains became an epidemic because HIV opened up a niche, though critics argue that such a thesis relies on several assumptions. “It's great to suggest the possibility that there's a causal relationship, but at the end of the day this is pretty classic correlation," Michael Worobey, an evolutionary biologist at the University of Arizona in Tucson, who was not involved in the study, told Science. "It's really quite possible that the dating [of when these lineages first surfaced] is off by enough so that [causal argument] doesn't make sense.”

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Avatar of: AlanB


Posts: 16

November 21, 2012

There is also quite a lot of literature on retroviruses including HIV being stimulated by bacteria, ie bacterial LPS, and in AID's, it has been found that a core problem is that the gut loses its integrity and cannot prevent bacterial translocation into the body, further, that in HIV infection the extent of bacterial translocation was more correlated to AID's symptoms than HIV titres, even when retroviral therapy lowered titres to virtually undetectible levels the AID's symptoms could persist, in proportion to that translocation.  A lot would also depend on how advanced the illness was ie in brain damage and active infection in the CNS, I'm sure, but nevertheless a strong correlation was reported. HIV damages the gut and allows bacteria to translocate into the blood and other tissues. The abnormal gut colonisation enables normally non-competitive pathogenic strains to take hold, over normal non-pathogethic bacteria, as could the wider distribution into other tissues resulting in further persistence and auto-reinfection. One reason why the abnormal colonisation favours more bad bugs is that the pathogenic strains are held back by having to produce bacterial toxins, immune disrupters and defenses from attack, which the good bugs dont need to do, at least  nearly as much, saving them energy and causing them to out populate the 'bad guys', and also gut inflammation reduces nutrient exchange to the bacteria, which are here causing the infection, but otherwise hampered as a result. The other inhibitory effects to organisms like salmonella, from the normal healthy flora like lactic acid bacteria and beneficial ecoli are lost due to gut inflammation and injury.  Bad bacteria and other bad organisms also may establish in the gut and disturb immune defenses against other bad bacteria, ie via 'Super-Antigen' production, and that prevents the immune system from propperly maintaining the flora, but also encourages the immune system to attack the body ie via production of auto-immune antibodies. Inflammation and tissue damage seems to be able to facilitate some pathogenic bacterial growth in the gut lining and in the blood stream, for example anti-inflammatories and iNOS inhibitors can help our bodies clear sepsis and persistent local infections, whilst inflammation so existing and also resulting from success of pathogenic bacterial strains contributes the very damage known to trigger replication of multiple viruses associated with AID's including HIV.  So I would expect (and already predicted) that immunally comprimised people with abnormal colonisation and persistant infections are harbouring multiple dangerous strains and acting to facilitate their evolution and spread in the populace, so that certain subsets of the population with chronic problems were where the future viruses, 'superbugs' and pathogenic strains and phages were going to come from.  The same problem exists in agricultural animals, where routine antibiotic treatment and other factors have led to abnormal colonisation in their bodies and in fact the superbugs we associate with people, generally are being carried and evolving in agricultural animals, and spreading back to us via contaminated meat - in recent tests, nearly all meat contains at least one antibiotic resistent 'superbug'.  Agricultural animals also are, quite apart from swine flu and numerous other often recently discovered possible human pathogens, the main reservoirs for malaria, which is why mosquito nets are not enough to erradicate it.  In the future, a lot more effort is needed to be applied to farm animals to protect humans, and it seems antibiotic feeding has generally evolved the resistent superbug population, rather than human antibiotic use. Having less livestock, more isolated and better housed/fed/medicated and monitored livestock (with use of probiotic strains for their GI tract), and rotating areas to be periodically free of all livestock, will help eradicate many of these risks.


Avatar of: AlanB


Posts: 16

November 21, 2012

-that also makes sense wrt particular bacterial strains that dont colonise farm animals, being the ones most correlated to immunocompromised people.

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