By consuming more food during infection, the hosts were able to prolong survival, which worked in favor of the Salmonella
. Through feces, the Salmonella
were able to spread to other animals, thus, increasing its transmission to a number of hosts, something that the bacteria would not have been able to do if the mice did not eat and “died sooner due to heightened bacterial virulence.”
So, how are the bacteria able to inhibit the appetite loss response? According to Rao, “in the intestine, the bacteria Salmonella
inhibits a specific cytokine, known as SIrP, and this SIrP, can transmit signals to the brain. The brain then induces this loss of appetite and causes this anorexic response. So, the Salmonella
basically inhibits this process, or slows down this process from occurring.” The researchers found that infected mice who could not make SIrP consumed less food, and thus, lost more weight and perished faster.
Although “the same gut-brain pathway” linked to loss of appetite also exists in humans as it does in mice, Dr. Ayres noted that responses to infection depend on a number of different factors. The impact that appetite loss has on an individual’s health during illness is dependent mainly on whatever the causative agent of the infection is.
In order to learn more about this link between appetite loss and infection, Dr. Ayres and her team want to look more closely at the human microbiome and identify other microbes that may affect the gut-brain pathways in a similar way. Through this exploration, the researchers hope to use their findings to inform new therapies related to appetite loss.
When speaking of the implications of their work, Dr. Ayres said, “This has a number of potentially important implications for human diseases. Again, we know that the anorexic response is a very common response in infectious diseases in humans and also cancer, inflammatory conditions, [and] the aging population; it’s also a very serious response or consequence of current medical interventions that we have. For example, chemotherapy causes an anorexic response.” She continued, “Understanding this gut-brain axis and how this is regulating appetite provides us [with] a means where we can go in and manipulate the gut-brain circuitry to perhaps inhibit the anorexic response in these patient populations.”
In addition, the research also may offer an alternative avenue when it comes to the treatment of infectious disease, one that uses nutritional intervention rather than antibiotics. With more than two million individuals infected each year by strains of bacteria that have managed to develop resistance to antibiotics, an alternative treatment option could really be a game changer in the fight against antibiotic resistance.
Editor’s Note: Read more about how bacteria creatively manipulate their hosts here.
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