How bacteria affect appetite

Salmonella manipulates the host's appetite to their advantage

Kirill Stasevich, "Science and Life", based on materials Science: Microbe that causes food poisoning exerts a sort of mind control over mice.

Salmonella bacteria entering the human cell

Infectious diseases are usually accompanied by fever, weakness and loss of appetite: we do not want to eat anything, do anything and move at all. However, general apathy, in fact, is necessary for a successful fight against the disease: the immune system also needs some resources, if we are not too "active", then the more energy remains to the immune system.

As for the loss of appetite, the situation is not so clear. On the one hand, the less we eat, the less we feed the infection itself, on the other hand, food is not only needed by bacteria, and therefore a weakening of appetite can harm the patient himself; finally, factors that we have not even suspected until now may play a role here.

Researchers from the Salk Institute decided to find out how changes in the diet affect salmonella – rather unpleasant bacteria that often cause food poisoning. The experiments were performed on mice, for which salmonella is often just deadly. It turned out that the fate of sick rodents largely depends on a bacterial protein called SlrP: if the infection was started by microbes that do not synthesize SlrP at all, then for the mouse, most likely, everything will end very sadly. At the same time, animals with such salmonella ate 20% less than those with bacteria capable of synthesizing SlrP.

In an article in Cell (Rao et al., Pathogen-Mediated Inhibition of Anorexia Promotes Host Survival and Transmission) the authors write that in sick mice, the vagus nerve connecting the intestine to the brain worked differently – it transmitted signals suppressing appetite to the hypothalamus. But with SlrP protein, appetite was restored. And, if salmonella itself turns on and off the synthesis of SlrP, it will be able to manipulate the eating behavior of the host. What is the meaning of such games for bacteria here?

If a sick mouse eats little, salmonella begins to disperse from the small intestine, where they live at first, to other organs: the spleen, liver, etc. In this case, the disease is greatly aggravated, and the animal is likely to die. If the mouse eats a lot, then there is no exacerbation, salmonella live in the small intestine and periodically, together with feces, go outside, where they can infect someone else. On the one hand, when a microbe does not make attempts to take root firmly in the body, settling in different organs, it can be relatively easily cleaned out by the immune system. On the other hand, bacteria that quickly bring the host to death miss chances to capture, so to speak, new territories. By manipulating appetite with the help of SlrP, salmonella can achieve a "golden mean", at the same time being firmly held in the infected body and successfully infecting new hosts.

As you can see, sometimes loss of appetite and starvation act in favor of infection – at least in some cases; and it is not always worth listening to the "voice of nature" during the illness – this "nature" may not be yours at all, but the bacteria that has settled inside you and has its own views on you.

Obviously, for more effective therapy, it is necessary to imagine exactly how a particular pathogen relates to the fact that its host eats a lot or a little. It is possible that the new results will also help in the treatment of other diseases (including cancer), which are accompanied by loss of appetite.

Portal "Eternal youth" http://vechnayamolodost.ru  30.01.2017