Feed a cold, starve a fever is bad advice, new study suggests

A new study has found that it may be down to the bacteria itself altering signals in the brain.

Containing an infection made it easier to treat, according to experts. However, she stressed that the host is only part of the host-pathogen equation, and that one limitation of previous studies is that they have not examined how the host's loss of appetite affects the pathogen's behavior and its ability to cause disease.

The study, conducted at the Salk Institute in California, had mice infected with the bacteria Salmonella Typhimurium.

What they say: Many people, including some pediatricians, believe that dairy products increase mucus production, therefore prolonging a cold.

But people who didn't know which milk they were drinking reported the same (minimal) effects.

"What we found was that appetite loss makes the Salmonella more virulent, perhaps because it needs to go beyond the intestines to find nutrients for itself", explained Sheila Rao, the first author of the study published in Cell. When infected, and the mice lost their appetite, the bacteria actually became more virulent, spreading outside of the intestines and into other tissues.

'The trade-off between transmission and virulence has not been appreciated before. This increased virulence kills its host too fast, which compromises the bacteria's ability to spread to new hosts. The bacteria in mice which did not eat was more virulent but the mice died sooner as a result, preventing its transmission.

Indeed, it was found that in the mice that kept their appetites and survived, Salmonella was released in their feces where it could spread to other animals.

The actual mechanism for this process was a molecule produced by the Salmonella called SIrP.

The bugs did so by producing a molecule called SlrP which keeps an immune protein known as a cyotikine from becoming active in the intestines.

"It's always been known that infections cause loss of appetite but the function of that, if any, is only beginning to be understood", says Janelle Ayres, assistant professor at Salk Institute's Nomis Foundation Laboratories for Immunobiology and Microbial Pathogenesis.

Docs now want to explore if appetite-boosting drugs could be used to treat other illnesses which trigger a loss of appetite.

The old adage "feed a cold, starve a fever" may seem like sensible advice but research indicates that those suffering from the latter could experience a more speedy recovery if they do not forgo food after all - though it could also increase the likelihood of transmitting a bug to other people.

"Now that we'd identified this mechanism that regulates appetite, we want to turn it on the flip side and see if we can decrease appetite...to help in cases of metabolic disease", Ms Ayres said.

The discovery could also to the possibility of treating infectious diseases with approaches other than antibiotics, such as nutritional intervention. "Finding alternatives to antibiotics is incredibly important as these drugs have already encouraged the evolution of deadly antibiotic-resistant strains", says Ayres.