The increased number of infections that afflict elderly and ill people may be due to an internal 'microbiome mutiny,' writes Carl Zimmer at the Loom.
He notes that most common explanation for why older people get sick more easily is that the immune system weakens as people age. But, Zimmer adds, researchers in Hungary have instead suggested that the microbiome might somehow be able to tell that its host is in declining health, whether from age or a health condition, and switch from a benign mode to a more virulent one.
In Biology Direct, Viktor Müller from Eötvös Loránd University and his colleagues write that such a change would increase the bacteria's changes of being transmitted to a new host. A number of observations seem to support their hypothesis, they say. For example, herpesviruses are often reactivated in older people; older people suffer more from diarrhea; and older people or people with type I or type II diabetes are at greater risk of developing opportunistic infections.
They further hypothesize that microbes might be able to tell that their host's health in decline through by detecting increased oxidative stress or other markers of senescence and, in cases of disease or injury, by detecting inflammation markers.
"Evolutionary theory suggests that increasing mortality might increase the optimal virulence of a symbiont: killing the goose that lays the golden eggs might not be such a bad idea if the goose is going to die soon, anyway," Müller and his colleagues write.