Fasting reduces viral susceptibility in oysters until energy depletion becomes detrimental

While abundant food supplies support host immunity, they may also fuel
pathogen proliferation, whereas food limitation restricts resources for
both host and parasite. The balance between these processes, and the
physiological limits to fasting as a protective strategy, remain poorly
understood. Here, we tested how the duration and timing of food
deprivation relative to pathogen exposure affect resistance to infection,
using the oyster Magallana gigas and its pathogen, Ostreid herpesvirus 1.
We used a cross-over design with two sequences differing in the timing of
starvation relative to infection. We hypothesized that (i) survival would
increase with fasting duration until a threshold is reached where energy
depletion becomes detrimental, and (ii) fasting would only protect when it
immediately precedes infection, because its effect relies on reduced host
metabolism. Consistent with these hypotheses, oysters fasted immediately
before infection showed increased survival peaking after 14-28 days,
followed by a sharp decline, while prior fasting with refeeding provided
no benefit. Biochemical analyses revealed that advanced protein catabolism
may underlie the tipping point where starvation shifts from protective to
detrimental effects on disease resistance.