Theory 041/Medicine & Health /Host defence
Fever Works by Kinetics
Fever is either helpful or harmful in arguments that assume monotonicity. It may be a window.
Fever improves host defence by shifting immune reaction rates rather than by directly harming pathogens, so the benefit should appear only within a narrow temperature band and disappear at both extremes.
01The evidence
Antipyretic use does not reliably improve outcomes and may prolong some infections, while extreme fever is clearly harmful.
02The tension
Fever is treated as a symptom to be controlled, with the decision driven by comfort and by the risk of febrile seizure. The possibility of an optimum temperature is rarely modelled.
03The mechanism
Immune reactions, like all chemical reactions, accelerate with temperature. Phagocytosis, cytokine production and lymphocyte proliferation all have temperature optima in the febrile range.
Above that range, host cell function degrades faster than pathogen fitness, so the net benefit falls. That produces a window, with an optimum inside the febrile range rather than above it.
04What this is not
Those models treat fever as a cost to be minimised. This treats it as a rate optimiser with a window.
05Predictions
- P1Outcomes should be best at intermediate fever.
- P2Antipyretics should prolong infection at low fever.
- P3The optimum should shift with pathogen growth rate.
06Refutation
Monotonic benefit or harm across the febrile range would remove the window.
07What it changes
It would change when antipyretics are given.