It is worth noting that not all fevers are cyclical.

It is also worth noting that not all fevers are related to viruses, In fact, as much as you can generalize, viruses are less pyrogenic than bacteria or other parasites.

It is also worth thing that while chills and sweats may cycle, this is not related to core body temp in any consistent way.

One of the reasons why chills and sweats alternate is that pyrogens alter the actual temp set point in hypothalamus . So it is more akin to setting your thermostat on your central heating to 80 and setting your AC to be at 80 also.

It is also worth noting that in many bacterial infections that cause fevers, some or most of the pyrogens are released by your own immune system , these are not really related to bacterial reproductive cycles in many cases in any functional way.

So a lot of people here are explaining phenomena that don’t really occur are are not occurring the way they describe.

Malaria has truly cyclical fevers that are related to the blood levels of parasites .

However, people who survive malaria and have cleared infections often have periodic fevers.

Before antibiotics, many people who once had some kind of fever and survive, often had periodic fevers for most of the rest of their lives, in a way that would also be unrelated to cycles of parasite reproduction the way people are talking about it here. The biographies and autobiographies of the colonial era explorers and geographers and botanists are useful in this regard.