Organon §243

Isolated cases of intermittent fever are often due to psora on the point of development. 

There are cases of intermittent fever that befall single individuals outside of marshy regions [where such fevers are endemic]. These are often very virulent. In these cases, treatment should be started by using, for several days, a general remedy from among the proven medicines, not an antipsoric. (This is how acute cases in general should be treated, which these fevers resemble with respect to their psoric origin.) If, after several days, recovery is nevertheless delayed, it means that this is a case of psora on the point of its development. Only antipsoric remedies can provide thorough [fundamental] help.