There is scarcely a single writer of the sixteenth, seventeenth, or eighteenth centuries on the subject of fevers, who has not commented on the concurrence of malignant fevers with epidemics of Oriental plague. It is true that they do not all identify the malignant fevers as typhus, simply because typhus, though distinguished as a morbid entity by Fracastorius as early as 1546, did not become generally recognized throughout Europe until the eighteenth century, and even then its identity was obscured under a multiplicity of synonyms. Ambroise Paré, in 1568, described a pestilential fever as prevailing in France along with true plague, in which the skin was marked with spots, like the bites of fleas or bugs. Vilalba says that on several occasions during the sixteenth century a spotted fever called Tabardiglio, which is now known to have been typhus, was rife in Spain at the same time as plague, and was much confused with it. According to Lotz a malignant spotted fever was present in London in 1624, which turned to plague in 1625, and back again to spotted fever in 1626. Similarly Sydenham states that the Great Plague of London was preceded and followed by a pestilent fever, which from his description was clearly typhus, and he remarks that it differed from the plague only in the milder character of its symptoms. According to Diemerbroeck spotted fever (typhus) preceded plague in Holland in 1636, and its malignity increased progressively, until finally it became converted into true plague. The same is true of the plague of Marseilles in 1720, of the plague of Aleppo in 1760, and of the plague of Moscow in 1771. Hancock, in 1821, asserted that nearly all the most remarkable plagues of the last two centuries had been preceded by typhus. So much for the confusion of these two diseases, due to their concurrence.
Murchison, whose treatise on typhus stands out as a monument of acute and accurate observation, traces out in detail the resemblance of the two diseases. It is no matter only of a general clinical resemblance, such as is common to most acute infectious fevers, though that is striking enough, but beyond this there is a remarkable similarity in particular symptoms, in clinical course, and in complications. There is a tendency to regard buboes as a distinctive feature of plague, but these are found in a small moiety of cases of typhus fever. On the other side of the picture, the petechial eruptions of typhus, its most distinctive feature, are common enough in plague.