Diagnosis
Clinical Diagnosis.—It is well to remember that we have a sure and simple means of diagnosis by bacteriological means so that in the first cases during an epidemic we should rest the determination of the case as one of plague solely upon such methods.
One should be suspicious of any case of fever of rapid onset in which there is marked dulling of intellect and impairment of speech, as of one intoxicated, together with evidences of rapidly developing heart weakness. In septicaemic plague we practically have no other symptoms to guide us—there is not the exquisitely tender bubo of bubonic plague nor the abundant, watery, sanguinolent sputum of pneumonic plague.
Typhus fever probably more nearly resembles plague at its onset than any other disease. There is marked clouding of the consciousness and intense prostration as with plague and the eruption does not appear before about the fourth day.
An influenza pneumonia may show the general prostration and cardiac weakness of plague. In influenza pneumonia we have an onset with the features of ordinary influenza, which, however, in the influenza epidemic in 1918 was often short. In plague pneumonia we have pneumonia from the start. The pulse in plague is early weak and rapid and the tendency to a stuporous state more marked. The early appearance of thin watery sputum, which quickly becomes blood-tinged and always contains plague bacilli is noted in plague pneumonia. Only a few hours elapse before we have bloody sputum which in influenza is a later and not constant sign. The dyspnoea is earlier and much more pronounced in the pneumonic plague. At autopsy Crowell notes the almost invariable presence of pleural exudates in plague while an acute vesicular emphysema is a feature of influenza pneumonia.
Malaria and septicaemic conditions may be confused with septicaemic plague. The sudden onset and prostration of relapsing fever may make one think of plague.
Many have thought climatic bubo a form of ambulant plague but the gradual onset, only slight tenderness of the swollen glands and slight prostration should differentiate. Venereal bubo cases are apt to be regarded with suspicion during epidemics.
Markedly toxic cases of typhoid fever with an exceptionally rapid onset may give rise to confusion.
Laboratory Diagnosis.—If the patient has a bubo we should introduce a hypodermic syringe needle into the swollen, oedematous glandular mass in order to obtain some of the gland juice. Smear a drop of this on a slide, stain with Loeffler’s blue or dilute carbol fuchsin and examine for bipolarly stained oval bacilli. When the bubo begins to soften we may not obtain plague bacilli.