There are very few tropical diseases which have not been mistaken for malaria and many of these have been considered as of malarial etiology before the discovery of the real cause.
Of the cosmopolitan diseases, typhoid fever, septic conditions, including malignant endocarditis, tuberculosis, influenza, pyelitis and even syphilis are to be considered in a diagnosis of malaria.
As regards tropical diseases, kala-azar, Malta fever, liver abscess, filariasis, trypanosomiasis, leprosy, relapsing fever and yellow fever are to be thought of in differential diagnosis.
As was noted under the discussion of the pernicious manifestations of malaria, scores of diseases may be simulated by the sporulation of the malarial parasite in certain organs or areas of organs. One should always keep in mind the possibility of pain in the appendix region or in the gall bladder area as connected with malaria if in the tropics. A polynuclear increase negatives malaria and indicates appendicitis or cholecystitis. Malarial pancreatitis has been referred to before.
Fig. 22.—A cluster of blood-plaques and two plaques lying upon a red cell and simulating malarial parasites (× 1000). (Todd.)
With malarial cachexia we must in particular keep from mistaking it for hookworm disease or other secondary anaemias due to intestinal parasites.
Provocative Measures.—Kohlbrugge’s recommendation to have patients suspected of malaria climb mountains and drink copiously of cold water, in order to bring on a relapse, is of value in the diagnosis. (Effects of fatigue and refrigeration.) It must always be borne in mind that quinine causes the parasites to disappear from the peripheral circulation. It is interesting to note that small doses of quinine given over ten days or two weeks may make a latent case active. Other provocative agents are subcutaneous injections of adrenalin (the best), or anti-typhoid inoculations. Certain physical methods, as hot and cold douches or alternating the hot air chamber at 55°C. for 10 minutes, followed by a cold bath for 3 minutes have been recommended. After injection of adrenalin the presence of parasites in the blood is at its height at the end of an hour. Sunlight is a factor in relapse.
The laboratory diagnosis of malaria has already been fully gone into in the section on etiology and that on blood examination under the heading of symptoms in detail.