During the afebrile period the parasites disappear from the peripheral circulation.
If the disease is first seen during the afebrile stage we may try Lowenthal’s reaction, which consists in taking a drop of the blood of the suspected patient, mixing it on a vaseline ringed slide with the blood of a patient showing spirochaetes, then covering with a cover-glass and incubating for thirty minutes at 37°C. A positive reaction shows clumping and loss of motility of the spirochaetes.
Reports vary as to the white count but on the whole there would seem to be more evidence in favor of a moderate leucocytosis although some observers have noted a fall from the normal. The usual statements give a leucocytosis of from 12 to 15 thousand with a polymorphonuclear increase to between 75 and 80%. The statement is usually made that the normal percentage of large mononuclears helps in the differentiation of malaria. Kieseritzky has reported leucopenia and slight increase in lymphocytes.
The leucocyte count tends to be higher about the time of crisis.
Weil’s Disease.—This spirochaete infection is due to Leptospira icterohaemorrhagiae. The spirochaete has been found in the blood and has possibly been cultured anaerobically from the blood. The practical method is by inoculating guinea pigs with blood or urine sediment. Spirochaetes are found in the liver smears of the sick guinea pigs. In the first week of Weil’s disease we have a leucocytosis—later on a leucopenia.
Filariasis.—The sheathed embryos of Filaria bancrofti are found in the peripheral circulation at night only, hence F. nocturna, while those of F. loa are only to be found in the daytime, hence F. diurna. In the islands of the South Pacific the filarial infection is considered as of F. bancrofti but the embryos are present in the peripheral circulation both by day and by night.
Instead of being uncommon it seems rather to be the rule to fail to find embryos in the blood preparations in cases showing marked evidences of filarial disease, as in elephantiasis, calabar swellings, etc. The positive blood findings are most frequent in those who do not as yet show symptoms. There has not yet been sufficient obstruction in the lymphatics to keep the embryos from reaching the blood stream.
In some countries where a large percentage of the population may show embryos in the peripheral circulation, manifestations of the disease are very rare.
We may examine the blood either with fresh preparations, when the movements of the embryos assist in their detection, or by staining dried smears. Haematoxylin staining is better than the Romanowsky one as the break in cells and other points are better brought out.
An eosinophilia is usually considered as constantly present but this is not invariable. The leucocyte count is about normal.