Dengue may be suspected, but the leucopenia, lack of splenic tenderness, lack of tendency to vomiting and presence of post-orbital pains should differentiate. As there is a leucocytosis in both relapsing fevers and smallpox, and similar headache and backache, confusion might exist were the parasites not found.
Yellow fever has many features in common with the bilious type of relapsing fever, but there is no leucocytosis in yellow fever, and there is no characteristic albuminuria and slow pulse in relapsing fever. Influenza has many points in common with relapsing fever.
In a case of relapsing fever with jaundice confusion might arise with Weil’s disease inasmuch as a blood smear might show spirochaete-like organisms.
Typhus fever shows a less abrupt onset and the marked mental symptoms (stupor) and dark macular eruptions about the trunk, on the 4th to 6th day, should differentiate. If the case is first seen in the apyrexial period one may take a drop of blood from a case showing spirochaetes and one from the suspected patient. After incubation for thirty minutes the spirochaetes should lose motility and agglutinate if the case be one of relapsing fever (Lowenthal’s Reaction).
In blood examinations we may use the dark-field illumination, although the spirochaetes stain readily with Wright’s stain. The India ink method is a good one. Hagler recommends smearing out a mixture of one loopful of blood and a collargol preparation made by diluting one part collargol with two parts water. The diluted collargol should stand 24 hours and be filtered before use.
Prognosis
The mortality is usually given as about 2 to 5% with the exception of the very serious form in which jaundice is present when the death rate may exceed 50%.
A serious feature of the disease is the length of its course, this often extending from six weeks to two months.
Since salvarsan and neosalvarsan have been found to be practically specifics in the treatment of the disease the mortality has been reduced to exceedingly low figures.