Endemic typhus fever in Texas shows but few differences from the same form of the disease in the southern states. It is characterized by its fourteen-day duration, its freedom from complications and sequellae, and its low mortality rate. It apparently spares infancy, childhood, and old age. The majority of the cases occur among workers of the middle class. Its preponderance in this group, particularly in males, appears to be concerned with the occupational background of the disease in that a great majority of the cases originate in shops, grocery stores, grain depots, and warehouses where rat infestation is quite high. At the same time, a considerable number of cases occur among members of the lower social strata whose homes and places of employment show the same degree of rat infestation.
Endemic typhus fever in Texas seems to be almost identical with the clinical manifestations of tropical (Malayan) typhus. At the same time, certain distinctions obtain: difference in vector; and failure of the serum of Texas cases to agglutinate the anindologenic strain of Proteus. In addition to the exhibition of established differences between this, the endemic and the epidemic form of typhus, the disease in the American southwest appears to show certain very definite clinical and epidemiological differences from Brill's disease however similar the two are immunologically. A summary of these differences is presented to support an argument for a complete distinction between Brill's disease and endemic typhus fever.