A temperature curve and gross pathology more or less typhus-like have been observed in natural Toxoplasma and Salmonella infections and have been produced experimentally by inoculations of Salmonella and Proteus X 19 cultures in guinea pigs. These infections could be transmitted in series through guinea pigs.
Proteus X 19 strains only were agglutinated by typhus immune serum. None of these infections confer immunity against typhus or Rocky Mountain tick fevers. Spontaneous intercurrent infections with the Toxoplasma or the Salmonella strains may kill off and replace typhus strains in guinea pigs unless the purity of the virus is controlled by cultures made at each transfer.
The development of a typical temperature curve and gross pathology of typhus in guinea pigs following the inoculation of suspected blood and the ability to transmit such an infection in series is not diagnostic of typhus unless confirmed by cultures or histological examination of the experimental animal, or agglutination tests of Proteus X 19 with the suspected blood.