Studies on Rocky Mountain spotted fever / U.S. Treasury Department, Public Health Service.

Date:
[1930]
Catalogue details

Licence: Public Domain Mark

Credit: Studies on Rocky Mountain spotted fever / U.S. Treasury Department, Public Health Service. Source: Wellcome Collection.

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    Inasmuch as the virus in the serum of animals infected with Rocky Mountain spotted fever can be thrown down only partially by high-speed centrifugation, one can not hold the view that the) retention of the virus by both red and white cells (normal and. infected) after slow contrifugation is due to the possession of the| same specific gravity by the cells and virus. It is unlikely that the specific gravity of the virus would be such that it stratifies at the same level of both red and white cells. Furthermore, when mixed with a suspension of fuller’s earth or charcoal and subjected to the same washing procedure it is not thrown down along with these particles. The test strongly suggests, therefore, that part of the virus remains lodged within or adherent to the cells. In a cytological study of rickettsiz in tissues of guinea pigs in- fected with Rocky Mountain spotted fever, Nicholson (Nicholson, 1923) says: “In some tissues it required several hours’ search with the aid of a mechanical stage and in others a day or more to find them * * *. In several cases also, they appeared to be present within erythrocytes.” As illustration, he gives a single figure which bears the title, “ One rickettsize apparently within an erythrocyte.” Fricks (Fricks, 1916a) has described, in the centrifuged red blood cells of infected animals, “ round or slightly elongated red chromatin bodies partially surrounded by or in close approximation to a some- what larger deep-blue staining body.” Such bodies were never found in control specimens. Fricks suggested that these bodies were of protozoan nature, but hesitated to draw definite conclusions from his findings. We are inclined to regard as highly significant the fact that, in the examination of hundreds of specimens of infected blood, rickettsiz could not be demonstrated by us within erythrocytes, and yet the infective agent could not be washed or diluted away from such cells. The difficulty with which rickettsie are demonstrated microscop- ically in tissues of infected animals is not compatible with the gen- eral intense plasmatic and systemic infection as shown by animal inoculation, although we realize the possibility that a single organism or very few organisms may be infective. It seems likely, however, that the few rickettsie (Dermacentroxenus rickettsi Wolbach) found represent, in part, one phase of the infective agent, but they do not convincingly represent all known manifestations of the blood virus. In this connection it may be stated that one receives the same im- pression when a study is made of the presence and distribution of rickettsiz in the tissues of infected ticks. Our tests might be regarded as suggesting that the virus of Rocky Mountain spotted Foren can assume in the mammalian host a phase which can not be demonstrated to the eye by methods thus far used.