V. Evaluation of Cross-Immunity against Type 1 Dengue Fever in Human Subjects Convalescent from Subclinical Natural Japanese Encephalitis Virus Infection and Vaccinated with 17D Strain Yellow Fever Vaccine
The quantitative susceptibility of native and standard laboratory rodents to infection with Rickettsia rickettsii was determined using the development of spotted fever group complement-fixing (CF) antibody as the criterion for determining infection. Most species of rodents were moderately to highly susceptible to infection, while two species appeared to be comparatively resistant to infection.
The development and persistence of rickettsemia in inoculated rodents was investigated. In most rodents a rickettsemia developed within two days and persisted for up to 16 days after the inoculation of R. rickettsii. The correlation of susceptibility as determined by CF antibody response with susceptibility observed by the development and persistence of rickettsemia was discussed. Of the many species of rodents tested, only one, the bushy-tailed wood rat, appeared to be highly resistant to infection as determined by the methods used.
In eight species of rodents tested there was no tendency to develop a latent infection as all rodents had cleared the rickettsiae from their tissues by the fourth week after inoculation of R. rickettsii, as determined by the method employed.
The development and persistence of spotted fever group CF antibody was observed in seven species of rodents. Peak titers occurred during the 2nd to 4th week after inoculation and low levels were detectable in most animals several months after inoculation.
Present address: Department of Microbiology, The Lovelace Foundation for Medical Research and Education, Albuquerque, New Mexico 87108.