A complement-fixing antigen specific for scrub typhus occurs in the body fluids and tissues of infected mice, white rats, and cotton rats.
The specific serological substance is demonstrable only in those animals which develop a rapidly fatal disease after an incubation period of a few days. Such an experimental infection is induced in mice and rats by the intravenous injection of suspensions of yolk sac rich in R. orientalis.
Ether extraction is an important step in the preparation of a complement-fixing antigen from tissues of mice dying with scrub typhus.
The Imphal No. 8 and Calcutta strains of R. orientalis are indistinguishable on the basis of complement fixation and cross-immunity tests.
The complement-fixing antigen in body fluids of infected mice and rats and in our preparations of tissues from such animals occurs as a soluble antigen. Under the proper conditions the soluble antigen can be stored or dehydrated without loss of serological activity.