AN ULTRASTRUCTURAL-STUDY OF VERTICAL TRANSMISSION OF RICKETTSIA-TSUTSUGAMUSHI DURING OOGENESIS AND SPERMATOGENESIS IN LEPTOTROMBIDIUM-PALLIDUM

Rickettsia tsutsugamushi in Leptotrombidium pallidum was observed by e lectron microscopy and rickettsiae were found in the various tissues a nd organs of both larvae and adults. Budding of rickettsiae, a manner of release from the host cells, was observed only in the rudiments of the reproductive organs in larvae. Oogonia and maturing oocytes in adu lt females and eggs after oviposition contained the microorganisms. In adult males, rickettsiae were also found in the spermatogonia, sperma tocytes, and spermatids in the early stage of spermatogenesis, but wer e eliminated from these cells during maturation. Only the maturing spe rmatids, but not the eliminated rickettsiae, migrated to another ricke ttsia-free area of the testis, resulting in the separation of spermati ds from rickettsiae and in the production of rickettsia-free spermatop hores. Based on these observations, the mechanism of vertical transmis sion of the rickettsiae to the progeny occurs only in the female paren ts. Most rickettsiae in the somatic cells of larvae and adults were co ccoid, but some rickettsiae in the ovary and the testis of adult mites showed bacillary forms and were enveloped by a membrane of unknown or igin.