ELECTRON MICROSCOPIC STUDY OF THE DISTRIBUTION AND THE VERTICAL TRANSMISSION OF RICKETTSIA TSUTSUGAMUSHI IN LEPTOTROMBIDIUM PALLIDUM

Abstract

Leptotrombidium pallidum naturally infected with Rickettsia tsutsugamushi was reared and bred in our laboratory for several generations by brother and sister mating. The larvae and adults at the 8th and 9th generations were sectioned and observed by electron microscopy for analysis for the distribution of rickettsiae in the mites. The distribution densities of rickettsiae were markedly different among organs in each mite, but rickettsiae were seen in all the organs and tissues. Rickettsiae were distributed in the highest density in the salivary gland of larvae, and in the salivary gland, excretory bladder, epidermal layer, ovary and testis of adult mites. Only a few rickettsiae were recognized in the muscle of both larvae and adults. On the other hand, we found, in the infected family line used, a significant number of mites in which no rickettsiae were found by electron microscopy. The grouping of rickettsia-positive and -negative mites according to the parent family revealed that the efficiency of vertical transmission of rickettsia was different from one parent family to another. Thus, it became clear that a significant number of rickettsia-negative mites are produced in an infected family line.