Failure of Ixodes ticks to inherit Borrelia afzelii infection.

To define conditions promoting inherited infection by Lyme disease spirochetes in Ixodes ticks, we variously infected ticks with Borrelia afzelii and examined their progenies by dark-field microscopy, immunofluorescence, PCR, and serial passage. No episode of inherited infection was evident, regardless of instar or gender infected or frequency of exposure. We suggest that these spirochetes rarely, if ever, are inherited by vector ticks.

An ultrastructural study of vertical transmission of Rickettsia tsutsugamushi during oogenesis and spermatogenesis in Leptotrombidium pallidum.

Rickettsia tsutsugamushi in Leptotromibidium pallidum was observed by electron microscopy and rickettsiae were found in the various tissues and 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 adult females and eggs after oviposition contained the microorganisms. In adult males, rickettsiae were also found in the spermatogonia, spermatocytes, and spermatids in the early stage of spermatogenesis, but were eliminated from these cells during maturation. Only the maturing spermatids, but not the eliminated rickettsiae, migrated to another rickettsia-free area of the testis, resulting in the separation of spermatids from rickettsiae and in the production of rickettsia-free spermatophores. Based on these observations, the mechanism of vertical transmission of the rickettsiae to the progeny occurs only in the female parents. Most rickettsiae in the somatic cells of larvae and adults were coccoid, but some rickettsiae in the ovary and the testis of adult mites showed bacillary forms and were enveloped by a membrane of unknown origin.

Rickettsiae-like microorganisms in the midgut and other visceral tissues during development of Drosophila auraria.

Rickettsiae-like organisms (RLOs) were identified for the first time in midgut, Malpighian tubules, wreath cells (ventral nephrocytes), spermatogonia and gut muscles in a species of Drosophila. Their number in the midgut cells of Drosophila auraria significantly increased at the late third larval instar and at the beginning of pupation. The RLO population in the larval midgut followed the fate of their host cells and was destroyed during metamorphosis. The RLOs pass from the larval to the adult midgut via the RLOs existing in the 'regenerative cells', which will form the adult midgut during population. The total volume of RLOs per anterior midgut cell increased analogically in relation to the absolute volume of the host cells till the 130 h larval stage. However, during the late-third instar and at the beginning of pupation the total volume of RLOs per host cell significantly increased. The physiological significance of the latter data as well as the relationship between RLOs and host cells are discussed.

Transovarial transmission of Rickettsia tsutsugamushi in Leptotrombidium pallidum successively reared in the laboratory.

Engorged larvae of Leptotrombidium pallidum were collected from a wild rodent, Apodemus speciosus, and reared in a plastic container fed with fresh eggs of colembolla, Sinella curviseta, under moist conditions at 25 degrees C. Fully developed adults were separated into individual containers and a proven male was paired with a suspected female. Of the pairings, 38 produced larvae and 4 infected colonies were established. Females in these colonies were shown to be infected with Karp type of Rickettsia tsutsugamushi (Rt) by the method of isolating Rt from individual mites using mouse passage. Males were negative for Rt. Vertical transmission of Rt was monitored in each infected colony. The female of parent generation (P) produced F1 and F2 generations. At F1 generation, 11 males and 12 females maintained until production of eggs and all adults were positive for Rt by detection from individual mites. By sibmating of F1 adults, 11 males and 14 females developed at F2 generation and all males and females were proven to be positive for Rt. From 4 pairs of infected males and infected females at F1 generation, 2, 5, 21 and 35 larvae were collected as samples, respectively, and all larvae were positive for Rt by individual detection. Spermatophores from infected males at F2 generation were examined for Rt and none of 29 spermatophores were positive for Rt. From these results, the transmission rate of Rt from P to F1 and from F1 to F2 was 100% through eggs from infected females but not through spermatophores from infected males.

Sexual transmission of spotted fever group rickettsiae by infected male ticks: detection of rickettsiae in immature spermatozoa of Ixodes ricinus.

Electron microscopic evidence is provided showing that the newly described "Swiss agent," a spotted fever group rickettsia, is incorporated into the reproductive cells of its male tick vector, Ixodes ricinus. Rickettsiae were found in spermatogonia, spermatocytes, and maturing spermatids. The potential significance of these observations is briefly discussed in relation to published data on sexual transmission of rickettsiae by ticks.