Observations on the ultrastructure and distribution of Rickettsia tsutsugamushi in naturally infected Leptotrombidium (Leptotrombidium) arenicola (Acari : Trombiculidae) [Scrub typhus]

Larval and adult L. (L.) arenicola mites naturally infected with R. tsutsugamushi were examined by electron microscopy. Rickettsiae were found in all tissues except muscle. Salivary glands of larvae, and ovaries and gastric caecae of 60-day-old adults were the most heavily infected tissues. Extracellular rickettsiae were not noted. Larval gonadal tissues were also infected. Elongate rickettsiae up to 4.0 mu m long with bundles of microtubules 18.0 nm in diam and 340.0 nm long at their poles were seen in epithelial, nervous, and ovarian tissues.