BORRELIA-BURGDORFERI IN REPLETE NYMPHAL IXODES-RICINUS - A LOCALIZATION STUDY USING LIGHT AND ELECTRON-MICROSCOPY

The ticks examined were in the early middle to middle pre-moulting per iod corresponding to the nymph-pharate adult transitional phase. Altho ugh Borrelia burgdorferi could be found intracellularly within Malpigh ian tubule, ovarian and syncytial muscular tissues, the spirochaete wa s predominantly located in the extracellular sites associated with dif ferent organs. A large number of borreliae were observed in the very n arrow endoperitrophic space resulting from the peritrophic membrane at rophy in systemically infected nymphs at day 15 after a non-infectious blood meal. This observation indicates that some spirochaetes in the midgut lumen of unfed nymphs are enveloped within the endoperitrophic space once the peritrophic membrane occurs and/or condenses and surviv e there at least until ticks begin to enter pharate stage of the adult . The absence of B. burgdorferi from the ectoperitrophic space in syst emically infected early middle to middle moulting nymphs suggests that spirochaetes persisting in this space may become systemic thereafter. The detection of borreliae only in the narrow endoperitrophic space o f a male nymph at day 15 after repletion indicates that all pre-feedin g midgut spirochaetes may be enclosed in this space when the peritroph ic membrane appears and/or condenses, and the peritrophic membrane may become a barrier preventing spirochaetes from penetrating the midgut epithelium.