Rickettsia-like microorganisms in the ovarian primordial of molting Ixodes ricinus (acari : ixodidae) larvae and nymphs

A large number of coccoid, or oval to spindle-shaped rickettsialike microorganisms are detected intracellularly within the primordial ovaries of all examined molting larvae and nymphs, descendants of a female Ixodes ricinus collected in a forest near Neuchâtel, Switzerland, and within all molting nymphal I. ricinus captured as starved ticks in the same area. The morphology of the microorganisms is identical in all ticks. They measure 0.3-0.4 µ m in diameter and 0.6-1.3 µ m, occasionally up to about 2.5 µ m in length. The microorganisms possess a highly rippled membranous outer cell wall and an inner plasma membrane. Both cellular boundaries show a thickness of approximately 6-10 nm. The microorganisms are always enclosed, singly or in groups, within membrane limited vacuoles of host cells, within vacuolated mitochondria, or within vacuoles with their wall consisting partially of a deformed mitochondrion and partially of a plasma membrane of host cells. With the advance of the development of the nymphal ovaries, the groups of microorganisms associated with mitochondria become larger and increase in number, and they are dominant within the posterior part of the organs in the nymphs examined at day 21 after repletion. The relationship between the microorganisms and the mitochondria is discussed. The morphology of the gonads of the examined immature ticks is also described.