Ultrastrukturen Und Cytochemie Der Pellikula Und Des Apikalkomplexes Der Kineten Von Babesia Bigemina Und Babesia Ovis In Hämolymphe Und Ovar Von Zecken*,†

Abstract

The term kinete is used in this paper for the cigar-shaped, motile development stages (vermicule) of Babesia occurring intra- and extracellularly in hemolymph and ovary (including oocytes) of vectors, hard ticks (Ixodoidea). The structure of and cytochemical activities of hydrolases (acid phosphatase, nonspecific esterase) in the pellicle and the apical complex were studied at the fine-structural level in kinetes of B. bigemina Smith et Kilborne, in hemolymph of female Boophilus microplus Canestrini. The cytochemistry of acid hydrolases was studied also in kinetes of Babesia ovis (Babes) Starcovici, in hemolymph and ovary of Rhipicephalus bursa Canestrini et Fanzago. The pellicle of the B. bigemina kinetes is composed of 3 membranes (pellicular complex): an outer membrane, .apprx. 8 nm thick (the plasmalemma) and 2 inner ones, each .apprx. 6 nm thick, lying closely together. The outer membrane appears to be covered by a structureless coat, 3 nm thick. The space between the inner double-membrane and the plasmalemma is 7.5 nm. The whole pellicular complex is 30 nm in diameter. The 2 inner pellicular membranes appear to be derived from the endoplasmic reticulum (ER). There are circular openings in the pellicular double-membrane with average diameters of 100 nm; despite some similarity to micropores, they have a specific structure. The term Intrapellikularfenster (IPF) (intrapellicular windows) or pseudomicropores is proposed for these pellicular differentiations. The margin of an IPF is formed by the 2 inner membranes folding into each other; cytoplasmic, electron-dense material is accumulated alongside this edge. Unlike that of micropores, the plasmalemma of the IPF is not invaginated. The IPF appears as a single, dark ring in tangential sections. At times, rhoptry-like bodies are associated with the openings. The function of the IPF is unknown. An intrapellicular opening similar to the IPF, although wider, is at the apex of the parasite. Its margin coincides with the inner edge of the apical ring. Typical subpellicular microtubuli were not observed in the Babesia kinetes. The apical complex of the B. bigemina kinetes consists of an Apikalschirm (apical umbrella), a crown of microtubuli beneath it and rhoptries: micronemes are also present in large numbers. The Apikalschirm is located beneath the pellicle of the apical pole of the parasite. It is a wheel-like structure composed of spokes radiating from a wide, hub-like central ring (apical ring). The apical ring is not identical with the polar ring described as an integral part of the pellicular complex in other Apicomplexa. Beneath each rib of the Apikalschirm there is 1 microtubule (subcostal microtubule). In kinetes ot B. ovis the ribs are less well developed. The Apikalschirm is more pointed in kinetes of this species in tick oocytes and ova. The rhoptries of the kinetes are spindle-shaped and largely located directly beneath the Apikalschirm. They are arranged radially and each row is associated with a rib. A conoid was not observed Occasionally low hydrolytic activity could be detected in micronemes. The rhoptries and the Apikalschirm were always negative for phosphatase and esterase activity. With regard to the number and arrangement of its membranes and to its hydrolase activity, the pellicle of the kinetes of Babesia closely resembles the pellicular complex of the Coccidia. It differs by the presence of the IPF and by the lack of micropores and of true subpellicular microtubules. In the complexity of their pellicle and in some details of the organization of their apical complex, the kinetes of Babesia resemble the ookinetes of the Hemosporidia.