Résultat de la recherche
Aspects nouveaux du rôle de vecteur joué par Ixodes Ricinus L. en Suisse. Note préliminaire
The authors, after having recalled their recent work on Ixodes ricinus ecology, give the new results about the part played by this species in the transmission of different infectious agents in Switzerland. I. ricinus was already known to be the most important vector of the tick borne encephalitis virus, and of protozoans of the Babesia genus. In this article, we describe the existence in the hemolymphe of different I. ricinus populations, of a rickettsia species related to the RMST group (Rocky-Mountain Spotted Fever), of a trypanosome, which is close to T. theileri, and of an infectious larval form (L3) of Dipetalonema rugosicauda. An outline is suggested with the object of illustrating the functioning of a natural foci of tick encephalitis. The biological significance of the unusual presence of trypanosomes and of larval filariae in ticks is also discussed. The authors underline the fact that rickettsia, trypanosomes and filarial forms are observed for the first time in Swiss I. ricinus.
Infection of field-collected Ixodes ricinus (Acari: Ixodidae) larvae with Borrelia burgdorferi in Switzerland
Free-living larvae from natural areas in five regions in Switzerland were collected to determine the infection rate of Ixodes ricinus L. larvae by Borrelia burgdorferi Johnson. Larvae were examined for the spirochetes using direct fluorescent antibody assay. Of 652 larvae examined, spirochetes were detected in 20 (3.1%). No differences in infection rate among sites were detected. The low prevalence of B. burgdorferi in larvae, compared with higher infection rate in nymphs (12.8%) and adults (14.5%), suggests that transovarial transmission is inefficient. These results suggest that I. ricinus can serve as a reservoir for B. burgdorferi in nature. Further study is needed on the relative importance of ticks, compared with mammals and birds, as reservoirs for B. burgdorferi.
Ixodes ricinus : vector of a hitherto undescribed spotted fever group agent in Switzerland
A tick/rickettsial survey in various parts of Switzerland revealed the presence of a new, hitherto undescribed spotted fever group rickettsia ("Swiss agent") in up to 11.7% of I ricinus collected off vegetation. Infection in ticks was found to be generalized with rickettsiae developing intracellularly and occasionally also intranuclearly. As a result of massive growth in ovarial tissues, including the germinative cells, the rate oftransovarial and filial infection was 100%.
The "Swiss agent" appears to be nonpathogenic for guinea pigs, domestic rabbits, and Swiss mice, but in male meadow voles (Microtus pennsylvanicus) it produces a microscopically detectable infection in the tunica vaginalis. The rickettsia grows well in tissue culture systems including chick embryo fibroblast, Vero, and vole tissue cells, when inoculated via yolk sac into 5-day-old hens' eggs, it kills 100% of the embryos after 5 to 7 days.
Antigenic relatedness of the "Swiss agent" to rickettsiae of the spotted fever group was indicated by indirect and direct fluorescent antibody staining. Preliminary serologic typing by microimmunofluorescence and by microagglutination indicated that the "Swiss agent" differs from all prototype strains of spotted fever group rickettsiae studied so far.
Rickettsia-like microorganisms in the ovarian primordial of molting Ixodes ricinus (acari : ixodidae) larvae and nymphs
Un grand nombre de micro-organismes de type rickettsien ont été observés dans les cellules des ébauches ovariennes de larves et de nymphes d'Ixodes ricinus, lors de la mue. La morphologie de ces organismes est identique chez toutes les tiques examinées. Ils mesurent 0,3-0,4 µm de diamètre et 0,6-1,3 µm, parfois jusqu’à 2,5 µm, de long. Ils possèdent une paroi externe membraneuse fortement ondulée et une membrane plasmique interne. L’épaisseur de chacune de ces 2 structures est de 6-10 nm. Les microorganismes sont toujours inclus, soit seuls soit en groupe, dans des vacuoles contenues dans le cytoplasme de la cellule hôte, dans des mitochondries vacuolées, ou dans des vacuoles dont les parois sont constituées en partie de restes de mitochondrie. Plus les ovaires des nymphes sont développés, plus le nombre de micro-organismes associés aux mitochondries augmente. La relation entre les microorganismes et les mitochondries est discutée, la morphologie des gonades chez les tiques immatures est décrite., 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 µm in diameter and 0.6-1.3 µm, occasionally up to about 2.5 µm 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.