André Aeschlimann

Isolation of a cultivable spirochete fromIxodes ricinus ticks of Switzerland

We have isolated in BSK medium a spirochete ofIxodes ricinus ticks. The ticks were collected from an area of Switzerland where erythema chronicum migrans, a tick-borne, penicillin-ameliorated inflammatory disorder, is endemic. TheI. ricinus spirochete was very similar in its morphology, polyacrylamide-gel-electrophoresis profile, and antigenic determinants to a spirochete that was previously isolated fromIxodes dammini ticks of the United States.

Confirmation that Rickettsia helvetica sp. nov. is a distinct species of the spotted fever group of rickettsiae.

We propose the name Rickettsia helvetica sp. nov. for a rickettsial serotype of unknown pathogenicity isolated in 1979 in Switzerland from Ixodes ricinus ticks and designated the Swiss agent. The growth characteristics and the results of microimmunofluorescence serologic typing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting (immunoblotting) with specific mice sera, and a polymerase chain reaction followed by restriction fragment length polymorphism analysis confirmed previously reported preliminary findings which suggested that this rickettsia, to which a name was given provisionally, does represent a new member of the spotted fever group of rickettsiae. The type strain is C3 (Reference Center for Rickettsioses, Marseille, France).

Ixodes (Pholeoixodes) hexagonus, an efficient vector of Borrelia burgdorferi in the laboratory

Abstract. Borrelia burgdorferi Johnson et al. was first isolated from the midgut of Ixodes dammini Spielman et al. in the U.S.A. and from the midgut of Lricinus (L.) in Europe. I.ricinus was considered to be the only tick vector of this borrelia, in Europe, until I.hexagonus Leach, the hedgehog tick, was found to harbour spirochaetes. This paper reports an evaluation of the vector competence of I. hexagonus for the spirochaete B. burgdorferi. Transovarial and trans‐stadial survival were demonstrated and the spirochaete was transmitted to laboratory mice via the bites of trans‐stadially infected I.hexagonus females.

SEX-BIASED GENETIC STRUCTURE IN THE VECTOR OF LYME DISEASE, IXODES RICINUS

Abstract.— We analyzed 725 Ixodes ricinus ticks (the principal vector of Lyme disease in Europe) collected in Switzerland in 1995 and 1996 (three and eight samples, respectively) and in Tunisia in 1996 (one sample) with five microsatellite markers. We found highly significant genetic differentiation between Swiss and Tunisian samples but detected almost no differentiation within Switzerland, even between those samples separated by the Alps. Interestingly, we found that I. ricinus females were more genetically related to one another than were males at a local scale, which would indicate a higher dispersal rate of immature males. Possible explanations for these findings in terms of sex‐specific association of ticks with certain hosts (e.g., birds) and their epidemiological consequences are discussed.

Population genetic structure of Ixodes ricinus in Switzerland from allozymic data: No evidence of divergence between nearby sites

Ixodes ricinus is a vector and reservoir of numerous infectious agents, especially Borrelia burgdorferi, the agent of Lyme disease. In Switzerland, its ecology and physiology have been well studied. Moreover, the foci of some infectious agents transmitted by this tick are identified. They can display relatively to extremely small geographical size depending on the diseases considered. In order to understand how the gene flows occur and to characterise the genetic structure of Ixodes ricinus populations, we used an indirect method based on genetic markers: allozymes. The sampling was carried out in 5 localities. Eighteen loci were analysed and 2 appeared polymorphic. This shows the low allozymic variability displayed by Ixodes ricinus. Based on these 2 loci, the populations appeared panmictic in Switzerland. This may be explained by the wide range of vertebrate species this tick can infest, especially birds. However, the result is surprising if we consider the extreme localisation of the foci of some infectious agents. We conclude that more powerful genetic markers could be used in order to better understand the epidemiology of tick-borne diseases in Switzerland.

Rickettsia conorii isolated from Rhipicephalus sanguineus introduced into Switzerland on a pet dog.

A tick/rickettsial survey in a household near Geneva, Switzerland, revealed that 30 (40%) of 75 nymphs and adults of the brown dog tick,Rhipicephalus sanguineus, were infected with a rickettsial agent biologically and antigenically indistinguishable fromR. conorii, the causative agent of boutonneuse fever. Introduced in 1976 from either southern France of Italy by the familys pet dog, the tick infestation had steadily increased until 1981 when control measures were initiated. During 1980 and 1981, four persons associated with the households pet dog contracted a febrile illness diagnosed as boutonneuse fever.

Changes in the protein profile and antigenicity of different Borrelia burgdorferi strains after reintroduction to Ixodes ricinus ticks

Summary Eight Swiss strains of Borrelia burgdorferi, with various protein profiles and the North‐American strain B31 were artificially introduced into Ixodes ricinus ticks and reisolated 10 days later. All isolates were subsequently examined by SDS‐PAGE analysis. Comparing initial isolates with the reisolates, we observed that 7 out of 9 strains changed their protein pattern with respect to the major proteins OspA, OspB and the 22 kDa protein after passage in the tick. The strains NE2, NE4 and NE83 with the initial phenotype of OspA and 22 kDa proteins changed to the phenotype of OspA and OspB, the strains B2 and NE202 with the initial phenotype of OspA acquired an additional protein of 22 kDa and the strain NE58 with the initial phenotype of OspA also acquired a protein of 22 kDa. Examination of these isolates by Western blot analysis demonstrated that the reaction with the monoclonal antibody H5332 and a monospecific polyclonal antibody PoAb/anti‐22 kDa differed between the initial isolates and the reisolates.

The peritrophic membrane of Ixodes ricinus.

A peritrophic membrane was found in all three stages ofIxodes ricinus at no later than 18 h after their placement on rabbits. It was found to remain intact until at least 11, 30 and 10 days after repletion in larvae, nymphs and females, respectively. In blood-feedingI. ricinus, the peritrophic membrane is an uneven single layer with a thickness of about 0.03–0.48 μm in larvae, 0.03–0.79 μm in nymphs and 0.04–0.93 μm in females. It covers the whole surface of the midgut epithelium at a distance of about 0.2–0.8 μm. After repletion, the peritrophic membrane becomes thicker and thicker and more and more winding and simultaneously becomes multi-layered mainly in its arched parts. The distance between the peritrophic membrane and the midgut epithelium increases considerably and in the arched parts can reach as much as about 13 and 16 μm in metamorphosing larvae and nymphs, respectively and 25 μm in ovipositing females.

Distribution of Rickettsia-like microorganisms in various organs of an Ornithodorus moubata laboratory strain (Ixodoidea, Argasidae) as revealed by electron microscopy.

SummaryLong, Rickettsia-like microorganisms have been found in all investigated organs of both sexes of the soft tick Ornithodorus moubata, Murray (Ixodoidea: Argasidae) with the exception of the spermioduct and the testicules. These microorganisms are often concentrated in “nests”.Coccoid microorganisms are limited to the Malpighian tubules and the oocytes. Intermediate forms have also been observed. It is discussed whether the two forms are different morphotypes of the same microorganisms.

Na, K-ATPase in the salivary gland of the ixodid tick Amblyomma hebraeum (Koch) and its relation to the process of fluid secretion

Total and ouabain-sensitive ATPase activities were determined in the salivary glands of ticks throughout the feeding cycle. Activities were very low in unfed specimens. In the glands of feeding females, the activities rose until a maximum was reached for both ATPase components at approximately 200 mg. The activities remain low in males throughout the feeding period. These findings are discussed in relation to the fluid secretory process of the salivary glands.