The authors examine the epidemiologic features of Mediterranean spotted fever in France in light of the bioecological peculiarities of each of the three known member of the Rhipicephalus sanguineus tick group (R. sanguineus, R. turanicus, R. pusillus). The results show that R. sanguineus is the main vector. Certain aspects of this tick species are of interest: affinity for man, close contact with humans for a long periods, peak of tick population (preimaginal stages) at the same time as the peak of the disease. The largest populations of R. sanguineus are noted in the endemic zone of human rickettsiosis. The fact that immature stages are more prevalent during the hot season and these forms' ability to bite humans is important and may suggest a role for them in the epidemiology of the disease. The sporadic isolation of this species outside the endemic zone may explain the occurrence of isolated cases of the disease in these areas. We cannot currently exclude vector roles for the two other species, which can parasitize humans, though none of our data supports this hypothesis.

The endoparasitic wasp Tranosema rostrale (Ichneumonidae) transmits a polydnavirus (PDV) to its host, Choristoneura fumiferana, during oviposition. Unlike most other PDVs examined, the virus of T. rostrale (TrPDV) does not appear to play an important role in suppressing the host cellular immune response. However, it inhibits host metamorphosis. In the present study, TrPDV gene expression was examined in parasitized and virus-injected last-instar caterpillars. Northern analysis with viral DNA as a probe revealed only one detectable mRNA, of about 650 bp. The corresponding cDNA, termed TrV1, was cloned and sequenced and found to encode a protein of 103 amino acids which, following cleavage of the putative signal peptide, has a predicted molecular mass of 9n3 kDa. This protein displays limited similarity to the VHv1.4 cysteine-rich protein from the PDV of Campoletis sonorensis, mostly within the signal peptide region. By using a TrV1-specific probe, the TrV1 gene was localized to segment G of the TrPDV genome. The cuticle and fat body were identified as the principal sites of TrV1 transcription, with little transcription observed in haemocytes and midgut. Western analysis of proteins extracted from selected tissues of parasitized insects suggested that the TrV1 protein is secreted in the haemolymph. As observed for other PDVs, injection of TrPDV did not suppress transcription of the gene that encodes juvenile hormone esterase, the activity of which is inhibited by the virus. We speculate that the TrV1 protein may play a role in the inhibition of C. fumiferana metamorphosis.

No abstract