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The bont tick, Amblyomma hebraeum, is the principal vector to southern African ruminants of heartwater (Cowdria ruminantium infection). The role of feeding male ticks, which emit an aggregation-attachment pheromone, in attracting unfed ticks to cattle was investigated. Calves infested with feeding male ticks were more attractive to unfed adult ticks than were uninfested calves. The presence of the pheromone on previously infested cattle apparently allows unfed ticks to discriminate between hosts on which these parasites have fed successfully (suitable hosts) and those on which they have not (potentially unsuitable hosts). The use of acaricides is thus unlikely to reduce bont tick populations in areas where adequate numbers of alternate (wild) hosts are present. Also, cattle so treated may lose their resistance to heartwater through lessened exposure to infected ticks.

Eight strains of mollicutes were isolated from pooled suspensions prepared from western black-legged ticks (Ixodes puciJicus) collected in Oregon. Morphologic examination by electron and dark-field microscopic techniques showed that each strain consisted of a mixture of motile, tightly coiled helical cells, small coccoid cells with diameters ranging from 300 to 500 nm, and pleomorphic, straight or branched filamentous forms. All cellular forms were surrounded by a single cytoplasmic membrane, and there was no evidence of a cell wall. The organisms were filterable and fastidious in their growth requirements. The optimum temperature for growth was 30°C, but multiplication occurred at temperatures ranging from 23 to 32°C. The strains catabolized glucose but did not hydrolyze arginine or urea. The genome size of strain Y32T (T = type strain) was 2,220 kbp, and the DNA base composition (guanine-plus-cytosine content) of this organism was 25 k 1 mol%. The eight isolates were serologically related to each other but were not related to 37 other type or representative strains belonging to the genus Spiroplasmu. Strain Y32 (= ATCC 33835) is the type strain of Spiroplasma ixodetis sp. nov.Spiroplasmas (class Mollicutes) are helical, motile, wall-less prokaryotes that are associated with a variety of insects, other arthropods, and some plant hosts (11,38,51). Although members of the genus Spiroplasma are usually commensal organisms in their arthropod hosts, several are pathogenic for insects and plants (11, 12,24,29,30).The occurrence of spiroplasmas in hematophagous arthropods was first demonstrated in 1976 when two serologically distinct helical mollicutes (represented by strains SMCA and 277F) were identified in rabbit ticks (Haemaphysalis leporispalustris) (4,41). Strain SMCA and two related strains were eventually characterized as Spiroplasma mirum (39). Strain 277F is serologically and genomically related to Spiroplasma citri and was assigned to subgroup 1-4 in an interim classification scheme for spiroplasmas (21,36,44). Subsequently, spiroplasmas have been identified in blood-sucking members of the Diptera, including horseflies (Tabanus spp.), deerflies (Chrysops spp.), and mosquitoes (Adedes spp., Culex spp., etc.). The current status of these organisms has been summarized in several recent reviews or reports (1, 10, 15, 18, 19,38,45).We described additional isolations of tick-associated spiroplasmas in 1981 (37), including primary isolation of seven helical mollicutes from triturates of the western black-legged tick, Ixodes pacificus. While these organisms were isolated directly in SP-4 spiroplasma culture medium (43), a later report showed that most of the same isolates could be cultivated from stored triturates in several continuously maintained cultured tick cell lines (53). An extensive serologic comparison of the strains isolated from I. pacificus showed that these organisms are closely related to each other but distinct from other previously described spiroplasmas. Strain Y32T (T = type strain) was selected ...

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Midway virus, a new tick-borne virus isolated from two species of Ornithodoros (Alectorobius) ticks of the capensis group (O capensis, O denmarki), is described from Midway, Kure, and Manana islands in the Central Pacific (Hawaiian Archipelago) and from northern Honshu (Japan). Midway virion is enveloped, unusually large, acid and temperature sensitive, and its type of nucleic acid is RNA. Complement-fixation (CF) tests show a close relation of Midway to Nyamanini virus, which has been isolated from ardeid birds and Argas ticks in Africa, the Indian subcontinent, and Southeastern Asia. However, cross-box tests (CF, mouse and tissue culture neutralization, immunofluorescence) show that these two viruses are quite distinct. Midway virus is lethal for newborn Swiss mice inoculated by intracerebral, but not intraperitoneal route. It fails to kill four-week-old mice by either route. Midway virus causes cytopathic effects in BHK-21 cells and titerable plaques in Vero cells. Antibodies to it were prevalent among nestlings of Larus crassirostris (Black-tailed Gull) on Aomatsushima I., but were scarce among those of Nycticorax nycticorax (Black-crowned Night Heron) of the same island.