The rickettsial bacterium Ehrlichia ruminantium is the causative agent of heartwater, a serious tick-borne disease in ruminants. The genetic diversity of organisms in the field will have implications for cross-protective capacities of any vaccine developed, and for an effective vaccine design strategy proper genotyping and understanding of existing genetic diversity in the field is necessary. We searched for variable-number tandem-repeat (VNTR) loci for use in a multi-locus VNTR analysis (MLVA). Sequencing analysis of 30 potential VNTRs using a panel of 17 reference strains from geographically diverse origins identified 12 VNTRs with allelic profiles differing between strains. Application of MLVA to 38 E. ruminantium-infected Amblyomma variegatum collected from indigenous cattle in 6 different districts of Uganda identified 21 MLVA types. The discriminatory power of MLVA was greater than that of map1 PCR-restriction fragment length polymorphism analysis, with which only 6 genotypes were obtained. The high discriminatory power as well as cost- effective performance of MLVA provide the potential for this technique to be applied in the future with respect to optimizing vaccine trials by identifying local strain diversity, and also raise the possibility of exploring the association between E. ruminantium genotypes and phenotypes such as pathological outcome in the ruminant host.

Tick distribution depends on the drop-off rhythm of the previous stage and on the suitability for tick survival of the environment where they are disseminated. Studies were implemented in Burkina Faso to assess detachment pattern of engorged Amblyomma variegatum nymphs. Experiments were carried out with naturally infested cattle kept in a paddock or monitored when grazing community pasture. In the pasture, 80% of the nymphs detached between 14.00 h and 17.00 h while less than 25% did so in the paddock. Further investigation was implemented to assess whether the density of adult ticks might be modified by herd management. During the early dry season, zebus grazed in 4 plots fenced in natural savannahs and fallows. Two of the plots were used in the morning and the two others in the afternoon. Six months later, zebus were put in these plots, in turn, on 9 occasions. The number of A. variegatum adults picked up by the cattle in each plot was highly variable: they captured more ticks in the plots installed on good lush savannah and 3-fold more ticks in those where the herd had grazed in the afternoon during the previous dry season. An integrated tick control strategy taking these results into account is proposed.

An in vitro feeding method using rabbit or cattle skin membranes, applied successfully to all stages (larvae, nymphae and adults) of the ixodid tick, Amblyomma variegatum, is described. The feeding apparatus consisted of a blood container with a membrane placed on top of a tick containment unit. A carbon dioxide atmosphere of between 5 and 10% and a temperature of 37 °C were used as stimulants for the attachment of the ticks. High CO2 concentrations in the atmosphere improved the feeding success of all instars. The effect of anticoagulation methods for the bloodmeal was investigated, and heparinized blood was found to be the most suitable for tick feeding. When the bloodmeal was replaced by tissue culture medium for feeding nymphs the subsequent moulting success was reduced. Adult ticks of both sexes remained attached for up to 16 days, until completion of their bloodmeals. All stages of the tick fed on whole blood in the artificial feeding system and all reached engorged weights less than those achieved by control ticks fed on experimental animals. A large proportion of ticks, fed artificially on whole blood, moulted or laid eggs successfully. The method was successfully applied for the transmission of Theileria mutans and Cowdria ruminantium to cattle.

A guinea-pig immunoglobulin-G linked agarose column was used to detect the immunoglobulin-G binding proteins (IGBP) in the ixodid ticks, Rhipicephalus appendiculatus, Amblyomma variegatum and Ixodes hexagonus. IGBPs were found in salivary gland extract (SGE) of the unfed ticks of all 3 species. The sizes of the IGBPs, as determined by SDS–polyacrylamide gel electrophoresis, differed between species. In R. appendiculatus 2 IGBP bands were detected in haemolymph collected from unfed females and males, and an additional 78 kDa IGBP was detected in haemolymph samples of male and female ticks that had fed for 6 days. Although there was no difference in the IGBP profile of SGE derived from unfed male and female R. appendiculatus, 2 new IGBPs were detected in the SGE of the male ticks after they had fed for 6 days. The possible function of IGBP in ticks is discussed.

Tick populations were monitored between October 1991 and September 1992 at monthly intervals on 10 Boran (Bos indicus) heifers at Didtuyura ranch, Yabelo district, Ethiopia. Twelve different tick species in four genera were identified from a total of 16 026 specimens collected. Of all the ticks collected, Rhipicephalus spp. constituted 84.7%, Amblyomma spp. 9.9%, Boophilus spp. 4.8% and Hyalomma spp. 0.24%. The ventral parts of cattle were found to be the most favoured feeding sites for most of the ticks collected. The size ranges of the standard ticks collected were 4–8 mm; 9–16 mm; 4–8 mm and 8–13 mm for R. pulchellus, A. variegatum, B. decoloratus and A. gemma, respectively, while their respective male to female sex ratios were 2:1; 3.2:1; 1:5.4 and 2.6:1. Packed cell volume (PCV) values of blood samples taken from 600 cattle were monitored monthly during the study period. There was a reduction in PCV during the dry season of the year but generally the values were within the normal range of 32–40%. The parasites causing anaplasmosis, babesiosis and theileriosis (T. mutans) were detected by microscopic examination of blood smears and serologically (ELISA) at seroprevalence rates of 94.68%, 77.19% and 30.9% respectively.

The lengths, breadths and areas of eggs oviposited at different times by female ticks (Amblyomma variegatum) of weight 2–3 and 0.5–1 were compared. The hatching patterns as well as mortality rates of different ovipositions of female A. variegatum of weight 2–3 g were studied at various incubation temperatures.

The eggs produced by female ticks of A. variegatum of weight 2–3 g were generally longer and broader, with a greater area also than those produced by female ticks of weight 0.5–1 g. The hatching pattern was influenced only by temperature and not by the order of oviposition of the eggs. The period of completion of all hatchings and the day of peak hatching vary according to the temperature at which the eggs were incubated. The occlusion periods of the eggs varied with their order of oviposition. It was longest in the first oviposition and shorter in the subsequent ones. Temperature also influenced the rate of mortality of the eggs. Mortality was low among eggs incubated at 24°C and rotational temperature.