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Human infection with Borrelia burgdorferi, the causative agent of Lyme disease, is unusually common in the "Scheelkopf" area of the town Bruchsal in north Baden (Germany), a situation which has led to considerable publicity and public concern. This study was carried out in order to clarify this situation by determining the prevalence of B. burgdorferi in both the free-living tick populations (Ixodes ricinus) and the rodent population from the "Scheelkopf" as well as from surrounding control areas. The polymerase chain reaction (PCR) was used to determine the presence of infection in whole tick preparations and in mouse bladders. The prevalence of B. burgdorferi in freeland ticks ranged from 19% to 44% and in mice from 6% to 29% depending on the area studied. The "Scheelkopf", with prevalences for ticks and mice of 33% and 10% respectively, was not significantly different from the control areas. Our results indicate that there is a high risk of human infection throughout the study area. This is probably related to the intensive use of the area for gardens and the related recreational behaviour of the human population in conjunction with the high rate of infection prevailing in I. ricinus.

A total of 1,640 stomach contents from 56 South African species of small and medium sized mammals were examined for ticks. Only six ticks were found in three specimens of the caracal Felis caracal. Although identification of the tick species was not possible owing to fragmentation and partial digestion, the genus Haemaphysalis was represented in four of these cases. We conclude that predation by small and medium sized mammals on ticks is uncommon in South Africa.

Goats acquired resistance to larvae of Amblyomma hebraeum following three repeated infestations. Resistance was associated with immediate Type I hypersensitivity reactions following intradermal skin tests using crude egg extracts. In a separate experiment, the inoculation of tick-naive goats with extracts of the larvae of A. hebraeum failed to induce observable effects on feeding larvae despite the development of anti-larval antibodies.

Three infestations of restrained Jersey and Friesland bull calves with adult Amblyomma hebraeum did not affect the rate of engorgement of female ticks and resulted in an insignificant decline in the mean engorgement weight of female ticks recovered from the Friesland group. Repeated infestations significantly affected the egg-laying capacity of engorged female ticks recovered from both groups of hosts. The Friesland calves manifested an enhanced resistance to the larvae and nymphs of Amblyomma hebraeum resulting in prolonged attachment, and a significant decline in engorgement rate of these instars compared with the Jersey group. Skin reaction tests using crude tick extracts yielded antigen-specific hypersensitivity reactions which were not related to resistance to A. hebraeum. Histological changes at the attachment site associated with tick rejection are discussed in relation to host resistance mechanisms.

Data collected on both free-living and parasitic tick populations are likely to be overdispersed. The use of means from few replicate samples of overdispersed data as quantitative estimators of tick population density is in turn likely to lead to inaccurate interpretations which may be scientifically misleading. In this paper ways of estimating overdispersion are listed and suggestions for the use of correct statistical tests for handling overdispersed data are given.

The ratio of variance to mean (s2/means) of numbers of Ixodes rubicundus (males and females) per sheep was used as a measure of the dispersion pattern of this tick within a naturally infested population of sheep. Sheep were divided into two groups, one with previous contact with I. rubicundus and the other with no previous contact. Samples of 10 sheep from each group were searched for ticks on a weekly basis for 19 weeks during the winter of 1986. In each group, both male and female ticks had an s2/means ratio greater than 1 for the majority of observation periods indicating an aggregated dispersion pattern. The degree of aggregation was greater with increasing density of the ticks. The implications of these results are discussed both in relation to sampling procedures and potential control strategies.

Competition for sites of attachment to hosts by three species of reptile tick, Aponomma hydrosauri, Amblyomma albolimbatum and Amb. limbatum was investigated as a possible cause for the parapatric distributions found in these species throughout southern Australia. Two localities were chosen for detailed study; a boundary between Ap. hydrosauri and Amb. limbatum near Mt. Mary in the mid-north of South Australia and a boundary between Ap. hydrosauri and Amb. albolimbatum near Arno Bay on the Eyre Peninsula of South Australia. Comparisons of sites of attachment to hosts were made between hosts infested by one species of tick and hosts infested by two species of tick. At Mt. Mary, Ap. hydrosauri and Amb. limbatum adults attach more commonly in the ears and on the midback of their hosts, however, no evidence was found to suggest that competition between the species occurred for these sites. At Arno Bay, Amb. albolimbatum adults had similar sites of attachment to hosts as the other two species, however, significantly more of this species attach in the ears of their hosts. There is no difference in sites of attachment to hosts of Ap. hydrosauri females at Arno Bay and Mt. Mary. Ap. hydrosauri males at Arno Bay, however, show a shift in sites of attachment to hosts away from those sites occupied by Amb. albolimbatum males and females. This shift occurs only in cases where Amb. albolimbatum did not infest the same host. Although the shift in male Ap. hydrosauri sites of attachment to hosts can be explained in terms of past competition, there is no evidence to suggest that such competition in the past, or competition at present, maintains the parapatric boundaries found in these species of thick.

A comparison of attachment, engorgement and moulting success of Amblyomma hebraeum larvae fed on domestic chickens and Himalayan giant white rabbits indicates that chickens are better hosts than the rabbits. Moreover the time needed for detachment of all engorged larvae is significantly less for chickens than for the rabbits. No evidence of induced immunity was found in chickens on re-infestation with larvae of A. hebraeum.

Lyme disease is a recently-described zoonotic disease occurring widely in the U.S.A., Europe and Asia. The causative organism, Borrelia burgdorferi, is transmitted predominantly by ticks of the genus Ixodes and infects a wide host range. The infection in humans causes the human disease syndrome erythema chronicum migrans resulting in arthritis, neurological symptoms and/or cardiac abnormalities. Similar clinical signs have been described in domestic animals. The status of Lyme disease in southern Africa is presently unknown but preliminary evidence indicates that the disease may occur in humans in the Republic of South Africa. The abundance of hosts and tick vectors would favour the establishment of the infection in Africa.

Two Australian tick species Aponomma hydrosauri and Amblyomma albolimbatum have the same major host species, the lizard Trachydosaurus rugosus. While females of Amb. albolimbatum are most often attached in the ears and on the neck of their hosts, Ap. hydrosauri females prefer to attach further back, under the forearms and on the back. Males show the same interspecific difference but there is also a difference between populations. Ap. hydrosauri males from populations in contact with Amb. albolimbatum attach more often in posterior positions than Ap. hydrosauri males from populations isolated from Amb. albolimbatum. These differences were found in both field populations and laboratory reared ticks. Phylogenetic evidence suggests that the change in male attachment site between Ap. hydrosauri populations followed the colonization of T. rugosus. We propose that the most likely reason for the change of attachment sites has been interspecific interactions with Amb. albolimbatum and that competition has been for space for efficient reception of female signals.

The success of natural infestations of various life history stages of Amblyomma hebraeum and Amblyomma marmoreum on the leopard tortoise, Geochelone pardalis, was compared. Success was measured by the time taken for ticks to detach, as well as the percentage of ticks engorging and subsequently either moulting to the next life history stage or laying viable eggs. Larvae of A. hebraeum were the only developmental stage not recovered. Nymphae and female A. hebraeum were less successful in moulting or laying eggs than the corresponding stages of A. marmoreum. Nevertheless, 48,7% of A. hebraeum nymphae moulted, while 1 of 6 females laid viable eggs.

Non-specificity of part of the sex pheromone system of three species of reptile tick has previously been suggested to result in reproductive interference between the species when they attach to the same host (Andrews et al. 1982). Two of the species, Aponomma hydrosauri and Amblyomma limbatum, have common aggregation pheromones which act when the ticks are detached from their hosts. As each species tends to occupy spatially separated microhabitats, the similarity of the aggregation pheromone could lead to interference between species when off their hosts by inducing one species to move away from its preferred microhabitat into that occupied by the other species. This study demonstrates that coaggregations of both species do occur, but that neither species shows a statistically significant shift in microhabitat preference attributable to interactions between species. We suggest that the behaviours leading to microhabitat choice in each species override the influence of the common aggregation pheromone.

Striped mice, Rhabdomys pumilio, were trapped over a 17 month period in the Thomas Baines Nature Reserve in the eastern Cape Province of South Africa. Captured mice were placed in cages, over water, and naturally detaching ticks were collected. Only 5 larvae and 1 nymph of Amblyomma hebraeum were recovered from the mice. These represented less than 0.1% of the total number of ticks recovered. No Amblyomma marmoreum were recovered. As the vegetation and large mammals and tortoises in the Thomas Baines Nature Reserve abound in larvae of both these vectors of heartwater the low infestation rates of R. pumilio indicate that it is either unsuitable or inaccessible for these ticks. R. pumilio is therefore unlikely to play a role in the epidemiology of heartwater.

Large numbers of birds, wild mammals and domestic stock from a variety of localities within the Republic of South Africa were examined for infestation with the ixodid ticks Amblyomma hebraeum and Amblyomma marmoreum. Every warthog (Phacochoerus aethiopicus), Burchell's zebra (Equus burchelli), impala (Aepyceros melampus) and kudu (Tragelaphus strepsiceros) from the Kruger National Park in the north-eastern Transvaal Lowveld was infested with A. hebraeum. In the eastern Cape Province every helmeted guinea fowl (Numida meleagris), scrub hare (Lepus saxatilis) and kudu from the Andries Vosloo Kudu Reserve; all but 1 of the 22 domestic cattle examined on the farm "Bucklands"; and all Angora goats plus nearly all Boer goats examined on the farm "Brakhill" were infested with this tick. Most animals examined appeared to be good hosts of the immature stages, and the larger the host species the greater the chances of it harbouring large numbers of adult ticks. The largest animals examined, such as eland, buffalo, giraffe and rhinoceros, harboured very large numbers of adult A. hebraeum. No adult A. marmoreum was recovered from any host. However, 50% or more of helmeted guinea fowl and kudu from the Andries Vosloo Kudu Reserve; helmeted guinea fowl, scrub hares and eland (Taurotragus oryx) from the Mountain Zebra National Park; helmeted guinea fowl, kudu, domestic sheep, goats and cattle on the farm "Bucklands", and caracal (Felis caracal) from the Cradock and Southwell areas of the eastern Cape Province were infested with immature A. marmoreum. In the Bontebok National Park in the south-western Cape Province more than 35% of scrub hares, vaal ribbok (Pelea capreolus) and bontebok (Damaliscus dorcas dorcas) were infested with immature ticks.

The weights of feeding female Ixodes rubicundus attaching to sheep was studied in a natural focus of Karoo paralysis. The studies showed fewer females in the middle weight ranges and more in the heavier and lighter categories than would be expected if the distribution was normal. Weights were also strongly skewed towards the lighter females between 0 and 400 mg. No differences in the pattern of attachment weights occurred over the four experimental groups used, suggesting that previous contact of sheep with I. rubicundus had no effect on the ability of the tick to engorge.

The accuracy of a general and a specific method of collecting and counting ixodid ticks on live hosts was compared with that of a destructive technique which can only be applied to dead animals. Destructive sampling provided considerably more accurate results than either of the live sampling methods when applied to domestic goats (Capra hircus) and a duiker (Sylvicapra grimmia). The smaller the life stage and the tick species the less likely it is that it will be recovered by either of the live sampling techniques. Both live and destructive sampling yielded similar results for adult Amblyomma hebraeum, a large tick. A sub-sampling method, used to estimate larval numbers, was repeatable and an accurate predictor of population size for populations ranging from 50 to 1000 of unengorged A. hebraeum larvae.

Domestic stock on a farm 30 km north of Grahamstown were treated with an acaricide at regular intervals over a period of several years. This resulted in a marked reduction in all stages of development of Amblyomma hebraeum on kudu (Tragelaphus strepsiceros), scrub hares (Lepus saxatilis) and helmeted guinea fowl (Numida meleagris) which were on the farm compared with the burdens of similar animals in an adjacent nature reserve. The populations of free-living larvae of A. hebraeum on this farm and on another farm 10 km south of Grahamstown, on which the domestic stock were also regularly treated with acaricides, were markedly reduced when a comparison was made with the free-living populations in the adjoining nature reserves.

Male Ixodes rubicundus were found in copula with attached females in 59% of individuals. The number of males attaching to the female integument or to the the host negligible. In laboratory experiments, males enclosed with females in a small vial had significantly longer life spans than solitary males. Paired males were found to be in copula on 20-34% of observations. Solitary males lost weight while paired males gained weight over a 2-day period. However, the specific energy content of the 2 groups remained constant.

Amitraz at a concentration of 2 ml litre-1 of water successfully induced detachment of Amblyomma marmoreum and Amblyomma hebraeum ticks from the mountain tortoise, Geochelone pardalis. Detached ticks died without reattaching. At the strength used, amitraz had no apparent adverse effects on the tortoises.

The hosts, sites of attachment, life cycle, habitat requirements and seasonal abundance of Amblyomma astrion, Amblyomma cohaerens, Amblyomma gemma, Amblyomma hebraeum, Amblyomma lepidum, Amblyomma marmoreum, Amblyomma pomposum, Amblyomma sparsum, Amblyomma tholloni and Amblyomma variegatum, the 10 potential vectors of heartwater in Africa, are listed. Factors influencing the distribution and abundance of the ticks as well as interactions with other species and the role of predators and pathogens are discussed.

Reproductive interference between three species of reptile tick, Aponomma hydrosauri, Amblyomma albolimbatum and Amb. limbatum was investigated. Adults of two species attach together on the same lizard hosts in narrow overlap zones at parapatric boundaries between species, providing opportunities for interference. The possibility of reproductive interference was suggested because of similarities in the sexual communication systems.Three forms of interference were found in laboratory experiments. Firstly male movement to search for sexually receptive females was inhibited when females of two species were present on the same host, probably because of signal interference. Secondly, a nonspecific, short range attractant pheromone led males into non-conspecific courtship attempts which reduced the time for conspecific courtships. Thirdly Amb. albolimbatum males physically blocked the genitalia of female Ap. hydrosauri after unsuccessful non-conspecific courtship attempts. Field data showed this behaviour was common in both Amblyomma species after conspecific matings. Reproductive interference would reduce the fitness of each species in sympatry, and may contribute to the maintenance of the narrow parapatric boundaries.

The epidemiology of Karoo paralysis, induced by the tick Ixodes rubicundus, was investigated in a paralysis-enzootic area of the southwestern Orange Free State, Republic of South Africa. Sheep became paralysed during the last week of April and the first week of May during the 1985 and 1986 seasons, respectively. Paralysis cases were recorded up until July, but most paralysis cases occurred during the first week of May with a second but smaller peak occurring during June. Tick numbers on paralysed sheep closely followed peak periods in paralysis. A total of 65 and 50% of the naive sheep became paralysed during the 1985 and 1986 seasons, respectively. The seasonal pattern of tick infestation by female I. rubicundus was similar on both previously exposed and on naive sheep. The results of this study indicate that a certain number of ticks per kilogram host body mass is required before symptoms of paresis of paralysis are observed. In general the tick burden per kilogram host mass was significantly greater in paralysed compared to non-paralysed sheep. The range in the number of ticks per kilogram host mass may, however, overlap between non-paralysed and paralysed groups. Previously exposed or previously paralysed sheep are less susceptible to paralysis in the following year. Differences in susceptibility between individual sheep seems likely.