Acquisition of resistance to the bont tick Amblyomma hebraeum (Acarina: Ixodidae) by goats

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.     

Resistance of restrained Bos taurus dairy bull calves to the bont tick Amblyomma hebraeum (Acarina: Ixodidae)

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.     

Some avian and mammalian hosts of Amblyomma hebraeum and Amblyomma marmoreum (Acari: Ixodidae)

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.     

Cross-reactivity between antigens from Amblyomma cajennense and A. hebraeum (Acari: Ixodidae)

Laboratory animals exposed to feeding ticks develop resistance which is reflected by a decline in tick engorgement weight, egg-laying by adults and reduced egg viability. Serum antibodies from these hosts and their reaction with tick antigens have been detected by different methods, including precipitation techniques, immunofluorescent techniques, ELISA and Western blots. However, little is known about the effects of antibodies on ticks that engorge on resistant hosts, or which tissues of the tick body are possibly immunogenic. Some researchers, using immunohistochemistry, have detected host antibodies in the gut, salivary glands and haemolymph of ticks engorged on resistant animals. The same technique has helped considerably in determining antigenic sites or antibody targets in other arthropods. Consequently, immunohistochemistry techniques were used in this study to detect cross-reactivity between sera raised against Amblyomma cajennense (Fabricius, 1787) with Amblyomma hebraeum (Koch, 1844), and vice versa. The results show the existence of shared antigens between the 2 tick species. In general, our results point more to a 1-way cross-reactivity of A. hebraeum with A. cajennense than a reciprocal cross-reactivity, suggesting that A. hebraeum is more immunogenic than A. cajennense.     

Climate changes and suitability for the ticks Amblyomma hebraeum and Amblyomma variegatum (Ixodidae) in Zimbabwe (1974-1999)

The spread of Amblyomma hebraeum has been reported in Zimbabwe. At the same time there was little or no spread in the distribution of Amblyomma variegatum. This paper examines the climatic cycles and their trends in the period 1974-1999 with a view to explaining the abiotic causes of this spread, and of forecasting the likely tendency in climate suitability for both tick species. An annual data-set of rainfall and air temperature was used as a source for climate, together with a habitat-modeling algorithm to estimate climate suitability for both ticks. Long-term suitable habitat for A. hebraeum exists mainly in the south and southeast of the country. Areas of adequate habitat for A. variegatum exist across the country, between approximately 17 degrees S and 18.5 degrees S, and are most suitable in regions of the northwest. The climate niches of the two species differ, and account for their almost allopatric distributions, as observed in the duration and intensity of the dry period and in total annual rainfall. Cyclic changes in both temperature and rainfall drive the periodic modifications in the distributions of the ticks. More intense periods of drought in the highveld, drive the expansion of A. hebraeum in this region. Temperature does not have any effect on the tendency in this area. Areas in south and southeast show a trend towards an increase in climatic suitability because of an increase in temperature. Zones in which habitat suitability is increasing for A. variegatum are restricted to the northwestern parts of the country, because warmer temperatures and a slight decrease in the intensity of the dry season. The progressive increase in temperatures seems to be forcing the dispersion of A. variegatum towards areas outside of zones that have a prolonged dry period. On the other hand A. hebraeum is compelled to spread northwards, following areas with adequate rainfall patterns, but halted by temperature limits and perhaps competition with A. variegatum. Without adequate control measures, invasive waves of A. hebraeum may occur over a background swell of northward expansion.     

Parasitic phase of Anocentor nitens (Acarina: Ixodidae) in cattle

The parasitic phase of Anocentor nitens (Neumann) in cattle was studied. Larval stage was present up to 15 days post-infestation (p.i.), concomitant with nymphae from day 8 p.i. Nymphae were observed up to day 23 p.i., adults being seen from day 15 p.i. onwards. Male ticks disclosed active movements from day 17 p.i. and detachment of engorged females began 22 to 24 days p.i. Massive detachment occurred from day 28 p.i. Preferential sites of parasitic stages were ear and neck (lateral side).     

Attempt to attract Amblyomma variegatum (Acarina:Ixodina) on cattle previously treated with aggregation-fixation pheromones and a pyrethrinoid acaricide]

The application of synthetic pheromonal aggregation-attachment compounds or male tick extracts on certain sites of the body of bull calves reared on infested pastures did not induce any attraction of free adults on these sites. Previously attached males were more attractive than synthetic pheromones or natural extracts. Very small amounts of flumethrin poured directly on testicles or on the dewalp induced a large decrease in the infestation of these sites.     

The transfer of Boophilus microplus (Acarina: Ixodidae) from infested to uninfested cattle under field conditions

The transfer of larvae and adult males of the cattle tick, Boophilus microplus, from infested to uninfested cattle, has been demonstrated under field conditions. The role of host to host transfers in the transmission and epidemiology of anaplasmosis and babesiosis is discussed.     

Moxidectin pour-on for control of natural populations of the cattle tick Boophilus microplus (Acarina: Ixodidae)

Fifty Bos taurus x Bos indicus heifers naturally infested with Boophilus microplus ticks were divided into two groups of 25 heifers each. Individuals of one group were treated with moxidectin 0.5% pour-on at a dosage of 500 microg of moxidectin/kg body weight and heifers from the other group remained as untreated controls. An efficacy higher than 95% was found on days 7-21 after treatment by using female ticks 4.5-8.0 mm long as the main infestation parameter. A lower, but significant efficacy (p < 0.05) was also found on days 1 (32.3% efficacy) and 27 (73.4% efficacy) post-treatment. Significantly (p < 0.05) lower numbers of immature ticks were also observed on heifers of the treated group from days 7 through 27 after treatment. A lower engorgement weight of female ticks from treated heifers was found on days 1 and 21 after treatment. Treatment also affected reproductive performance (oviposition, egg hatch and number of eggs laid) of female ticks collected on Day 1.     

Studies on the ability of different strains or populations of female Rhipicephalus evertsi evertsi (Acarina:Ixodidae) to produce paralysis in sheep

Simultaneous infestation of 3-6 month-old Black-head sheep with 15 South African wild strains of Rhipicephalus evertsi evertsi males and females as well as a strain from Rwanda clearly showed that all strains are capable of inducing paralysis. Assessment of the infestation-rate of engorging female ticks during the period that their mass ranged between 15 and 21 mg/kg sheep body mass indicated that toxicity is quantitatively identical and exhibits no intraspecific gradations. The period between the beginning of infestation to the manifestation of the first clinical symptoms is, however, strain dependent: 4 days for ticks from Warmbaths, and at least 5 days for all other strains.     

Oviposition and incubation in Boophilus decoloratus (Koch, 1844) (Acarina: Ixodidae)

Studies on the duration of the oviposition and incubation periods of Boophilus decoloratus (Koch, 1844) revealed that these non-parasitic periods are temperature dependent, increase in temperature causing shortening of the periods. Humidity had no effect on duration of either the oviposition or the incubation periods. The relation between the mass of engorged female ticks and that of the eggs they produced was found to be linear. The viability of eggs produced during the first 13 days of oviposition (at 26 degrees C) was greater than that of eggs laid subsequently. The critical temperature for B. decoloratus eggs was found to be 42 degrees C and they were shown to be unable to take up water vapour from damp atmospheres. Both temperature and humidity affected the hatch of eggs. A simple model of the relations between the physical factors of the environment and the various biological phenomena studied has been given.     

Seasonal dynamics and hosts of Amblyomma triste (Acari: Ixodidae) in Argentina

The seasonal dynamics and host usage of Amblyomma triste in Argentina were analyzed. Adults of A. triste were present from early winter to mid-summer, with the peak of abundance from late winter to mid-spring (August to October). Larvae and nymphs were found from December to June, with the peak of abundance in summer. There were no differences among the biological parameters (pre-moult period of larvae and nymphs, pre-oviposition period of females, and minimum incubation period of eggs) of engorged ticks exposed to different photoperiod regimens at the laboratory, but the periods for each biological parameter obtained from ticks exposed in the field were significantly longer than those from the laboratory. Field results fit better with the data of seasonal distribution of each stage. Morphogenetic diapause was not detected, but complementary studies should test the presence of behavioral diapause. Rodents of the subfamily Sigmodontinae (Akodon azarae, Oligoryzomys flavescens, Oligoryzomys nigripes, Oxymycterus rufus and Scapteromys aquaticus) are the principal hosts for immature stages of A. triste, the caviid Cavia aperea could be another potential host for these stages, and birds are exceptional hosts for larvae and nymphs. Regarding hosts of adults in Argentina, domestic and wild large-sized mammals belonging to different orders (cattle, dog, horse, Blastocerus dichotomus and Hydrochoerus hydrochaeris) serve as hosts for adults of this tick species. In conclusion, A. triste has a life cycle of 1 year with adults feeding on large endemic and introduced mammals and immature stages using sigmodontine and caviid rodents as hosts.     

Acaricidal activity of thymol on larvae and nymphs of Amblyomma cajennense (Acari: Ixodidae)

The aim of the present study was to evaluate the acaricidal efficacy of thymol on unengorged and engorged larvae and engorged nymphs of Amblyomma cajennense. To perform the test for unengorged larvae, the larval packet technique was employed and mortality was evaluated 24h after the test, while for engorged larvae and engorged nymphs the immersion technique was employed and mortality was evaluated after 15 days. In all the experiments, the following concentrations of thymol were tested: 2.5, 5.0, 10.0, 15.0 and 20.0mg the thymol/ml. The control group was exposed to water and 1% DMSO and there were 10 repetitions for each treatment. The values found for mortality of unengorged larvae were 18.2%, 51.8%, 97.6%, 93.5% and 94.5%, and for engorged nymphs the values were 26.0%, 92.2%, 100.0%, 100.0%, 100.0%, in concentrations of 2.5, 5.0, 10.0, 15.0 and 20.0mg of thymol/ml, respectively. In the test with engorged larvae, mortality was 100.0% in all treatments. Based on the results, it is possible to conclude that thymol has acaricidal activity against immature stages of A. cajennense.     

Effect of moxidectin against natural infestation of the cattle tick Boophilus microplus (Acarina: Ixodidae) in the Mexican tropics

The study was divided in to two trials and carried out in a ranch in eastern Yucatan state, Mexico. In the first trial, two groups of 15 BostaurusxBosindicus heifers, 6-12 month of age and naturally infested with Boophilus microplus ticks were used. Heifers in Group 1 were treated with a 1% injectable formulation of moxidectin at the dose of 0.20mg/kg body weight by subcutaneous injection. The other group remained as untreated controls. Number of immature and engorging female ticks were assessed on days 0, 7, 14, 21, 28 and 35 post-treatment (PT). The efficacy of moxidectin on adult ticks from day 7 to 28 PT was greater than 95%. The efficacy decreased to 74.9% by day 35. In the second trial, animals in Group 1 were treated with the moxidectin product as before, while cattle in Group 2 were treated according to the routine procedure for the control of ticks on that property (125 g/l amitraz as a dip). Treatment of all cattle was repeated four times at intervals of 28 days. The efficacy of the experimental moxidectin treatment was similar to that of the routine amitraz treatment, i.e., greater than 99%.     

The developmental success of Amblyomma hebraeum and Amblyomma marmoreum on the leopard tortoise, Geochelone pardalis

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.     

The ecology of the African vectors of heartwater, with particular reference to Amblyomma hebraeum and Amblyomma variegatum

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.     

Biochemical studies on the salivary glands and haemolymph of Amblyomma hebraeum

The functional significance of some components of salivary glands and of their secretion and of haemolymph of Amblyomma hebraeum and other tick species is reviewed with respect to host responses at the attachment site, the survival of specific pathogens in the vector, the transmission of pathogens and immunological responses of the host to tick infestation.     

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.     

Amblyomma aureolatum (Pallas, 1772) and Amblyomma ovale Koch, 1844 (Acari: Ixodidae): hosts,distribution and 16S rDNA sequences

DNA sequences of Amblyomma aureolatum (Pallas, 1772) and Amblyomma ovale Koch, 1844 were obtained to determine genetic differences between these tick species. Collections of these species are discussed in relation to distribution and hosts. Seven ticks collections (four from Brazil, one from Argentina, one from Uruguay and one from USA) house a total of 1272 A. aureolatum (224 males, 251 females, 223 nymphs and 574 larvae) and 1164 A. ovale (535 males, 556 females, 66 nymphs and 7 larvae). The length of the sequenced mitochondrial 16S rRNA gene fragment for A. aureolatum was 370bp and for A. ovale was 373bp. The DNA sequence analysis showed a 13.1% difference between the two species. Apart from one male A. ovale found on a toad, all adult ticks were found on mammals. The majority of adult specimens of both tick species were removed from Carnivora (96.1 and 84.3% of A. aureolatum and A. ovale, respectively), especially from dogs (53.1% of A. aureolatum, and 46.4% of A. ovale). Collections on wild Canidae were higher for A. aureolatum (23.3%) than for A. ovale (7.1%). On the other hand, collections of A. ovale adults on wild Felidae were higher (18.3%) than findings of A. aureolatum (9.2%). The contribution of other mammalian orders as hosts for adults of A. aureolatum and A. ovale was irrelevant, with the exception of Perissodactyla because Tapiridae contributed with 13.0% of the total number of A. ovale adults. Adults of both tick species have been found occasionally on domestic hosts (apart of the dog) and humans. Most immature stages of A. aureolatum were found on Passeriformes birds, while rodents and carnivores were the most common hosts for nymphs and larvae of A. ovale. A. aureolatum has been found restricted to the Neotropical region, covering the eastern area of South America from Uruguay to Surinam, including northeastern Argentina, eastern Paraguay, southeastern Brazil and French Guiana. A. ovale showed a distribution that covers the Neotropical region from central-northern Argentina throughout the Neotropics into the Nearctic region of Mexico with a few records from the USA, also with collection sites in Paraguay, Bolivia, most Brazilian states, Peru, Ecuador, French Guiana, Surinam, Guyana, Trinidad & Tobago, Venezuela, Colombia, Panama, Costa Rica, Nicaragua, Belize, Guatemala and several states of Mexico.