The effects of nutritional status of rabbits and sheep on their resistance to the ticksRhipicephalus evertsi evertsi andR. appendiculatus

Rabbits and sheep were exposed to low-and high-protein diets and subsequently infested three times with adults ofRhipicephalus appendiculatus andRhipicephalus evertsi evertsi. The mean weight ofR.e. evertsi females which dropped from rabbits maintained on a high-protein diet decreased from 515.0±24.9 mg (naive) to 381.5±25.0 (second infestation) to 340.3±23.3 mg (third infestation) while the weight of ticks fed on animals which were exposed to a low-protein diet did not change significantly (2.7%). The mean weight of engorged females ofR. appendiculatus which completed their blood meal on rabbits (high protein) decreased from 520.9±31.8 (naive) to 369.3±39 mg (3rd infestation), a significant decrease of 29.1% compared to a 12.3% decrease in weight between the 1 st and 3rd infestation of females fed on animals on a low-protein diet.Rhipicephalus e. evertsi fed on sheep exhibited the same phenomenon. The mean decrease in weight of 4rd-infestation ticks which dropped from sheep fed lucerne was 26.2% compared to 16.6% for ticks from sheep which were fed on grass.Hosts maintained on a low-protein diet failed to acquire resistance to ticks, lost weight and developed anaemia while those on a high-protein diet developed resistance, maintained weight and did not develop anaemia.The nutritional stress of the hosts and its application in South Africa are discussed.     

The effects of tick numbers and intervals between infestations on the resistance acquired by guinea-pigs to adults of Rhipicephalus evertsi evertsi (Acari: Ixodidae)

Guinea-pigs were infested three times at short (1 week) intervals or long (10 week) intervals between successive infestations with low (1), medium (8) and high (15) numbers of adult Rhipicephalus evertsi evertsi. To compare the resistance developed by the hosts at short and long intervals between infestations, a challenge (fourth) infestation was performed with the high number of ticks. Resistance was assessed by comparing the mean weight of engorged female ticks that dropped from the hosts. Concentrations of beta globulins in the host sera were also monitored. Different tick Ioads (low, medium and high) and infestation intervals had a similar influence on the reduction in weight of the females which was between 60–70% after the final challenge. However, the concentration of beta globulins, was highest in the guinea-pigs exposed to medium and high numbers of ticks with long infestation intervals, probably because of an increase in the production of protective antibodies in response to more intensive antigenic challenge. The relationship between engorgement weight and beta globulin levels in host sera is discussed.     

Rhipicephalus appendiculatus feeding on rabbits and cattle: Salivary-gland responses to varying host resistance

AdultRhipicephalus appendiculatus ticks were fed as three sequential infestations on both rabbits and cattle. The feedings at first infestation on naive hosts were optimum for the ticks, whereas at third infestation the hosts were resistant, as expressed by reduced tick feeding performance. Ticks from naive and resistant hosts were examined for histological differences of salivary glands. In ticks fed on resistant rabbits there was a large increase in the synthesis of glycoprotein secretory granules in thec ₁ cells compared with ticks fed on naive rabbits. In ticks fed on naive and resistant cattle, the activity of thec ₁ cells was less than in ticks fed on naive and resistant rabbits. It was concluded that the salivary glands are able to respond selectively to conditions at the feeding site, and that this may be advantageous to the tick.     

Acquired resistance to ixodid ticks induced by tick cement antigen

Antisera from guinea pigs made resistant to infestation with an ixodid tick of east and central Africa,Rhipicephalus appendiculatus, were used to identify the tick antigens they recognized by immunoblotting. Most of the antigens were found in tick salivary glands and in tick attachment cement. Antisera fromR. appendiculatus-resistant guinea pigs also recognized some salivarygland antigens in ticks of other species (R. pulchellus, R. evertsi, Amblyomma variegatum andA. gemma). Antibodies against the most strongly recognizedR. appendiculatus antigen, a 20-kDa molecule, were only poorly reactive with similar-sized molecules in the other ticks. A 94-kDa antigen, which appeared to have broader cross-reactivity, was purified fromR. appendiculatus attachment cement, and a monospecific rabbit serum was raised against it. This antiserum clearly recognized a molecule of similar molecular weight inR. pulchellus andR. evertsi. Intravenous inoculation of rabbits with the purified molecule elicited delayed-type hypersensitivity to the antigen. The hypersensitive rabbits demonstrated resistance to feeding ofR. appendiculatus ticks but slight enhanced feeding ofR. pulchellus ticks. These results are discussed with respect to their relevance for artificial induction of tick-feeding resistance.     

Investigations into lymphocyte transformation and histamine release by basophils in sheep repeatedly infested with Rhipicephalus evertsi evertsi ticks

The immune response of a natural host of Rhipicephalus evertsi evertsi to feeding by this tick species was investigated with respect to the effects of tick salivary gland extracts on the transformation of peripheral blood lymphocytes and the release of histamine by basophils obtained from repeatedly infested sheep.The results indicated that there was no stimulation of lymphocyte transformation but that histamine release was elevated 10 fold after four infestations.Although this suggests a hypersensitivity reaction, believed to be a major factor in resistance to tick feeding, it was observed that ticks fed normally even after four infestations with 28 day intervals in between. These results emphasize the adaptation of ticks to feeding on their natural hosts.     

C3 levels in the sera of rabbits infested and reinfested withIxodes ricinus L. and in midguts of fed ticks

Serum C3 levels of rabbits infested 3 times withIxodes ricinus L. females and C3 in midgut extracts of fed ticks have been measured by a single radial immunodiffusion test.From the first tick attachment, the mean serum C3 level of hosts increased. A peak of C3 occurred 6 days after the beginning of each infestation and was highest during the third infestation (about 8 times more pronounced than the level measured before the first). After the end of all infestations of the rabbits, the serum C3 level decreased and approached normal levels.Modifications of serum C3 levels during reinfestations influenced C3 contents in the blood meal of fed ticks. Midguts of ticks fed during the third infestation contained more C3 than midguts of ticks of the same engorged weights fed during the first or second infestations.     

Monitoring of naturally acquired and artificially induced immunity toAmblyomma variegatum andRhipicephalus appendiculatus ticks under field and laboratory conditions

The ability of rabbits, goats and cattle to acquire immunity to the ixodid ticksAmblyomma variegatum andRhipicephalus appendiculatus was studied under laboratory and field conditions. Rabbits were successfully immunized with crude salivary gland extract (SGE) and midgut extract (ME) obtained from flat or partly fed femaleR. appendiculatus ticks. The lowest numbers of larvae were produced by females fed on rabbits immunized with unfed midgut extract. Similar reductions in larval production could be induced after three infestations of rabbits with adultR. appendiculatus. Also, successive feedings of nymphs ofR. appendiculatus on rabbits resulted in significantly reduced engorgement weights. Skin testing with SGE induced delayed-type hypersensitivity reactions, which could be correlated with immunity toR. appendiculatus in rabbits. Moreover, circulating antibodies were detected in rabbits with an ELISA using SGE ofR. appendiculatus.Immunity toA. variegatum nymphs could be induced in rabbits by repeated infestations, but this failed in goats. Immunization of goats with midgut extract from adultA. variegatum did not protect against subsequent nymphal challenge, but strong skin reactions were noticed when adults ticks fed on immunized goats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of SGE and ME fromA. variegatum revealed the presence of 48 protein bands in SGE and 29 bands in midgut extract. Western blotting employing serum from a rabbit immune toR. appendiculatus recognized a number of bands in SGE fromR. appendiculatus, but also in SGE ofA. variegatum.Immunity acquired by cattle to ixodid tick infestations under field conditions was monitored by skin testing with SGE and western blot analysis. In general, cattle with the lowest tick numbers manifested the strongest delayed-type hypersensitivity responses. Finally, western blot analysis employing sera from tick-infested and tick-naive cattle could not be related to actual immune status.     

Resistance and cross-resistance in rabbits to adults of three species of African ticks (Acari: Ixodidae)

Resistance to Rhipicephalus appendiculatus, Amblyomma variegatum and Amblyomma hebraeum was investigated in the laboratory by infesting rabbits with adults of each of the three species followed by homospecific or heterospecific secondary infestations. Significantly lower female engorged weights and egg mass weights were taken as evidence of protective immunity. Following a single infestation with adults, rabbits developed homospecific protective immunity (resistance) to only R. appendiculatus and A. hebraeum; primary infestation with A variegatum did not protect against secondary infestation with the same species. There was no cross-resistance (heterospecific protective immunity) between the species except for one-way protection between R. appendiculatus and A. variegatum; primary infestation with R. appendiculatus protected against secondary infestation with A. variegatum, but not vice versa. The results from ELISA did not indicate any correlation between serum antibodies to soluble antigens from salivary gland extracts and protective immunity. Post-infestation sera from rabbits infested with each of the three species reacted strongly to their respective salivary gland extracts. Despite the high reactivity of A. variegatum serum with salivary gland antigens from all three species, A. variegatum-infested rabbits did not show any homospecific or heterospecific immunity; on the other hand, although R. appendiculatus serum did not react positively to A. variegatum antigens, infestation with R. appendiculatus protected against a subsequent A. variegatum infestation.     

Development of resistance in laboratory animals to adults of the tick Rhipicephalus evertsi evertsi

Acquired resistance to adults of the two-host tick Rhipicephalus evertsi evertsi Neumann has been demonstrated in guinea-pigs and rabbits. Four infestations of both hosts with R.e.evertsi adults resulted in a significant reduction in the mean weight of the engorged females. A decline in the mean weight of the female ticks was also observed in ticks which fed on a rabbit previously injected with serum taken from a rabbit resistant to R.e.evertsi. This suggests that humoral immunity may have an important role in the acquired resistance to ticks. In both hosts an increase in the level of serum globulins was recorded. In rabbits the level of gamma globulin was affected, while in guinea-pigs an increase was observed in the concentration of alpha 1 and beta globulins. The differences in host responses to the R.e.evertsi adults are discussed.     

Changes in immunity to Ixodes ricinus by rabbits infested at different levels

Abstract. Two groups of rabbits were infested twice with different numbers of Ixodes ricinus adults: one group (high infestation) with twenty-five females and twenty-five males and the other group (low infestation) with five pairs. A third infestation was performed in both groups with fifteen adult pairs. Tick biology was monitored for resistance effects. At the second infestation, the feeding and the egg production were more perturbed in ticks fed on high infestation rabbits. The embryogenesis was only affected in ticks from high infestation rabbits. At the third infestation, resistance was increased only in low infestation rabbits, which became more resistant than high infestation rabbits. The blastogenic response of peripheral blood lymphocytes and antibody production against ticks were assessed. A salivary gland extract and an integumental antigen from Lricinus adult females were able to initiate lymphocyte proliferation. The response was significantly higher in high infestation rabbits, especially at the end of the second infestation, and higher in low infestation rabbits during the third infestation. Non-specific proliferation with concanavalin A was temporarily decreased in both rabbits groups during the first and the second infestations. Specific antibody response to salivary and integument antigens were always the highest in high infestation rabbits. The involvement of tick-induced immunosuppression is discussed.     

Development of acquired resistance precipitating antibody in rabbits experimentally infested with females of Haemaphysalis longicornis (Ixodoidea: Ixodidae).

The resistance to the ixodid tick, Haemaphysalis longicornis (parthenogenetic Okayama strain), manifested as a reduction in engorged body weight, developed in rabbits subjected to a series of adult female infestations. A single infestation with females always produced resistance in hosts. This production appeared to depend little on the number of ticks per infestation. Unlike the previous papers, this study revealed that there was no reduction in the mean recovery rate of engorged females when ticks fed on a rabbit repeatedly infested with the ticks. A series of infestations were carried out comparatively to investigate the major biological characters of ticks, such as feeding, oviposition, and hatchability of eggs. As a result, there were no marked differences in these characters among the infestations. Especially, no differences were noticed in the concentration of ingested blood meal in detached females among the infestations. Precipitating antibodies were found in the sera of rabbits resistant to the tick-bite. They were subjected to fractionation by Sephadex G-200 chromatography and tested for sensitivity to 2-mercaptoethanol. As a result, they were proved to be of immunoglobulin of 7 S class.     

Control of induced infestations of three African multihost tick species with sustained-release ivermectin

The efficacy of ivermectin, released intraruminally from a 28-day-delivery device was evaluated in two titration studies against induced infestations of adultRhipicephalus appendiculatus, R. evertsi andHyalomma truncatum on cattle. Cattle were given a sufficient number of devices to release ivermectin at approximately 20, 40, 60 or 80 g kg^–1 day^–1 at a steady-state rate 7–28 days after administration. Tick mortality was recorded, engorged female ticks were weighed and individually incubated, and reproductive data were recorded to determine a reproductive index for the species at various dose levels. Mortality of male and female ticks compared to that of controls was directly related to the daily dose of ivermectin, as was the number of ticks not engorging. Ticks fed on ivermectin-treated cattle had a smaller mass when engorged and laid smaller egg-masses, both absolutely and as a proportion of engorged mass.The index of reproduction ofR. appendiculatus was reduced by more than 99.9% at 20 g kg^–1 day^–1, and the reproductive indices ofR. evertsi andH. truncatum were reduced by more than 99.9% at dose rates of 40 g kg^–1 day^–1 and above.Practical implications of the application of sustained-release ivermectin for the control of multihost ticks and tick-borne diseases are discussed.     

Feeding performance ofAmblyomma variegatum (Acarina: Ixodidae) fed repeatedly on rabbits

Rabbits infested with different stages ofAmblyomma variegatum Fabricius, 1794 became resistant to subsequent infestations by the same tick. Resistance was manifested by a reduction of 73.6% in the mean engorged weight of female ticks by the 3rd infestation. By the 5th infestation, only 70% of the nymphs engorged and their mean engorged weight was 57.7% of that of nymphs fed on tick-naive control rabbits. In the case of larvae, there was a 22.8% reduction in their mean engorged weight by the 6th infestation. Based on increases in body length while feeding on tick-naive rabbits, the nymphs could be divided into four feeding categories, i.e. Nl (unfed), N2, N3 and N4 (increasing states of engorgement). While 92–96% of ticks which dropped from susceptible rabbits fitted into feeding category N4, only 28% of those that dropped from tick-resistant rabbits fitted into that category. The remainder of the ticks fitted into categories N3 (60%) and N2 (12%). The majority of those ticks with reduced weight developed into adults which had an atypical scutal ornamentation pattern, in that an additional pair of lateral spots was regularly observed on the males. The females of such ticks deposited small numbers of eggs from which no larvae hatched.     

Enhancement of tick-borne encephalitis virus transmission by tick salivary gland extracts

Abstract. To investigate the role of ticks in TBE virus transmission, salivary gland extract (SGE) was derived from partially fed female Ixodes ricinus, Dermacentor reticulatus and Rhipicephalus appendiculatus ticks. Guinea-pigs were infested with uninfected R.appendiculatus nymphs and inoculated with a mixture of TBE virus and SGE or with virus alone. The number of ticks which on average acquired virus from feeding on animals inoculated with TBE virus and SGE from partially fed ticks was 4-fold greater than the number that became infected by feeding on animals inoculated with virus alone or virus plus SGE from unfed I.ricinus. Viraemia was detected in 67% of guinea-pigs inoculated with virus plus SGE compared to 30% of guinea-pigs inoculated with virus alone. Virus titres in the blood were similar for both groups of animals [range 2.0-2.8 log₁₀ plaque-forming units (PFU)/ml of blood]; however, the number of ticks that became infected was significantly higher on animals inoculated with virus plus SGE from partially fed ticks. No significant difference was observed with respect to the tick species used to derive SGE. The results indicate that TBE virus transmission is enhanced by factor(s) associated with the salivary glands of feeding ticks, and that these factor(s) may facilitate efficient transmission of TBE virus between infected and uninfected ticks even when they feed on hosts that have no detectable viraemia.     

Attractivity of cattle infested by Amblyomma variegatum (Acari: Ixodidae) for conspecific adult ticks from the field in Guadeloupe

Four field experiments were conducted with creole cattle in Guadeloupe to study the attractivity for adult ticks of animals previously infested with males of Amblyomma variegatum producing aggregation attachment pheromones (AAPs). In each experiment, two groups of cattle were used; the first group was infested with adult A. variegatum and the second group was kept free of ticks and pheromones by acaricidal treatment and by washing the hair and skin of previously infested sites. Both groups were then exposed to natural infestation by ticks present in the environment or by ticks bred in the laboratory and released on the pasture. The number of additional ticks infesting animals were compared between the treated and control groups. There were no significant differences between both groups in the numbers of new male ticks infesting the animals during the first days following the beginning of the experiment. Thereafter, comparison of the slopes of infestation indicated that infested cattle were no more attractive for male ticks than uninfested hosts. Uninfested cattle were spontaneously and rapidly infested by male ticks. It is concluded that carbon dioxide or another host component was a major attractant for A. variegatum males. Female ticks attached on predilection sites exclusively in the presence of AAP-producing males, i.e. 5–10 days after the attachment of the first males. Based on these results we postulate that slow-release devices impregnated with pheromones have no additional attractive effect on A. variegatum males under Caribbean conditions. However, they may be useful in inducing the attachment of females, but only in the first days preceding the arrival of pioneer AAP-producing males. © Rapid Science Ltd. 1998     

Morphological identification of ticks (Acari: Ixodidae) infesting donkeys (Equus asinus) in Maputo Province,Mozambique

Donkeys (Equus asinus) are rustic animals, but in Africa’s poorest regions, they can present multiple health problems, including tick infestation. The study’s objective was to determine the species composition of ticks that infest donkeys in Maputo Province (Mozambique). Ticks were collected in five conveniently selected southern districts of Maputo Province (Moamba, Matutuíne, Marracuene, Boane, and Matola) and were identified to species level using a stereoscopic microscope with the aid of dichotomous identification keys. In total, 500 ticks were collected from all 88 selected donkeys. Three genera of ticks were identified, namely Rhipicephalus (97.2%; 486/500), Amblyomma (2.2%; 11/500), and Hyalomma (0.6%; 3/500). Seven species were identified, of which Rhipicephalus evertsi evertsi with 50.4% (252/500) was the most prevalent, followed by Rhipicephalus appendiculatus (27.4%; 137/500), Rhipicephalus turanicus (11.6; 10/500), Rhipicephalus (boophilus) microplus (6.8; 20/500), Amblyomma hebraeum (2.2%; 11/500), Rhipicephalus sanguineus (1%; 5/500) and Hyalomma truncatum (0.6%; 3/500). Rhipicephalus evertsi evertsi occurred in all locations, whereas Hyalomma truncatum occurred only in the Boane district. Males were the most prevalent (67.2%; 336/500). The study revealed that donkeys in Maputo Province were infested with seven tick species of which R. evertsi evertsi was the main species.

     

Ecology and phenology of ticks in Zambia: Seasonal dynamics on cattle

A study of the seasonality and infestation rates of ticks was carried out in 11 cattle herds in different ecological habitats in Zambia between 1980 and 1982. Wherever possible supplementary data were obtained from opportunistic collections from cattle and other hosts.Analysis of over 1000 tick collections from cattle indicated that infestation rates of the most important species,Amblyomma variegatum andRhipicephalus appendiculatus vary in different ecological habitats: (i) In Western Province, infestations are much lower than elsewhere; (ii) in Central and Southern Provinces, moderate to high infestations occur; and (iii) in Eastern Province,R. appendiculatus numbers are generally low andA. variegatum numbers are moderate.These two species, however, have similar life cycles throughout their range with one generation per year. Larvae occur mainly from March to May, nymphae from May to September, and adults ofA. variegatum from October to December and ofR. appendiculatus from December to April. Boophilus decoloratus appears to have two to four generations per year but is uncommon during the rainy season. In some areas in central ZambiaRhipicephalus compositus adults are seasonally common in September–October whereasRhipicephalus evertsi is more or less ubiquitous. Low to moderate infestations ofHyalomma truncatum andHyalomma rufipes occur in most areas.At least 14 other less common or rare species ofRhipicephalus, Amblyomma, Haemaphysalis andIxodes were taken infrequently from cattle. These and other host-specific species were also collected from dogs, sheep, various wildlife hosts and the environment.Infestation rates, seasonality and host-relationship of tick species are discussed in relation to their ecology. Relevant biosystematic and disease relationships are reviewed briefly. The baseline data derived from this study are adequate for integrated analysis with those from other ecological and economic investigations to formulate tick control strategies.     

Resistance in cattle againstRhipicephalus appendiculatus with an assessment of cross-resistance toR. pulchellus (Acari: Ixodidae)

A comparison of the yield of engorged nymphs ofRhipicephalus appendiculatus andR. pulchellus was carried out between cattle highly resistant toR. appendiculatus but susceptible toR. pulchellus, and cattle and rabbits susceptible to both species.Resistant cattle yielded fewer and smallerR. appendiculatus nymphs than either susceptible cattle or rabbits. More nymphs of both tick species dropped from susceptible cattle but no differences were detected in the mean weight of engorgedR. pulchellus nymphs fed onR. appendiculatus-resistant and susceptible cattle, although resistant animals yielded more nymphs ofR. pulchellus than ofR. appendiculatus.An acute inflammatory reaction, accompanied by intense pruritus and grooming, was observed in the ears of the resistant cattle infested withR. appendiculatus, but no reaction was detected in the opposite ears whereR. pulchellus was feeding.The low cross-resistance between these two closely related tick species suggests that different antigens may be involved in the development of resistance in cattle to different tick species.     

Immunisation of rabbits against the brown ear tick,Rhipicephalus appendiculatus using tick haemolymph

Tick naive rabbits were immunised with haemolymph components from partially fed Rhipicephalus appendiculatus adult ticks and subsequently challenged with all the developmental instars of the tick. The results obtained showed that the rabbits were rendered resistant to all the instars of the tick. However, the resistance was more pronounced in adult ticks than in the immature stages. The resistance was manifested as a reduction in the number of ticks that fed successfully to engorgement, reduced engorgement weights and reduced fecundities. Re challenging the resistant experimental rabbits with all the developmental instar stages of Rhipicephalus appendiculatus showed that resistance was maintained in subsequent infestations.     

<Emphasis Type="Italic">In vitro</Emphasis> splenocyte proliferation responses of BALB/c mice to salivary gland extracts of three ixodid tick species (Acari: Ixodidae)

In vitro proliferation and cytokine production were investigated in BALB/c mice splenic cell cultures that were stimulated with concanavalin A (ConA) and lipopolysaccharide (LPS) and simultaneously exposed to salivary gland extracts (SGE) of unfed and partially fed adult ixodid ticks (Ixodes ricinus, Rhipicephalus appendiculatus, Amblyomma variegatum). Generally, tick SGE enhanced proliferation of unstimulated splenocytes and SGE of unfed ticks suppressed mitogen induced proliferation. Partially fed R. appendiculatus and A. variegatum suppressed ConA responses, while partially fed I. ricinus stimulated both ConA and LPS induced proliferation. A. variegatum and R. appendiculatus females slightly enhanced LPS responses 2 days after attachment but suppressed them at the end of the slow feeding phase. In 72 h ConA induced cell cultures, interferon gamma (IFN-γ) production was suppressed by SGE of all ticks, interleukin (IL)-10 production was enhanced by unfed I. ricinus and partially fed A. variegatum males and IL-5 production was enhanced by feeding R. appendiculatus females and A. variegatum males. The study revealed variability in the responsiveness of murine splenocytes to SGE of different ixodid tick species, whereby patterns of host immunomodulation within one tick species differed between sexes and changed during feeding.