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.     

Experimental infection of the rabbit tick,<Emphasis Type="Italic"> Haemaphysalis leporispalustris</Emphasis>, with the bacterium<Emphasis Type="Italic"> Rickettsia rickettsii</Emphasis>, and comparative biology of infected and uninfected tick lineages

The present study consisted of two experiments that evaluated experimental infections of Haemaphysalis leporispalustris ticks by a Brazilian strain of Rickettsia rickettsii, and their effect on tick biology. In experiment I, ticks were exposed to R. rickettsii during the larval, nymphal or adult stages by feeding on rabbits (Oryctolagus cuniculus) needle-inoculated with R. rickettsii, and thereafter reared on uninfected rabbits for the entire next tick generation. Regardless of the tick stage that acquired the infection, all subsequent tick stages were shown to be infected by PCR (infection rates varying from 1.3 to 41.7%), and were able to transmit R. rickettsii to uninfected rabbits, as demonstrated by rabbit seroconversion, guinea pig inoculation with rabbit blood, and PCR on rabbit blood. In Experiment II, ticks were exposed to R. rickettsii during the larval stage by feeding on rabbits co-infested with R. rickettsii-infected adult ticks, and thereafter reared on uninfected rabbits until the next generation of larvae. Again, all subsequent tick stages were shown to be infected by PCR (infection rates varying from 3.0 to 40.0%), and were able to transmit R. rickettsii to uninfected rabbits. Thus, it was demonstrated that larvae, nymphs, and adults of H. leporispalustris were able to acquire and maintain the R. rickettsii infection by transstadial and transovarial transmissions within the tick population, with active transmission of the bacterium to susceptible rabbits by all parasitic stages. Analyses of biological parameters of uninfected and R. rickettsii-infected tick lineages were performed in order to evaluate possible deleterious effects of R. rickettsii to the infected tick lineages. Surprisingly, all but one of the four R. rickettsii-experimental groups of the present study showed overall better biological performance than their sibling uninfected control ticks. Results of the present study showed that H. leporispalustris could support infection by a high virulent strain of R. rickettsii for at least two generations, in which infected tick lineages tended to have better performance than uninfected ticks. Our results support a possible role of H. leporispalustris in the enzootic maintenance of R. rickettsii in Latin America, as previously suggested by earlier works.     

Immunology of interactions between ticks and laboratory animals

There is good reason to believe that the resistance to ixodid ticks acquired by guinea pigs, rabbits and mice is immunologically mediated. One proposed mechanism for this resistance, which may well be common to all these laboratory animals, involves cutaneous hypersensitivity reactions. Basophils accumulate at tick attachment sites in the skin of resistant animals and degranulate in response to tick salivary antigens, releasing histamine and other mediators. The mediators may directly cause ticks to cease salivating and feeding and then to detach, or they may induce reflex grooming reactions by the host, leading to the removal of ticks from the itching skin.There are gaps in the evidence supporting this hypothesis, and it is likely that other modes of tick resistance remain to be described. However, it should be recognized that, although there have been a few details added to the story in the last fifty years, William Trager's original classic observations and conclusions still stand as the core of the current dogma.     

A Review of Studies on the Transmission of Anaplasma phagocytophilum from Sheep: Implications for the Force of Infection in Endemic Cycles

We review the findings of a longitudinal study of transmission of the intracellular tick-borne bacterium Anaplasma phagocytophilum from sheep to Ixodes ricinus ticks under natural conditions of tick attachment in the UK. In this study, sheep-to-tick transmission efficiency varied in a quadratic relationship with the number of adult ticks that were feeding on the sheep. We raise the hypothesis that this relationship may be due to conflicting effects of the density of ticks on bacterial survival and target cell (neutrophil) fluxes at the tick-host interface: in the same sheep at the same time, resistance to ticks was progressively inhibited with increasing number of feeding adult ticks, and investigation of serological responses to tick antigens suggesting loss of resistance may be associated with polarisation of host Th1 to Th2 type responses to ticks. We also raise the hypothesis that these properties, with superimposed effects on tick survival, may mean that variation in tick density is an important causal factor of observed variations in the force of A. phagocytophilum infection amongst different geographic foci. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Spatial genetic structure of the ectoparasite Ixodes uriae within breeding cliffs of its colonial seabird host

To examine the potential importance of the spatial subdivision of hosts for the functioning of parasite populations, we analysed patterns of local genetic structure within natural populations of the seabird ectoparasite, Ixodes uriae, at the scale of the host breeding cliff. The seabird hosts of this parasite nest in dense colonies with a hierarchical spatial organisation (individual nests-breeding cliffs-colony). Using eight microsatellite markers and samples from three breeding cliffs of the Black-legged kittiwake (Rissa tridactyla), we found that tick populations were indeed genetically structured at this spatial scale. However, the nature of this structuring depended on the characteristics of the cliffs considered. Both the host nest and cliff topography seemed to be important factors in the isolation of tick groups, but their relative roles may depend on the size of the local parasite population. We found no evidence of isolation by distance within a cliff suggesting that independent tick dispersal may not be a significant force influencing population structure in highly infested cliffs. However, genetic structure seemed to decrease with tick life stage, nymphal ticks being more strongly structured than adult ticks. These results may be related to the clustering of tick progeny combined with differential mortality and dispersal probabilities of each life stage. Overall, results indicate that the spatial organisation of hosts can indeed have important consequences for the population genetic structure of their parasites and, thus, may modify parasite dynamics and the scale at which local coevolutionary processes occur.     

Goats,hares, and rabbits as hosts for the New Zealand cattle tick,Haemaphysalis longicornis

Abstract

Feral goats and hares were commonly infested by immature stages of the New Zealand cattle tick, Haemaphysalis longicornis. No explanation could be found for the low prevalence of adult ticks on these hosts. The ears of both host species were almost the exclusive feeding site of the ticks and this may be a consequence of grooming behaviour. Another potential host, the rabbit, was examined but few were found to be infested.

The less restricted range of non-domesticated hosts, together with feeding habits that differ from domestic stock, make them an important additional source of information on the ecology and seasonal pattern of activity of H. longicornis. Also, they are a source of contamination for tick-free pasture, and could possibly maintain the tick population in the absence of sheep and cattle. It is important that their role as alternative hosts be understood and considered in tick-control programmes.     

A comparison of infestation patterns by Ixodes ticks in urban and rural populations of the Common Blackbird Turdus merula

Although spatial variation in the patterns of parasite infestations among host populations may have important ecological and epidemiological consequences, the causes underlying such variation are poorly known. In the context of a long-term study on the population biology of Common Blackbirds Turdus merula , we examined the prevalence and intensity of infestation by Ixodes ticks between birds living in rural vs. urban habitats. The overall prevalence of tick infestations was significantly higher in the rural habitat where 74% of individuals ( n  = 130) were infested. This result contrasted markedly with the situation in the urban habitat where less than 2% of individuals ( n  = 360) carried ticks. There was no significant effect of the sex of the host on the intensity or prevalence of tick infestations. There was a significant effect of the age of the host on tick infestations essentially due to the absence of ticks on nestlings. Possible mechanisms responsible for the differences between habitats could include differences in tick survival and/or host resistance towards ticks. Previous studies have shown higher population densities and suggested longer survival for Blackbirds in urban than in rural habitats. Given that ixodid ticks are known to transmit pathogens like Borrelia spp. to wild birds, and that Blackbirds can act as reservoirs for these pathogens, the infection patterns observed in our study area provide a suitable situation to study the interrelations between ticks, Blackbirds and pathogens.     

Host-dependent genetic structure of parasite populations: differential dispersal of seabird tick host races

Abstract Despite the fact that parasite dispersal is likely to be one of the most important processes influencing the dynamics and coevolution of host-parasite interactions, little information is available on the factors that affect it. In most cases, opportunities for parasite dispersal should be closely linked to host biology. Here we use microsatellite genetic markers to compare the population structure and dispersal of two host races of the seabird tick Ixodes uriae at the scale of the North Atlantic. Interestingly, tick populations showed high within-population genetic variation and relatively low population differentiation. However, gene flow at different spatial scales seemed to depend on the host species exploited. The black-legged kittiwake ( Rissa tridactyla ) had structured tick populations showing patterns of isolation by distance, whereas tick populations of the Atlantic puffin ( Fratercula arctica ) were only weakly structured at the largest scale considered. Host-dependent rates of tick dispersal between colonies will alter infestation probabilities and local dynamics and may thus modify the adaptation potential of ticks to local hosts. Moreover, as I. uriae is a vector of the Lyme disease agent Borrelia burgdorferi sensu lato in both hemispheres, the large-scale movements of birds and the subsequent dispersal of ticks will have important consequences for the dynamics and coevolutionary interactions of this microparasite with its different vertebrate and invertebrate hosts.     

Competition,facilitation or mediation via host? Patterns of infestation of small European mammals by two taxa of haematophagous arthropods

1. We studied the effect of flea infestation on the pattern of tick (Ixodes ricinus and Ixodes trianguliceps) infestation on small mammals. 2. We asked (1) whether the probability of an individual host being infested by ticks was affected by its infestation of fleas (number of individuals and species) and (2) whether the abundance and prevalence of ticks in a host population was affected by the abundance, prevalence, level of aggregation, and species richness of fleas. 3. The probability of a host individual being infested by ticks was affected negatively by flea infestation. At the level of host populations, flea abundance and prevalence had a predominantly positive effect on tick infestation, whereas flea species richness had a negative effect on tick infestation. 4. The effect of flea infestation on tick infestation was generally greater in I. ricinus than in I. trianguliceps, but varied among host species. 5. It can be concluded that the effect of fleas on tick infestation of small mammals may be either negative or positive depending on the level of consideration and parameters involved. The results did not provide support for direct interactions between the two ectoparasite taxa, but suggested population and community dynamics and the defence system of the hosts as possible factors.     

Ticks (Acari: Ixodidae) parasitizing humans in an Atlantic rainforest reserve of Southeastern Brazil with notes on host suitability

While conducting projects on ticks from deer and on tick ecology in animal trails in an Atlantic rainforest reserve in Southeastern Brazil, researchers of our group were bitten by ticks several times. Some of these episodes were recorded. Three species of adult ticks attached to humans: Amblyomma brasiliense Aragão, Amblyomma incisum Neumann, and Amblyomma ovale Koch. Eight nymphal attachments with engorgement on humans were recorded. From these, six molted to adults of A. incisum, one to an adult of A. brasiliense, and one had an anomalous molting, therefore the adult tick could not be properly identified. Local reactions to tick attachment varied among individual hosts from almost imperceptible to intense. Especially itching, but hyperemia and swelling as well, were prominent features of the reaction. Overall it can be affirmed that human beings can be a physiologically suitable host species for ticks in the Atlantic rainforest and that itching was an important if not the major component of the resistance to tick bite.     

Towards a permanent solution for controlling cattle ticks

Acaricides are essential in the short-term but do not offer a permanent solution to tick control. This situation will not change without a change of approach. A vaccine against Boophilus microplus confers partial long-term control but has little immediate effect on tick burdens. The effectiveness of acaricides and vaccination is greatest for breeds of high tick resistance. High host resistance is the key to effective long-term tick control with total resistance the ultimate aim. While improvements to acaricides and vaccines are continuously pursued, improvements to the most important single factor controlling ticks, host resistance, have been neglected. Resistance is as heritable as milk yield or growth and in tropical breeds can be increased to very high levels by selection. Despite this there are no current examples of sustained selection for tick resistance. Temperate breeds have low resistance but because of high production potentials are favoured for crossbreeding with tropical breeds. This perpetuates the need for reliance on acaricides. Selection to increase polygenic resistance of temperate breeds is impractical. However, a quantum increase can be achieved by introgressing major resistance genes. Such a gene occurs in the Belmont Adaptaur and in suitable genetic backgrounds confers 100% resistance. Total resistance is achievable and provides a permanent solution to ticks.     

Genomic evidence for host-associated differentiation in an animal parasite,Dermacentor variabilis,the American dog tick

The process responsible for the formation of genetically distinct populations associated with different host species is known as host-associated differentiation (HAD). Many insect parasites of plants have been shown to exhibit HAD but there have been fewer studies of HAD in parasites of vertebrate animals. Previous to this study, HAD has been documented in at least three species of ticks. The American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae) was chosen as the focal species for this study due to its importance as the vector of tularemia and Rocky Mountain spotted fever. Previous population genetic studies of this tick found the existence of various haplotypes but the tick’s host origins were unknown. In this study, ticks were collected from 15 vertebrate host species to test for HAD using single nuclear polymorphisms (SNPs). In total, 136 individual D. variabilis ticks were sequenced using ddRADseq. Genomic evidence was found to point to D. variabilis exhibiting HAD on eight different hosts. A STRUCTURE analysis showed that the highest posterior probability was obtained with a population size of eight and these populations correlated with host species. Pairwise F_ST values were as high as 0.622 and indicated a range of genetic distinction between host groups. In addition, ticks collected from the vegetation appeared as one homogenous distinct genotype suggesting the existence of nidicolous (nest dwelling) and non-nidicolous genotypes. The identification of host race formation occurring in this animal parasite has implications for the understanding of D. variabilis pathogen transmission and targeted control efforts because genetically distinct populations can differ in traits relevant to these applications.     

Immunization effect of recombinant P27/30 protein expressed in Escherichia coli against the hard tick Haemaphysalis longicornis (Acari: Ixodidae) in rabbits

We investigated the induction of resistance to Haemaphysalis longicornis infestation in rabbits that had been immunized with recombinant H. longicornis P27/30 protein. The success of immunological control methods is dependent upon the use of potential key antigens as tick vaccine candidates. Previously, we cloned a gene encoding 27 kDa and 30 kDa proteins (P27/30) of H. longicornis, and identified P27/30 as a troponin I-like protein. In this study, rabbits that were immunized with recombinant P27/30 expressed in Escherichia coli showed the statistically significant longer feeding duration for larval and adult ticks (P<0.05), low engorgement rates in larval ticks (64.4%), and an apparent reduction in egg weights, which suggest that H. longicornis P27/30 protein is a potential candidate antigen for a tick vaccine. These results demonstrated that the recombinant P27/30 protein might be a useful vaccine candidate antigen for biological control of H. longicornis.     

Tick antigens recognized by serum from a guinea pig resistant to infestation with the tick Rhipicephalus appendiculatus

Immune resistance to infestation by an ixodid tick, Rhipicephalus appendiculatus, the vector of the cattle disease East Coast Fever, was induced in a guinea pig by repeated tick infestation. This resistance is expressed as the ability of the host to interfere with tick feeding. Resistance to ixodid tick feeding is an acquired response mediated by host antibody. We report the use of antibodies from a resistant host animal, in immunoblotting, to characterize the tick antigens recognized. The major tick antigens identified had molecular weights of 120,000, 94,000, 88,000, 77,000, 58,000, 46,000, 35,000, 31,000, 28,000, 25,000, 20,000 and 16,000. Most of these antigens were found in tick salivary glands. The presence and concentration of many tick salivary antigens appeared to vary with relation to the tick feeding cycle. Many of the antigens present in salivary glands were also detected in tick cement. Tick gut extract, although a poorer source of antigens, contained more of the 31,000 dalton antigen than salivary glands. Larval and nymphal tick extract lacked many of the antigens present in adult ticks. The data suggest that tick resistance is a complex phenomenon probably elicited by several different tick antigens.     

Tick infestations of the eastern cottontail rabbit (Sylvilagus floridanus) and small rodentia in northwest Alabama and implications for disease transmission.

Studies were conducted over a four-county area of northwest Alabama to determine the association of eastern cottontail rabbits with Dermacentor variabilis, the eastern United States vector of Rocky Mountain spotted fever. A secondary objective was to compare infestations of this tick on rabbits with infestations on commonly encountered rodent species as a means of determining the relative importance of each in the disease transmission cycle. These epidemiologic surveys were conducted in response to reported fatal cases of Rocky Mountain Spotted Fever in two counties of the study area. From 202 eastern cottontail rabbits, 3,956 ticks were collected. Of this total, 79.87% were Haemphysalis leporispalustris, 9.15% Amblyomma americanum, 8.22% Ixodes dentatus, and 2.76% D. variabilis. Only immature stages of D. variabilis were collected from cottontail rabbits. Ticks were collected on rabbits in all months except November, and only one specimen was taken in January. Based on the average number of ticks per host collected in each month, April was the peak month for D. variabilis and I. dentatus. High values for H. leporispalustris also occurred at this time, but even higher values occurred in October and December. The heaviest infestation of A. americanum occurred during the month ofAugust and coincides with the activity period for the larvae of this species. Two hundred sixty-nine of the smaller Rodentia, comprising 13 species, yielded 264 ticks, all D. variabilis, and all but two were immature stages. Five rodent species, Microtus ochragaster Orozomys palustris, Peromyscus gossypinus, Peromyscus leucopus, and Sigmodon hispidus accounted for 95.83% of the ticks collected, and appeared to be preferred hosts for D. variabilis; all five had higher infestation levels per host than did the eastern cottontail rabbit. Data on host relationships in association with seasonal activity are presented.     

Life cycle and host specificity of Amblyomma triste (Acari: Ixodidae) under laboratory conditions

We report biological data of two generations of Amblyomma triste in laboratory and compared the suitability of different host species. Infestations by larval and nymphal stages were performed on guinea pigs (Cavia porcellus), chickens (Gallus gallus), rats (Rattus norvegicus), rabbits (Oryctolagus cuniculus), wild mice (Calomys callosus), dogs (Canis familiaris) and capybaras (Hydrochaeris hydrochaeris). Infestations by adult ticks were performed on dogs, capybaras and rabbits. Tick developmental periods were observed in an incubator at 27 degrees C and RH 90%. Guinea pigs were the most suitable hosts for larvae and nymphs, followed by chickens. The remaining host species were less suitable for immature ticks as fewer engorged ticks were recovered from them. Mean larval feeding periods varied from 3.8 to 4.7 d between different host species. Mean larval premolt periods ranged from 8.9 to 10.4 d. Nymphal mean feeding periods varied from 4.2 to 6.2 d for ticks fed on different host species. Premolt period of male nymphs (mean: 15.4 d) was significantly longer than that of female nymphs (14.7 d). Female nymphs were significantly heavier than male nymphs. The overall sex ratio of the adult ticks emerged from nymphs was 0.9:1 (M:F). Capybaras were the most suitable host for the tick adult stage as significantly more engorged females were recovered from them and these females were significantly heavier than those recovered from dogs or rabbits. The life cycle of A. triste in laboratory could be completed in an average period of 155 d. The potential role of guinea pigs, birds and capybaras, as hosts for A. triste in nature, is discussed.     

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.     

Prevalence,Diversity, and Load of Borrelia species in Ticks That Have Fed on Humans in Regions of Sweden and ?land Islands,Finland with Different Lyme Borreliosis Incidences

The incidence of Lyme borreliosis (LB) in a region may reflect the prevalence of Borrelia in the tick population. Our aim was to investigate if regions with different LB incidences can be distinguished by studying the prevalence and diversity of Borrelia species in their respective tick populations. The Borrelia load in a feeding tick increases with the duration of feeding, which may facilitate a transmission of Borrelia Spirochetes from tick to host. Therefore, we also wanted to investigate how the Borrelia load in ticks that have fed on humans varies with the duration of tick feeding. During 2008 and 2009, ticks that had bitten humans were collected from four regions of Sweden and Finland, regions with expected differences in LB incidence. The duration of tick feeding was estimated and Borrelia were detected and quantified by a quantitative PCR assay followed by species determination. Out of the 2,154 Ixodes ricinus ticks analyzed, 26% were infected with Borrelia and seven species were identified. B. spielmanii was detected for the first time in the regions. The tick populations collected from the four regions exhibited only minor differences in both prevalence and diversity of Borrelia species, indicating that these variables alone cannot explain the regions’ different LB incidences. The number of Borrelia cells in the infected ticks ranged from fewer than ten to more than a million. We also found a lower number of Borrelia cells in adult female ticks that had fed for more than 36 hours, compared to the number of Borrelia cells found in adult female ticks that had fed for less than 36 hours.     

Experimental evaluation of birds as disseminators of the cosmopolitan tick Rhipicephalus sanguineus (Acari: Ixodidae)

Rhipicephalus sanguineus is believed to be the most widespread tick species of the world and its dissemination seems to rely on the diffusion of its main host, the dog. Empirical observations indicate that several bird species in urban areas regularly steal dog food. Such circumstances create a chance for R. sanguineus ticks to climb on birds and carry ticks to another site. In this work we evaluated experimentally the likelihood of birds (chicks) to either feed and/or carry R. sanguineus ticks from an infested site to another and to infest a host (rabbit) in the new location. Chicks were not suitable hosts for R. sanguineus ticks. Not a single adult tick engorged on chicks, yield as well as weight of engorged larvae and nymphs were very low and feeding period of these ticks was very long. However, a few larvae and, chiefly, nymphs were delivered to a new location either mechanically or after attachment and engorging total or partially on chicks. A few of these ticks fed successfully on rabbits. Further evidence on the capacity of birds to introduce R. sanguineus into non-infested dog settings should be provided by systematic examination of birds from urban areas, close to tick infested households.