What makes bradycardia tick tick tick tick tick tick tick? Tick.
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The major tick salivary gland proteins and toxins from the soft tick, Ornithodoros savignyi, are part of the tick Lipocalin family: implications for the origins of tick toxicoses.
The origins of tick toxicoses remain a subject of controversy because no molecular data are yet available to study the evolution of tick-derived toxins. In this study we describe the molecular structure of toxins from the soft tick, Ornithodoros savignyi. The tick salivary gland proteins (TSGPs) are four highly abundant proteins proposed to play a role in salivary gland granule biogenesis of the soft tick O. savignyi, of which the toxins TSGP2 and TSGP4 are a part. They were assigned to the lipocalin family based on sequence similarity to known tick lipocalins. Several other tick lipocalins were also identified using Smith-Waterman database searches, bringing the tick lipocalin family up to 20. Phylogenetic analysis showed that most tick lipocalins group within genus-specific clades, suggesting that gene duplication and divergence of tick lipocalin function occurred after tick speciation, most probably during the evolution of a hematophagous lifestyle. TSGP2 and TSGP3 show high sequence identity and group terminal to moubatin, an inhibitor of collagen-induced platelet aggregation from the tick, O. moubata. However, no platelet aggregation inhibitory activity is associated with the TSGPs using ADP or collagen as agonists, suggesting that TSGP2 and TSGP3 duplicated after divergence of O. savignyi and O. moubata. This timing is supported by the absence of TSGP2-4 in the salivary gland extracts of O. moubata. The absence of TSGP2 and TSGP4 in salivary gland extracts from O. moubata correlates with the nontoxicity of this tick species. The implications of this study are that the various forms of tick toxicoses do not have a common origin, but must have evolved independently in those tick species that cause pathogenesis.
Amino Acid Sequence↗
Characterization of tick antigens inducing host immune resistance. II. Description of rabbit-acquired immunity to Amblyomma americanum ticks and identification of potential tick antigens by Western blot analysis.
Feeding by adult Amblyomma americanum ticks induced a level of immunity in rabbits to subsequent tick feeding that resulted in a significant decrease in tick feeding success and fecundity. Histological analysis of tick feeding sites in hosts expressing resistance revealed a predominant eosinophil response, with weak basophil and neutrophil infiltrates. While the basophil was never the dominant granulocyte at the tick feeding sites in resistant hosts, this cell exhibited the greatest increase in density (tenfold) over levels observed in hosts experiencing their first infestation; eosinophils and neutrophils exhibited increases of five- and twofold, respectively. Serum from animals that expressed resistance was tested for the presence of anti-tick antibodies to tick-derived salivary gland substances (SGA) by Western blotting. Western blot analysis of female-derived SGA compared to male-derived SGA, using the Avidin/Biotin technique, resulted in the identification of approximately 25 proteins from the female preparation, but only seven from the male. The use of 125I labeled protein-A as the probe for anti-tick antibody in Western blot analysis resulted in fewer recognized proteins. Serum from rabbits immunized with A. americanum-derived SGA emulsified with complete (CFA) Freund's adjuvant recognized most of the proteins identified by active serum, whereas serum from animals immunized with SGA in incomplete (IFA) Freund's adjuvant did not. Furthermore, both sera recognized a multiplicity of proteins from extracts of larval A. americanum Dermacentor variabilis and Boophilus microplus ticks, suggesting the presence of common antigens between these distantly related ticks. The results from this study demonstrate that rabbits acquire a strong immunity to A. americanum ticks characterized by the production of antibody. Furthermore, ticks secrete a number of substances into rabbits during feeding, as seen by Western blot analysis but only three may be crucial to the induction of host immunity; proteins at 41, 40 and 39 kDa. The purified anti-tick antibody will be used for subsequent isolation and characterization of crucial antigens.
Animals↗
Interaction of virulent and attenuated tick-borne encephalitis virus strains in ticks and a tick cell line.
An interference between a thermosensitive (ts) mutant and the wild-type (wt) of tick-borne encephalitis (TBE) virus in Ixodes ricinus L. and Rhipicephalus appendiculatus (Neumann) ticks is reported. I. ricinus females were dually infected by a parenteral inoculation of ts and wt strains at 10-day interval. Interference was demonstrated by the lowered ability of wt virus to replicate in ticks previously infected by ts virus. The wt virus was demonstrated in only 30% of the ticks; the average virus titre was lowered by 2.1 log10 compared with the control group, which was infected with the wt virus only. The oral infection of R. appendiculatus ticks with the same viruses also revealed an interference with the growth of the superinfecting wt virus. While in the control group all the ticks became infected, in the dually infected group the wt virus was found in only 50% of the ticks. However, when the ticks were infected orally with ts virus and superinfected parenterally with the wt virus, no interference was observed. In a R. appendiculatus-derived cell line persistently infected with the ts virus (100% of the cells), a partial inhibition of the growth of the superinfecting wt virus was observed. The ts virus retained its thermosensitive phenotype throughout the persistent infection of both the ticks and the tick cell line.
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Ability of the Lyme disease spirochete Borrelia burgdorferi to infect rodents and three species of human-biting ticks (blacklegged tick, American dog tick, lone star tick) (Acari:Ixodidae).
The infectivity of a diverse collection of Borrelia burgdorferi strains from North America for mice was determined as a prelude to vector competence experiments with the 3 primary human-biting tick species in the eastern United States (Ixodes scapularis Say, Dermacentor variabilis (Say), Amblyomma americanum (L.)]. Of the 34 B. burgdorferi strains inoculated into mice, 29 were infectious; the exceptions were 5 isolates from Texas. Vector competence experiments were conducted with 2 strains from the southern United States (North Carolina and Georgia). Both strains were extremely infectious to I. scapularis larvae. Moreover, I. scapularis efficiently maintained these spirochetes transstadially and transmitted infection as nymphs. D. variabilis larvae were intermediate in susceptibility but generally did not maintain the infection transstadially. A. americanum larvae were completely refractory to infection with these 2 southern B. burgdorferi strains. Three isolates from Michigan D. variabilis were inoculated into mice, subsequently exposed to I. scapularis and D. variabilis larvae. Larval I. scapularis were 5-fold more susceptible to infection with these strains than were larval D. variabilis. Although nymphal I. scapularis efficiently transmitted a Michigan isolate, nymphal D. variabilis did not. In all these experiments, I. scapularis was the only species that proved to be vector competent for B. burgdorferi.
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Tick sweep: modification of the tick drag-flag method for sampling nymphs of the deer tick (Acari: Ixodidae).
We describe a version of the standard tick drag-flag modified for use in close-growing and tangled vegetation, as well as under ornamental shrubbery and fallen branches. Two major features of the sweep are: (1) it allows the user to remain upright with the flag parallel to the ground, thus sampling effectively beneath low and fallen branches and around shrubs, as well as capturing host-seeking ticks in advance of the operator; and (2) the use of a flannel rubberized-laminate fabric (crib sheet) for the flag that is snag-proof and highly durable in dense and thorny vegetation. In simultaneous 100-m samples, the sweep was as effective as the 1-m standard tick drag for capturing nymphs of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, where understory vegetation was sparse, but was twice as effective in dense vegetation, capturing significantly more I. dammini nymphs. The sweep also captured nymphs of the American dog tick, Dermacentor variabilis (Say); rabbit tick, Haemaphysalis leporispalustris (Packard); and lone star tick, Amblyomma americanum (L.).
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Immunology of the tick-host interaction and the control of ticks and tick-borne diseases.
The first experimental vaccination against ticks was carried out 60 years ago. Since then, progress has been slow, although the recent commercial release of a recombinant vaccine against Boophilus microplus is significant. The nature of naturally acquired protective immunity against ticks is poorly understood, particularly in the important, domesticated ruminant hosts. Characterization of the antigens of naturally acquired immunity remains limited, although more has been achieved with 'concealed' antigens. Crucial questions remain about the true impact of tick-induced immunosuppression and the effect of immunity on the transmission of tick-borne diseases, despite some fascinating and important recent results, as discussed here by Peter Willadsen and Frans Jongejan.
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Seasonal prevalence of ticks and tick-transmitted haemoparasites in traditionally managed N'Dama cattle with reference to strategic tick control in the Gambia.
A survey of tick spatial and seasonal distribution in traditional managed N'Dama cattle over 1 year old was carried out in The Gambia over 16 months. Presence of Anaplasma marginale and Babesia spp. in the blood smears and their antibodies in the serum of same animals were also examined. Tick species, in decreasing order of abundance, were: Boophilus geigy, Rhipicephalus senegalensis, B.decoloratus, Hyalaomma truncatum, H.marginatum rufipes and Amblyomma variegatum. All tick species peaked during the rainy season. Additional B.geigy peaks occurred towards the end of the dry season. The most infested animal body areas were anogenital, udder and abdomen. A.variegatum, Hyalomma spp. and, to a lesser extent, Boophilus spp. showed strong preferences for these anatomical regions. Overall prevalence of A.marginale, B.bigemina and B.bovis haemoparasites were 3.2%, 0.9% and 0.1%, respectively. Peaks of A.marginale and B.bigemina occurred at the end of the rainy season-beginning of the dry season; an additional A.marginale peak was observed at mid-end dry season. Overall antibody seroprevalence were 29.6% for A.marginale, 44.7% for B.bigemina and 5.2% for B.bovis; monthly fluctuations in percentage of seroreactors were limited. Endemic stability for A.marginale and B.bigemina is postulated. Implications of the outcomes are discussed in relation to tick-control strategy in The Gambia.
Anaplasma↗
Ticks and tick-borne diseases: a vector-host interaction model for the brown ear tick (Rhipicephalus appendiculatus).
An analytical model is derived for the interaction of the brown ear tick (Rhipicephalus appendiculatus) with its hosts. Such models are rare due to the complexity and lack of information on the entire stages of ticks life cycles. Most models are simulations rather than analytical. The vector is categorized into a discrete number of compartments according to its life cycle. The starting model in this article consists of a system of differential equations with constant coefficients. A general model on a stage structured population with unlimited host density is developed. From the characteristic polynomial of the system a sensitivity analysis for the population parameters is carried out in detail. The model is then improved by incorporating host abundance and availability. This is done on the basis of a demand-driven and ratio-dependent functional response model. The improved model adequately represents the dynamics of a stage-structured vector population under conditions of varying host density. The model allows the qualitative evaluation of several management strategies and is expected to guide future research work.
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Reaction of the host to the tick-bite. II. Distribution of tick borne encephalitis virus in sucking ticks.
No reactive histological changes of the dermis and no cement cone formation were observed at the insertion site of tick mouthparts by feeding of H. inermis larvae. Conversely, cement formation was observed by feeding of H. inermis female. Fully fed D. marginatus larvae on viraemic mice showed bright fluorescence in oesophagus, suboesophageal ganglion, salivary glands, a few gut cells and in lumen of Malpighian tubuli. We consider the penetration of virus from oesophagus to suboesophageal ganglion as the possible route of primary virus infection. Sections through the D. reticulatus nymphs during virus transmission (38 hours after attachment) showed specific fluorescence in epidermis and gut cells. This finding is in agreement with the secretory activity of epidermial and gut cells during feeding.
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Grooming in impala: role of oral grooming in removal of ticks and effects of ticks in increasing grooming rate.
In Experiment 1, five adult female impala were fitted with harnesses that restrained oral self-grooming of the anterior part of the body. At the same time, six cohoused female impala were fitted with control harnesses that allowed normal oral grooming. The impala were allowed to habituate to the harnesses for 10 days, and both groups were then exposed to larval ticks (Boophilus decoloratus) by herding them into a tick-seeding corral. During the third week following tick seeding, when female ticks were estimated to have developed into engorging adults, the impala were immobilized, tick numbers on the animals sampled by patch sampling, and the harnesses removed. Observations continued for 5 days following removal of the harnesses. Twenty-minute focal observations were conducted daily on each impala during the habituation, tick-seeded, and postharness phases. Restrained impala had a median of 20 times more adult female ticks (both engorged and unengorged) than control impala. Oral grooming, which had been suppressed in the restrained impala during habituation and tick-seeded phases, increased 10-fold once the harnesses were removed and occurred 2.5 times more frequently than in control impala during the postharness phase. In Experiment 2, 15 adult female impala were seeded with larval ticks as in Experiment 1; in week 3 after tick seeding all ticks were removed from animals by application of an acaricide. Grooming was recorded during 3 weeks of baseline observations prior to tick seeding, 3 weeks after tick seeding, and then for 3 weeks beginning 1 week after acaricide treatment. Oral grooming and scratch grooming significantly increased from baseline during tick seeding and significantly declined following removal of the ticks with acaracide. Taken together, the two experiments demonstrate that oral grooming is very effective and important in removing fitness-compromising ticks in free-ranging impala. Correspondingly, exposure to, and subsequent infestation by, ticks increases the rate of grooming.
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The efficiency of patch sampling for determination of relative tick burdens in comparison with total tick counts.
Quantitative data on host tick burdens are fundamental for the initiation of control strategies and effective management of wildlife populations, but the methods of live sampling employed for domestic animals are unsuitable for sampling wild animals. Despite advances in the use of destructive methods (the scrub and digestion techniques) to obtain measures of the total tick burden on wildlife, these methods are too involved for many field workers, who often need only measures of relative tick burden. Recently, patch sampling methods have been introduced whereby only certain predilection sites are sampled, the presumption being that the number of ticks collected gives an indication of the relative degree of infestation. We examined the validity of patch sampling as a measure of relative tick burden by comparing adult ticks collected from the ears, head, neck, foreleg and perianal region of impala (Aepyceros melampus) with total tick burdens of the same animals derived from the digestion technique. Adult ticks from patch sampling were positively and significantly correlated with total adults and total ticks (larvae, nymphs, and adults) on impala, with ticks patch sampled from the neck showing the highest correlation with the total tick burden. Comparison of relative tick loads from patch sampling with absolute tick loads from digestion for three classes of impala (females, bachelor males and territorial males) gave qualitatively similar results. We conclude that, when measures of relative tick load are sufficient and destructive sampling is not feasible, patch sampling can provide reliable information on relative tick burdens that are positively correlated with the total tick burden.
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Annual and seasonal variation of tick-borne encephalitis virus (TBEV) prevalence in ticks in selected hot spot areas in Germany using a nRT-PCR: results from 1997 and 1998.
The prevalence of tick-borne encephalitis virus (TBEV) in Ixodes ricinus tick populations in endemic areas of Germany with the highest TBE risk is unknown. Annual and seasonal differences in TBEV prevalence have also not been studied. Against this background, in May 1997 we started a systematic virus surveillance programme in ticks collected in locations known to have a high incidence of autochthonous TBE cases. These were 5 locations in Baden-Württemberg (Black Forest) and 8 locations in Bavaria (surrounding Passau). Field-collected ticks were randomly assigned to pools of 10 adults or 20 nymphs, respectively. The tick pools were tested for the presence of TBEV-RNA using a newly developed, sensitive nested reverse transcriptase polymerase chain reaction assay (nRT-PCR). The primer pairs were selected from the 5'-terminal noncoding region, a highly conserved part of the virus. The specificity was tested by computer homology searches of sequences, as well as by sequencing of the first and the second amplificates, by Southern blot hybridisation with a DIG-labelled oligonucleotide probe, and by restriction enzyme analysis. The method has proved to be very sensitive, with a detection limit of 20 fg of TBEV RNA per PCR run, or a single positive tick. Based on biostatistical considerations a sample size of at least 1000 ticks per estimation point was chosen. The estimated TBEV prevalence and confidence intervals (CI) were calculated from the nRT-PCR results of pooled samples (10 adults or 20 nymphs) using appropriate formulae for pooled testing. In order to identify the estimated TBEV prevalence as well as to assess the influence of annual and seasonal factors on TBEV prevalence, ticks were sampled twice a year (May and September) in 1997 and 1998 at exactly identical sites. These sites were selected because they were known to have had the highest incidence of autochthonous TBE cases during the previous 10 years. On sampling days, relevant local meteorological data were also noted. In total, 8500 I. ricinus ticks were investigated in this study, 4270 (3540 nymphs, 730 adults) from the Black Forest habitats, and 4230 (3680 nymphs, 550 adults) from the Bavarian locations. In the foci near Freiburg (Black Forest), the estimated virus prevalence was relatively high in the whole tick population, during 1997 with only slight seasonal differences [3.4% (confidence interval, CI, 2.3-4.8%) in May and 2.9% (CI 1.7-4.5%) in September]. In contrast, in 1998, in the same foci the estimated TBEV prevalence was considerably lower [1.1% (CI 0.5-2.0%) in May and 0.6% (CI 0.2-1.4%) in September]. Thus, while the seasonal differences again remained low, the annual variation was marked. In the Bavarian foci in 1997, the estimated virus prevalence of the whole tick population studied was lower than in the Black Forest foci and the seasonal fluctuations were low: in May 1997 0.9% (CI 0.4-1.8%) of the ticks were positive, in September 1.1% (CI 0.5-1.9%). In 1998, in May 2.0% (CI 1.1-3.3%) of the ticks were positive, and in September 1.1% (CI 0.5-2.1%). For the whole study period, every 50th to 100th I. ricinus nymph or adult in the Passau region was calculated to give a positive signal in the nRT-PCR. The TBEV prevalence data indicate that residents and visitors of areas in Germany known for high endemic activity take a significant risk of contracting TBEV infection, if bitten by ticks. In addition, the data suggest that annual fluctuations may exist in the whole tick population studied. Seasonal fluctuations of the virus prevalence in ticks were small.
Adult↗
[Ixodid ticks and the causative agents of tick-borne encephalitis. I. Relationship between the virus and the ticks of the genus Ixodes].
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Animals↗
Seasonal population dynamics of ixodes ticks and tick-borne encephalitis virus.
Seasonality of the epidemic and epizootic processes of tick-borne encephalitis (TBE) depend on the period of activity of ixodid ticks Ixodes persulcatus Schulze and I. ricinus Linnaeus, which are the main reservoirs and vectors of TBE virus, and also on the process of their activation. The period of activity is the period during which the ticks occur in the active state. Activation is the transition into this state of ticks that moulted from the preceding stage and completed post-moulting development. For I. persulcatus, the first adult ticks generally emerge between April 10 and May 9. Under a variety of natural conditions, activation of adult I. persulcatus after wintering lasts for 45-86 days and this period may be even longer in certain areas of the Far East. The period during which one-half of the entire tick population becomes activated (AT50) comprises no more than 10-20 days. In adult I. ricinus ticks the activation period may last even longer than in I. persulcatus. The data on duration of the period of activity and on activation of larval and nymphal stages of both tick species were considered. Ticks exhausting their nutrient reserves and failing to find a host die quickly. The period during which 50% of the entire tick population die under natural conditions is designated LT50. The main types of I. persulcatus and I. ricinus seasonal activity within their species ranges were reviewed. Data on the relationship between TBE virus reproduction in a natural focus and physiological age, pattern of activation, and seasonal changes in age structure of the tick population were analyzed. Seasonal changes in the prevalence of infection among active unfed adult ticks in a natural population are determined by virus content in individual ticks at the moment of their activation and also by the duration of subsequent virus persistence (the rate of virus loss) in ticks. Apparently, the opportunity and frequency of horizontal TBE virus transmission under natural conditions, change during the season of tick activity.
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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.
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Contact with ticks and awareness of tick-borne diseases among the Czech population--a pilot study.
In the Czech Republic, the incidence of Lyme borreliosis (LB) has shown a rising trend since 1988. The goal of this study has been to find out to what extent a selected part of population is aware of ticks and of the relationship between ticks and LB. The study was based on a questionnaire survey. A total of 110 respondents were selected, including 19 secondary school students, 32 blood donors, 44 park-goers, 15 countryside people. As many as 99% of the respondents were aware of the presence of ticks, 91% knew that ticks are sucking blood of humans and animals, 1.8% thought they eat leaves. 74.5% of the respondents expect ticks to reach them from the vegetation while 22% believe that ticks fall from the trees. Furthermore, 87% and 75% of the respondents indicated to have had ticks attached to the skin or to have removed a tick from other persons' skin, respectively. Only 6.7% of them had never come into contact with ticks. 17% of the respondents use disinfectant when removing a tick, while 67% use oil for tick removal. Almost 30% remove ticks with naked hands. Over 14% destroy the ticks by squashing them with naked fingers. Finally, about 11% of the population studied had never heard about LB and 41% were not aware of the risk of tick-borne encephalitis.
Adolescent↗
Ticks as the main target of human tick-borne disease control: Russian practical experience and its lessons.
For several decades, the emphasis in human tick-borne disease control has been on the epidemiologically-based preventive (non-specific) approach where tick vectors were the main target of control impact. A long-term, large-scale campaign for controlling the taiga tick Ixodes persulcatus, the main vector of tick-borne encephalitis, was carried out in Russia in the 1950s to 1970s. The practical experience accumulated during that campaign could be of great value for the current development of strategies of tick-borne disease control. A general scheme of human protection from tick-borne diseases is presented where the required investment into protection is proportional to the risk of human infection and particular strategies of control and protection are differentiated. The critical point in the preventive approach is the necessity of radical tick suppression in the areas with the highest risk of human infection that can be successfully achieved only through chemical treatment directed at the eradication of the entire tick population. The following aspects are considered: the tick population (or a group of populations) as a desirable target of any acaricidal impact (biological and geographic aspects, the fate of the population after treatment); the advantage of long-term planning for control campaigns; and the influence of acaricidal impact on foci of tick-borne diseases. The conception of losses of potential pesticidal impact efficacy provides much room for the improvement of conventional tick control strategies making them more efficient and safe to the environment. The current tendency to make humans the main target of control through vaccination and/or medical treatment (specific approach) does not fit the objectives of effective human protection from tick-borne diseases, especially because of a tick population's ability to carry and transmit more than one pathogen over the same area.
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