Hyalomma truncatum (Acari; Ixodidae): evidence for the inability of adult ticks to discriminate between colours

Behavioural investigations into the perception and differentiation of coloured objects by unfed adult Hyalomma truncatum ticks revealed that silhouettes of blue, green, red and yellow colour, under illumination by a sun-simulating waveband spectrum, are perceived by the ticks and responded to equally by a directed response. Two green or dark grey rectangles each with a luminance contrast ratio of 5 : 1 against the white wall of the test arena in combination with an overlapping, equally sized dark grey or green target were consistently reached by ticks in a ratio of 2 : 1. Since the outer targets were occupied by the double number of ticks compared with the central silhouette this shows that the response is independent of the colour of the object. Investigations into target perception under monochromatic radiation of different wavelength ranges which were evenly adjusted in their irradiances revealed that ticks responded equally to a black target irradiated by blue, green, yellow and red light of wavelengths 428–472, 517–563, 549–591 and 606–654 nm, respectively. These results indicate the lack of true colour vision in H. truncatum.     

Hyalomma truncatum (Acari; Ixodidae): investigations into the scototaxis of unfed adult ticks

Under controlled test conditions, unfed male and female Hyalomma truncatum ticks exhibited a positive scototaxis to stationary, two-dimensional targets. Upright-positioned rectangles were the most attractive targets. The attractiveness of these targets increased with their size. Significantly more ticks responded scototactically positively to the targets under a luminance contrast ratio of 5:1, as compared with other luminance contrast ratios. Targets with an elevation angle of 13° were occupied more frequently than objects with higher elevation angles. Scototaxis was the same towards a stationary and a sinusoid oscillating target. When an upright-positioned rectangle was combined with a CO₂ gradient, the number of ticks that migrated into the CO₂ gradient and contacted the target did not increase significantly. The interval between exposure and first locomotion of the ticks, however, was significantly shorter under the influence of a CO₂ gradient than in all other experiments without a CO₂ gradient. A temperature gradient simulating a natural host (cattle) did not alter the scototaxis. The results of these investigations suggest that the positive scototaxis exhibited by adult H. truncatum ticks is not likely to be part of their appetence behaviour but rather searching behaviour to find adequate protection from harsh climatic conditions.     

Morphology of the foveal glands and foveae dorsales in male Hyalomma truncatum and Rhipicephalus evertsi mimeticus ticks (Acari; Ixodidae) before and during feeding

The ultrastructure of the foveae dorsales and foveal glands in unfed and attached male Hyalomma truncatum and Rhipicephalus evertsi mimeticus ticks was studied. Both species are provided with a paired foveal gland system, which is similar in unfed as well as in attached ticks. This gland system consists of the fovea dorsalis with pores and pore tubes as the external part, the foveal neck zone as a link between the fovea dorsalis and the lobes of the gland and the bulbous lobes as the innermost part. The fovea dorsalis is located on either side of the dorsal midline in the midsection of the body and appears as a roundish plate containing 15±6.5 and 21±7 slit-like pores in R. evertsi mimeticus (n=210) and H. truncatum (n=210), respectively. Each pore leads into a cuticular lined channel containing a pore tube. Below each fovea, the foveal neck zone is located within a groove of the cuticle and consists of the termini of the pore tubes which enlarge basally to form a cup-shaped ampulla each. Furthermore, secretory lobes are located below the foveal neck zone. Each lobe consists of secretory cells and a central excretory duct which leads into the ampulla. The ducts are lined with microvilli. The secretory cells contain numerous vesicles of varying size with one or more granules. In male ticks of both species the secretory lobe cells remained unchanged in size, structure and granule content irrespective of whether they were unfed or attached for up to 30 days. Axons occur in the fascicles between the secretory lobe cells containing numerous neurosecretory vesicles. A possible role of the foveal glands in the production of pheromones is hypothesized.     

On the visual perception of the eyes in adult Hyalomma truncatum ticks (Acari: Ixodidae)

Adult Hyalomma truncatum ticks with uncovered and foil-covered eyes were exposed to an upright-positioned rectangle as a target giving a luminance contrast ratio of 5:1 at a sun-simulating radiation. The transmission rate of the foil was less than 0.003%. Significantly (p0.05) more locomotorally active ticks with uncovered eyes (36.6%) responded to the target than ticks with foil-covered eyes (7.3%). When the rectangle was illuminated by monochromatic light at wavelengths ranging between 420 and 648 nm, the target induced a positive scototaxis in ticks with uncovered eyes regardless of the wavelength range. In contrast, ticks with covered eyes did not exhibita positive scototaxis at wavelength ranges of 553–585 and 608–648 nm and very few ticks responded only to other wavelength ranges. The results indicate that the eyes are the only or at least the most essential sense organs in the visual system of adult H. truncatum ticks.     

Morphology of the Eyes in adult Hyalomma Truncatum Ticks (Acari: Ixodidae)

The eyes of Hyalomma truncatum ticks are morphologically similar in both sexes. They appear aspaired hemispherical structures situated dorsally between the first and second pair of legs on thelateral scutal margin. Each eye consists of a lens and photoreceptor cells, which are separated by afine fibrillar layer and the hypodermis. The lens contains numerous channels which open beneaththe epicuticle, converge uninterruptedly to the interior of the lens and end below the fine fibrillarlayer. The inner closure of the lens is formed as an oval plateau with a cone-like projectionsituated caudolaterally and eccentrically to the longitudinal axis of the lens. The hypodermis is asingle layer of cells, situated immediately below the fine fibrillar layer. Beneath the hypodermis,directly below the cone-like projection of the inner lens are the photoreceptor cells localized in arosette-like arrangement. Facing the hypodermis, each photoreceptor cell is provided withnumerous microvilli. The microvilli consistently border the microvilli regions of other cells atdifferent angles but are always oriented at a right angle to the lenticular channels. Thephotoreceptor cells are unipolar neurons, whose axons arise from the basal portion of the cell andjoin to nerve fibre bundles forming the optic nerve. It is concluded that the eyes in adult H.truncatum ticks possess all the structures necessary to perceive and conduct light stimuli andvisual signals.     

The genus Hyalomma. VI. Systematics of H. (Euhyalomma) truncatum and the closely related species, H. (E.) albiparmatum and H. (E.) nitidum (Acari: Ixodidae)

The geographic distribution of three closely related Hyalomma species, namely Hyalomma (Euhyalomma) truncatum Koch, 1844, Hyalomma (Euhyalomma) albiparmatum Schulze, 1919 and Hyalomma (Euhyalomma) nitidum Schulze, 1919 is confined to Africa. A detailed comparison of all stages of development of the three taxa reveals that they possess many more shared than distinguishing characters. In fact differentiation between these species is based on single or dual qualitative characters on their adults. These are a conspicuous, ivory-coloured parma on H. (E.) albiparmatum males, and the absence or reduction in clarity of ivory-coloured bands on the leg segments of H. (E.) nitidum adults, as well as the shape of the external cuticular preatrial fold of the genital operculum of females of the latter species. The adults of all three species and the larva of H. (E.) truncatum are redescribed. The nymph of H. truncatum and the larva and nymph of H. (E.) albiparmatum and H. (E.) nitidum are described for the first time. Data on their geographic distributions and hosts are provided.     

The effect of various host species on the feeding performance of immature stages of the tick Hyalomma truncatum (Acari: Ixodidae)

In order to determine the effect of various hosts on the feeding performance of the tick Hyalomma truncatum, we used three mammalian species as hosts. Larvae and nymphs of H. truncatum were fed, under controlled laboratory conditions, on gerbils, guinea-pigs and rabbits. The larvae fed for 4.3±1.4 days on gerbils, 5.6±1.3 days on guinea-pigs and 4.7±1.2 days on rabbits. The mean weights of the larvae which fed on the rabbits, guinea-pigs and gerbils were 0.58± 0.09, 0.46±0.04 and 0.45±0.04 mg. respectively. The feeding periods of the nymphs on gerbils, guinea-pigs and rabbits were 7.9±1.3, 8.6±1.3 and 9.6±2.2 days respectively. The mean weights of the nymphs which fed on the gerbils, guinea-pigs and rabbits were 22.5±2.8, 19.7±1.3 and 15.8±1.4 mg, respectively. Hyalomma truncatum demonstrated a life cycle of a three-host tick on gerbils and guinea-pigs and of a two-host tick on rabbits. The evolutionary advantage of a two-host cycle over a three-host cycle in metastriate ticks is discussed.     

Isolation and characterization of an anticoagulant present in the salivary glands of the bont-legged tick,Hyalomma truncatum

A low molecular mass anticoagulant (17 kDa) was isolated from the salivary glands of prefed female Hyalomma truncatum ticks by means of reverse phase and anion-exchange HPLC. Trypsin digestion and amino acid analysis confirmed the protein nature of the anticoagulant. The inhibitor appears to be uncompetitive with a K_i of 6.9×10^–10M. The target of the anticoagulant is factor Xa at the junction of the extrinsic and intrinsic pathways. This may be crucial for the survival of the tick, making it feasible to investigate the possibility of vaccination with this antihaemostatic against tick feeding. In addition, tick anticoagulants may possibly have therapeutic application in controlling thrombosis.     

Beauveria bassiana: Synergistic effect with acaricides against the tick Hyalomma anatolicum anatolicum (Acari: Ixodidae)

Owing to the need to combat the spread of chemical acaricide resistance in ticks, we evaluated the efficacy of a mixture of the entomopathogenic fungus Beauveria bassiana AT17 and acaricides for the control of Hyalomma anatolicum anatolicum in China. A mixture of B. bassiana AT17 at the concentration of 10⁸ conidia/mL and the synthetic pyrethroid deltamethrin at concentrations of 2500, 250, 25, 5, 2.5, 0.5 and 0.25 ppm was tested in vitro. The germination capability, vegetative growth, conidia production, and viability of B. bassiana AT17 were assessed and the efficacy of the mixture in killing engorged H. anatolicum anatolicum females was measured. High mortality rates were achieved when the entomopathogen was combined with different concentrations of deltamethrin. Neither B. bassiana AT17 nor deltamethrin alone at the same concentrations could cause the higher mortality rates seen with the combination. In addition the combination killed the ticks more rapidly than did either agent alone (3–5 days more rapidly). Our results indicate that the mixture of B. bassiana AT17 and deltamethrin has potential as a new type of reagent for integrated control of H. anatolicum anatolicum.     

Isolation and properties of two forms of thrombin inhibitor from the nymphs of the camel tick Hyalomma dromedarii (Acari: Ixodidae)

Two forms of the nymphal thrombin inhibitors (NTI) 3.2 kDaand 14.9 kDa were purified by chromatography on CM-cellulose,Sephacryl S-300 and Sephadex G-50 columns and designated NTI-1 and NTI-2respectively. The NTI-2 turned out to be homogenous monomeric protein in bothnative-PAGE and denatured SDS-PAGE with M(r) value of 14.9 kDaapproximately and its pI value ranged from 7.2 to 7.5. The NTI-1 and NTI-2displayed anticoagulant activity since they prolonged both the activatedpartialthromboplastin time (APTT) and the prothrombin time (PT) of the camel plasma ina concentration-dependent manner. The potency of NTI-1 toward thrombin was5-fold higher than that toward FXa, while NTI-2 was 3-fold active toward FXathan thrombin. However, both of them did not inhibit any of the other examinedproteases. The types of inhibition of thrombin by NTI-1 and NTI-2 were non-competitive and competitive with inhibition constants (Ki) values of 11.7M and 211 nM respectively. One binding site wasdeduced on thrombin for each inhibitor.     

Detection of a questing <Emphasis Type="Italic">Hyalomma marginatum</Emphasis><Emphasis Type="Italic">marginatum</Emphasis> adult female (Acari,Ixodidae) in southern Germany

The first finding of a questing Hyalomma marginatum marginatum female tick in Germany is described. The tick was found in May 2006 on the clothing of a person who had spent the preceding day in rural surroundings in southern Germany. As the infested person had also been visiting Spain where H. m. marginatum is known to occur some weeks prior to finding the tick, it is not clear whether the tick had been imported by him as a female or by another host in a preimaginal stage and succeeded to develop to an adult in Germany. H. m. marginatum is a thermophilic tick species usually occurring in relatively dry and warm regions of southern Europe, northern Africa and some parts of Asia. It is a vector of several disease agents of human relevance including Crimean-Congo hemorrhagic fever virus. Although, by PCR examination, the female was found neither infected with this virus nor with Rickettsia aeschlimannii, another human pathogen which has been found in Spanish Hyalomma ticks, its mere finding should be taken seriously and draw further attention to the increasing problem of the import and spread of putatively tropical vectors of disease to central Europe.     

The seasonal occurrence of ticks (Acari: Ixodidae) on sheep and in the field in the Judean area of Israel

A 2 year survey of ixodid ticks in the Judean area of Israel between 1983 and 1985 showed that sheep were parasitized by the following species:Rhipicephalus sanguineus group (30.6%),Rhipicephalus bursa (25.3%),Haemaphysalis cretica (20.5%),Haemaphysalis otophila (20.1%) andHyalomma anatolicum excavatum (3.1%). Three other species,Hyalomma marginatum rufipes, Boophilus annulatus andAmblyomma lepidum were also present but in very low numbers. A total of 50 816 specimens (78.1% adult ticks) were collected from the sheep. In the field, a total of 4780 ticks (8.7% adults) were collected and 64.3% consisted ofR. bursa. Other species found wereH. cretica (14.5%),H. a. excavatum (13.7%),H. otophila (3.4%),R. sanguineus group (1.9%) and 1.7% wasIxodes eldaricus. The number of ticks collected varied from year to year and seasonal activity was observed in all species except forH. a. excavatum. In all species, males outnumbered females, with the exception ofH. cretica. The seasonal occurrence, tick ecology and disease relationship is discussed for each species.     

Isolation ofNosema slovaca (Microsporidiae) fromDermacentor reticulatus ticks (Acari: Ixodidae) collected in Hungary

Nosema slovaca (Microsporidiae) was isolated from a maleDermacentor reticulatus tick collected in the Mélykút locality, Bács-Kiskun province, Hungary. This parasitic protozoan caused an acute infection in partly engorgedD. reticulatus females when inoculated intracoelomically resulting in death of the ticks within 5–15 days post-infection. This strain ofNosema can be maintained in the laboratory by passaging between partly engorgedD. reticulatus females and is currently being studied for its potential as a biological control agent of ixodid ticks.     

Molecular detection of pathogen DNA in ticks (Acari: Ixodidae): A review

Ticks play an important role in human and veterinary medicine, in particular due to their ability to transmit a wide spectrum of pathogenic micro-organisms of protozoal, rickettsial, bacterial and viral origin. Pathogens in ticks can be identified by conventional methods such as indirect immuno-fluorescence, isolation in cell culture or by using histological staining techniques. However, the advent of the polymerase chain reaction (PCR) has resulted in tremendous improvements in the specific and sensitive detection of pathogen DNA in ticks. In this paper, literature on DNA extraction methods, PCR protocols, primers and probes, which are in use for the successful detection and identification of pathogens in ticks, are critically reviewed. Some recommendations are also given towards the end of tht review.     

Lyme borreliosis spirochetes in Ixodes ricinus and Haemaphysalis punctata ticks (Acari: Ixodidae) on three islands in the Baltic Sea

The prevalence of infection with Lyme borreliosis spirochetes in nymphal Ixodes ricinus and Haemaphysalis punctata was examined on three Swedish islands in the Baltic Sea. The proportion of H. punctata nymphs infected with Borrelia spirochetes (2%) was lower than that of I. ricinus nymphs (11–16%), even on the island of Stora Karlsö where both tick species feed on the single mammalian host present, the varying hare, Lepus timidus. Ten of the 12 infected questing H. punctata nymphs harboured very few spirochetes, whereas the remaining two harboured as many as 30–40 spirochetes. However, it remains to be seen whether H. punctata nymphs are capable of transmitting spirochetes during their blood meal and, thus, serving as vectors for Lyme borreliosis spirochetes. On Gotland and Fårö, I. ricinus was more abundant than H. punctata in deciduous and coniferous forest, whereas H. punctata was equally or more abundant than I. ricinus in juniper brush areas on open land. Host preference and biotope usage of H. punctata seems, in general, to prevent this tick from feeding on highly infective Borrelia reservoirs, such as Apodemus mice.     

Detection of a novel spotted fever group rickettsia in <Emphasis Type="Italic">Amblyomma parvum</Emphasis> ticks (Acari: Ixodidae) from Argentina

The present study evaluated the rickettsial infection in Amblyomma parvum ticks collected in Northwestern Córdoba Province, Argentina. Each tick was subjected to DNA extraction and tested by polymerase chain reaction (PCR) targeting fragments of the rickettsial genes gltA and ompB. Nine (69.2%) out of 13 adult ticks yielded expected PCR products for the two rickettsial genes. Products from the ompB PCR were sequenced, generating DNA sequences 100% identical for the nine PCR-positive ticks. Three of these ticks were tested in another battery of PCR targeting fragments of the rickettsial genes gltA, htrA, and ompA. Products from the gltA, htrA, and ompA PCRs were sequenced generating DNA sequences 100% identical for the three PCR-positive ticks. The rickettsia detected in the A. parvum ticks was designated as Rickettsia sp. strain Argentina. Phylogenetic analyses performed with partial sequences of the rickettsial genes gltA, htrA, ompB, and ompA showed that Rickettsia sp. strain Argentina belonged to the spotted fever group, being distinct from all known Rickettsia species and genotypes available in GenBank, representing possibly a new Rickettsia species. This was the first evidence of rickettsial infection in the tick A. parvum, and the third report of rickettsial infection among the Argentinean tick fauna. The role of Rickettsia sp. strain Argentina as a human pathogen is unknown. Further studies are needed to obtain tissue-cultured isolates of Rickettsia sp. strain Argentina, in order to better characterize it and to determine its taxonomic status as a new species.     

Differences in Borrelia infections in adult Ixodes persulcatus and Ixodes ricinus ticks (Acari: Ixodidae) in populations of north-western Russia

Dark-field microscopy was used to determine the number of Borrelia spirochetes in 630 standard preparations obtained from adult ixodid ticks (344 Ixodes persulcatus and 286 I. ricinus) collected in 1989-92 in the Leningrad region of Russia. The average numbers of Borrelia in I. persulcatus and I. ricinus preparations were 34.7 and 23.3 per 100 microscopic fields, respectively. The maximal individual values registered each year for ticks of both species were several hundred times greater than the minimal values. Ticks carrying relatively small numbers of Borrelia generally predominated. Proportions of more heavily infected ticks varied considerably from year to year. These parameters were significantly higher in foci with predominance of I. persulcatus ticks. As a consequence, risk to acquire Lyme borreliosis in such foci is considered greater than in foci where I. ricinus predominates.     

Seasonal incidence of Ixodes ricinus ticks (Acari: ixodidae) on rodents in western France

Data collected from a longitudinal survey carried out over 2 years on four farms in western France were used to assess the incidence and infestation of Ixodes ricinus on rodents. Once a month, on each farm, 25 Sherman live traps were set in hedges bordering selected pastures. A total of 799 micromammals were examined, including Apodemus sylvaticus, Clethrionomys glareolus, Microtus agrestis, Microtus arvalis, and Crocidura spp. Larvae and nymphs of I. ricinus were found. Small numbers of Ixodes (Exopalpiger) trianguliceps were also recovered from each farm. The mean infestation rate of the I. ricinus larvae (1.6–5.9) among all animals examined varied between farms Most animals were infested by only a single tick, but one M. agrestis harboured 43 I. ricinus larvae. Larvae or nymphs were found throughout the year, with peaks from March to October.     

The distribution of ticks (Acari: Ixodidae) of domestic livestock in Portugal

This paper introduces the first countrywide faunistic study of the tick parasites on ruminants in Portugal. The aim of this study was to map accurately the distribution of the ticks Dermacentor marginatus, Rhipicephalus (Boophilus) annulatus, R. bursa, Hyalomma m. marginatum, H. lusitanicum and Ixodes ricinus in Portugal. Additional information about the abiotic preferences of these species has been obtained through the use of abiotic (temperature- and vegetation-derived) variables have been recorded from remotely sensed information at a nominal resolution of 1.1 km². A further aim was the development of predictive models of distribution using Classification and Regression Trees (CART) methodologies. Four species (R. annulatus, R. bursa, D. marginatus and H. m. marginatum) are mostly restricted to south-eastern parts of the country, under hot and dry climate conditions of Mediterranean type. H. lusitanicum has been collected almost only in the southern half of Portugal. I. ricinus has a very patchy distribution and is mainly associated with vegetation of Quercus spp., found in southern zones of the country, but it is present also in the more humid western part. A variable number of abiotic variables, mainly temperature derived, are able to describe the preferences of the tick species. It is remarkable that variables derived from maximum values of the Normalized Derived Vegetation Index (yearly or summer-derived) only apply to discriminate areas where I. ricinus has been collected. CART models are able to map the distribution of these ticks with accuracy ranging within 75.3 and 96.4% of actual positive sites.     

Inheritance of weight in Rhipicephalus appendiculatus ticks (Acari: Ixodidae) in the laboratory

A selection of the 10% lightest and 10% heaviest males and females of a population of individually weighed Rhipicephalus appendiculatus Neumann adults was made in two experiments. The offspring of homologous pairs were followed until the next adult stage (light x light, control x control and heavy x heavy). The engorged nymphal weights, unfed adult weights, engorged female weights of the parents, egg mass weights, egg weights, larval scutal lengths, engorged larval weights, unfed nymphal weights, engorged nymphal weights and adult weights of the progeny were determined. No significant differences could be demonstrated between the two lines for egg weight, larval scutal length, engorged larval weight and unfed nymphal weight. Significant differences were found between the egg masses, engorged nymphal weights and adult weights of the two lines. The heritability coefficients of body weight determined from adult to adult were 0.14 and 0.10, respectively, during the first and second experiments. Considering females and males separately, the coefficients were 0.10 and 0.18 during the frist experiment and 0.12 and 0.09 during the repeat experiment respectively.