Seasonal incidence and ecology of the tick Ixodes ricinus (Acari: Ixodidae) on grazing pastures in Western France

A longitudinal survey was carried out during a 2 year period in Western France to assess the infestation level of grazing pastures byIxodes ricinus ticks. Four farms were visited once a month and each of the grazing pastures was sampled in the centre and at the border using the blanket dragging method. A total of 3562I. ricinus (34 adults, 900 nymphs and 2628 larvae) were collected and the infestation was significantly higher during the first year (p<0.0001). The infestation level byI. ricinus varied between grazing pastures and farms. Grazing pastures in the vicinity of forest were more infested than the others, all through the study. The seasonal distribution of ticks showed peaks, with low fluctuations between farms, years and stages. Tick abundance could not be related to vegetation, but only to the vicinity of woods.     

A case of abnormal size in eggs and larvae of the Taiga tick,Ixodes persulcatus (Acari: Ixodidae)

Egg batches laid by females of Ixodes persulcatus (maintained under a photoperiod of L:D 20:4 before feeding) contained eggs of two sizes: numerous normal eggs of 0.578 × 0.421 mm and some giant eggs of 0.776×0.515 mm. Giant eggs were 32–34% greater in length and 22–24% greater in width than normal eggs. Females maintained under a short-day photoperiod (L:D 12:12) laid only normal eggs (0.588×0.417 mm). There were no differences between these eggs in viability and developmental time, but larvae hatched from giant eggs were larger (length of body 23–28% greater and of gnathosoma 12–15% greater) than larvae from normal eggs. This dimorphism of eggs and larvae was not sex determined, but may be a maternal photoperiodic effect.     

Parasitism of lizards by immature stages of the blacklegged tick,Ixodes scapularis (Acari,Ixodidae)

From 1982–1985 and 1993–1999, a total of 309 individual reptiles, mostly lizards and snakes, belonging to 12 species (American alligator, six lizard species, five snake species) was captured on St. Catherine's Island, Liberty County, Georgia, USA, and examined for ticks. Three lizard species, the broad-headed skink Eumeces laticeps, southeastern 5-lined skink Eumeces inexpectatus, and eastern glass lizard Ophisaurus ventralis, were severely infested with larvae and nymphs of the blacklegged tick, Ixodes scapularis. Ticks were not found on any of the other reptile species. Overall, 80% of 65 E. inexpectatus examined were parasitized by a mean intensity of 21.5larvae and 88% were parasitized by a mean intensity of 4.8 nymphs. Corresponding figures for E. laticeps (n=56) were 93% and 51.3 for larvae and 89% and 7.4 for nymphs, and for O. ventralis (n=3) were 67% and 22.5 for larvae and 100% and 21.3 for nymphs. Larvae and nymphs attached along the lateral grooves of O. ventralis. Nymphs attached mainly behind the ears and in the foreleg axillae whereas larvae mainly attached to these sites and on the hindlegs in Eumeces spp. Seasonally, both larvae and nymphs were recorded on lizards from April through October. A unimodal larval peak was recorded in May or June. Seasonal data for nymphs did not reveal any distinct peaks but small bimodal peaks in mean intensities may have occurred (one in early summer, the other in late summer)suggesting that some ticks complete their life cycle in one year, and others in two years, on St. Catherine's Island. Potential epidemiological consequences of these findings with respect to Lyme disease in the southeastern United States are briefly addressed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sex ratio characteristics in Ixodes rubicundus (Acari: Ixodidae), the Karoo paralysis tick

The sex ratio is an important parameter which characterizes the state and dynamics of natural populations of animals. Although ixodid ticks are specialized ectoparasites, most species are bisexual and are characterized by a 1:1 sex ratio for their progeny. In natural populations and even in laboratory colonies, biased sex ratios are often observed. Ixodes rubicundus, the Karoo paralysis tick, parasitizes domestic stock and wild ungulates in South Africa. Adults quest from vegetation, can mate off or on the host and males are seldom parasitic. We hypothesized that the sex ratio for I. rubicundus would be 1:1 when observed directly in the progeny but that it would be strongly biased towards females in samples of parasitic adults. The results mostly supported the hypothesis but it was also shown that unexplained and unpredictable variations can occur. On hosts, females dominated strongly, except on adult angora goats where the sex ratio was biased in favour of the males. This disparity may be related to a greater retention of males in the coarse, curly hair of angora goats compared to the other hosts. Monthly variations in the sex ratios of the tick on hosts are believed to be related to the large fluctuations in sex ratios of questing ticks.     

Natural attachment duration of nymphs of the tick Ixodes uriae (Acari: Ixodidae) on kittiwake Rissa tridactyla nestlings

Daily searches of the plumage of 62 kittiwake (Rissa tridactyla) chicks were carried out for 3 weeks to determine the attachment duration of the tick Ixodes uriae. All ticks recorded were nymphs and their mean duration of attachment was 5.2±1.7 days (n=93). Seventy-four per cent of the ticks survived to engorgement and were assumed to have fed successfully. The mean duration of attachment of successful ticks was 5.8±1.0 days (n=69), significantly longer than that of unsuccessful ticks (3.3±2.1 days, n=24). There was no difference in survival rates to engorgement between ticks attached to feathered and unfeathered parts of the body (78.3 and 79.2%, respectively), but the duration of attachment of successful ticks was significantly longer on unfeathered compared to feathered areas. There were no significant differences in the survival to engorgement or duration of attachment between ticks found on young (c.11 days) and old (>11 days) kittiwake nestlings. The attachment duration was not related to the total number of ticks found on the host or the number of ticks present in the immediate vicinity of the site of attachment. This work provides important data on the parameter of attachment durations of nymphal I. uriae on free-living kittiwakes; the data can be used for incorporation into the application of population modelling.     

Treatment of clothing with a permethrin spray for personal protection against the western black-legged tick,Ixodes pacificus (Acari: Ixodidae)

The synthetic pyrethroid, permethrin, when applied to clothing with a pressurized spray at an application rate estimated previously to be 4 g a.i./cm², was found to be 100% effective for personal protection against all three parasitic stages of the western black-legged tick,Ixodes pacificus Cooley and Kohls. This tick has been implicated as the primary vector of the Lyme disease spirochete (Borrelia burgdorferi) to humans in the far-western United States. Periods of exposure to permethrin-treated cloth as brief as 10 and 45 seconds incapacitated 100% of subadult and adult ticks, respectively, within 1–3 h post-treatment. Under field conditions, permethrin appareatly does not repel questing adult ticks, though 100% of ticks recovered from treated clothing after exposures as brief as 15 seconds were moribund 1 h later.     

Development of the salivary glands in embryos of Ixodes ricinus (Acari: Ixodidae)

We examined Ixodes ricinus embryos between 18 and 28 days of development with light, scanning and transmission electron microscopy. The differences in inner structure attested to establish three successive developmental stages: days 18–20, day 23, and days 26–28. Between 18 and 20 days the embryos are at early stages of organogenesis. Salivary glands cannot be identified at that stage. In 23-day-old embryos salivary glands are already outlined but the structure of alveoles is still different from that in larvae in which the embryonic development has been completed. Gland cells start to form alveoles and become active between 26 and 28 days of the development. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vector competence of Ixodes angustus (Acari: Ixodidae) for Borrelia burgdorferi sensu stricto

The vector competence of Ixodes angustus for Borrelia burgdorferi sensu stricto (s.s.) was investigated in the laboratory. The larval progeny of female ticks from Washington State were placed on Swiss-Webster mice that had been inoculated intravenously with 10⁸ spirochetes each of a Californian isolate of B. burgdorferi. Spirochetes were detected in 6 (12%) of 50 nymphs derived from larvae that had fed on these animals. Ten nymphs from the same cohort of experimentally infected ticks were placed on each of 4 naive deer mice (Peromyscus maniculatus). One of the mice seroconverted to B. burgdorferi and spirochetes were isolated from its ear tissues 4 weeks after exposure to ticks. Further vector competence trials were conducted with I. angustus ticks from California. Larvae were fed on deer mice that had been inoculated intradermally with B. burgdorferi along with larvae of I. spinipalpis as a comparison group. There was no significant difference in the prevalence of infection in nymphs of I. angustus (8.2%) versus those of I. spinipalpis (12.1%). We conclude that I. angustus is a competent experimental vector of B. burgdorferi s.s. and its efficiency for acquiring and transstadially passing such spirochetes is similar to that of I. spinipalpis.     

An evaluation of strategic and threshold control measures against the Karoo paralysis tick,Ixodes rubicundus (Acari: Ixodidae) in South Africa

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.     

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.     

Densities of Ixodes ricinus ticks (Acari: Ixodidae) on moorland vegetation communities in the UK

Unfed (questing) Ixodes ricinus ticks were collected by blanket dragging on a monthly basis from heather-dominated, Vaccinium-dominated and bracken-dominated vegetation communities from two different biogeographical regions of the UK (the Quantock Hills in Somerset, south west England and the North York Moors, north east England) throughout the spring and summer months of 1991 and 1992. Eighteen sites were monitored across the two regions and a total of 1920 blanket drags were carried out. Vaccinium sites showed high tick densities at all life stages, as did bracken sites. Significantly lower numbers of larval and nymphal ticks per drag were collected on heather sites than were collected on either Vaccinium (bilberry/whortleberry) or bracken sites, while similar numbers of adult ticks per drag were collected from each of the three vegetation communities. There was no significant difference between the mean numbers of any tick life stage collected on the Quantock Hills and those collected on the North York Moors on these vegetation communities or between the mean numbers of any tick life stage collected in 1991 and those collected in 1992 on these vegetation communities.     

Acquired resistance in dogs to repeated infestation with Ixodes scapularis (Acari: Ixodidae) reduces tick viability and reproductive success

The purpose of this study was to determine whether dogs develop acquired resistance to adult Ixodes scapularis infestation in an experimental model. Five dogs were each infested with ten mating pairs of ticks every week for 7 consecutive weeks, another five dogs were each infested with ten mating pairs once every 2 weeks for 10 weeks and four dogs served as controls not exposed to ticks. All ticks were allowed to feed to repletion and were collected only after dropping from the host. Several variables were measured to determine the extent of blood feeding success. Regression analysis indicated that the engorgement success, survival and mean tick engorgement weight declined with repeated infestation in both groups of dogs (p<0.05). Tick oviposition as well as the F1 viability declined with each successive infestation in both groups. These results suggest that repeated infestation with I. scapularis elicits a protective immune response against tick feeding and could serve as a limiting factor in the spread and transmission of Borrelia burgdorferi.     

Regeneration of Haller's sensory organ in the tick, Ixodes rubicundus (Acari: Ixodidae)

A study of regeneration in nymphs and adults of the South African tick Ixodes (Afrixodes) rubicundus, from which the forelegs had been amputated during the previous instar, revealed that the structural changes in regenerated Haller's sensory organs resemble those observed in other ixodid ticks, in particular in another prostriate tick, Ixodes (Ixodes) ricinus. The adult regenerates re-establish their atavistic features in terms of the increased number of different sensilla on the distal knoll, in the anterior pit and the capsule. The nymphal regenerates, in contrast, re-establish the features of the previous instar through a reduction in the number of some sensilla on the distal knoll and in the post-capsular area. The structural changes in different compartments of the organ appear independent. The phenomenon of regenerative induction through the appearance of specific changes in Haller's organ of the contralateral non-treated foreleg is probably characteristic only of prostriate ticks. A unique modification in the regenerated Haller's organ as revealed by duplication of the Haller's organ capsule was discovered in both I. rubicundus nymphs and adult ticks.     

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.     

Borrelia burgdorferi sensu lato in the female cement plug of Ixodes persulcatus ticks (Acari,Ixodidae)

Borrelia burgdorferi sensu lato was detected in one out of five cement plugs of female Ixodes persulcatus ticks. The spirochetes were found by dark field microscopy as early as 18 h after attachment of the ticks to the skin of a white mouse. The relevance of this finding is discussed in relation to the epidemiology of Lyme Borreliosis.     

A comparison of Ixodes rubicundus (Acari: Ixodidae) infestations on Friesian and Bonsmara cattle in South Africa

This study was conducted to compare the relative resistance of crossbred Bos indicus X B. taurus Bonsmara and B. taurus Friesian cattle to Ixodes rubicundus (Karoo paralysis tick) infestations. During periods of peak abundance of the ticks, Friesian oxen harboured almost twice or more than twice as many ticks as either Bonsmara oxen or cows. During periods of low tick abundance tick burdens on both cattle breeds were closely similar. It is envisaged that cattle can play an important role in an integrated control strategy against the Karro paralysis tick.     

Optimal sampling and spatial distribution of Ixodes pacificus, Dermacentor occidentalis and Dermacentor variabilis ticks (Acari: Ixodidae)

A common method for sampling tick populations is flagging, which is a method of dragging a white cloth over a plant substrate for a fixed distance along a transect. Flagging over rough physical surfaces or using long subtransect lengths could lead to the underestimation of tick densities. Using estimates of the drop-off rates of adult Ixodes pacificus in flag sampling, optimal sampling schemes (the length and number of subtransects) were examined using the relationships between the tick drop-off rates (c), the tick density and distribution patterns and the roughness of the sampled plant substrate. It was found that the optimal number of subtransects and Lmax, the longest subtransect length which did not significantly underestimate the tick density from c, were affected by the tick density, substrate roughness and tick distribution pattern. This study also showed that the density and distribution of I. pacificus and Dermacentor occidentalis varied greatly over time in the populations sampled, while the Dermacentor variabilis densities were low and showed no significant changes over time. Both I. pacificus and D. occidentalis had clumped distributions along trails and these clumps were aggregated. However, the clump sizes (or individual clump areas) changed significantly over time because of density fluctuation or the movement of ticks. Finally, a positive association between the number of I. pacificus and D. occidentalis adults was observed from 2 m subtransect flag collections in March 1995; no relationship was found in 1994. © Rapid Science Ltd. 1998     

Hosts and Pathogen Detection for Immature Stages of Ixodes ricinus (Acari: Ixodidae) in North-Central Spain

To determine hosts of the immature stages of a southern population of Ixodes ricinus, we trapped rodents and birds in an area of north-central Spain in May–June and August–September of 1998 and 1999. The most frequently trapped rodents were Apodemus sylvaticus (230 specimens) and Clethrionomys glareolus (99), with a larval infestation prevalence of 49% and 81%, respectively (in spring) and 21% and 41% (in summer). C. glareolus was always more heavily parasitized by larvae (mean numbers 19.8 in spring, 3.4 in summer) than A. sylvaticus (6.1 and 1.2, respectively). No nymphs were collected from the rodents. The larval distribution pattern differed considerably between rodent host species but not according to the season of the year. The most commonly trapped birds were members of the Turdidae, which had infestation incidences of about 70% (larvae) and 10% (nymphs) in spring and 20–15% in summer. We also used molecular methods for the identification of reservoir hosts of the larval ticks and of the pathogens they contained, from nymphs collected in the same site in June of 2002 and 2003. The study showed that most of the ticks had fed on birds and few on rodents and ruminants. Pathogens detected in these ticks included Babesia microti, Borrelia garinii, B. valaisiana and B. afzelii. Borrelia afzelii was detected in a tick that had apparently fed on a wild boar.     

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.