Differential detachment from resting hosts of replete larval and nymphal Ixodes ticks

To determine whether replete subadult Ixodes ticks detach more frequently from resting than from active hosts, diverse rodents and lizards were caged in an apparatus designed to record the ticks' sites of detachment relative to the resting site of the host. Replete larval Ixodes ricinus and Ixodes dammini accumulated mainly beneath the resting places of the mice (Apodemus agrarius and Peromyscus leucopus) most frequently parasitized in nature. Although nymphal I. ricinus similarly detached where these mice rested, nymphal I. dammini detached more randomly. When lizards were used as hosts, both subadult stages of I. ricinus tended to detach away from their main resting sites; these ticks detached from squirrels more randomly. Detachment ratios for other rodent hosts, that are abundantly infested by the larvae of these ticks in nature (Apodemus flavicollis and Clethrionomys glareolus), could not be derived because nymphs generally failed to attach. Our observations are consistent with reports that both subadult stages of I. dammini, but not the adult, feed on the same kind of nest-dwelling hosts and that the host range of I. ricinus is less focused. Detachment of mouse-feeding larvae from resting mice promotes subsequent nymphal attachment to conspecific hosts, and the absence of such behavior among nymphs facilitates access of the resulting adults to deer.     

Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

By serving as hosts for native vectors, introduced species can surpass native hosts in their role as major reservoirs of local pathogens. During a 4-year longitudinal study, we investigated factors that affected infestation by ixodid ticks on both introduced Siberian chipmunks Tamias sibiricus barberi and native bank voles Myodes glareolus in a suburban forest (Forêt de Sénart, Ile-de-France). Ticks were counted on adult bank voles and on adult and young chipmunks using regular monthly trapping sessions, and questing ticks were quantified by dragging. At the summer peak of questing Ixodes ricinus availability, the average tick load was 27-69 times greater on adult chipmunks than on adult voles, while average biomass per hectare of chipmunks and voles were similar. In adult chipmunks, individual effects significantly explained 31% and 24% of the total variance of tick larvae and nymph burdens, respectively. Male adult chipmunks harboured significantly more larvae and nymphs than adult females, and than juveniles born in spring and in summer. The higher tick loads, and more specifically the ratio of nymphs over larvae, observed in chipmunks may be caused by a higher predisposition - both in terms of susceptibility and exposure - to questing ticks. Tick burdens were also related to habitat and seasonal variation in age- and sex-related space use by both rodents. Introduced chipmunks may thus have an important role in the dynamics of local vector-borne pathogens compared with native reservoir hosts such as bank voles.     

Borrelia Burgdorferi Sensu Lato in Ixodes Ricinus Ticks and Rodents in a Recreational Park in South-Western Ireland

Ixodes ricinus ticks infected with Borrelia burgdorferi sensu lato were numerous on the edges of paths and roads in a recreational park in south-western Ireland. The abundance of ticks at different sites was related to the presence of deer, but a negative relationship was shown between tick abundance and tick infection rates. This is thought to be due to the deposition of large numbers of uninfected ticks by deer, which are apparently not good reservoir hosts of B. burgdorferi s.l. Blood meal analysis only detected deer DNA in uninfected nymphs. Reservoir competent rodents, Apodemus sylvaticus and Clethrionomys glareolus, were abundant at all sites and a high proportion of captured specimens were infested with larval ticks. However, very few rodents were infected with B. burgdorferi s.l. and none of the unfed infected nymphs analysed for the identity of their larval blood meal had fed on rodents. The spirochaetes detected in I. ricinus in the study area may be poorly adapted to rodents or are not transmitted readily because of the absence of nymphal infestation. The majority of spirochaetes in these ticks were apparently acquired from non-rodent hosts, such as birds.     

Additional observations to the biology of Hepatozoon erhardovae Krampitz 1964 in bank voles from the south-western Styria and from areas around the Neusiedlersee (Burgenland) (author's transl)]

The incidence of Hepatozoon erhardovae in the blood of bank voles (Clethrionomys glareolus) captured in the investigated areas is examined. The biology of schizonts, their distribution in the lobes of the lung and the further development of natural infections in vertebrate hosts kept strictly free of ectoparasites are observed. The accumulation of gametocytes in larvae of the tick Ixodes ricinus and of the mite Neotrombicula zachvatkini after sucking on strongly infected bank voles is pointed out. Occasionally a parasitaemia is produced in the non-specific host (Apodemus flavicollis), but only with a specific transmitter (Megabothris turbidus).     

Characteristics of the distribution of Ixodes persulcatus in the forest-park area of Novosibirsk

Only one species of ixodid ticks Ixodes persulcatus occurs in the forest-park zone. Conditions of foliage forests with high grass, where occur hosts of all developmental phases of ticks (elks, hares, rodents, insectivores), are most favourable for I. persulcatus. Preimaginal phases of I. persulcatus feed, in general, on dominant species (common shrew, redbacked and narrow-skulled voles, field mouse and northern birch mouse).     

Borreliae in Ixodes ricinus ticks feeding on humans

A total of 298 Ixodes ricinus (L.) ticks (Acari: Ixodidae) feeding on humans in the Czech Republic were tested for borreliae (Borrelia burgdorferi sensu lato) by darkfield microscopy between 1997 and 2003. A majority (68%) of the supplied I. ricinus ticks were nymphs, 25% were females and 7% were larvae. Overall, 20% of 74 examined females and 9% of 203 examined nymphs (but none of 21 examined larvae) were infected with borreliae. The proportion of ticks with a high infection load (>100 spirochetes) was 4% in females and 2% in nymphal I. ricinus. During the year, the highest numbers and proportions of infected nymphal and female ticks were taken from humans in June. Detection of borreliae in the ticks feeding on humans might be helpful in the prophylaxis of Lyme borreliosis.     

Questing behaviour of Ixodes ricinus ticks (Acari: Ixodidae)

The vertical distribution in the vegetation of questing Ixodes ricinus ticks was investigated in two different vegetation types (high and low vegetation) at two localities in south-central Sweden during 1992-1993 (Toro) and 1995 (Bogesund). Significant correlations were found between the vertical distribution of immature ticks and the height of the vegetation. The greatest mean availabilities of the larvae and nymphs in low vegetation were in the intervals 0-9 and 30-39 cm, respectively. The larval numbers were greatest close to the ground (0-29 cm) in both high and low vegetation. The larval : nymphal ratio, at ground level at localities free of ground vegetation, varied between 8 : 1 and 32 : 1. In high vegetation, the greatest mean numbers of nymphal and adult ticks were at height intervals of 50-59 and 60-79 cm, respectively. These ranges are within the estimated height interval (40-100 cm) of the main part of the body surface of their preferred host, the roe deer (Capreolus capreolus). The presence of most questing I. ricinus larvae at ground level would favour the transmission of Borrelia burgdorferi s.l., since this is where the highly reservoir-competent rodents and shrews usually occur.     

The role of medium-sized mammals as reservoirs of Borrelia burgdorferi in southern New York

The ability of raccoons (Procyon lotor), striped skunks (Mephitis mephitis) and opossums (Didelphis virginiana) to serve as reservoirs of Borrelia burgdorferi, the spirochetal agent of Lyme disease, was compared with that of white-footed mice (Peromyscus leucopus). Twenty-eight (28) medium-sized mammals and 34 white-footed mice were captured in Westchester County, New York (USA) in summer 1986. Animals were caged over pans of water for 1 to 2 days to recover engorged tick larvae (Ixodes dammini) that detached from the hosts after feeding. With the exception of mice, numbers of engorged tick larvae recovered exceeded those counted during initial examinations of the hosts by 30% (opossums) to nearly 90% (raccoons). Newly-molted nymphal ticks derived from the engorged larvae were examined for the presence of spirochetes by darkfield microscopy. Percentage infection was 5% (n = 22) for ticks from skunks and 14% (n = 191) for ticks from raccoons. None of 24 nymphs from larvae that fed on opossums survived long enough for spirochete examination. By comparison, 40% (n = 72) of nymphs from larvae which fed on white-footed mice were infected. Of the individual hosts from which molted nymphs had fed as larvae, 67% of mice, 33% of skunks, and 55% of raccoons produced spirochete-positive ticks.     

Host associations of ticks parasitizing rodents at Borrelia burgdorferi enzootic sites in South Carolina.

A total of 237 rodents was collected in 4 regions of South Carolina from July 1994 through December 1995. Eight species were collected, including cotton mouse, hispid cotton rat, eastern woodrat, marsh rice rat, white-footed mouse, eastern harvest mouse, golden mouse, and black rat. Of the 1,514 ticks recovered from these hosts, Ixodes minor Neumann, including larvae, nymphs, and adults, was the most abundant species, representing 54% of the total. Only immature stages of other tick species were found, including larvae and nymphs of Dermacentor variabilis (Say), Amblyomma maculatum Koch, Ixodes affinis Neumann, and Ixodes scapularis Say. All 5 tick species parasitized cotton mice, cotton rats, and woodrats, which were the most important small mammal hosts for ticks at the localities studied. Rice rats were hosts of A. maculatum, D. variabilis, and L. minor. Amblyomma maculatum was more strongly associated with cotton rats than other rodent species. Ixodes scapularis was most strongly associated with cotton mice, and I. minor was more strongly associated with both woodrats and cotton mice than other species of rodents. Ixodes minor parasitized hosts in the Coastal Zone only, where among spirochete-infected hosts, it was present in significantly greater numbers than other ticks. Furthermore, I. minor was the only tick species that showed a statistically significant positive association with spirochetal infection in rodents. More I. affinis parasitized spirochete-infected hosts than I. scapularis, but fewer than I. minor. The findings discussed herein provide evidence that implicates I. minor as the possible primary enzootic vector of the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt and Brenner in the Coastal Zone of South Carolina. They also indicate that the high level of B. burgdorferi infection in rodents from this region may be a function of the combined involvement of I. minor, I. affinis, and I. scapularis in the enzootic transmission of the spirochete.     

Tick species parasitizing people in an area endemic for tick-borne diseases in north-western Italy

In 1995 and 1996, 318 ticks were recovered from 240 people in Liguria (Province of Savona, Italy). Most of the ticks (284; 89.3%) were sheep ticks, Ixodes ricinus. Rhipicephalus sanguineus (31; 9.8%) and Dermacentor marginatus (3; 0.9%) were also recorded. All three life stages of I. ricinus were found on humans while only nymphs and adults of R. sanguineus and adults of D. marginatus were collected. Human tickbites were most frequent in the municipalities of the Province where roe deer density was highest. The number of tickbites in this area was about 500 per 100,000 residents over the period of observation. Most cases of tickbite were observed in children (11.2%), students (25.6%), workers (22.4%) and retired people (24%). Although ticks were recovered from people throughout the year, the highest frequencies of I. ricinus bites were in May, June and July. In the study area natural hosts were also studied. Six tick species were identified (I. ricinus, I. hexagonus, D. marginatus, R. bursa, R. sanguineus, R. turanicus). I. ricinus and R. sanguineus were the most abundant species. I. ricinus was recorded more frequently from ruminants particularly roe deer, while R. sanguineus was found to be associated with the dog.     

The occurrence of ixodid ticks on wild mink Mustela visonin England and Wales

Abstract. Four species of ticks found to infest 1391 American mink (Mustela vison) in Britain in five years were, in declining order of frequency, Ixodes hexagonus, Ixodes canisuga, Ixodes ricinus and Ixodes acuminatus. Ixodes hexagonus and I.canisuga occurred on 40% and 2.5% of mink respectively. Infestation rates (the proportion of infested mink) of adult females, nymphs and larvae were similar and tended to be lower in summer. The distribution of infestation size (the number of ticks per host) for adult females describes a negative binomial. The mean infestation size of nymphs varied with the sex of the host and was 5.2 for males and 4.2 for females. Mink are competent hosts for /. hexagonus.     

Seasonal patterns of abundance and host relationships of the Australian paralysis tick,Ixodes holocyclus Neumann (Acarina: Ixodidae), in southeastern Queensland

Estimates of seasonal abundance of larvae, nymphs and females of the paralysis tick, Ixodes holocyclus, were obtained by collecting ticks that engorged on small mammals and birds trapped in two localities in southeastern Queensland: Brisbane (wet sclerophyll forest) and Tamborine Mountain (cleared rain forest). The long-tailed short-nosed bandicoot, Isoodon macrourus, was the most common mammal trapped but small numbers of other marsupials, rodents and ground frequenting birds were also captured. Small numbers of five other tick species were also collected. In both habitats there was clearly one dominant generation of I. holocyclus;7er year, although the presence of all stages at most times of the year indicated overlapping of smaller cohorts. Females were most abundant in spring and early summer, larvae in summer-autumn, and nymphs in autumn-winter. I. holocyclus was abundant on I. macrourus and rare on most other mammals and birds captured. At the peak of abundance of each instar, each bandicoot dropped from 500 to 2000 engorged larvae, 100 to 200 engorged nymphs, and four to six engorged females. Life tables were compiled for the tick in both habitats and these indicate that there was relatively high survival from engorged larva to engorged nymph and thence to engorged female and that most mortality occurred between detaching of the engorged female and the detaching of the engorged larva. The tick was more abundant on bandicoots from cleared rain forest and rain forest edge, than on those from sclerophyll woodland. The survival of engorged larvae and nymphs of I. holocyclus and the larval productivity of engorged females were examined in a warm moist climate where the tick was abundant (Tamborine Mountain) and in a hotter dryer climate where the tick was rare or absent (Amberley). In both localities engorged larvae and nymphs survived to the next instar in all seasons of the year. On most occasions engorged females produced eggs which hatched. Mature bandicoots from tick infested areas showed little or no resistance to infestation with larvae or nymphs of I. holocyclus, whereas other small mammals from the same area showed an appreciable degree of resistance to the immature stages of the tick. Feeding larvae and nymphs exposed to normal light-dark cycles in the laboratory detached during the afternoon and early evening. This behaviour and host resistance are discussed in relation to the daily activity cycles of host species, their habitat preferences, and their role as hosts for I. holocyclus.     

Testosterone depresses innate and acquired resistance to ticks in natural rodent hosts: a force for aggregated distributions of parasites

The effects of testosterone on acquired resistance to ticks, Ixodes ricinus, in their natural rodent hosts (voles, Clethrionomys glareolus, and wood-mice, Apodemus sylvaticus) were investigated by manipulating testosterone levels and exposing the hosts to repeated tick infestations. Testosterone reduced both innate and acquired resistance to tick feeding. During primary infestations, attachment rates were higher on rodents with high testosterone levels than on oil-implanted controls. Successive infestations on voles were accompanied by a decrease in tick feeding success and survival, but this decrease was significantly greater in ticks fed on control voles than in those fed on voles implanted with testosterone. When reduced feeding success had been induced, either by vaccination with tick salivary gland extract or by 4 successive infestations, implantation with testosterone partially reversed the acquired resistance. These effects of testosterone will generate heterogeneities within the rodent population with respect to tick distribution and microparasite transmission. The lowest innate and acquired resistance to tick feeding occurs in that fraction of the host population, i.e., sexually active males, most actively involved in the transmission of both Babesia microti and Borrelia burgdorferi s.l.     

Granulocytic Ehrlichia infection in Ixodid ticks and mammals in woodlands and uplands of the U.K.

Abstract .The prevalence of infection with Ehrlichiae of the Ehrlichia phagocytophila genogroup (the granulocytic Ehrlichiae), in questing Ixodes ricinus ticks of U.K. upland and woodland habitats, was investigated by PCR. The prevalence of infection in the three feeding stages of I. ricinus indicated that granulocytic Ehrlichiae are transmitted transstadially with no, or inefficient, transovarial transmission. The presence of infected ticks in both habitats indicates that endemic cycles of granulocytic Ehrlichia (GE) infection are maintained by both domesticated sheep and by wild reservoirs, and coexist with endemic cycles of Borrelia burgdorferi infection. Moreover, demonstration, for the first time, of GE infection in engorged Ixodes trianguliceps ticks and blood collected from wild rodents, suggests that European wild rodents are competent reservoirs. GE infection prevalence in nymphal and adult I. ricinus was significantly greater in uplands than woodlands, which is consistent with ticks of all three feeding stages feeding on reservoir-competent sheep in uplands. In one woodland studied, pheasants are important hosts for nymphal I. ricinus but are incompetent or inefficient reservoirs, so reducing GE infection prevalence in I. ricinus ticks in this habitat. 16S rRNA sequences of GE from ticks of these U.K. habitats, showed a high degree of homology with those of granulocytic Ehrlichiae isolated from humans, but also showed some evidence of genetic diversity of granulocytic ehrlichiae in the U.K. The implications of these findings, for the taxonomy of granulocytic ehrlichiae and the potential for human infections to occur in the U.K., is discussed.     

<Emphasis Type="Italic">Ixodes </Emphasis>(<Emphasis Type="Italic">Ixodes</Emphasis>) <Emphasis Type="Italic">pararicinus</Emphasis> Keirans &; Clifford, 1985 (Acari: Ixodidae): description of the immature stages,distribution, hosts and medical/veterinary importance

The immature stages of the Neotropical tick Ixodes (Ixodes) pararicinus Keirans & Clifford, 1985 are described from specimens in a laboratory colony initiated from engorged females collected on cattle and larvae fed on mice and chickens. The larva and nymph of I. pararicinus are described using SEM micrographs as well as drawings for some features of the larva. Additionally, immature stages of I. pararicinus collected on wild mice and birds in Uruguay and Argentina were compared with specimens from the laboratory colony. A taxonomic key to the nymphs of the species of the ricinus complex established in the Western Hemisphere is presented. The distribution of I. pararicinus comprises Argentina, Colombia and Uruguay, but it is also probably established in Bolivia, Brazil, Chile and Peru. Most adult ticks of this species have been found on introduced domestic artiodactyles, although Neotropical deer species must have been the ancestral host. Larvae and nymphs of I. pararicinus have also been found on sigmodontine rodents and passeriform birds. Although I. pararicinus is a member of the ricinus complex, which contains the main vectors of Borrelia burgdorferi (sensu lato), there are few studies concerning its potential for pathogen transmission.     

Risk factors in habitats of the tick Ixodes ricinus influencing human exposure to Ehrlichia phagocytophila bacteria

Ixodes ricinus L. (Acari: Ixodida) were sampled during 1996-99 in southern Scotland, on vegetation using cloth drags, on humans by removal from clothing and on roe deer (Capreolus capreolus L.) by searching legs of culled deer. Developmental microclimate was recorded by automatic recorders and questing microclimate by portable instruments during tick collections. Ticks and deer were examined for infection with Ehrlichia phagocytophila bacteria (Rickettsiales) using microscopy and polymerase chain reaction. This pathogen causes tick-borne fever of sheep in Europe and human granulocytic ehrlichiosis in North America, but in Europe human clinical ehrlichiosis due to E. phagocytophila has not been recorded despite serological evidence of exposure. Among three types of habitat, coniferous woodland was most infested with questing ticks (560 ticks/km of drag; mean numbers collected on long trousers: 24.3 larvae, 13.5 nymphs and 0.8 adult ticks/km walked), deciduous woodland had slightly lower infestation (426 ticks/km drag) and upland sheep pasture had much lower infestation (220 ticks/km drag). Of the three main vegetation types, bracken was least infested (360 ticks/km drag), ericas most (430 ticks/km drag) and grassland had intermediate infestation density (413 ticks/km drag). Questing and developmental microclimates were poor predictors of exposure within these habitats, except lower infestation of pastures was attributed to greater illumination there. Collectors who walked a total of 300 km through all habitats (taking 360 h in all seasons), wearing cotton trousers hanging outside rubber boots, were bitten by only four nymphs and 11 larvae of I. ricinus (but no adult ticks). There was a negative correlation between densities of deer and ticks collected, although presence of deer remains a major indicator of exposure. The proportion of infected ticks was fairly uniform at four sites studied. Overall prevalence of E. phagocytophila in I. ricinus was 3.3% in nymphs (40/1203) but only approximately 1.5% in adults of both sexes (although males do not bite). It was estimated that nymphs of I. ricinus gave 4.4% probability of one infected bite/person/year (for occupational exposure during this research) due to presence in all seasons and habitats, their human biting rate of 0.011 nymphs/h or 0.013 nymphs/km and widespread infection with E. phagocytophila. The frequency distribution of intensity of infection in ticks was approximately normal (mean 98 morulae/nymph infected), thus there is a high risk of receiving a high dose from any one infected tick bite.     

Tick infestation of small mammals in an English woodland

Tick infestations on small mammals were studied from April to November, 2010, in deciduous woodland in southern England in order to determine whether co‐infestations with tick stages occurred on small mammals, a key requirement for endemic transmission of tick‐borne encephalitis virus (TBEV). A total of 217 small mammals was trapped over 1,760 trap nights. Yellow‐necked mice (Apodemus flavicollis) made up the majority (52.5%) of animals, followed by wood mice (A. sylvaticus) 35.5% and bank voles (Myodes glareolus) 12%. A total of 970 ticks was collected from 169 infested animals; 96% of ticks were Ixodes ricinus and 3% I. trianguliceps. Over 98% of ticks were larval stages. Mean infestation intensities of I. ricinus were significantly higher on A. flavicollis (6.53 ± 0.67) than on A. sylvaticus (4.96 ± 0.92) and M. glareolus (3.25 ± 0.53). Infestations with I. ricinus were significantly higher in August than in any other month. Co‐infestations with I. ricinus nymphs and larvae were observed on six (3.6%) infested individuals, and fifteen small mammals (8.9%) supported I. ricinus – I. trianguliceps co‐infestations. This work contributes further to our understanding of European small mammal hosts that maintain tick populations and their associated pathogens, and indicates that co‐infestation of larvae and nymph ticks does occur in lowland UK. The possible implications for transmission of tick‐borne encephalitis virus between UK ticks and small mammals are discussed.     

Diversity and seasonal patterns of ticks parasitizing wild birds in western Portugal

The diversity and abundance of questing ticks and ticks parasitizing birds was assessed during 1?year in two recreational forests in western Portugal, a suburban forest and an enclosed game area. The aim of this study was to assess the distribution and seasonality of tick species and to understand the role of bird species as hosts for ticks. Ixodes ricinus was the most abundant questing tick collected in the enclosed game area, whereas in the suburban forest, only three ticks were collected by blanket dragging. Tick species parasitizing birds included I. ricinus, I. frontalis, I. arboricola, I. acuminatus, Haemaphysalis punctata, Hyalomma marginatum and H. lusitanicum. This is the first record of I. arboricola in Portugal. Tick prevalence and intensity of infestation differed between study areas and was higher in birds from the game area where a large population of deer and wild boar may support tick populations. Ground and shrub dwelling bird species such as Turdus merula, Erithacus rubecula and Sylvia melanocephala were the most heavily parasitized by ticks, but the importance of different bird species as hosts of larvae and nymphs of I. ricinus and I. frontalis differed. Therefore, different bird species may contribute differently for tick population maintenance.     

Water vapour uptake from subsaturated atmospheres by engorged immature ixodid ticks

Contrary to current opinion, fully engorged and detached larvae and nymphs of some ixodid ticks consistently take up substantial amounts of atmospheric water vapour and thereby display their regulative capacity for maintaining water balance in subsaturated air. Net uptake of vapour generally begins some days after detachment and the capability persists until shortly after initiation of apolysis, a period which in diapausing specimens may extend up to several months. This was shown forIxodes ricinus, Haemaphysalis punctata, and the North AmericanI. dammini. Apparently, some other engorged ixodid immatures fail to exhibit net vapour uptake, as was shown for both larvae and nymphs ofDermacentor marginatus and nymphs ofHyalomma anatolicum excavatum. But there is some evidence for engorged nymphs ofD. marginatus that active uptake of vapour does occur, masked by spiracular transpiration. Net uptake of vapour is apparently not possible during the pharate phases. InI. ricinus both teneral nymphs and adults are capable of achieving net water gains by active vapour uptake on the first day following ecdysis. There is new evidence from fully engorgedI. ricinus immatures for the decisive role of agranular alveoli in the production of the salivary secretion involved in vapour uptake.