Seasonality of Ixodes ricinus ticks on vegetation and on rodents and Borrelia burgdorferi sensu lato genospecies diversity in two lyme borreliosis-endemic areas in Switzerland

We compared Ixodes ricinus questing density, the infestation of rodents by immature stages, and the diversity of Borrelia burgdorferi sensu lato (sl) in questing ticks and ticks collected from rodents in two Lyme borreliosis (LB)-endemic areas in Switzerland (Portes-Rouges [PR] and Staatswald [SW]) from 2003 to 2005. There were variations in the seasonal pattern of questing tick densities among years. Questing nymphs were globally more abundant at PR than at SW, but the proportion of rodents infested by immature ticks was similar (59.4% and 61%, respectively). Questing tick activity lasted from February to November with a strong decline in June. The seasonal pattern of ticks infesting rodents was different. Ticks infested rodents without decline in summer, suggesting that the risk of being bitten by ticks remains high during the summer. Rodents from SW showed the highest infestation levels (10±21.6 for larvae and 0.54±1.65 for nymphs). The proportion of rodents infested simultaneously by larvae and nymphs (co-feeding ticks) was higher at SW (28%) than at PR (11%). Apodemus flavicollis was the species the most frequently infested by co-feeding ticks, and Myodes glareolus was the most infective rodent species as measured by xenodiagnosis. At PR, the prevalence of B. burgdorferi sl in questing ticks was higher (17.8% for nymphs and 32.4% for adults) than at SW (10.4% for nymphs and 24.8% for adults), with B. afzelii as the dominant species, but B. garinii, B. burgdorferi sensu stricto, and B. valaisiana were also detected. Rodents transmitted only B. afzelii (at PR and at SW) and B. bavariensis (at SW) to ticks, and no mixed infection by additional genospecies was observed in co-feeding ticks. This implies that co-feeding transmission does not contribute to genospecies diversity. However, persistent infections in rodents and co-feeding transmission contribute to the perpetuation of B. afzelii in nature.     

Antigenic profile of Ixodes ricinus: effect of developmental stage, feeding time and the response of different host species

Antigens recognized by host species in response to ectoparasite infestation have been widely reported. Although differences in the immune responses of different host species have been described, only a very few of these studies compare the range of antigens recognized by different host species in response to infestation. We used Western blot analysis to investigate antigenic responses of different host species that were repeatedly infested with Ixodes ricinus ticks. Antigenic profiles of larval and nymphal whole tick homogenates were compared with the respective salivary gland extract (SGE) samples using sera from rabbits repeatedly infested with either adults, nymphs or larvae. SGE samples were also analysed using sera from hamsters infested with adults, nymphs or larvae. Sera from BALB/C mice, Apodemus flavicollis (yellow-necked mouse) or Clethrionomys glareolus (bank vole) repeatedly infested with larvae were used to compare the antigenic profiles of SGE and larval homogenate samples. We also investigated different sources of tick antigens, using rabbit sera, by comparing midgut extracts from female adult ticks and SGE from unfed ticks and from ticks throughout the 6-day feeding period with whole tick homogenates of female and male adults, nymphs and larvae. The pattern of antigenic tick-molecules recognized by infested host species varies with the period of feeding, developmental stage and the particular host species parasitized.     

The root-vole Microtus oeconomus (Pallas, 1776): a new potential reservoir of Anaplasma phagocytophilum

Anaplasma phagocytophilum infection is a recently emerged tick-borne zoonosis. The bacterium's reservoirs likely comprise cervids, some ruminants, rodents, and perhaps other small and intermediate-size mammals; the main vector in Europe is the Ixodes ricinus tick. The Bia?owieza Primeval Forest is an ecosystem with a known prevalence of tick-borne pathogens. We studied the root-vole Microtus oeconomus to evaluate the natural infection of A. phagocytophilum. Intragranulocytic bacterial clusters (morulae) were not seen, but the A. phagocytophilum-specific nested polymerase chain reaction (PCR) product, targeting the rrs gene, was detected in two out of 30 rodent samples (GenBank accession nos. DQ361024 and DQ361025). Twenty-six root vole (86.6%) hosted ticks, mainly Dermacentor reticulatus larvae and nymphs. Only two rodents were parasitazed by I. ricinus single larvae. These data show the presence of natural infection of A. phagocytophilum among the root-vole M. oeconomus in the Bia?owieza Primeval Forest ecosystem.     

小五台山地区长角血蜱若虫日间寻求节律

目的 旨在了解长角血蜱若虫日间寻求活动节律及其变化原因,为研究者规划合理采样时间,从而准确评估蜱传疾病风险提供理论依据。方法 在河北省小五台山地区选取半封闭山路设置3处样带,于长角血蜱种群数量高峰期内,连续5 d从6∶00-19∶00,每隔1 h采用拖旗法对处于寻求状态若虫进行有放回抽样调查,同时记录气温,相对温度和露点温度。结果 不同样带间蜱采样数量差异显著(F=66.50,P<0.01),离居住地越近蜱数量越多;各样带间长角血蜱若虫均表现出相同寻求活动节律,受气温和露点温度影响,6∶00-8∶00若虫数量下降,8∶00-12∶00有一起伏,随后逐渐上升至16∶00趋于稳定并于19∶00达到最大,16∶00-19∶00为日间长角血蜱若虫采集数量最高时段,占总采集数量的48.4%。结论 宿主活动强度对蜱数量分布有较大影响;蜱寻求节律与空气中水汽含量有关,清晨水汽含量过大植被凝集露水,中午水汽含量过小,空气干燥,都可降低蜱寻求活动,导致不同时间下采样可造成蜱种群密度估计和蜱传疾病风险评估误差,16∶00-19∶00环境条件适宜,蜱寻求活动强烈,是最接近蜱种群密度的采样时间,建议在制定林间蜱种群密度调查方案时,应统一采样时间以便数据具有可比性。     

Sympatric Ixodes trianguliceps and Ixodes ricinus ticks feeding on field voles (Microtus agrestis): potential for increased risk of Anaplasma phagocytophilum in the United Kingdom?

The importance of wild rodents as reservoirs of zoonotic tick-borne pathogens is considered low in the United Kingdom because, in studies to date, those parasitized by exophilic Ixodes ricinus ticks carry almost exclusively larvae and thus have a minor role in transmission cycles. In a cross-sectional study, 11 (6.7%) of 163 field voles (Microtus agrestis) captured at field sites in Northern England were PCR-positive for Anaplasma phagocytophilum. The voles were found to act as hosts for both larval and nymphal I. ricinus and all stages of the nidicolous tick I. trianguliceps, and eight individuals were infested with ticks of both species at the same time. Two of 158 larval and one of 13 nymphal I. ricinus, as well as one of 14 larval and one of 15 nymphal I. trianguliceps collected from the rodents were PCR-positive. These findings suggest that habitats where field voles are abundant in the United Kingdom may pose a risk of A. phagocytophilum infection because (i) field voles, the most abundant terrestrial mammal in the United Kingdom, may be a competent reservoir; (ii) the field voles are hosts for both nymphal and larval ixodid ticks so they could support endemic cycles of A. phagocytophilum; and (iii) they are hosts for nidicolous I. trianguliceps, which may alone maintain endemic cycles, and exophilic I. ricinus ticks, which could act as a bridge vector and transmit infections to humans and domesticated animals.     

Spatiotemporal variation in a Lyme disease host and vector: black-legged ticks on white-footed mice

We monitored population density of white-footed mice (Peromyscus leucopus), burdens of immature black-legged ticks (Ixodes scapularis) on mice, and infection prevalence of host-seeking ticks on six forest plots in southeastern New York State from 1995 through 1999. Despite densities of mice that fluctuated two orders of magnitude, average larval and nymphal tick burdens per mouse remained remarkably constant. Spatial variability in mouse density and tick burdens was modest. The total number of larval and nymphal ticks that fed on the mouse population each year depended strongly on population density of mice; a steady increase was observed in both mouse density and total tick meals on mice from 1996 through 1999. The result was a steady increase in the infection prevalence of nymphal and adult ticks with the etiological agent of Lyme disease, Borrelia burgdorferi, over this time. We suggest that fluctuations in population density of mice, combined with possible regulation of tick burdens on mice, may influence risk of human exposure to Lyme disease.     

Wild cervids are host for tick vectors of babesia species with zoonotic capability in Belgium

Babesiosis is a tick-borne disease caused by different species of intraerythrocytic protozoan parasites within the genus Babesia. Different species of Babesia are described as potentially zoonotic and cause a malaria-like disease mainly in immunocompromised humans. Interest in the zoonotic potential of Babesia is growing and babesiosis has been described by some authors as an emergent zoonotic disease. The role of cervids to maintain tick populations and act as a reservoir host for some Babesia spp. with zoonotic capability is suspected. To investigate the range and infection rate of Babesia species, ticks were collected from wild cervids in southern Belgium during 2008. DNA extraction was performed for individual ticks, and each sample was evaluated for the absence of PCR inhibition using a PCR test. A Babesia spp. genus-specific PCR based on the 18S rRNA gene was applied to validated tick DNA extracts. A total of 1044 Ixodes ricinus ticks were collected and 1023 validated samples were subsequently screened for the presence of Babesia spp. DNA. Twenty-eight tick samples were found to be positive and identified after sequencing as containing DNA representing: Babesia divergens (3), B. divergens-like (5), Babesia sp. EU1 (11), Babesia sp. EU1-like (3), B. capreoli (2), or unknown Babesia sp. (4). This study confirms the presence of potentially zoonotic species and Babesia capreoli in Belgium, with a tick infection rate of 2.7% (95% CI 1.8,3.9%). Knowledge of the most common reservoir source for transmission of zoonotic Babesia spp. will be useful for models assessing the risk potential of this infection to humans.     

An enzootic transmission cycle of Lyme borreliosis spirochetes in the southeastern United States

Lyme borreliosis, or Lyme disease (LD), is a tick-borne zoonotic infection of biomedical significance, caused by Borrelia burgdorferi sensu lato (s.l.) spirochetes and transmitted by Ixodes species ticks. It usually circulates among wildlife vertebrate reservoirs and vector ticks but may infect humans, causing multisystem problems. In far western and northern North America, the host reservoirs, tick vectors, and genospecies of Borrelia are well known but not so in the southern U.S., where there is controversy as to the presence of "true" LD. Here we report the presence of the LD spirochete B. burgdorferi sensu stricto (s.s.) and Borrelia bissettii, three main reservoir hosts, and two enzootic tick vectors in the southeastern U.S. The two enzootic tick vectors, Ixodes affinis and Ixodes minor, rarely bite humans but are more important than the human biting "bridge" vector, Ixodes scapularis, in maintaining the enzootic spirochete cycle in nature. We also report extraordinary longevities and infections in the reservoir rodents Peromyscus gossypinus, Sigmodon hispidus, and Neotoma floridana.     

Experimental studies on the transmission cycle of Thogoto virus, a candidate orthomyxovirus, in Rhipicephalus appendiculatus

Thogoto (THO) virus, a candidate orthomyxovirus, replicated in and was transmitted by larvae, nymphs, and adults of the brown ear tick, Rhipicephalus appendiculatus. Larvae fed on viremic hamsters (10(7-8) PFU/ml blood) acquired an average of 10(2.5) PFU per tick. Following engorgement the titer dropped to 10(1.9) PFU on day 2 but increased by day 6 to 10(3.3) PFU. Virus survived transstadially in these ticks as demonstrated by the fact that, on day 10, newly moulted nymphs contained, on average, 10(3.5) PFU/tick. When 10 such infected nymphs were placed on a hamster a fatal infection of the animal developed involving a viremia of 10(6.7) PFU/ml blood. Another group of 6 infected nymphs did not elicit a detectable viremia in a hamster, or cause death. However the animal seroconverted to THO, virus indicating that virus transmission had occurred. Following acquisition of THO virus at the larval stage, virus was detected in adult ticks 138 days later. Uninfected nymphs fed on viremic hamsters acquired an average of 10(4) PFU/nymph. No virus was detected in the nymphs 4 days post-engorgement. Virus was, however, recovered by 6 days post-engorgement (10(4.7) PFU/nymph). Virus persisted transstadially as shown by the presence of an average of 10(3.4) PFU in newly moulted adults. Three groups of these infected adults (5-6 ticks/group) induced viremia in hamsters with blood titers of the order 10(2.8-3.5) PFU/ml. Virus persisted in engorged adults for up to 66 days following nymphal engorgement.(ABSTRACT TRUNCATED AT 250 WORDS)     

Questing ticks in suburban forest are infected by at least six tick-borne pathogens

The role of Ixodes ricinus ticks in the transmission of pathogens of public health importance such as Borrelia burgdorferi s.l. is widely recognized and is suspected in several emerging vector-borne pathogens in Europe. Here, we assess prevalence rates of several endemic and emerging zoonotic pathogens in tick populations in an area of high human population density in France, to contribute to a risk assessment for potential transmission to humans. Pathogen prevalence rates were evaluated by polymerase chain reaction detection and sequencing in questing ticks, individually for adults and in pools of 10 for nymphs. In addition to finding micro-organisms corresponding to symbionts, we found high prevalence rates of B. burgdorferi s.l. (32% of adult females and 10% of nymphs) and low to moderate ones of Anaplasma phagocytophilum (~1%), spotted fever group Rickettsia spp. (~6%), Babesia sp. EU1 (~1%), Bartonella birtlesii (0.1%), and Francisella tularensis (!1%). Our findings extend the knowledge of the geographical distribution of these endemic and emergent pathogens and support the conclusion that ticks are important vectors of pathogenic micro-organisms in suburban forests. Moreover, tick coinfection with multiple pathogens was found to occur frequently, which poses a serious challenge for diagnosis and appropriate treatment. The incrimination of these pathogens in potentially severe pathologies requires widespread surveillance to assess the risk of infection, thereby facilitating diagnosis and treatment, as well as raising local awareness of tick-borne diseases.     

A trial at using the systemic action of ivermectin for suppressing the vector capacity of ticks (Ixodidae) infected with the tick-borne encephalitis virus]

Adult Dermacentor marginatus hatched from nymphs infected with TBE virus and poisoned with ivermectin retain their vector abilities. Even small individuals with a 1.5-2 times lesser mass as against the reference mass contain the virus in the body in the same titers and the virions in salivary gland alveoli. Administration of an oil solution of ivermectin into the stomach of white mice, nymph feeders, in a dose surpassing threefold the dose recommended for intramuscular injection of this agent completely suppressed shedding of intact nymphs but did not suppress it in those infected. The nymph mass, size and mass of adult ticks hatched from them dropped under the effect of ivermectin dosage build-up in both intact and infected ticks, but these processes were slower in ticks infected with TBE virus. The authors suggest that the ticks infected with TBE virus are much more resistant to the process of gamma-aminobutyric acid depression, the mechanism of ivermectin action. They emphasize the necessity of bearing in mind the possible differences in the reactions to systemic poisons of intact and infected ticks when organizing vector control measures.     

Disruption of the salivary protein 14 in Ixodes scapularis nymphs and impact on pathogen acquisition.

We previously examined the physiological role of the anticoagulant salivary protein 14 (salp14) in adult Ixodes scapularis and showed that Salp14 played a role in tick feeding and engorgement. We now analyze whether the disruption of the salp14 family expression by RNA interference affects tick weight in na?ve nymph I. scapularis. Salp14 expression after dsRNA injection was significantly reduced, as shown by mRNA and protein analysis. However, nymph engorgement weight was not altered in salp9pac (salp14 paralog) dsRNA-injected ticks. We also determined Borrelia burgdorferi and Anaplasma phagocytophilum acquisition in I. scapularis nymphs that had reduced Salp14 expression. B. burgdorferi and A. phagocytophilum acquisition was not affected 72 hours after feeding. Our results suggest that different mechanisms govern nymph and adult feeding in I. scapularis.     

长角血蜱、嗜群血蜱经期传播莱姆病螺旋体Borrelia garinii的实验研究

目的　探讨长角血蜱、嗜群血蜱经期传播莱病螺旋体的可能性。方法　通过皮下注射KM鼠建立实验感染动物模型 ,以此阳性感染鼠感染试蜱非感染种群 ,观察试蜱的感染能力以及以莱姆病螺旋体的保持能力。结果　通过剌叮阳性KM鼠 ,长角血蜱、嗜群血蜱幼蜱饱血后分别获得 6 1 3%、75 0 %的阳性感染 ,但所感染的螺旋体在感染后 2d即死亡消解 ,不能重新获得分离 ,PCR扩增阳性也只能持续到饱血后 8d ,幼蜱蜕化为若蜱后 ,所有检测结果均为阴性 ;这两种蜱的若蜱也都可通过吸血获得 70 0 %的检测阳性率 ,感染后长角血蜱、嗜群血蜱可分别在在饱血后 5、10d内保持螺旋体的活性 ,PCR检测阳性率可延迟至饱血后 15d。此后直至蜕化成为成蜱 ,所有血、蜱检测结果均呈阴性 ;长角血蜱、嗜群血蜱的不同种群在感染和保持螺旋体能力上表现一致。结论　长角血蜱、嗜群血蜱的幼蜱和若蜱虽可以感染莱姆病螺旋体但不能经期传播到下一发育阶段 ,不具备经期传播能力 ,作为莱姆病主要媒介的可能性不大。     

Molecular survey of tick-borne pathogens in Ixodid ticks collected from hunted wild animals in Tuscany,Italy

Objective: To determine the prevalence of zoonotic tick-borne bacteria in feeding ticks removed from hunted wild animals. Methods: PCR was executed on DNA extracted from 77 tick pools to detect Anaplasma phagocytophilum, Bartonella spp., Borrelia burgdorferi sensu lato, Coxiella burnetii and Rickettsia spp. Results: A total of 432 ticks were collected: 30(6.94%) Haemaphysalis punctata, 72(16.7%) Dermacentor marginatus and 330(76.38%) Ixodes ricinus. For each animal one or two pools of 3 ticks of the same species was constituted. Seventy-seven tick pools were examined by PCR: 58(75.32%) resulted infected and among them 14(18.18%) showed co-infections. In particular, 29(37.66%) pools were positive for Bartonella spp., 23(29.87%) for Anaplasma phagocytophilum, 16(20.78%) for Rickettsia spp., and 5(6.49%) for Borrelia burgdorferi s.l. All samples were negative for Coxiella burnetii. Conclusions: The results demonstrate the presence of several zoonotic tick-borne pathogens in the studied area, and underline the risk of exposure to infections for hunters not only during the outdoor activity, but also when they manipulate hunted animals infested by infected ticks.     

Identification of a novel strain of Borrelia hermsii in a previously undescribed northern California focus.

An epizootiologic investigation testing for the presence of tick-borne relapsing fever spirochetes in rodent and tick hosts was conducted at Eagle Lake in Lassen County, California. Six of 211 O. hermsii ticks and none of 180 rodents were polymerase chain reaction (PCR)-positive for Borrelia spirochetes. Sequencing of the PCR-amplified flagellin gene fragment suggests that the spirochetes from Eagle Lake represent a previously undescribed strain of Borrelia hermsii.     

Detection of Anaplasma-marginale-infected tick vectors by using a cloned DNA probe.

Anaplasmosis is the most widely distributed of several important tick-borne diseases that constrain cattle production throughout much of the world. Evaluation of the effectiveness of disease control strategies that integrate vaccination with tick control requires the ability to monitor tick and cattle infection rates. To detect Anaplasma marginale in ticks and bovine erythrocytes, a 2-kilobase DNA fragment from a cloned A. marginale gene coding for a surface protein having a Mr of 105,000 was prepared and evaluated as a probe. The probe was species specific and detected A. marginale DNA derived from infected bovine erythrocytes and adult Dermacentor ticks infected either as nymphs or adults. Tick infection was confirmed by microscopy and test feeding on a susceptible calf. The sensitivity of the probe is suitable for detecting infected ticks in experimental and field epizootiology studies.     

Quantitative ecology of ticks as a basis for transmission models of tick-borne pathogens

Tick population ecology is the basis of spatiotemporal variation in the risk of infection by tick-borne pathogens. The continental distribution of tick-borne encephalitis (TBE) in Europe is statistically associated with a specific pattern of the seasonal dynamics of Ixodes ricinus, and a particular characteristic of the seasonal land surface temperature profile. A tick population model would allow us to move from this statistical analysis to a biological, process-based model for TBE virus and the many other pathogens vectored by Ixodes spp. ticks in Europe and the United States. Long-term field data on I. ricinus are analyzed to provide empirical estimates of rates of the major demographic processes, development, questing, attachment to hosts, and mortality.     

Growth kinetics of the Lyme disease spirochete (Borrelia burgdorferi) in vector ticks (Ixodes dammini)

Lyme disease spirochetes (Borrelia burgdorferi) multiplied rapidly in larval Ixodes dammini, reaching a mean density of 2,735 spirochetes/tick on day 15 post-repletion. A 5-fold drop in spirochete levels occurred during the subsequent premolting period. Recently molted nymphs contained a mean of less than 300 spirochetes/tick. Following nymphal repletion, spirochete multiplication renewed, reaching a mean abundance of 61,275 spirochetes/nymph on day 75 post-repletion. A 10-fold drop in spirochete abundance occurred again when ticks molted to the adult stage. Tick-derived spirochetes proved to be infectious when greater than 10(4) spirochetes were inoculated ip into hamsters (4 of 4 animals infected). Inocula of 10(3-4) spirochetes were not always infectious (8 of 23 animals infected), and inocula of less than 10(3) spirochetes were insufficient for establishing infection (0 of 8 animals infected).     

Factors influencing the distribution of larval blacklegged ticks on rodent hosts

Because of differences among hosts in reservoir competence for tick-borne diseases, the distribution of larval blacklegged ticks on hosts might determine tick infection prevalence and disease risk to humans. We conducted a three-part study to determine the factors responsible for greater burdens of larval blacklegged ticks on white-footed mice than on eastern chipmunks. A microhabitat study indicated that questing ticks have higher encounter rates with mice than with chipmunks. Laboratory experiments demonstrated that ticks oriented more strongly toward mice. However, larval ticks fed more successfully from chipmunks. Our results strongly suggest that mice are both more likely to use larval tick-infested microhabitats and to attract questing larvae than are chipmunks, leading to a dramatically higher initial infestation rate, which is then reduced by greater grooming activity by mice. The high mortality rate of larvae that were experimentally introduced onto mice suggests that grooming is a significant cause of mortality to larval blacklegged ticks.     

Use of a sentinel host system to study the questing behavior of Ixodes spinipalpis and its role in the transmission of Borrelia bissettii, human granulocytic ehrlichiosis, and Babesia microti.

Ixodes spinipalpis maintains Borrelia bissettii spirochetes in Colorado in a cycle involving wood rats and deer mice. This tick has been described as nidicolous, remaining either attached to its rodent hosts or in the rodent nest. Nidicolous ticks pose little risk of pathogen transmission to humans if they do not actively quest for hosts. To investigate the questing potential of I. spinipalpis, sentinel mice were placed in an area where I. spinipalpis had been commonly found on wood rats and deer mice. Concurrently, wild rodent populations were trapped and analyzed for Lyme disease spirochetes, the agent of human granulocytic ehrlichiosis (aoHGE), and Babesia microti. A total of 122 I. spinipalpis larvae and 10 nymphs were found on 19% of 244 sentinel mice. In addition, 4 sentinel mice became infested with Malaraeus telchinus or Orchopeas neotomae fleas. Questing I. spinipalpis were positively associated with woody shrubs and negatively associated with sunny and grassy areas. Four sentinel mice became infected with aoHGE after having been fed upon only by I. spinipalpis larvae. One sentinel mouse became infected with B. bissettii after having an I. spinipalpis nymph feed on it, and one sentinel mouse became coinfected with aoHGE and B. bissettii after it was fed upon by a single I. spinipalpis nymph. These sentinel mouse conversions suggest the possibility that the aoHGE is transovarially transmitted by I. spinipalpis, and that I. spinipalpis is capable of simultaneously transmitting B. bissettii and the aoHGE. The findings that I. spinipalpis quest away from rodent nests and will attach to and infect sentinel mice may be of public health importance. It suggests the potential transmission of the agents of human granulocytic ehrlichiosis and Lyme disease to other hosts by I. spinipalpis, in regions of the western United States where Ixodes pacificus is not found.