Prevalence of Ehrlichia, Borrelia, and Rickettsial agents in Amblyomma americanum (Acari: Ixodidae) collected from nine states

Ambyomma americanum (L.) (Acari: Ixodidae) is an aggressive tick that feeds on humans during all postembryonic life stages. In many regions of the United States, it is the tick most commonly found attached to humans. Public health interest has grown recently, due to the recognition of new human pathogens transmitted by A. americanum and the expanding distribution of the tick. A. americanum is a vector of several bacteria pathogenic to humans. Ehrlichia chaffeensis and Ehrlichia ewingii cause moderate-to-severe febrile illness. "Rickettsia amblyommii," a member of the spotted fever group Rickettsia, also has recently been implicated as a possible human pathogen based on serologic evidence from persons recovering from illness after a tick bite. We have determined the prevalence of infection of Ehrlichia chaffeensis, E. ewingii, "Borrelia lonestari", and R. amblyommii within A. americanum ticks from 29 sites in nine states. Overall infection prevalences were 4.7% for E. chaffeensis (range, 0-27%), 3.5% for E. ewingii (range, 0-18.6%), 2.5% for B. lonestari (range, 0-12.2%), and 41.2% for R. amblyommii (range, 0-84.0%). In addition, 87 ticks (4.3%) were infected with two or more bacteria. This report documents new distribution records for E. ewingii, B. lonestari, and R. amblyommii and underscores the nonhomogeneous distribution of pathogen foci of infection. Additional surveillance throughout the range ofA. americanum is warranted to increase physician and public awareness of the risk of disease to humans from exposure to the agents transmitted by this tick.     

Defining plasmids required by Borrelia burgdorferi for colonization of tick vector Ixodes scapularis (Acari: Ixodidae)

Maintenance in nature of Borrelia burgdorferi, the pathogenic bacterium that causes Lyme disease, requires transmission through an infectious cycle that includes a tick vector and a mammalian host. The genetic requirements for persistence in these disparate environments have not been well defined. B. burgdorferi has a complex genome composed of a chromosome and >20 plasmids. Previous work has demonstrated that B. burgdorferi requires two plasmids, lp25 and lp28-1, in the mammalian host. To investigate the requirement for these same two plasmids during tick infection, we experimentally infected larval ticks with B. burgdorferi lacking either lp25 or lp28-1 and then assessed the spirochete load in ticks at different points of the infection. Whereas plasmid lp28-1 was dispensable in ticks, plasmid lp25 was essential for tick infection. Furthermore, we investigated the requirement in ticks for the lp25 gene bbe22, which encodes a nicotinamidase that is necessary and sufficient for mammalian infection by B. burgdorferi clones lacking lp25. This gene was also sufficient in ticks to restore survival of spirochetes lacking lp25. This is the first study to investigate the requirement for specific plasmids by B. burgdorferi within the tick vector, and it begins to establish the genomic components required for persistence of this pathogen throughout its natural infectious cycle.     

Experimental Lyme disease in rabbits: spirochetes found in erythema migrans and blood.

In attempts to produce experimental Lyme disease, 33 rabbits were inoculated with Lyme spirochetes by tick feeding or from tick organ homogenates or cultures. Two rabbits developed erythema chronicum migrans at the site of inoculation, in one instance 2 days after injection of a tick organ homogenate and in the other instance, 17 days after feeding of infected Ixodes dammini ticks. Spirochetes were seen in skin biopsy specimens of the second lesion with Warthin-Starry and immunoperoxidase stains. Spirochetes were also recovered from blood cultures of two additional rabbits 2 weeks post-inoculation. These findings are characteristic of early Lyme disease in humans and give additional support for the spirochetal etiology of Lyme disease.     

Infestation of Peromyscus leucopus and Tamias striatus by Ixodes scapularis (Acari: Ixodidae) in relation to the abundance of hosts and parasites

The risk of humans acquiring Lyme disease is a function of the local density of nymphal and adult ticks that are infected with Lyme disease spirochetes. This in turn, will be related to host-use patterns of ticks and to the densities of both juvenile ticks and their hosts. At a forested site in Dutchess County, NY, we quantified host-use patterns of larval and nymphal Ixodes scapularis Say infesting the 2 dominant vertebrate hosts, white-footed mice and eastern chipmunks, during a 3-yr period. Larval tick burdens were 2-3 times higher on mice than they were on chipmunks, whereas nymphal tick burdens were > 3 times higher on chipmunks than they were on mice. We used multiple regression analysis to examine juvenile tick and host densities as independent variables influencing tick burdens. The density of questing larval ticks was positively correlated with larval tick burdens on mice, whereas the density of questing nymphs was weakly related to nymphal burdens on either host. Effects of the densities of mice and chipmunks on tick burdens were strong in some years, but weak in others. Moreover, the sign of the regression coefficients changed from one year to the next. We argue that these results are inconsistent with a passive encounter model of host selection, and suggest instead that either tick behavior or host responses cause strong biases in the distribution of juvenile ticks on their hosts.     

Acquisition of coinfection and simultaneous transmission of Borrelia burgdorferi and Ehrlichia phagocytophila by Ixodes scapularis ticks

The agents of Lyme disease (Borrelia burgdorferi) and human granulocytic ehrlichiosis (Ehrlichia phagocytophila) are both transmitted by the tick Ixodes scapularis. In nature, ticks are often infected with both agents simultaneously. We studied whether previous infection with either Borrelia or Ehrlichia in ticks would affect acquisition and transmission of a second pathogen. Ehrlichia-infected I. scapularis nymphs were fed upon Borrelia-infected mice, and Borrelia-infected I. scapularis nymphs were fed upon Ehrlichia-infected mice. The efficiency with which previously infected nymphal ticks acquired a second pathogen from infected hosts was compared to that of uninfected ticks. An average of 51% +/- 15% of ticks acquired Ehrlichia from infected mice regardless of their prior infection status with Borrelia. An average of 85% +/- 10% of ticks acquired Borrelia from infected mice regardless of their prior infection status with Ehrlichia. Also, we assessed the efficiency with which individual nymphs could transmit either agent alone, or both agents simultaneously, to individual susceptible hosts. An average of 76% +/- 9% of Borrelia-infected ticks and 84% +/- 10% of Ehrlichia-infected ticks transmitted these agents to mice regardless of the presence of the other pathogen. There was no evidence of interaction between the agents of Lyme disease and human granulocytic ehrlichiosis in I. scapularis ticks. The presence of either agent in the ticks did not affect acquisition of the other agent from an infected host. Transmission of the agents of Lyme disease and human granulocytic ehrlichiosis by individual ticks was equally efficient and independent. Dually infected ticks transmitted each pathogen to susceptible hosts as efficiently as ticks infected with only one pathogen.     

Passive surveillance for I. scapularis ticks: enhanced analysis for early detection of emerging Lyme disease risk

Lyme disease (LD) is emerging in Canada because of the northward expansion of the geographic range of the tick vector Ixodes scapularis (Say). Early detection of emerging areas of LD risk is critical to public health responses, but the methods to do so on a local scale are lacking. Passive tick surveillance has operated in Canada since 1990 but this method lacks specificity for identifying areas where tick populations are established because of dispersion of ticks from established LD risk areas by migratory birds. Using data from 70 field sites in Quebec visited previously, we developed a logistic regression model for estimating the risk of I. scapularis population establishment based on the number of ticks submitted in passive surveillance and a model-derived environmental suitability index. Sensitivity-specificity plots were used to select an optimal threshold value of the linear predictor from the model as the signal for tick population establishment. This value was used to produce an "Alert Map" identifying areas where the passive surveillance data suggested ticks were establishing in Quebec. Alert Map predictions were validated by field surveillance at 76 sites: the prevalence of established I. scapularis populations was significantly greater in areas predicted as high-risk by the Alert map (29 out of 48) than in areas predicted as moderate-risk (4 out of 30) (P < 0.001). This study suggests that Alert Maps created using this approach can provide a usefully rapid and accurate tool for early identification of emerging areas of LD risk at a geographic scale appropriate for local disease control and prevention activities.     

Effects of reduced deer density on the abundance of Ixodes scapularis (Acari: Ixodidae) and Lyme disease incidence in a northern New Jersey endemic area

We monitored the abundance of Ixodes scapularis Say (Acari: Ixodidae) and the Lyme disease incidence rate after the incremental removal of white-tailed deer, Odocoileus virginianus Zimmermann, within a suburban residential area to determine whether there was a measurable decrease in the abundance of ticks due to deer removal and whether the reduction in ticks resulted in a reduction in the incidence rate within the human population. After three seasons, the estimated deer population was reduced by 46.7%, from the 2002 postfawning estimate of 2,899 deer (45.6 deer per km2) to a 2005 estimate of 1,540 deer (24.3 deer per km2). There was no apparent effect of the deer culling program on numbers of questing I. scapularis subadults in the culling areas, and the overall numbers of host-seeking ticks in the culling areas seemed to increase in the second year of the program. The Lyme disease incidence rate generated by both passive and active surveillance systems showed no clear trend among years, and it did not seem to vary with declining deer density. Given the resources required to mount and maintain a community-based program of sufficient magnitude to effectively reduce vector tick density in ecologically open situations where there are few impediments to deer movement, it may be that deer reduction, although serving other community goals, is unlikely to be a primary means of tick control by itself. However, in concert with other tick control interventions, such programs may provide one aspect of a successful community effort to reduce the abundance of vector ticks.     

Lyme disease: a selective medium for isolation of the suspected etiological agent, a spirochete.

A simple procedure with a new selective culture medium for the isolation of the suspected etiological agent of Lyme disease from ticks is described. Live ticks (Ixodes dammini) were ground with a mortar and pestle, and the suspensions were inoculated into a selective and nonselective medium. The selective medium, which contained kanamycin and 5-fluorouracil, yielded positive spirochete cultures from 100% of the pooled ticks and from 79% of the single tick specimens. The isolation rate for the nonselective medium was 0% from the tick pools and 58% from the single tick specimens.     

Feasibility of controlling Ixodes scapularis ticks (Acari: Ixodidae), the vector of Lyme disease, by parasitoid augmentation

A theoretical analysis of the feasibility of controlling tick populations (Ixodidae) by the release of reared Ixodiphagus parasitoids in tick ecosystems yielded promising results. The analysis suggested that if reasonable progress could be made in mass-rearing the parasitoids, it would be possible to control the blacklegged tick, Ixodes scapularis (Say), the vector of Lyme disease, by this biological control procedure. Lyme disease has become the most important vector-borne disease in the United States. In a field-release experiment conducted in Africa by members of the International Center for Insect Physiology and Ecology, effective control of Amblyomma variegatum (F.) was obtained by the release of Ixodiphagus parasitoids in tick habitats. Encouraging theoretical results along with the encouraging results of a field-release experiment indicate the need for civil and political leaders in countries where ticks are a major problem to sponsor strong and well-coordinated research initiatives focused on the development of this new method of dealing with tick problems.     

Ixodes scapularis ticks collected by passive surveillance in Canada: analysis of geographic distribution and infection with Lyme borreliosis agent Borrelia burgdorferi

Passive surveillance for the occurrence of the tick Ixodes scapularis Say (1821) and their infection with the Lyme borreliosis spirochaetes Borrelia burgdorferi s.l. has taken place in Canada since early 1990. Ticks have been submitted from members of the public, veterinarians, and medical practitioners to provincial, federal, and university laboratories for identification, and the data have been collated and B. burgdorferi detected at the National Microbiology Laboratory. The locations of collection of 2,319 submitted I. scapularis were mapped, and we investigated potential risk factors for I. scapularis occurrence (in Quebec as a case study) by using regression analysis and spatial statistics. Ticks were submitted from all provinces east of Alberta, most from areas where resident I. scapularis populations are unknown. Most were adult ticks and were collected in spring and autumn. In southern Québec, risk factors for tick occurrence were lower latitude and remote-sensed indices for land cover with woodland. B. burgdorferi infection, identified by conventional and molecular methods, was detected in 12.5% of 1,816 ticks, including 10.1% of the 256 ticks that were collected from humans and tested. Our study suggests that B. burgdorferi-infected I. scapularis can be found over a wide geographic range in Canada, although most may be adventitious ticks carried from endemic areas in the United States and Canada by migrating birds. The risk of Lyme borreliosis in Canada may therefore be mostly low but more geographically widespread than previously suspected.     

Computer simulation of Rocky Mountain spotted fever transmission by the American dog tick (Acari: Ixodidae)

A computer model was developed for simulation of the transmission of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF), by the American dog tick, Dermacentor variabilis (Say). The model of RMSF was combined with a model for population dynamics of the American dog tick and included simulation of infection and transmission of rickettsiae between ticks and host mammals and transmission of RMSF to humans. The model simulated the effects of biotic and environmental variables such as weather, host density, habitat, transovarial transmission, fecundity of infected ticks, and infectivity level of ticks and mammals. Some parameters in the model were fitted by iterative simulations to produce realistic rates of R. rickettsii infection in adult ticks and small and medium-sized mammal hosts. Parameters also were fitted to yield the historical average number of RMSF cases for Virginia. Comparisons of the simulated and actual number of cases for nine other states indicated a reasonable level of validity for the model. A theoretical tick density threshold of 252 unfed adult ticks/ha for transmission of RMSF was determined from a relationship between rate of transmission to humans and density of ticks. The transmission threshold can be used for additional modeling efforts to study the effects of management technologies on tick densities and RMSF human cases. The model can serve as a framework for modeling other tick-borne diseases such as Lyme disease, babesiosis, and heartwater.     

"Candidatus Neoehrlichia mikurensis," Anaplasma phagocytophilum, and lyme disease spirochetes in questing european vector ticks and in feeding ticks removed from people

To estimate the likelihood of people coming into contact with the recently described tick-borne agent "Candidatus Neoehrlichia mikurensis," we compared its prevalence to those of Lyme disease spirochetes and Anaplasma phagocytophilum in questing adult Ixodes ricinus ticks collected in various Central European sites and examined ticks, which had been removed from people, for the presence of these pathogens. Whereas spirochetes infected questing adult ticks most frequently (22.3%), fewer than a third as many ticks were infected by "Ca. Neoehrlichia mikurensis" (6.2%), and about a sixth harbored A. phagocytophilum (3.9%). On average, every twelfth encounter of a person with an I. ricinus tick (8.1%) may bear the risk of acquiring "Ca. Neoehrlichia mikurensis." Although a fifth of the people (20%) had removed at least one tick infected by "Ca. Neoehrlichia mikurensis," none displayed symptoms described for this pathogen, suggesting that its transmission may not be immediate and/or that immunocompetent individuals may not be affected. Because immunosuppressed patients may be at a particular risk of developing symptoms, it should be considered that "Ca. Neoehrlichia mikurensis" appears to be the second most common pathogen in I. ricinus ticks. In our survey, only Borrelia afzelii appears to infect Central European vector ticks more frequently.     

Human babesiosis--an unrecorded reality. Absence of formal registry undermines its detection, diagnosis and treatment, suggesting need for immediate mandatory reporting

Human babesiosis, caused by parasitic protozoa of erythrocytes, has escaped usual associates--lower mammals. Thriving in tick guts, it has spread inland from the coasts of America, adopting mankind as a host. Babesia spp. threaten life quality of unsuspecting humans in quickly expanding territories worldwide, including the state of Pennsylvania, USA. The causative spirochetes of Lyme disease often similarly co-exist in ticks. Singly or together they may, by causing persistent and chronic infections, duplicate any symptom in the medical literature--including depression and hypochondriasis. Physicians practicing throughout Pennsylvania have identified patients with symptomatic babesiosis, but without governmental surveillance or health registries that require doctors to consider and report babesiosis, these cases have not prompted epidemiological concern. Misunderstandings such as, "Isn't that an obscure tropical disease?" are usual responses when doctors are asked about babesiosis, inadvertently trivializing patients and disease. Mandatory reporting of babesiosis should now be considered a medical necessity.     

首次从金华地区蜱中检测到莱姆病螺旋体

为了解金华的蜱类及蜱类宿主动物中自然感染莱姆病螺旋体的状况,用PCR法检测鼠体寄生蜱类和宿主动物脏器中莱姆病DNA片段。共采集鼠体寄生蜱41只,从寄生于1只黑线姬鼠和2只小林姬鼠(2只)的3只中华硬蜱雌性若蜱中检测到阳性莱姆病感染。后以引物VS461扩增,此3只中华硬蜱均为阳性。后经克隆测序为B.afzelli(VS461同源株)。初步认为金华地区存在莱姆病病原,尚需进一步调查和病原分离加以证实。     

Passive surveillance in Maine, an area emergent for tick-borne diseases

In 1989, a free-of-charge, statewide tick identification program was initiated in Maine, 1 yr after the first Ixodes scapularis Say (=I. dammini Spielman, Clifford, Piesman & Corwin) ticks were reported in the state. This article summarizes data from 18 continuous years of tick submissions during which >24,000 ticks of 14 species were identified. Data provided include tick stage, degree of engorgement, seasonal abundance, geographical location, host, and age of the person from whom the tick was removed. Maps depict the distributions of the three major species submitted. I. scapularis emerged first along the coast, and then it advanced inland up major river valleys, Dermacentor variabilis Say slowly expanded centrifugally from where it was initially reported in southwestern Maine, and the distribution of long-established Ixodes cookei Packard remained unchanged. Submissions of nymphal I. scapularis closely correlated with reported Lyme diseases cases at the county level. Annual fluctuations of nymphal submissions in Maine correlated with those of Lyme disease cases for New England, supporting the possibility of a regional influence on tick abundance. More ticks were removed from people < or =14 and > or =30 yr of age, and their degree of engorgement was greatest in people < or =20 yr of age and progressively increased in people > or =30 yr of age. This study demonstrates the usefulness and potential of tick identification programs.     

Coinfection of Ixodes ricinus (Acari: Ixodidae) in northern Poland with the agents of Lyme borreliosis (LB) and human granulocytic ehrlichiosis (HGE)

Adult Ixodes ricinus ticks were collected from Pomerania province, northern Poland, to determine the presence of infection with agents of human granulocytic ehrlichiosis (HGE) and Lyme borreliosis by using the polymerase chain reaction (PCR). Of the 424 ticks 19.2% and 11.6% contained ehrlichiae and spirochetes, respectively. Frequency of single infection with the HGE agent was 63/424 while frequency of single infection with Borrelia burgdorferi sensu lato was 28/424. As many as 21/424 ticks (5%) contained both pathogens. This finding supports suggestions that both HGE agent and B. burgdorferi s. 1. perpetuate in the same foci and frequently co-infect the same tick vector thereby increasing the risk of humans acquiring mixed infection.     

长角血蜱、草原革蜱经期传播莱姆病螺旋体的实验研究

为了明确长角血蜱、草原革蜱在我国北方莱姆病传播中的地位和作用,以全沟硬蜱为对照,在实验室内对它们经期传播莱姆病螺旋体的可能性进行了研究.结果表明,全沟硬蜱可保持活的螺旋体到下一发育阶段,并且其体内的莱姆病螺旋体具备感染敏感KM鼠的能力.长角血蜱和草原革蜱虽然可以通过吸血获得莱姆病螺旋体,但它们对莱姆病螺旋体的保持期较短,不能跨越蜕皮阶段,因而不具备经期携带、传播的能力.所以它们作为莱姆病媒介的可能性不大.在长角血蜱或草原革蜱体内检测到的莱姆病螺旋体可能是它们与全沟硬蜱共同吸血的原因所致.     

Foci of tick-borne diseases in Southwest Germany

Presently known tick-borne diseases in Germany include Lyme borreliosis, tick-borne encephalitis (TBE-virus, western subtype), Q-fever, babesiosis and presumably ehrlichiosis. Blood samples of 4,368 forestry workers in the State of Baden-Wuerttemberg (B-W), southwestern Germany, were tested for the presence of antibodies against Borrelia burgdorferi sensu lato, TBE-virus and Ehrlichia spp. (genogroup E. phagocytophila). Furthermore 12,327 ticks (Ixodes ricinus) collected in various areas of B-W were analysed by PCR and genotyping for the prevalence of pathogen RNA and DNA. The human seroprevalence rates of antibodies to B. burgdorferi sensu lato ranged from 18 % to 52 %, for TBE-virus from 0 % to 43 % and for Ehrlichia spp. from 5 % to 16 % in various counties of the State. The foci of B. burgdorferi and TBE-virus as indicated by antibody prevalence in humans are only partly overlapping with each other. The highest rates of TBE-virus antibodies are in concordance with available clinical data. However antibody prevalence up to 27 % in areas with no reports of clinical cases was found, suggesting that TBE occurs throughout the State of B-W, The prevalence of Ehrlichia spp. antibodies suggests that ehrlichiosis plays a role as a tick-borne disease in Germany, but as long as no clinical data are available, this will remain unclear.Investigations of ticks for TBE-virus (n = 9,189) by nested PCR showed prevalence rates from 0% to 2.3% and for Ehrlichia spp. (n = 1,963) from 2.6% to 3.1%. Examination of ticks (n = 3,138) for the presence of B. burgdorferi sensu lato DNA was performed by PCR and revealed prevalence rates from 13.9% up to 24%. Furthermore 1,106 samples positive for B. burgdorferi sensu lato were used for genotyping. B. afzelii DNA was found in 407 ticks (36.8%), followed by B. garinii (21.9 %), B. valaisiana (13.7%), and B. burgdorferi sensu stricto (9.9 %). Double infection was found in 6.4% and triple infection in 0.8% of the ticks. 10.5% of the positive samples could not be classified.Prevention of tick-borne diseases has to focus on behavioural intervention to reduce individual tick exposure by proper behaviour in the environment, as a large-scale control of the tick population seems impossible and thus reduction of Lyme borreliosis and TBE through tick control is unlikely. Vaccination against TBE-virus should not only be recommended for high endemic areas but also for persons with a high individual risk.     

Detection of Borrelia burgdorferi, Ehrlichia chaffeensis, and Anaplasma phagocytophilum in ticks (Acari: Ixodidae) from a coastal region of California

A study was conducted in Santa Cruz County to estimate the prevalence and distribution of the agents of Lyme disease, human granulocytic (HGE), and human monocytic (HME) ehrlichiosis in 1,187 adult ixodid ticks collected from eight public-use recreation areas over a 2-yr period. Borrelia burgdorferi, the causative agent of Lyme disease, was detected by a polymerase chain reaction (PCR) in 44 of 776 (5.67%) Ixodes pacificus ticks and in 3 of 58 (5.17%) Dermacentor variabilis ticks. Anaplasma phagocytophilum, the causative agent of HGE, was detected by PCR in 48 (6.19%) I. pacificus ticks and 5 (8.62%) D. variabilis ticks. Ehrlichia chaffeensis, the causative agent of HME, was detected by nested PCR in just five (0.64%) I. pacificus ticks and four (6.9%) D. variabilis ticks. Interestingly, eight (1.03%) I. pacificus ticks were co-infected with B. burgdorferi and A. phagocytophilum, and just one (0.12%) tick was co-infected with B. burgdorferi and E. chaffeensis. Less than 1% of 353 Dermacentor occidentalis ticks showed evidence of infection with any of the agents tested. To our knowledge, this is the first reported identification of A. phagocytophilum and E. chaffeensis in D. occidentalis ticks from California This study represents the first extensive survey of Lyme and the ehrlichial diseases across multiple areas of Santa Cruz County, and suggests that prevalence of B. burgdorferi in Santa Cruz County may be higher than other areas of the state.     

Tick-borne encephalitis virus-specific RT-PCR--a rapid test for detection of the pathogen without viral RNA purification

Among diseases transmitted by ticks in the Czech Republic, tick-borne encephalitis (TBE) caused by Tick-borne encephalitis virus (TBEV) and Lyme disease caused by Borrelia burgdorferi spirochete are most important. We propose an effective and specific test for detection of TBEV in a single tick or a pool of ticks based on the detection of TBEV RNA using an RT-PCR technique without RNA purification. The method is very sensitive with the detection limit of about 14 fg TBEV RNA in total RNA obtained from brain suspension from suckling mice infected with TBEV per reaction. The primers were derived from the 5'-terminal non-coding region, a highly conserved part of the virus. The method was successfully applied to field-collected ticks in detecting TBEV RNA. This method can be used in studies of several aspects of TBEV: epidemiology, screening of natural foci, circulation and detection of virus genome sequences in clinical materials.