甘肃、湖南和广东三省蜱体内嗜吞噬细胞无形体与伯氏疏螺旋体共感染研究

目的 嗜吞噬细胞无形体和伯氏疏螺旋体是由媒介蜱传播的引起人粒细胞无形体病和莱姆病的病原。目前,对两种病原在蜱体内共感染流行情况的研究相对较少。方法 以甘肃、湖南和广东三个省采集到3个蜱种、共543份样品为研究对象,检测嗜吞噬细胞无形体和伯氏疏螺旋体在蜱体内的感染情况。结果 嗜吞噬细胞无形体和伯氏疏螺旋体在不同地区采集到的蜱体内的感染率不同,分别为3.2%~20.0%和2.3%~19.3%。在检测的样品中,共发现有7份样品中同时感染嗜吞噬细胞无形体和伯氏疏螺旋体。青海血蜱、血红扇头蜱和微小牛蜱中均检测到这两种病原。结论 青海血蜱、血红扇头蜱和微小牛蜱均能够携带嗜吞噬细胞无形体和伯氏疏螺旋体,可能为这两种病原在自然界的持续存在和循环提供了条件。此研究结果丰富了人粒细胞无形体病和莱姆病的流行病学信息,有利于提高这两种病的防控策略。     

Prevalence of Anaplasma phagocytophilum and coinfection with Borrelia burgdorferi sensu lato in the hard tick Ixodes ricinus in the city of Hanover (Germany)

The castor bean tick Ixodes ricinus has been found to be the main vector for Lyme borreliosis spirochetes and Anaplasma phagocytophilum in Central Europe. 1646 I. ricinus ticks from Hanover, a city located in Northern Germany, were examined for infection with A. phagocytophilum and coinfection with Borrelia burgdorferi sensu lato (sl) to obtain so far missing prevalence data for this region. The total A. phagocytophilum infection rate was 3.2% (52/1646 ticks), divided into 4.1% (32/777) adults and 2.3% (20/869) nymphs. Coinfections with B. burgdorferi sl were found in 0.9% of all tick stages. The detected genospecies were B. afzelii, B. garinii, B. burgdorferi sensu stricto (ss), and B. garinii, which was the most frequent species in coinfected ticks.     

Predicted outcomes of vaccinating wildlife to reduce human risk of Lyme disease

Vaccination efforts for Lyme disease prevention in humans have focused on wildlife reservoirs to target the causative agent, Borrelia burgdorferi, for elimination in vector ticks. Multiple host species are involved in the transmission and maintenance of the bacterium, but not all host species can be vaccinated effectively. To evaluate vaccinating a subset of hosts in the context of host-tick interactions, we constructed and evaluated a dynamic model of B. burgdorferi transmission in mice. Our analyses indicate that on average, a mouse-targeted vaccine is expected to proportionally reduce infection prevalence among ticks by 56%. However, relative to mouse vaccination, human risk of exposure is dominated by the number of tick bites received per person, the proportion of tick blood meals taken from the highly reservoir-competent white-footed mouse relative to other hosts, and the average number of tick bites per mouse. Variation in these factors reduces the predictability of vaccination outcomes. Additionally, contributions of nonmouse hosts to pathogen maintenance preclude elimination of B. burgdorferi through mouse vaccination alone. Our findings indicate that to increase the impact of wildlife vaccination, reducing tick populations by acaricide application, in addition to targeting additional reservoir-competent host species, should be employed.     

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.     

Ultrastructural evidence of the ehrlichial developmental cycle in naturally infected Ixodes persulcatus ticks in the course of coinfection with Rickettsia, Borrelia, and a flavivirus

Ehrlichiae are small gram-negative obligately intracellular bacteria that multiply within vacuoles of their host cells and are associated for a part of their life cycle with ticks, which serve as vectors for vertebrate hosts. Two morphologically and physiologically different ehrlichial cell types, reticulate cells (RC) and dense-cored cells (DC), are observed during experimental infection of cell cultures, mice, and ticks. Dense-cored cells and reticulate cells in vertebrate cell lines alternate in a developmental cycle. We observed ultrastructure of RC and DC of Ehrlichia muris in morulae in salivary gland cells and coinfection with Borrelia burgdorferi sensu lato (sl), "Candidatus Rickettsia tarasevichiae," and a flavivirus (presumably, tick-borne encephalitis virus [TBEV]) of Ixodes persulcatusticks collected in the Cis-Ural region of Russia. Polymerase chain reaction revealed 326 (81.5%) of 400 ticks carrying at least one infectious agent, and 41.5% (166 ticks) were coinfected with two to four agents. Ehrlichiae and rickettsiae were identified by sequencing of 359 bp of the 16S rRNA gene of E. muris and of 440 bp of the 16S rRNA gene and 385 bp of the gltA gene of "R. tarasevichiae." Different organs of the same tick harbored different microorganisms: TBEV in salivary gland and borreliae in midgut; E. muris in salivary gland; and "R. tarasevichiae" in midgut epithelium. Salivary gland cells contained both RC and DC, a finding that confirmed the developmental cycle in naturally infected ticks. Dense-cored cells in tick salivary glands were denser and of more irregular shape than DC in cell cultures. Ehrlichia-infected salivary gland cells had lysed cytoplasm, suggesting pathogenicity of E. muris for the tick host at the cellular level, as well as potential transmission during feeding. Rickettsiae in the midgut epithelial cells multiplied to significant numbers without altering the host cell ultrastructure. This is the first demonstration of E. muris, "R. tarasevichiae," and the ehrlichial developmental cycle in naturally infected I. persulcatus sticks.     

Potential vertebrate reservoir hosts and invertebrate vectors of Anaplasma marginale and A. phagocytophilum in central Spain

Organisms in the genus Anaplasma are obligate intracellular pathogens that multiply in both vertebrate and invertebrate hosts. The type species, A. marginale, causes bovine anaplasmosis and only infects ticks and ruminants. A. phagocytophilum causes human and animal granulocytic anaplasmosis, and genetically closely related strains show a wide host range, including ticks, ruminants, rodents, equids, canids, birds, and humans. Recent reports demonstrated that A. marginale and A. phagocytophilum co-exist in geographic areas and that concurrent infections occur in ruminants and ticks. In this study, we characterized A. marginale and A. phagocytophilum infections in wild and domestic animals, and ticks collected in central Spain by serology, PCR, and sequence of 16S rRNA genotypes. Species tested included humans, cattle, dogs, rodents, Iberian red deer, European wild boar, birds, and ticks. Species of hematophagous Diptera were analyzed as potential mechanical vectors of Anaplasma spp. A. marginale was detected in tabanids, ticks, cattle, and deer, while A. phagocytophilum was detected in ticks, deer, cattle, and birds. Concurrent infections of the two Anaplasma were found in cattle and deer. These results illustrate the complexity of the epizootiology of A. marginale and A. phagocytophilum in regions where both pathogens co-exist and share common reservoir hosts and vectors. The increasing contact between wildlife, domestic animals, and human populations increases the risk of outbreaks of human and bovine anaplasmosis, and the difficulty of implementing surveillance and control measures.     

The ecology of infectious disease: effects of host diversity and community composition on Lyme disease risk

The extent to which the biodiversity and community composition of ecosystems affect their functions is an issue that grows ever more compelling as human impacts on ecosystems increase. We present evidence that supports a novel function of vertebrate biodiversity, the buffering of human risk of exposure to Lyme-disease-bearing ticks. We tested the Dilution Effect model, which predicts that high species diversity in the community of tick hosts reduces vector infection prevalence by diluting the effects of the most competent disease reservoir, the ubiquitous white-footed mouse (Peromyscus leucopus). As habitats are degraded by fragmentation or other anthropogenic forces, some members of the host community disappear. Thus, species-poor communities tend to have mice, but few other hosts, whereas species-rich communities have mice, plus many other potential hosts. We demonstrate that the most common nonmouse hosts are relatively poor reservoirs for the Lyme spirochete and should reduce the prevalence of the disease by feeding, but rarely infecting, ticks. By accounting for nearly every host species' contribution to the number of larval ticks fed and infected, we show that as new host species are added to a depauperate community, the nymphal infection prevalence, a key risk factor, declines. We identify important "dilution hosts" (e.g., squirrels), characterized by high tick burdens, low reservoir competence, and high population density, as well as "rescue hosts" (e.g., shrews), which are capable of maintaining high disease risk when mouse density is low. Our study suggests that the preservation of vertebrate biodiversity and community composition can reduce the incidence of Lyme disease.     

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.     

Elimination of Borrelia burgdorferi and Anaplasma phagocytophilum in rodent reservoirs and Ixodes scapularis ticks using a doxycycline hyclate-laden bait

A field trial was conducted in a Lyme disease-endemic area of New Jersey to determine the efficacy of a doxycyline hyclate rodent bait to prophylactically protect and cure small-mammal reservoirs and reduce infection rates in questing Ixodes scapularis ticks for Borrelia burgdorferi and Anaplasma phagocytophilum. The doxycycline-laden bait was formulated at a concentration of 500 mg/kg and delivered during the immature tick feeding season in rodent-targeted bait boxes. The percentage of infected small mammals recovered from treated areas after 2 years of treatment was reduced by 86.9% for B. burgdorferi and 74% for A. phagocytophilum. Infection rates in questing nymphal ticks for both B. burgdorferi and A. phagocytophilum were reduced by 94.3% and 92%, respectively. Results from this study indicate that doxycycline-impregnated bait is an effective means of reducing infection rates for B. burgdorferi and A. phagocytophilum in both rodent reservoirs and questing I. scapularis ticks.     

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.     

An ecological approach to preventing human infection: vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle

Many pathogens, such as the agents of West Nile encephalitis and plague, are maintained in nature by animal reservoirs and transmitted to humans by arthropod vectors. Efforts to reduce disease incidence usually rely on vector control or immunization of humans. Lyme disease, for which no human vaccine is currently available, is a commonly reported vector-borne disease in North America and Europe. In a recently developed, ecological approach to disease prevention, we intervened in the natural cycle of the Lyme disease agent (Borrelia burgdorferi) by immunizing wild white-footed mice (Peromyscus leucopus), a reservoir host species, with either a recombinant antigen of the pathogen, outer surface protein A, or a negative control antigen in a repeated field experiment with paired experimental and control grids stratified by site. Outer surface protein A vaccination significantly reduced the prevalence of B. burgdorferi in nymphal blacklegged ticks (Ixodes scapularis) collected at the sites the following year in both experiments. The magnitude of the vaccine's effect at a given site correlated with the tick infection prevalence found on the control grid, which in turn correlated with mouse density. These data, as well as differences in the population structures of B. burgdorferi in sympatric ticks and mice, indicated that nonmouse hosts contributed more to infecting ticks than previously expected. Thus, where nonmouse hosts play a large role in infection dynamics, vaccination should be directed at additional species.     

Epidemiology and impact of coinfections acquired from Ixodes ticks

Ixodes scapularis and other ticks in the Ixodes ricinus complex may transmit multiple pathogens, but research on coinfections has been limited. Coinfections occur with varying frequency in ticks, but single infections are more common than dual infections. The proportion of I. scapularis or I. ricinus ticks coinfected with both Borrelia burgdorferi sensu lato and Anaplasma phagocytophila is generally low, ranging from < 1% to 6% in six geographic areas. A higher prevalence of tick coinfection (26%) has been reported in Westchester County, New York. Genetic variants of the human disease-causing strain of A. phagocytophila are present in some tick populations, and they may affect the risk of coinfection or clinical illness. The proportion of Ixodes ticks coinfected with B. burgdorferi and Babesia microti has ranged from 2% in New Jersey to 19% on Nantucket Island, Massachusetts. In humans, cross-sectional seroprevalence studies have found markers of dual infection in 9-26% of patients with a tick-borne infection, but such studies often fail to distinguish simultaneous coinfection from sequential infections. Several studies have prospectively assessed the occurrence of acute coinfection. Among patients with a confirmed tick-borne infection, coinfection rates as high as 39% have been reported. The most commonly recognized coinfection in most of the eastern United States is Lyme borreliosis (LB) and babesiosis, accounting for approximately 80% of coinfections. LB and human granulocytic ehrlichiosis coinfections are less common, occurring in 3-15% of patients with a tick-borne infection in Connecticut or Wisconsin. Studies of clinical outcomes suggest that patients with acute Babesia coinfection have more severe symptoms and a longer duration of illness than patients with LB alone, but the risk of spirochete dissemination is similar. Coinfections can modify the immune response and alter the severity of arthritis in animal models. Future coinfection research should focus on long-term clinical outcomes, the role of genetic variants, immunologic effects, and the potential role of Bartonella species as tick-borne pathogens.     

Field studies on Lyme disease in North America

The primary tick vector of Borrelia burgdorferi in eastern and central North America is Ixodes dammini; in western North America, Ixodes pacificus. Searching for the appropriate vector is the first step in determining whether a region is endemic and enzootic for the spirochete B burgdorferi, the etiological agent of Lyme disease, followed by examination of the ticks (questing or already attached to hosts) and wildlife for the spirochete. Questing ticks can be collected through a variety of methods. The two major animal hosts for I dammini are the white-footed mouse Peromyscus leucopus and the white-tailed deer Odocoileus virginianus. Sampling strategies should consider habitat and season. All three life stages of the vector tick should be located, indicating a self-sustaining population. Although B burgdorferi can be detected in many ways, there is no substitute for isolating the spirochete in Barbour-Stoenner-Kelly II medium for definitive proof of the presence of the Lyme disease spirochete.     

Ticks infesting wild and domestic animals and humans of Sri Lanka with new host records

An island-wide collection of tick species infesting humans, domesticated and wild animals and questing ticks in domestic and peridomestic environments was carried out during 2009–2011. A total of 30,461 ticks were collected from 30 different hosts and free living stages from the ground. The collection consisted of 22 tick species from 30 different hosts recording 12 tick species from humans, 19 from domesticated animals and 21 from wild animals, with a total of 97 new host records. The most common tick species on humans were Dermacentor auratus and Amblyomma testudinairum, while Haemaphysalis intermedia, Rhipicephalus microplus and Rhipicephalus sanguineus were common in domesticated and wild animals sharing 20 host species. Among the questing ticks, immature D. auratus was the most abundant. Humans and domesticated animals were mostly infested by the nymphal stages while adult ticks were found on wild animals. High number of new host records could be due to domestic animals picking tick species from wildlife and vise versa at the human/animal interface. Habitat destruction due to forest fragmentation has lead to wild animals roaming in urban and semi-urban neighbourhoods increasing the interactions of wild animals with domesticated animals. Wild animals play a significant role as a reservoir of many tick borne infections which can easily be spread to domesticated animals and then to humans via tick infestations. Data in this paper are useful for those interested in tick infesting wild and domestic animals and humans in describing the zoonotic potential of tick borne infections.     

Investigations on the mode and dynamics of transmission and infectivity of Borrelia burgdorferi sensu stricto and Borrelia afzelii in Ixodes ricinus ticks

Borrelia burgdorferi sensu lato (sl), the agent of Lyme disease, is transmitted to the host during the blood meal of Ixodes ticks. In most unfed ticks, spirochetes are present in the midgut and migrate during blood feeding to the salivary glands, from which they are transmitted to the host via saliva. In the present study, the efficiency of Ixodes ricinus ticks to transmit B. afzelii and B. burgdorferi sensu stricto (ss) and their infectivity for mice were examined in relation to the duration of the blood meal. In addition, we investigated whether these two Borrelia species can penetrate intact skin. Three modes of infection of mice were studied: tick-bite infection, inoculation of tick homogenates, and transcutaneous infection by topical application of tick homogenates on mouse skin. Transmission of B. burgdorferi sl from I. ricinus nymphs to mouse increased with duration of tick attachment. B. afzelii-infected ticks start to transmit infection earlier (< or = 48 h) than B. burgdorferi ss-infected ticks. As previously shown for B. burgdorferi ss in Ixodes scapularis, B. burgdorferi ss and B. afzelii in unfed I. ricinus were noninfectious for mice when tick homogenates were inoculated. However, the inoculation of homogenates of ticks fed for 24 h readily produced infection in mice. Therefore, B. burgdorferi ss and B. afzelii spirochetes are potentially infectious in the tick before natural transmission can occur. None of the mice (n = 33) became infected by transcutaneous transmission when tick homogenates were applied on mouse skin, showing that B. burgdorferi ss and B. afzelii are unable to penetrate intact skin, in contrast to relapsing fever spirochetes. This study also shows that B. afzelii is transmitted by I. ricinus to the host earlier than B. burgdorferi ss and that I. ricinus seems to be a more efficient vector of B. afzelii than B. burgdorferi ss.     

Clethrionomys glareolus, but not Apodemus flavicollis, acquires resistance to lxodes ricinus L, the main European vector of Borrelia burgdorferi

The European rodents Clethrionomys glareolus (bank vole) and Apodemus flavicollis (yellow-necked-mouse) are important hosts of the tick species Ixodes ricinus, the main European vector of Borrelia burgdorferi. We have addressed the question whether or not these tick hosts develop resistance to I. ricinus larvae. C. glareolus and A. flavicollis were exposed to 40 I. ricinus larvae for five consecutive times at two week intervals. Resistance was tested by the following parameters: percentage of ticks fully engorged, time of attachment, engorgement index, percentage of recovered ticks and proportion of larvae moulting to nymphs. Repeated infestation ofC. glareolus resulted in progressive and significant reductions in the percentage of fully engorged ticks, the time of attachment of partially engorged ticks, the scutal index of partially engorged ticks and the moulting success. In contrast, repeatedly infested A. flavicollis did not acquire resistance to larval I. ricinus. Effects of resistance in C glareolus could be partially disrupted by treatment with the immunosuppressive agent, cyclosporin A (CsA), indicating that T helper cells participate in the immune responses to tick bites. The data suggest that acquired immunity to I. ricinus larvae in C. glareolus is a density-dependent factor regulating natural tick burdens and that it may have an impact on the transmission cycle of B. burgdorferi in Central Europe.     

Capacity of European animals as reservoir hosts for the Lyme disease spirochete.

The abundance of spirochete-infected Ixodes ricinus ticks naturally derived from endemic rodents was compared to identify the reservoir hosts of the agent of Lyme disease at a series of enzootic sites in Central Europe. Black-striped mice appear to be the most important rodent host for the tick and infect more ticks with Borrelia burgdorferi than do other mice and voles tested. Although rodents infect about half of the ticks that feed on them, lizards infect none. These spirochete-incompetent hosts dilute the force of transmission because many nymphal ticks feed on them. Older male hosts are more heavily infested by subadult ticks than are younger or female hosts. The intensity of transmission of the agent of Lyme disease at particular Central European sites appears to correlate directly with the presence of black-striped mice and inversely with that of lizards.     

Borrelia burgdorferi intercepts host hormonal signals to regulate expression of outer surface protein A

The Borrelia burgdorferi infectious cycle requires that the organism adapt to vast differences in environmental conditions found in its tick and mammalian hosts. Previous studies have shown that B. burgdorferi accomplishes this accommodation in part by regulating expression of its surface proteins. Outer surface protein A (OspA) is a borrelial protein important in colonization of the tick midgut. OspA is up-regulated when the organism is in its tick host and down-regulated when it is in a mammalian host. However, little is known about how it is up-regulated again in a mammalian host in preparation for entry into a feeding tick. Here, we report that the host neuroendocrine stress hormones, epinephrine and norepinephrine, are specifically bound by B. burgdorferi and result in increased expression of OspA. This recognition is specific and blocked by competitive inhibitors of human adrenergic receptors. To determine whether recognition of catecholamines, which are likely to be present at the site of a tick bite, may play a role in preparing the organism for reentry into a tick from a mammalian host, we administered a beta-adrenergic blocker, propranolol, to infected mice. Propranolol significantly reduced uptake of B. burgdorferi by feeding ticks and decreased expression of OspA in B. burgdorferi recovered from ticks that fed on propranolol-treated mice. Our studies suggest that B. burgdorferi may co-opt host neuroendocrine signals to inform the organism of local changes that predict the presence of its next host and allow it to prepare for transition to a new environment.     

Co-detection of Bartonella henselae, Borrelia burgdorferi, and Anaplasma phagocytophilum in Ixodes pacificus ticks from California, USA

Presence of Bartonella DNA was explored in 168 questing adult Ixodes pacificus ticks from Santa Cruz County, California. Bartonella henselae type I DNA was amplified from 11 ticks (6.55%); previously, two (1.19%) were found to be infected with Borrelia burgdorferi and five (2.98%) with Anaplasma phagocytophilum. Detection of B. henselae was not dependent on co-infection. The present study offers additional evidence that Ixodes spp. ticks may act as hosts and possibly vectors for B. henselae.