Anaplasma phagocytophilum--a widespread multi-host pathogen with highly adaptive strategies

The bacterium Anaplasma phagocytophilum has for decades been known to cause the disease tick-borne fever (TBF) in domestic ruminants in Ixodes ricinus-infested areas in northern Europe. In recent years, the bacterium has been found associated with Ixodes-tick species more or less worldwide on the northern hemisphere. A. phagocytophilum has a broad host range and may cause severe disease in several mammalian species, including humans. However, the clinical symptoms vary from subclinical to fatal conditions, and considerable underreporting of clinical incidents is suspected in both human and veterinary medicine. Several variants of A. phagocytophilum have been genetically characterized. Identification and stratification into phylogenetic subfamilies has been based on cell culturing, experimental infections, PCR, and sequencing techniques. However, few genome sequences have been completed so far, thus observations on biological, ecological, and pathological differences between genotypes of the bacterium, have yet to be elucidated by molecular and experimental infection studies. The natural transmission cycles of various A. phagocytophilum variants, the involvement of their respective hosts and vectors involved, in particular the zoonotic potential, have to be unraveled. A. phagocytophilum is able to persist between seasons of tick activity in several mammalian species and movement of hosts and infected ticks on migrating animals or birds may spread the bacterium. In the present review, we focus on the ecology and epidemiology of A. phagocytophilum, especially the role of wildlife in contribution to the spread and sustainability of the infection in domestic livestock and humans.

Emerging Tick-Borne Diseases

Increases in tick-borne disease prevalence and transmission are important public health issues. Efforts to control these emerging diseases are frustrated by the struggle to control tick populations and to detect and treat infections caused by the pathogens that they transmit. This review covers tick-borne infectious diseases of nonrickettsial bacterial, parasitic, and viral origins. While tick surveillance and tracking inform our understanding of the importance of the spread and ecology of ticks and help identify areas of risk for disease transmission, the vectors are not the focus of this document. Here, we emphasize the most significant pathogens that infect humans as well as the epidemiology, clinical features, diagnosis, and treatment of diseases that they cause. Although detection via molecular or immunological methods has improved, tick-borne diseases continue to remain underdiagnosed, making the scope of the problem difficult to assess. Our current understanding of the incidence of tick-borne diseases is discussed in this review. An awareness of the diseases that can be transmitted by ticks in specific locations is key to detection and selection of appropriate treatment. As tick-transmitted pathogens are discovered and emerge in new geographic regions, our ability to detect, describe, and understand the growing public health threat must also grow to meet the challenge.

N Increased risk of tick-borne diseases with climate and environmental changes

Climate warming and other environmental changes have contributed to the expansion of the range of several tick species into higher latitudes in North America. As temperatures increase in Canada, the environment becomes more suitable for ticks and the season suitable for tick activity lengthens, so tick-borne diseases are likely to become more common in Canada. In addition to Lyme disease, four other tick-borne diseases (TBDs) have started to emerge and are likely to increase: Anaplasmosis; Babesiosis; Powassan virus; and Borrelia miyamotoi disease. Increased temperature increases the survival and activity period of ticks, increases the range of both reservoir and tick hosts (e.g. mice and deer) and increases the duration of the season when people may be exposed to ticks. Other ticks and TBDs may spread into Canada as the climate changes. The public health strategies to mitigate the impact of all TBDs include surveillance to detect current and emerging TBDs, and public health actions to prevent infections by modifying environmental and social-behavioral risk factors through increasing public awareness. Clinical care strategies include patient education, early detection, laboratory testing, and treatment.

Opening the black box of Anaplasma phagocytophilum diversity: current situation and future perspectives

Anaplasma phagocytophilum is a zoonotic obligate intracellular bacterium known to be transmitted by ticks belonging to the Ixodes persulcatus complex. This bacterium can infect several mammalian species, and is known to cause diseases with variable symptoms in many domestic animals. Specifically, it is the causative agent of tick-borne fever (TBF), a disease of important economic impact in European domestic ruminants, and human granulocytic anaplasmosis (HGA), an emerging zoonotic disease in Asia, USA and Europe. A. phagocytophilum epidemiological cycles are complex and involve different ecotypes, vectors, and mammalian host species. Moreover, the epidemiology of A. phagocytophilum infection differs greatly between Europe and the USA. These different epidemiological contexts are associated with considerable variations in bacterial strains. Until recently, few A. phagocytophilum molecular typing tools were available, generating difficulties in completely elucidating the epidemiological cycles of this bacterium. Over the last few years, many A. phagocytophilum typing techniques have been developed, permitting in-depth epidemiological exploration. Here, we review the current knowledge and future perspectives regarding A. phagocytophilum epidemiology and phylogeny, and then focus on the molecular typing tools available for studying A. phagocytophilum genetic diversity.

Are Apodemus spp. mice and Myodes glareolus reservoirs for Borrelia miyamotoi, Candidatus Neoehrlichia mikurensis, Rickettsia helvetica, R. monacensis and Anaplasma phagocytophilum?

In Europe, in addition to Borrelia burgdorferi sensu lato and tick-borne encephalitis (TBE) virus, other zoonotic pathogens, like B. miyamotoi, a species related to the relapsing fever spirochaetes, Candidatus Neoehrlichia mikurensis (N. mikurensis), Rickettsia helvetica, Rickettsia monacensis, and Anaplasma phagocytophilum have been reported in the ixodid tick Ixodes ricinus. No study was conducted to identify reservoir hosts for these pathogens. Here, we investigated the role played by wild rodents in the natural transmission cycle of B. miyamotoi, N. mikurensis, R. helvetica, R. monacensis, and A. phagocytophilum in Switzerland. In 2011 and 2012, small mammals were captured in an area where these pathogens occur in questing ticks. Ixodes ricinus ticks infesting captured small mammals were analysed after their moult by PCR followed by reverse line blot to detect the different pathogens. Xenodiagnostic larvae were used to evaluate the role of rodents as reservoirs and analysed after their moult. Most of the 108 captured rodents (95.4%) were infested by I. ricinus ticks; 4.9%, 3.9%, 24.0%, and 0% of the rodents were infested by Borrelia, N. mikurensis, Rickettsia spp., and A. phagocytophilum-infected larvae, respectively. Borrelia afzelii, B. miyamotoi, N. mikurensis, Rickettsia spp., and A. phagocytophilum were detected in 2.8%, 0.17%, 2.6%, 6.8%, and 0% of the ticks attached to rodents, respectively. Borrelia afzelii was transmitted by 4 rodents to 41.2% of the xenodiagnostic ticks, B. miyamotoi by 3 rodents to 23.8%, and N. mikurensis was transmitted by 6 rodents to 41.0% of the xenodiagnostic ticks. None of the tested rodent transmitted Rickettsia spp. or A. phagocytophilum to I. ricinus xenodiagnostic larvae. This study showed that rodents are reservoir hosts for B. miyamotoi and N. mikurensis in Europe.

Spatiotemporal dynamics of emerging pathogens in questing Ixodes ricinus

Ixodes ricinus transmits Borrelia burgdorferi sensu lato, the etiological agent of Lyme disease. Previous studies have also detected Rickettsia helvetica, Anaplasma phagocytophilum, Neoehrlichia mikurensis, and several Babesia species in questing ticks in The Netherlands. In this study, we assessed the acarological risk of exposure to several tick-borne pathogens (TBPs), in The Netherlands. Questing ticks were collected monthly between 2006 and 2010 at 21 sites and between 2000 and 2009 at one other site. Nymphs and adults were analysed individually for the presence of TBPs using an array-approach. Collated data of this and previous studies were used to generate, for each pathogen, a presence/absence map and to further analyse their spatiotemporal variation. R. helvetica (31.1%) and B. burgdorferi sensu lato (11.8%) had the highest overall prevalence and were detected in all areas. N. mikurensis (5.6%), A. phagocytophilum (0.8%), and Babesia spp. (1.7%) were detected in most, but not all areas. The prevalences of pathogens varied among the study areas from 0 to 64%, while the density of questing ticks varied from 1 to 179/100 m². Overall, 37% of the ticks were infected with at least one pathogen and 6.3% with more than one pathogen. One-third of the Borrelia-positive ticks were infected with at least one other pathogen. Coinfection of B. afzelii with N. mikurensis and with Babesia spp. occurred significantly more often than single infections, indicating the existence of mutual reservoir hosts. Alternatively, coinfection of R. helvetica with either B. afzelii or N. mikurensis occurred significantly less frequent. The diversity of TBPs detected in I. ricinus in this study and the frequency of their coinfections with B. burgdorferi s.l., underline the need to consider them when evaluating the risks of infection and subsequently the risk of disease following a tick bite.

Anaplasma marginale and Anaplasma phagocytophilum: Rickettsiales pathogens of veterinary and public health significance

Anaplasma marginale and Anaplasma phagocytophilum are the most important tick-borne bacteria of veterinary and public health significance in the family Anaplasmataceae. The objective of current review is to provide knowledge on ecology and epidemiology of A. phagocytophilum and compare major similarities and differences of A. marginale and A. phagocytophilum. Bovine anaplasmosis is globally distributed tick-borne disease of livestock with great economic importance in cattle industry. A. phagocytophilum, a cosmopolitan zoonotic tick transmitted pathogen of wide mammalian hosts. The infection in domestic animals is generally referred as tick-borne fever. Concurrent infections exist in ticks, domestic and wild animals in same geographic area. All age groups are susceptible, but the prevalence increases with age. Movement of susceptible domestic animals from tick free non-endemic regions to disease endemic regions is the major risk factor of bovine anaplasmosis and tick-borne fever. Recreational activities or any other high-risk tick exposure habits as well as blood transfusion are important risk factors of human granulocytic anaplasmosis. After infection, individuals remain life-long carriers. Clinical anaplasmosis is usually diagnosed upon examination of stained blood smears. Generally, detection of serum antibodies followed by molecular diagnosis is usually recommended. There are problems of sensitivity and cross-reactivity with both the Anaplasma species during serological tests. Tetracyclines are the drugs of choice for treatment and elimination of anaplasmosis in animals and humans. Universal vaccine is not available for either A. marginale or A. phagocytophilum, effective against geographically diverse strains. Major control measures for bovine anaplasmosis and tick-borne fever include rearing of tick-resistant breeds, endemic stability, breeding Anaplasma-free herds, identification of regional vectors, domestic/wild reservoirs and control, habitat modification, biological control, chemotherapy, and vaccinations (anaplasmosis and/or tick vaccination). Minimizing the tick exposure activities, identification and control of reservoirs are important control measures for human granulocytic anaplasmosis.

A review on the eco-epidemiology and clinical management of human granulocytic anaplasmosis and its agent in Europe

Anaplasma phagocytophilum is the agent of tick-borne fever, equine, canine and human granulocytic anaplasmosis. The common route of A. phagocytophilum transmission is through a tick bite, the main vector in Europe being Ixodes ricinus. Despite the apparently ubiquitous presence of the pathogen A. phagocytophilum in ticks and various wild and domestic animals from Europe, up to date published clinical cases of human granulocytic anaplasmosis (HGA) remain rare compared to the worldwide status. It is unclear if this reflects the epidemiological dynamics of the human infection in Europe or if the disease is underdiagnosed or underreported. Epidemiologic studies in Europe have suggested an increased occupational risk of infection for forestry workers, hunters, veterinarians, and farmers with a tick-bite history and living in endemic areas. Although the overall genetic diversity of A. phagocytophilum in Europe is higher than in the USA, the strains responsible for the human infections are related on both continents. However, the study of the genetic variability and assessment of the difference of pathogenicity and infectivity between strains to various hosts has been insufficiently explored to date. Most of the European HGA cases presented as a mild infection, common clinical signs being pyrexia, headache, myalgia and arthralgia. The diagnosis of HGA in the USA was recommended to be based on clinical signs and the patient’s history and later confirmed using specialized laboratory tests. However, in Europe since the majority of cases are presenting as mild infection, laboratory tests may be performed before the treatment in order to avoid antibiotic overuse. The drug of choice for HGA is doxycycline and because of potential for serious complication the treatment should be instituted on clinical suspicion alone.

Anaplasma phagocytophilum evolves in geographical and biotic niches of vertebrates and ticks

Background

Anaplasma phagocytophilum is currently regarded as a single species. However, molecular studies indicate that it can be subdivided into ecotypes, each with distinct but overlapping transmission cycle. Here, we evaluate the interactions between and within clusters of haplotypes of the bacterium isolated from vertebrates and ticks, using phylogenetic and network-based methods.

Methods

The presence of A. phagocytophilum DNA was determined in ticks and vertebrate tissue samples. A fragment of the groEl gene was amplified and sequenced from qPCR-positive lysates. Additional groEl sequences from ticks and vertebrate reservoirs were obtained from GenBank and through literature searches, resulting in a dataset consisting of 1623 A. phagocytophilum field isolates. Phylogenetic analyses were used to infer clusters of haplotypes and to assess phylogenetic clustering of A. phagocytophilum in vertebrates or ticks. Network-based methods were used to resolve host-vector interactions and their relative importance in the segregating communities of haplotypes.

Results

Phylogenetic analyses resulted in 199 haplotypes within eight network-derived clusters, which were allocated to four ecotypes. The interactions of haplotypes between ticks, vertebrates and geographical origin, were visualized and quantified from networks. A high number of haplotypes were recorded in the tick Ixodes ricinus. Communities of A. phagocytophilum recorded from Korea, Japan, Far Eastern Russia, as well as those associated with rodents had no links with the larger set of isolates associated with I. ricinus, suggesting different evolutionary pressures. Rodents appeared to have a range of haplotypes associated with either Ixodes trianguliceps or Ixodes persulcatus and Ixodes pavlovskyi. Haplotypes found in rodents in Russia had low similarities with those recorded in rodents in other regions and shaped separate communities.

Conclusions

The groEl gene fragment of A. phagocytophilum provides information about spatial segregation and associations of haplotypes to particular vector-host interactions. Further research is needed to understand the circulation of this bacterium in the gap between Europe and Asia before the overview of the speciation features of this bacterium is complete. Environmental traits may also play a role in the evolution of A. phagocytophilum in ecotypes through yet unknown relationships.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3583-8) contains supplementary material, which is available to authorized users.

Development of a new PCR-based assay to detect Anaplasmataceae and the first report of Anaplasma phagocytophilum and Anaplasma platys in cattle from Algeria

Bovine anaplasmosis is a hemoparasitic disease considered as a major constraint to cattle production in many countries. This pathology is at least partially caused by Anaplasma phagocytophilum, Anaplasma marginale, Anaplasma centrale, and Anaplasma bovis. The global threat and emergence of these species in animals require the reliable identification of these bacteria in animal samples. In this study, we developed a new qPCR tool targeting the 23S rRNA gene for the detection of Anaplasmataceae bacteria. The primers and probe for the qPCR reaction had 100% specificity and could identify at least A. phagocytophilum, A. marginale, A. centrale, Anaplasma ovis, Anaplasma platys, Ehrlichia canis, Ehrlichia ruminantium, Neorickettisa sennetsu, and Neorickettsia risticii. We used this tool to test samples of bovines from Batna (Algeria), an area from which bovine anaplasmosis have never been reported. We identified three genetic variants of A. phagocytophilum, A. platys and Anaplasma sp. "variant 4". This finding should attract the attention of public authorities to assess the involvement of these pathogens in human and animal health.

Melting pot of tick-borne zoonoses: the European hedgehog contributes to the maintenance of various tick-borne diseases in natural cycles urban and suburban areas

Background

European hedgehogs (Erinaceus europaeus) are urban dwellers and host both Ixodes ricinus and Ixodes hexagonus. These ticks transmit several zoonotic pathogens like Borrelia burgdorferi (sensu lato), Anaplasma phagocytophilum, Rickettsia helvetica, Borrelia miyamotoi and “Candidatus Neoehrlichia mikurensis”. It is unclear to what extent hedgehogs in (sub) urban areas contribute to the presence of infected ticks in these areas, which subsequently pose a risk for acquiring a tick-borne disease. Therefore, it is important to investigate to what extent hedgehogs contribute to the enzootic cycle of these tick-borne pathogens, and to shed more light at the mechanisms of the transmission cycles involving hedgehogs and both ixodid tick species.

Methods

Engorged ticks from hedgehogs were collected from (sub) urban areas via rehabilitating centres in Belgium. Ticks were screened individually for presence of Borrelia burgdorferi (sensu lato), Borrelia miyamotoi, Anaplasma phagocytophilum, Rickettsia helvetica and “Candidatus Neoehrlichia mikurensis” using PCR-based methods. Infection rates of the different pathogens in ticks were calculated and compared to infection rates in questing ticks.

Results

Both Ixodes hexagonus (n = 1132) and Ixodes ricinus (n = 73) of all life stages were found on the 54 investigated hedgehogs. Only a few hedgehogs carried most of the ticks, with 6 of the 54 hedgehogs carrying more than half of all ticks (624/1205). Borrelia miyamotoi, A. phagocytophilum, R. helvetica and B. burgdorferi genospecies (Borrelia afzelii, Borrelia bavariensis and Borrelia spielmanii) were detected in both I. hexagonus and I. ricinus. Anaplasma phagocytophilum, R. helvetica, B. afzelii, B. bavariensis and B. spielmanii were found significantly more in engorged ticks in comparison to questing I. ricinus.

Conclusions

European hedgehogs seem to contribute to the spread and transmission of tick-borne pathogens in urban areas. The relatively high prevalence of B. bavariensis, B. spielmanii, B. afzelii, A. phagocytophilum and R. helvetica in engorged ticks suggests that hedgehogs contribute to their enzootic cycles in (sub) urban areas. The extent to which hedgehogs can independently maintain these agents in natural cycles, and the role of other hosts (rodents and birds) remain to be investigated.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2065-0) contains supplementary material, which is available to authorized users.

Passive Surveillance of Ixodes scapularis (Say), Their Biting Activity, and Associated Pathogens in Massachusetts

A passive surveillance of tick-borne pathogens was conducted over a 7-year period (2006-2012), in which a total of 3551 ticks were submitted to the University of Massachusetts for PCR testing. The vast majority of these ticks were Ixodes scapularis from Massachusetts (N = 2088) and hence were the focus of further analysis. Two TaqMan duplex qPCR assays were developed to test I. scapularis ticks for the presence of three human pathogens: Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti. I. scapularis submissions were concentrated from Cape Cod, the eastern half of the state outside of the Boston metropolitan area, parts of Franklin and Hampshire counties along the Quabbin Reservoir watershed, and southwestern Berkshire county. Differences in seasonal activity pattern were observed for different developmental stages of I. scapularis. The largest proportion of tick bite victims were age 9 years and under. Nymphal ticks were found more often on lower extremities of their hosts, while more adult ticks were found on the head. Overall infection rate of B. burgdorferi, A. phagocytophilum, and B. microti in human-biting ticks was 29.6%, 4.6%, and 1.8%, respectively. B. burgdorferi-infected ticks were widely distributed, but A. phagocytophilum- and B. microti-infected I. scapularis were found mainly in the eastern half of the state. We found that 1.8%, 1.0%, and 0.4% of ticks were coinfected by B. burgdorferi and A. phagocytophilum, B. burgdorferi and B. microti, and A. phagocytophilum and B. microti, respectively, and 0.3% of ticks had triple coinfection.

Global proteomic analysis of two tick-borne emerging zoonotic agents: anaplasma phagocytophilum and ehrlichia chaffeensis

Anaplasma phagocytophilum and Ehrlichia chaffeensis are obligatory intracellular α-proteobacteria that infect human leukocytes and cause potentially fatal emerging zoonoses. In the present study, we determined global protein expression profiles of these bacteria cultured in the human promyelocytic leukemia cell line, HL-60. Mass spectrometric (MS) analyses identified a total of 1,212 A. phagocytophilum and 1,021 E. chaffeensis proteins, representing 89.3 and 92.3% of the predicted bacterial proteomes, respectively. Nearly all bacterial proteins (≥99%) with known functions were expressed, whereas only approximately 80% of “hypothetical” proteins were detected in infected human cells. Quantitative MS/MS analyses indicated that highly expressed proteins in both bacteria included chaperones, enzymes involved in biosynthesis and metabolism, and outer membrane proteins, such as A. phagocytophilum P44 and E. chaffeensis P28/OMP-1. Among 113 A. phagocytophilum p44 paralogous genes, 110 of them were expressed and 88 of them were encoded by pseudogenes. In addition, bacterial infection of HL-60 cells up-regulated the expression of human proteins involved mostly in cytoskeleton components, vesicular trafficking, cell signaling, and energy metabolism, but down-regulated some pattern recognition receptors involved in innate immunity. Our proteomics data represent a comprehensive analysis of A. phagocytophilum and E. chaffeensis proteomes, and provide a quantitative view of human host protein expression profiles regulated by bacterial infection. The availability of these proteomic data will provide new insights into biology and pathogenesis of these obligatory intracellular pathogens.

Molecular Detection of Zoonotic Rickettsiae and Anaplasma spp. in Domestic Dogs and Their Ectoparasites in Bushbuckridge, South Africa

Members of the order Rickettsiales are small, obligate intracellular bacteria that are vector-borne and can cause mild to fatal diseases in humans worldwide. There is little information on the zoonotic rickettsial pathogens that may be harbored by dogs from rural localities in South Africa. To characterize rickettsial pathogens infecting dogs, we screened 141 blood samples, 103 ticks, and 43 fleas collected from domestic dogs in Bushbuckridge Municipality, Mpumalanga Province of South Africa, between October 2011 and May 2012 using the reverse line blot (RLB) and Rickettsia genus and species-specific quantitative real-time PCR (qPCR) assays. Results from RLB showed that 49% of blood samples and 30% of tick pools were positive for the genus-specific probes for Ehrlichia/Anaplasma; 16% of the blood samples were positive for Ehrlichia canis. Hemoparasite DNA could not be detected in 36% of blood samples and 30% of tick pools screened. Seven (70%) tick pools and both flea pools were positive for Rickettsia spp; three (30%) tick pools were positive for Rickettsia africae; and both flea pools (100%) were positive for Rickettsia felis. Sequencing confirmed infection with R. africae and Candidatus Rickettsia asemboensis; an R. felis-like organism from one of the R. felis-positive flea pools. Anaplasma sp. South Africa dog strain (closely related to Anaplasma phagocytophilum), A. phagocytophilum, and an Orientia tsutsugamushi-like sequence were identified from blood samples. The detection of emerging zoonotic agents from domestic dogs and their ectoparasites in a rural community in South Africa highlights the potential risk of human infection that may occur with these pathogens.

Ticks and associated pathogens in camels (Camelus dromedarius) from Riyadh Province, Saudi Arabia

BACKGROUND

Camel production in Saudi Arabia is severely affected by various diseases and by inadequate veterinary services. Ticks and tick-borne pathogens (TBPs) affect the health and wellbeing of camels consequently diminishing their productivity and performances. In addition, camels may act as hosts for TBPs (e.g. Anaplasma phagocytophilum) causing diseases in humans. The current study aimed to determine the prevalence of ixodid ticks and molecularly investigate the associated pathogens in camels from Saudi Arabia.

METHODS

Blood and tick samples were collected from camels (n = 170) in Riyad Province of Saudi Arabia. Ticks were morphologically identified, and blood of camels were molecularly screened for apicomplexan (i.e. Babesia spp., Theileria spp., Hepatozoon spp.) and rickettsial parasites (i.e. Ehrlichia spp. and Anaplasma spp.).

RESULTS

Of the 170 camels examined, 116 (68.2%; 95% CI: 60.9-75.1%) were infested by ticks with a mean intensity of 2.53 (95% CI: 2.4-2.6). In total of 296 ticks collected, Hyalomma dromedarii was the most prevalent (76.4%), followed by Hyalomma impeltatum (23.3%) and Hyalomma excavatum (0.3%). Of the tested animals, 13 (7.6%; 95% CI: 4.3-12.8%) scored positive to at least one TBP, with Anaplasma platys (5.3%; 95% CI: 2.7-9.9%) being the most prevalent species, followed by Anaplasma phagocytophilum, Anaplasma sp., Ehrlichia canis and Hepatozoon canis (0.6% each; 95% CI: 0.04-3.4%). None of the camels were found to be co-infected with more than one pathogen. All samples tested negative for Babesia spp. and Theileria spp.

CONCLUSIONS

The present study reveals the occurrence of different tick species and TBPs in camels from Saudi Arabia. Importantly, these camels may carry A. phagocytophilum and A. platys, representing a potential risk to humans.

Impact of vertebrate communities on Ixodes ricinus-borne disease risk in forest areas

Background

The density of questing ticks infected with tick-borne pathogens is an important parameter that determines tick-borne disease risk. An important factor determining this density is the availability of different wildlife species as hosts for ticks and their pathogens. Here, we investigated how wildlife communities contribute to tick-borne disease risk. The density of Ixodes ricinus nymphs infected with Borrelia burgdorferi (sensu lato), Borrelia miyamotoi, Neoehrlichia mikurensis and Anaplasma phagocytophilum among 19 forest sites were correlated to the encounter probability of different vertebrate hosts, determined by encounter rates as measured by (camera) trapping and mathematical modeling.

Result

We found that the density of any tick life stage was proportional to the encounter probability of ungulates. Moreover, the density of nymphs decreased with the encounter probability of hare, rabbit and red fox. The density of nymphs infected with the transovarially-transmitted B. miyamotoi increased with the density of questing nymphs and the encounter probability of bank vole. The density of nymphs infected with all other pathogens increased with the encounter probability of competent hosts: bank vole for Borrelia afzelii and N. mikurensis, ungulates for A. phagocytophilum and blackbird for Borrelia garinii and Borrelia valaisiana. The negative relationship we found was a decrease in the density of nymphs infected with B. garinii and B. valaisiana with the encounter probability of wood mouse.

Conclusions

Only a few animal species drive the densities of infected nymphs in forested areas. There, foxes and leporids have negative effects on tick abundance, and consequently on the density of infected nymphs. The abundance of competent hosts generally drives the abundances of their tick-borne pathogen. A dilution effect was only observed for bird-associated Lyme spirochetes.

Functional Evolution of Subolesin/Akirin

The Subolesin/Akirin constitutes a good model for the study of functional evolution because these proteins have been conserved throughout the metazoan and play a role in the regulation of different biological processes. Here, we investigated the evolutionary history of Subolesin/Akirin with recent results on their structure, protein-protein interactions and function in different species to provide insights into the functional evolution of these regulatory proteins, and their potential as vaccine antigens for the control of ectoparasite infestations and pathogen infection. The results suggest that Subolesin/Akirin evolved conserving not only its sequence and structure, but also its function and role in cell interactome and regulome in response to pathogen infection and other biological processes. This functional conservation provides a platform for further characterization of the function of these regulatory proteins, and how their evolution can meet species-specific demands. Furthermore, the conserved functional evolution of Subolesin/Akirin correlates with the protective capacity shown by these proteins in vaccine formulations for the control of different arthropod and pathogen species. These results encourage further research to characterize the structure and function of these proteins, and to develop new vaccine formulations by combining Subolesin/Akirin with interacting proteins for the control of multiple ectoparasite infestations and pathogen infection.

Human Granulocytic Anaplasmosis-A Systematic Review of Published Cases

Anaplasma phagocytophilum is an emerging, Gram-negative, obligate intracellular pathogen that is transmitted by a tick vector. Human infection ranges from asymptomatic to severe disease that can present with pancytopenia, multiorgan failure, and death. The aim of this systematic review is to analyze case reports and case series reported over the last two decades in peer-reviewed journals indexed in the Medline/PubMed database according to the PRISMA guidelines. We found 110 unique patients from 88 case reports and series. The most common mode of transmission was tick bite (60.9%), followed by blood transfusion (8.2%). Infection was acquired by blood transfusion in nearly half (42%) of the immunocompromised patients. Most patients reported fever (90%), followed by constitutional (59%) and gastrointestinal symptoms (56%). Rash was present in 17% of patients, much higher than in previous studies. Thrombocytopenia was the most common laboratory abnormality (76%) followed by elevated aspartate aminotransferase (AST) (46%). The diagnosis was most commonly established using whole-blood polymerase chain reaction (PCR) in 76% of patients. Coinfection rate was 9.1% and Borrelia burgdorferi was most commonly isolated in seven patients (6.4%). Doxycycline was used to treat 70% of patients but was only used as an empiric treatment in one-third of patients (33.6%). The overall mortality rate was 5.7%, and one patient died from trauma unrelated to HGA. The mortality rates among immunocompetent and immunocompromised patients were 4.2% (n = 4/95) and 18.2% (n = 2/11), respectively. Four of the six patients who died (66.6%) received appropriate antibiotic therapy. Among these, doxycycline was delayed by more than 48 h in two patients.

Does co-infection with vector-borne pathogens play a role in clinical canine leishmaniosis?

BACKGROUND

The severity of canine leishmaniosis (CanL) due to Leishmania infantum might be affected by other vector-borne organisms that mimic its clinical signs and clinicopathological abnormalities. The aim of this study was to determine co-infections with other vector-borne pathogens based on serological and molecular techniques in dogs with clinical leishmaniosis living in Spain and to associate them with clinical signs and clinicopathological abnormalities as well as disease severity.

METHODS

Sixty-one dogs with clinical leishmaniosis and 16 apparently healthy dogs were tested for Rickettsia conorii, Ehrlichia canis, Anaplasma phagocytophilum and Bartonella henselae antigens by the immunofluorescence antibody test (IFAT) and for E. canis, Anaplasma spp., Hepatozoon spp., Babesia spp. and filarioid DNA by polymerase chain reaction (PCR).

RESULTS

Among the dogs examined by IFAT, the seroprevalences were: 69% for R. conorii, 57% for E. canis, 44% for A. phagocytophilum and 37% for B. henselae; while the prevalences found by PCR were: 8% for Ehrlichia/Anaplasma, 3% for Anaplasma platys and 1% for H. canis. No other pathogen DNA was detected. Statistical association was found between dogs with clinical leishmaniosis and seroreactivity to R. conorii antigen (Fisher's exact test: P = 0.025, OR = 4.1, 95% CI = 1-17) and A. phagocytophilum antigen (Fisher's exact test: P = 0.002, OR = 14.3, 95% CI = 2-626) and being positive to more than one serological or molecular tests (co-infections) (Mann-Whitney test: U = 243, Z = -2.6, n ₁  = 14, n ₂  = 61, P = 0.01) when compared with healthy dogs. Interestingly, a statistical association was found between the presence of R. conorii, E. canis, A. phagocytophilum and B. henselae antibodies in sick dogs and some clinicopathological abnormalities such as albumin and albumin/globulin ratio decrease and increase in serum globulins. Furthermore, seroreactivity with A. phagocytophilum antigens was statistically associated with CanL clinical stages III and IV.

CONCLUSIONS

This study demonstrates that dogs with clinical leishmaniosis from Catalonia (Spain) have a higher rate of co-infections with other vector-borne pathogens when compared with healthy controls. Furthermore, positivity to some vector-borne pathogens was associated with more marked clinicopathological abnormalities as well as disease severity with CanL.

Infections with Candidatus Neoehrlichia mikurensis and Cytokine Responses in 2 Persons Bitten by Ticks, Sweden

The prevalence of Candidatus Neoehrlichia mikurensis infection was determined in 102 persons bitten by ticks in Sweden. Two infected women had erythematous rashes; 1 was co-infected with a Borrelia sp., and the other showed seroconversion for Anaplasma phagocytophilum. Both patients had increased levels of Neoehrlichia DNA and serum cytokines for several months.

Anaplasma phagocytophilum Infection Subverts Carbohydrate Metabolic Pathways in the Tick Vector, Ixodes scapularis

The obligate intracellular pathogen, Anaplasma phagocytophilum, is the causative agent of human, equine, and canine granulocytic anaplasmosis and tick-borne fever (TBF) in ruminants. A. phagocytophilum has become an emerging tick-borne pathogen in the United States, Europe, Africa, and Asia, with increasing numbers of infected people and animals every year. It has been recognized that intracellular pathogens manipulate host cell metabolic pathways to increase infection and transmission in both vertebrate and invertebrate hosts. However, our current knowledge on how A. phagocytophilum affect these processes in the tick vector, Ixodes scapularis is limited. In this study, a genome-wide search for components of major carbohydrate metabolic pathways was performed in I. scapularis ticks for which the genome was recently published. The enzymes involved in the seven major carbohydrate metabolic pathways glycolysis, gluconeogenesis, pentose phosphate, tricarboxylic acid cycle (TCA), glyceroneogenesis, and mitochondrial oxidative phosphorylation and β-oxidation were identified. Then, the available transcriptomics and proteomics data was used to characterize the mRNA and protein levels of I. scapularis major carbohydrate metabolic pathway components in response to A. phagocytophilum infection of tick tissues and cultured cells. The results showed that major carbohydrate metabolic pathways are conserved in ticks. A. phagocytophilum infection inhibits gluconeogenesis and mitochondrial metabolism, but increases the expression of glycolytic genes. A model was proposed to explain how A. phagocytophilum could simultaneously control tick cell glucose metabolism and cytoskeleton organization, which may be achieved in part by up-regulating and stabilizing hypoxia inducible factor 1 alpha in a hypoxia-independent manner. The present work provides a more comprehensive view of the major carbohydrate metabolic pathways involved in the response to A. phagocytophilum infection in ticks, and provides the basis for further studies to develop novel strategies for the control of granulocytic anaplasmosis.

Tick-borne pathogens induce differential expression of genes promoting cell survival and host resistance in Ixodes ricinus cells

Background

There has been an emergence and expansion of tick-borne diseases in Europe, Asia and North America in recent years, including Lyme disease, tick-borne encephalitis and human anaplasmosis. The primary vectors implicated are hard ticks of the genus Ixodes. Although much is known about the host response to these bacterial and viral pathogens, there is limited knowledge of the cellular responses to infection within the tick vector. The bacterium Anaplasma phagocytophilum is able to bypass apoptotic processes in ticks, enabling infection to proceed. However, the tick cellular responses to infection with the flaviviruses tick-borne encephalitis virus (TBEV) and louping ill virus (LIV), which cause tick-borne encephalitis and louping ill respectively, are less clear.

Results

Infection and transcriptional analysis of the Ixodes ricinus tick cell line IRE/CTVM20 with the viruses LIV and TBEV, and the bacterium A. phagocytophilum, identified activation of common and distinct cellular pathways. In particular, commonly-upregulated genes included those that modulate apoptotic pathways, putative anti-pathogen genes, and genes that influence the tick innate immune response, including selective activation of toll genes.

Conclusion

These data provide an insight into potential key genes involved in the tick cellular response to viral or bacterial infection, which may promote cell survival and host resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2011-1) contains supplementary material, which is available to authorized users.

Prevalence Rates of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae), Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), and Babesia microti (Piroplasmida: Babesiidae) in Host-Seeking Ixodes scapularis (Acari: Ixodidae) from Pennsylvania

The etiological agents responsible for Lyme disease (Borrelia burgdorferi), human granulocytic anaplasmosis (Anaplasma phagocytophilum), and babesiosis (Babesia microti) are primarily transmitted by the blacklegged tick, Ixodes scapularis Say. Despite Pennsylvania having in recent years reported the highest number of Lyme disease cases in the United States, relatively little is known regarding the geographic distribution of the vector and its pathogens in the state. Previous attempts at climate-based predictive modeling of I. scapularis occurrence have not coincided with the high human incidence rates in parts of the state. To elucidate the distribution and pathogen infection rates of I. scapularis, we collected and tested 1,855 adult ticks statewide from 2012 to 2014. The presence of I. scapularis and B. burgdorferi was confirmed from all 67 Pennsylvania counties. Analyses were performed on 1,363 ticks collected in the fall of 2013 to avoid temporal bias across years. Infection rates were highest for B. burgdorferi (47.4%), followed by Ba. microti (3.5%) and A. phagocytophilum (3.3%). Coinfections included B. burgdorferi+Ba. microti (2.0%), B. burgdorferi+A. phagocytophilum (1.5%) and one tick positive for A. phagocytophilum+Ba. microti. Infection rates for B. burgdorferi were lower in the western region of the state. Our findings substantiate that Lyme disease risk is high throughout Pennsylvania.

Anaplasma marginale and A. phagocytophilum in cattle in Tunisia

Background

Tick-borne diseases caused by Anaplasma species put serious constraints on the health and production of domestic cattle in tropical and sub-tropical regions. After recovering from a primary infection, cattle typically become persistent carriers of pathogens and play a critical role in the epidemiology of the disease, acting as reservoirs of the Anaplasma spp.

Methods

In this study a duplex PCR assay was used for the simultaneous detection of Anaplasma marginale and Anaplasma phagocytophilum in cattle using two primer pairs targeting msp4 and msp2 genes, respectively. We used this method to analyze DNA preparations derived from 328 blood cattle samples that were collected from 80 farms distributed among Tunisia’s four bioclimatic zones.

Results

The prevalence of the A. marginale infection (24.7 %) was significantly higher and more widespread (in all bioclimatic areas) than that of A. phagocytophilum (0.6 %), which was found in a mixed infection with A. marginale.

Conclusions

The duplex PCR assay used proved to be a rapid, specific and inexpensive mean for the simultaneous detection of Anaplasma marginale and Anaplasma phagocytophilum in cattle blood. It allowed us to report the identification of A. phagocytophilum for the first time in cattle in Tunisia and confirm the presence of A. marginale in cattle from several geographical areas of the country. Further epidemiological studies undertaken using this assay will help improve the surveillance of the associated diseases in the regions where they are endemic.