Immune Response to Tick-Borne Hemoparasites: Host Adaptive Immune Response Mechanisms as Potential Targets for Therapies and Vaccines.

Tick-transmitted pathogens cause infectious diseases in both humans and animals. Different types of adaptive immune mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen antigens or indirectly through soluble factors, such as cytokines and/or chemokines, secreted by host cells as response. Adaptive immunity effectors, such as antibody secretion and cytotoxic and/or T helper cell responses, are mainly involved in the late and long-lasting protective immune response. Proteins and/or epitopes derived from pathogens and tick vectors have been isolated and characterized for the immune response induced in different hosts. This review was focused on the interactions between tick-borne pathogenic hemoparasites and different host effector mechanisms of T- and/or B cell-mediated adaptive immunity, describing the efforts to define immunodominant proteins or epitopes for vaccine development and/or immunotherapeutic purposes. A better understanding of these mechanisms of host immunity could lead to the assessment of possible new immunotherapies for these pathogens as well as to the prediction of possible new candidate vaccine antigens.

New Real-Time PCRs to Differentiate Rickettsia spp. and Rickettsia conorii.

Rickettsia species are an important cause of emerging infectious diseases in people and animals, and rickettsiosis is one of the oldest known vector-borne diseases. Laboratory diagnosis of Rickettsia is complex and time-consuming. This study was aimed at developing two quantitative real-time PCRs targeting ompB and ompA genes for the detection, respectively, of Rickettsia spp. and R. conorii DNA. Primers were designed following an analysis of Rickettsia gene sequences. The assays were optimized using SYBR Green and TaqMan methods and tested for sensitivity and specificity. This study allowed the development of powerful diagnostic methods, able to detect and quantify Rickettsia spp. DNA and differentiate R. conorii species.

Innate Immune Response to Tick-Borne Pathogens: Cellular and Molecular Mechanisms Induced in the Hosts.

Many pathogens are transmitted by tick bites, including Anaplasma spp., Ehrlichia spp., Rickettsia spp., Babesia and Theileria sensu stricto species. These pathogens cause infectious diseases both in animals and humans. Different types of immune effector mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen-derived antigens or indirectly by molecules released by host cells binding to these antigens. The components of innate immunity, such as natural killer cells, complement proteins, macrophages, dendritic cells and tumor necrosis factor alpha, cause a rapid and intense protection for the acute phase of infectious diseases. Moreover, the onset of a pro-inflammatory state occurs upon the activation of the inflammasome, a protein scaffold with a key-role in host defense mechanism, regulating the action of caspase-1 and the maturation of interleukin-1ß and IL-18 into bioactive molecules. During the infection caused by different microbial agents, very similar profiles of the human innate immune response are observed including secretion of IL-1α, IL-8, and IFN-α, and suppression of superoxide dismutase, IL-1Ra and IL-17A release. Innate immunity is activated immediately after the infection and inflammasome-mediated changes in the pro-inflammatory cytokines at systemic and intracellular levels can be detected as early as on days 2-5 after tick bite. The ongoing research field of "inflammasome biology" focuses on the interactions among molecules and cells of innate immune response that could be responsible for triggering a protective adaptive immunity. The knowledge of the innate immunity mechanisms, as well as the new targets of investigation arising by bioinformatics analysis, could lead to the development of new methods of emergency diagnosis and prevention of tick-borne infections.

Seroprevalence of Coxiella burnetii in dairy cattle from Sicily.

Q fever is a widespread zoonotic disease caused by Coxiella burnetii, an obligate intracellular bacterium with a wide range of hosts. The aim of this study was to estimate the seroprevalence of C. burnetii infection in cattle in Sicilian farms. A total of 4,661 serum samples, from cattle belonging to 198 Sicilian farms, were examined by ELISA test and 246 resulted positive. The average seroprevalence at the farm level was 38.8% (77/198) (95% CI), while at the animal level it was 5.28% (246/4,661) (95% CI). The present study highlights the need for continuous monitoring of C. burnetii spread as it represents a serious risk for human health.

Analysis of interferon-gamma producing cells during infections by Yersinia enterocolitica O:9 and Brucella abortus in cattle.

One of the major constraints in the diagnosis of animal brucellosis is the cross-reactivity that occurs between Brucella and Yersinia surface antigens. With the aim to find a method to distinguish Brucella from Yersinia infection, the expansion of interferon gamma producing (IFN-γ+) T cell subsets obtained from peripheral blood mononuclear cells (PBMC) isolated from cattle either infected by Brucella abortus or experimentally immunized with Yersinia enterocolitica O:9 were compared. The lymphocytes were analyzed by flow cytometry after PBMC were in vitro re-exposed to Yersinia or Brucella antigens. The results highlighted a statistically significant difference in the expansion of the CD4+ and CD8+ IFN-γ+ T cells occurring when PBMC of animals immunized with Yersinia are in vitro exposed to Y. enterocolitica O:9 antigen but not to Brucella antigen. This method could thus be suggested in those cases where results obtained by serodiagnosis need to be further clarified.

Cross-reactivity in serological tests for brucellosis: a comparison of immune response of Escherichia coli O157:H7 and Yersinia enterocolitica O:9 vs Brucella spp.

According to European Union (EU) regulations, the serological tests for the eradication of bovine and ovine brucellosis are the Rose Bengal Test, Complement Fixation Test, and i-ELISA. These methods, also recommended by the World Organization for Animal Health (OIE) for international trades, have limitations related to the use of suspensions of smooth Brucellae or LPS extracts. Limitations include false-positive serological reactions to brucellosis, which in turn impedes accurate diagnosis in some herds. False positive reactions should be considered carefully during the final stages of an eradication programme and for surveillance purposes in brucellosis-free areas. In this study, we produced specific sera through the experimental infection of sheep with Y. enterocolitica O:9 and E. coli O157:H7. These are the most important cross-reactive bacteria with Brucella. We then evaluated the antibody response of groups of sheep that had been immunised towards homologous antigens and official antigens for brucellosis, in order to identify a differential diagnostic protocol to distinguish cross-reaction in Brucella-infected animals.

A Geographical Information System Based Approach for Integrated Strategies of Tick Surveillance and Control in the Peri-Urban Natural Reserve of Monte Pellegrino (Palermo, Southern Italy).

Ticks (Acari: Ixodidae) are bloodsucking arthropods involved in pathogen transmission in animals and humans. Tick activity depends on various ecological factors such as vegetation, hosts, and temperature. The aim of this study was to analyse the spatial/temporal distribution of ticks in six sites within a peri-urban area of Palermo (Natural Reserve of Monte Pellegrino) and correlate it with field data using Geographical Information System (GIS) data. A total of 3092 ticks were gathered via dragging method from June 2012 to May 2014. The species collected were: Ixodes ventalloi (46.09%), Hyalomma lusitanicum (19.99%), Rhipicephalus sanguineus (17.34%), Rhipicephalus pusillus (16.11%), Haemaphisalis sulcata (0.36%), Dermacentor marginatus (0.10%), and Rhipicephalus turanicus (0.03%). GIS analysis revealed environmental characteristics of each site, and abundance of each tick species was analysed in relation to time (monthly trend) and space (site-specific abundance). A relevant presence of I. ventalloi in site 2 and H. lusitanicum in site 5 was observed, suggesting the possible exposure of animals and humans to tick-borne pathogens. Our study shows the importance of surveillance of ticks in peri-urban areas and the useful implementation of GIS analysis in vector ecology; studies on temporal and spatial distribution of ticks correlated to GIS-based ecological analysis represent an integrated strategy for decision support in public health.

The First Serological Study of Q Fever in Humans in Lebanon.

OBJECTIVE: The aim of this study was to estimate, for the first time, the human seroprevalence of Q fever in Lebanon, by assessing the presence of antibodies against the causative agent, Coxiella burnetii. A total number of 421 serum samples (226 females and 196 males) were collected in February 2015 from hospitals and laboratories dispersed in five Lebanese provinces: Akkar, Bekaa, Mount Lebanon, Nabatieh, and South Lebanon. METHODS: Serial testing approach was used. Samples were first screened for IgG phase II antibodies against C. burnetii by Enzyme Linked Immunosorbent Assay (ELISA) Kit. Then, both positive and inconclusive sera were reexamined by immunofluorescence assay (IFA) test with the aims to confirm and specify the infection status (past or probably acute infection) by detecting IgG (I/II) and IgM (I/II) in human sera. RESULTS: Screening of 421 samples was estimated to be 38.70% (95% CI 34-43.3) positive samples, 5.90% (95% CI 3.7-8.2) suspect samples (as doubtful results), and 55.40% (95% CI 50.7-60.1) negative samples. Furthermore, all positive and suspect samples by ELISA test were retested by immunofluorescence assay test (IFAT), and the prevalence of positive sample was 37% and the infection case was recorded: 23.75% (95% CI 19.7-27.8) samples resulted from past infection, 1.9% (95% CI 0.6-3.2) probably acute infection characterized by several dominance clinical symptoms as: fever, cough, headache, difficulty breathing, and atypical pneumonia, and 0.23% (95% CI 0-0.7) inconclusive sample accompanied by different symptoms as bone metastasis and lung cancer. CONCLUSION: The study records the exposition of 37% of 421 patients to C. burnetii distributed in five Lebanese provinces with the highest seroprevalence in Bekaa and Akkar provinces and the lowest reported in Mount Lebanon. This difference may be due to the presence of high density of livestock production and of major agricultural areas in these two provinces.

Timing of activation of CD4+ memory cells as a possible marker to establish the efficacy of vaccines against contagious agalactia in sheep.

Mycoplasma agalactiae is a major pathogen of sheep and goats in many areas of the world and particularly in Mediterranean countries. It causes contagious agalactia, an infectious disease primarily affecting mammary glands. Many vaccines against the pathogen are currently under development. The aim of the study was to investigate the involvement of T cell-mediated immunity during vaccination and challenge experiments against Mycoplasma agalactiae. A comparison of the antigen-specific expansion of interferon gamma positive T cell memory and naïve subsets was performed between vaccinated and non-vaccinated sheep to identify cellular subsets whose activation was different between protected and non-protected sheep. Data reported in this manuscript demonstrated that two out of the three vaccines used in this study protected sheep from the disease. In the protected groups CD4(+) memory interferon-γ(+) T cells underwent an early expansion (p<0.05 when compared to unprotected groups), whilst memory CD8(+) Interferon-γ(+) T cells increased in non-protected animals 7 days after infection (p<0.05). γδ(+) Interferon-γ(+) T cells reached peaks of expansion in infected and in two vaccinated groups thus indicating that these cells are not preferentially involved in protection or pathogenesis (p<0.05). Hereby we propose that the early activation of CD4(+) memory Interferon-γ(+) T cells could be considered as a marker of protection from the disease as well as a tool to establish vaccine efficacy.

Antigen-specific T cells and cytokines detection as useful tool for understanding immunity against zoonotic infections.

Zoonoses include a broad range of diseases, that are becoming of great interest, due to the climate changing, that cause the adaptation of vectors to new niches and environments. Host immune responses play a crucial role in determining the outcome of infections, as documented by expansion of antigen-specific T cells during several zoonotic infections. Thus, understanding of the contribution of antigen-specific T-cell subsets in the host immune response is a powerful tool to evaluate the different immunological mechanisms involved in zoonotic infections and for the development of effective vaccines. In this paper we discuss the role of T cells in some eukaryotic and prokaryotic infectious models.