Ultrastructural study of the life cycle of Rickettsia slovaca, wild and standard type, cultivated in L929 and Vero cell lines

Ticks and their epidemiological role in Slovakia: from the past till present

In Slovakia, 22 tick species have been found to occur to date. Among them, Ixodes ricinus, Dermacentor reticulatus, D. marginatus and marginally Haemaphysalis concinna, H. inermis and H. punctata have been identified as the species of public health relevance. Ticks in Slovakia were found to harbour and transmit zoonotic and/or potentially zoonotic agents such as tick-borne encephalitis virus (TBEV), spirochaetes of the Borrelia burgdorferi sensu lato (s.l.) complex, the relapsing fever sprirochaete Borrelia miyamotoi, bacteria belonging to the orders Rickettsiales (Rickettsia spp., Anaplasma phagocytophilum, Neoehrlichia mikurensis), Legionellales (Coxiella burnetii), and Thiotrichales (Francisella tularensis), and Babesia spp. parasites (order Piroplasmida). Ixodes ricinus is the principal vector of the largest variety of microorganisms including viruses, bacteria and piroplasms. TBEV, B. burgdorferi s.l., rickettsiae of the spotted fever group, C. burnetii and F. tularensis have been found to cause serious diseases in humans, whereas B. miyamotoi, A. phagocytophilum, N. mikurensis, Babesia microti, and B. venatorum pose lower or potential risk to humans. Distribution of TBEV has a focal character. During the last few decades, new tick-borne encephalitis (TBE) foci and their spread to new areas have been registered and TBE incidence rates have increased. Moreover, Slovakia reports the highest rates of alimentary TBE infections among the European countries. Lyme borreliosis (LB) spirochaetes are spread throughout the distribution range of I. ricinus. Incidence rates of LB have shown a slightly increasing trend since 2010. Only a few sporadic cases of human rickettsiosis, anaplasmosis and babesiosis have been confirmed thus far in Slovakia. The latest large outbreaks of Q fever and tularaemia were recorded in 1993 and 1967, respectively. Since then, a few human cases of Q fever have been reported almost each year. Changes in the epidemiological characteristics and clinical forms of tularaemia have been observed during the last few decades. Global changes and development of modern molecular tools led to the discovery and identification of emerging or new tick-borne microorganisms and symbionts with unknown zoonotic potential. In this review, we provide a historical overview of research on ticks and tick-borne pathogens in Slovakia with the most important milestones and recent findings, and outline future directions in the investigation of ticks as ectoparasites and vectors of zoonotic agents and in the study of tick-borne diseases.

Survival and Intra-Nuclear Trafficking of Burkholderia pseudomallei: Strategies of Evasion from Immune Surveillance?

Background

During infection, successful bacterial clearance is achieved via the host immune system acting in conjunction with appropriate antibiotic therapy. However, it still remains a tip of the iceberg as to where persistent pathogens namely, Burkholderia pseudomallei (B. pseudomallei) reside/hide to escape from host immune sensors and antimicrobial pressure.

Methods

We used transmission electron microscopy (TEM) to investigate post-mortem tissue sections of patients with clinical melioidosis to identify the localisation of a recently identified gut microbiome, B. pseudomallei within host cells. The intranuclear presence of B. pseudomallei was confirmed using transmission electron microscopy (TEM) of experimentally infected guinea pig spleen tissues and Live Z-stack, and ImageJ analysis of fluorescence microscopy analysis of in vitro infection of A549 human lung epithelial cells.

Results

TEM investigations revealed intranuclear localization of B. pseudomallei in cells of infected human lung and guinea pig spleen tissues. We also found that B. pseudomallei induced actin polymerization following infection of A549 human lung epithelial cells. Infected A549 lung epithelial cells using 3D-Laser scanning confocal microscopy (LSCM) and immunofluorescence microscopy confirmed the intranuclear localization of B. pseudomallei.

Conclusion

B. pseudomallei was found within the nuclear compartment of host cells. The nucleus may play a role as an occult or transient niche for persistence of intracellular pathogens, potentially leading to recurrrent episodes or recrudescence of infection.

Burkholderia pseudomallei (B. pseudomallei), the causative agent of melioidosis, is endemic across parts of South East Asia and Northern Australia. Of the key features of B. pseudomallei, is its ability to remain latent in the host causing recrudescent disease years after initial infection. However, it still remains unclear as to where B. pseudomallei resides to escape from host immune sensors and antimicrobial pressure. Here, we have found that B. pseudomallei was able to enter into the nuclear compartment of host cells. The nucleus may play a role as a temporary abode for persistence, leading to recurrrent episodes of infection.

Dermacentor marginatus and Ixodes ricinus ticks versus L929 and Vero cell lines in Rickettsia slovaca life cycle evaluated by quantitative real time PCR

Ticks transmit many different pathogens to animals, humans and their pets. Rickettsia slovaca, as a member of the spotted-fever-group rickettsiae is an agent of the human disease Tick-borne lymphadenopathy (TIBOLA), also called Dermacentor-borne necrosis erythema and lymphadenopathy (DEBONEL), which occurs from the Mediterranean to central Europe, transmitted by Dermacentor reticulatus and Dermacentor marginatus (Acari: Ixodidae). In this study, quantitative real time PCR was used to characterize the growth of R. slovaca, strain B in static (mammalian L929 and Vero cells without replacement of growth medium) and dynamic (D. marginatus and Ixodes ricinus ticks) cultivation systems. Curves of bacterial growth in static cultivations were modeled with exponential, stationary and death phases, whereas in dynamic systems the stationary phase was absent. The highest point of multiplication of R. slovaca was recorded on the 4th day post infection in both cell lines and the rickettsial DNA copy number in L929 and Vero cells at this point was 21 and 27 times greater than rickettsial DNA copy number of inoculum, respectively. In the dynamic system, the highest point of multiplication was on the 21th and 12th day after feeding of ticks and rickettsial DNA copy numbers were 7,482 and 865 times greater than the inoculum in D. marginatus and I. ricinus, respectively. Life cycle of R. slovaca in mammalian cell lines was shorter; supposedly, bacteria destroyed these cells and ticks, especially D. marginatus, were considered a more appropriate environment.