Arsenophonus nasoniae and Rickettsiae Infection of Ixodes ricinus Due to Parasitic Wasp Ixodiphagus hookeri

Abstract Arsenophonus nasoniae, a male-killing endosymbiont of chalcid wasps, was recently detected in several hard tick species. Following the hypothesis that its presence in ticks may not be linked to the direct occurrence of bacteria in tick's organs, we identified A. nasoniae in wasps emerging from parasitised nymphs. We confirmed that 28.1% of Ixodiphagus hookeri wasps parasitizing Ixodes ricinus ticks were infected by A. nasoniae. Moreover, in examined I. ricinus nymphs, A. nasoniae was detected only in those, which were parasitized by the wasp. However, in part of the adult wasps as well as in some ticks that contained wasp's DNA, we did not confirm A. nasoniae. We also found, that in spite of reported malekilling, some newly emerged adult wasp males were also infected by A. nasoniae. Additionally, we amplified the DNA of Rickettsia helvetica and Rickettsia monacensis (known to be Ixodes ricinus-associated bacteria) in adult parasitoid wasps. This may be related either with the digested bacterial DNA in wasp body lumen or with a role of wasps in circulation of rickettsiae among tick vectors

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Arsenophonus nasoniae and Rickettsiae Infection of Ixodes ricinus Due to Parasitic Wasp Ixodiphagus hookeri

International audienceArsenophonus nasoniae, a male-killing endosymbiont of chalcid wasps, was recently detected in several hard tick species. Following the hypothesis that its presence in ticks may not be linked to the direct occurrence of bacteria in tick's organs, we identified A. nasoniae in wasps emerging from parasitised nymphs. We confirmed that 28.1% of Ixodiphagus hookeri wasps parasitizing Ixodes ricinus ticks were infected by A. nasoniae. Moreover, in examined I. ricinus nymphs, A. nasoniae was detected only in those, which were parasitized by the wasp. However, in part of the adult wasps as well as in some ticks that contained wasp's DNA, we did not confirm A. nasoniae. We also found, that in spite of reported male-killing, some newly emerged adult wasp males were also infected by A. nasoniae. Additionally, we amplified the DNA of Rickettsia helvetica and Rickettsia monacensis (known to be Ixodes ricinus-associated bacteria) in adult parasitoid wasps. This may be related either with the digested bacterial DNA in wasp body lumen or with a role of wasps in circulation of rickettsiae among tick vectors

<i>Rickettsia</i> Deregulates Genes Coding for the Neurotoxic Cell Response Pathways in Cerebrocortical Neurons In Vitro

Rickettsial infections of the central nervous system (CNS) are manifested by severe neurological symptoms and represent a serious life-threatening condition. Despite the considerable health danger, only a few studies have been conducted focusing on the pathogenesis induced by Rickettsia sp. in CNS. To investigate the signaling pathways associated with the neurotoxic effects of rickettsiae, we employed an experimental model of cerebrocortical neurons combined with molecular profiling and comprehensive bioinformatic analysis. The cytopathic effect induced by Rickettsia akari and Rickettsia slovaca was demonstrated by decreased neuronal viability, structural changes in cell morphology, and extensive fragmentation of neurites in vitro. Targeted profiling revealed the deregulation of genes involved in the neuroinflammatory and neurotoxic cell response pathways. Although quantitative analysis showed differences in gene expression response, functional annotation revealed that the biological processes are largely shared between both Rickettsia species. The identified enriched pathways are associated with cytokine signaling, chemotaxis of immune cells, responses to infectious agents, interactions between neurons, endothelial and glial cells, and regulation of neuronal apoptotic processes. The findings of our study provide new insight into the etiopathogenesis of CNS infection and further expand the understanding of molecular signaling associated with neuroinvasive Rickettsia species

The questionable role of parasitic wasps in the transmission of rickettsiae, illustrated on the tick’s life cycle.

<p>Adult female <i>I</i>. <i>hookeri</i> oviposits in larvae and nymphs of ixodid ticks, but the wasp eggs start to develop only in fully engorged nymphs. The immature parasitoid wasps consume the nymph’s tissue and its ingested blood meal, causing nymph death. During the tick’s life cycle (eggs, larvae, nymphs, adults), rickettsiae can pass from stage to stage. In our experiments we successfully amplified rickettsial DNA not just in unfed nymphs but also in emerged adult wasps. More experiments will be needed to demonstrate if <i>I</i>. <i>hookeri</i> may act as a biological vector of <i>A</i>. <i>nasoniae</i> and <i>Rickettsia</i> sp.</p

<i>Ixodiphagus hookeri</i> adults.

<p>(A) Habitus of a female after treatment with <i>Marc André</i> solution. (B) Magnified female genitalia. (C) Habitus of a male. (D) Magnified male genitalia. Scale bar represents 0.5 mm.</p

Reports on <i>Ixodiphagus hookeri</i> detected in hard ticks.

<p>Reports on <i>Ixodiphagus hookeri</i> detected in hard ticks.</p

Published studies on detection of <i>Arsenophonus nasoniae</i> in ticks.

<p>Published studies on detection of <i>Arsenophonus nasoniae</i> in ticks.</p

Workflow of laboratory experiments.

<p>A total of 360 <i>I</i>. <i>ricinus</i> nymphs were fed on 12 Balb/c mice. Of those, 50 engorged nymphs were parasitized by <i>I</i>. <i>hookeri</i> wasps. The obtained 96 parasitoids were subsequently screened for the presence of <i>A</i>. <i>nasoniae</i> and rickettsiae by PCR. The DNA of <i>A</i>. <i>nasoniae</i> was found in 27 wasps (28.1%), <i>Rickettsia</i> sp. in 22 wasps (22.9%). Eight wasps were positive for both bacteria—<i>A</i>. <i>nasoniae</i> and <i>Rickettsia</i> sp.</p