Biology subjects

Rakotoarivony, I.

Publications and source records attributed to Rakotoarivony, I..

3 recordsLinked to original sources

bioRxiv2025

How an arthropod-borne virus manages host switches: exploration of host-specific mutations and gene formula in bluetongue virus

Arthropod-borne viruses, also known as arboviruses, cause disease worldwide. These viruses alternate between vertebrates and arthropods, facing distinct selection pressures in each host type. Surprisingly, whether specific mechanisms facilitate host alternation remains unclear. Here, we use bluetongue virus (BTV) as a model to investigate two phenomena potentially facilitating host alternation: adaptive mutations and genome formula variation (GFV). First, we searched for mutations indicative of host adaptation in cattle, sheep, and midges infected during an epizooty. We found a limited number of parallel mutations. This result suggests that adaptive mutations are not a main mechanism facilitating host alternation in BTV. Second, we investigated a link of GFV with a proxy of viral fitness, the speed of virus dissemination in midges. We analyzed the genome formula (GF) in experimentally-infected Culicoides imicola midges, either with an infection disseminated into the head or not. GFs differed between dissemination levels, suggesting a link between GF and the speed of virus dissemination. Finally, we investigated the mechanisms underlying GF generation. Currently, two scenarios have been proposed: random generation followed by selection, or directed generation through molecular mechanisms. To limit the influence of selection, we analyzed the GF after a single replication cycle in cell culture. GF values converged towards specific values among replicates. Moreover, GFs differed between arthropod and vertebrate cells. Thus, GF generation is not purely stochastic and is probably influenced by host-specific mechanisms. Overall, our findings highlight GFV as a potential mechanism facilitating BTV alternation across hosts, but not classical mutation-driven evolution. Author SummaryArthropod-borne viruses are important public health problems in the world. These viruses follow a complex cycle involving alternation between arthropods and vertebrates. Surprisingly, we know little on the mechanisms that facilitate alternation between the two host types. Knowledge on such mechanisms could allow the development of antiviral tools. Here, using Bluetongue virus as a model, we investigated two potential mechanisms facilitating alternation: adaptive mutations and genome formula variation (GFV). We found limited evidence for host-specific mutations in natural populations. We observed a potential link between GFV and viral fitness. Moreover, our results suggest that molecular mechanisms generate GFV in a host-specific way from the first round of cell infection.

microbiology↗

bioRxiv2024

Spatial patterns of Hyalomma marginatum-borne pathogens in the Occitanie region (France), a focus on the intriguing dynamics of Rickettsia aeschlimannii

Hyalomma marginatum is an invasive tick species recently established in mainland southern France. This tick is known to host a diverse range of human and animal pathogens such as Rickettsia aeschlimannii, Theileria equi, Anaplasma phagocytophilum, Anaplasma marginale, Ehrlichia minasensis, Crimean-Congo hemorrhagic fever and West Nile virus. While information about the dynamics of these pathogens is crucial to assess disease risk and develop effective monitoring strategies, few data on the spatial dynamics of these pathogens are currently available. We thus collected ticks in 27 sites in the Occitanie region to characterize spatial patterns of H. marginatum- borne pathogens. Several pathogens have been detected: Theileria equi (9.2%), Theileria orientalis (0.2%), Anaplasma phagocytophilum (1.6%), Anaplasma marginale (0.8%) and Rickettsia aeschlimannii (87.3%). Interestingly, we found a spatial clustered distribution for the pathogen R. aeschlimannii between two geographically isolated areas with infection rates and bacterial loads significantly lower in Herault/Gard departments (infection rate 78.6% in average) compared to Aude/Pyrenees-Orientales departments (infection rate 92.3% in average). At a smaller scale, R. aeschlimannii infection rates varied from one site to another, ranging from 29% to 100%. Overall, such high infection rates (87.3% in average) and the effective maternal transmission of R. aeschlimannii might suggest a role as a tick symbiont in H. marginatum. Moreover, currently identified as a human pathogen, such results also question about its pathogenic status in humans given the low number of human cases. Further studies are thus needed to understand both the status and the role of R. aeschlimannii in H. marginatum ticks. IMPORTANCETicks are obligatory hematophagous arthropods which transmit pathogens of medical and veterinary importance. Their infections cause serious health issues in humans and considerable economic loss in domestic animals. Information about the presence of pathogens in ticks and their dynamics is crucial to assess disease risk for public and animal health. Analysing tick-borne pathogens in ticks collected in 27 sites in the regions Occitanie, our results highlight clear spatial patterns in the Hyalomma marginatum-borne pathogen distribution and strengthen the postulate that it is essential to develop effective monitoring strategies and consider the spatial scale to better characterize the circulation of tick-borne pathogens.

microbiology↗

bioRxiv2021

The mosquito microbiome includes habitat-specific but rare symbionts

Microbial communities are known to influence mosquito lifestyles by modifying essential metabolic and behavioral processes that affect reproduction, development, immunity, digestion, egg survival, and ability to transmit pathogens. Many studies have used 16S rRNA gene amplicons to characterize mosquito microbiota and investigate factors that influence host-microbiota dynamics. However, a relatively low taxonomic resolution due to clustering methods based on arbitrary threshold and the overall dominance of Wolbachia or Asaia populations obscured the investigation of rare members of mosquito microbiota in previous studies. Here, we used high resolution Shannon entropy-based oligotyping approaches to analyze the microbiota of Culex pipiens, Culex quinquefasciatus and Aedes individuals from continental and overseas regions in Southern France and Guadeloupe as well as from laboratories with or without antibiotics treatment. Our experimental design that resulted in a series of mosquito samples with a gradient of Wolbachia density and relative abundance along with high-resolution analyses of amplicon sequences enabled the recovery of a robust signal from typically less accessible bacterial taxa. Our data confirm species-specific mosquito-bacteria associations with geography as a primary factor that influences bacterial community structure. But interestingly, they also reveal co-occurring symbiotic bacterial variants within single individuals for both Elizabethkingia and Erwinia genera, distinct and specific Asaia and Chryseobacterium in continental and overseas territories and a putative rare Wolbachia variant. Overall, our study reveals the presence of previously-overlooked microdiversity and multiple closely related symbiotic strains within mosquito individuals with a remarkable habitat-specificity.

microbiology↗