Year-to-year variation in the density of Ixodes ricinus ticks and the prevalence of the rodent-associated human pathogens Borrelia afzelii and B. miyamotoi in different forest types

The human pathogens Borrelia afzelii, which causes Lyme borreliosis and B. miyamotoi, which causes relapsing fever, both circulate between Ixodes ricinus ticks and rodents. The spatiotemporal dynamics in the prevalence of these pathogens have not yet been fully elucidated, but probably depend on the spatiotemporal population dynamics of small rodents. We aimed to evaluate the effect of different forest types on the density of infected nymphs in different years and to obtain more knowledge about the spatial and temporal patterns of ticks and tick-borne pathogens. We analysed unfed nymphal ticks from 22 stands of four different forest types in Belgium in 2009, 2010, 2013 and 2014 and found that the density of nymphs in general and the density of nymphs infected with B. afzelii and B. miyamotoi varied yearly, but without temporal variation in the infection prevalence. The yearly variation in density of infected nymphs in our study thus seems to be caused most by the variation in the density of nymphs, which makes it a good predictor of disease risk. The risk for rodent-associated tick-borne diseases also varied between forest types. We stress the need to elucidate the contribution of the host community composition to tick-borne disease risk.</p

The impact of parasites on host insect epigenetics

The epigenetic regulation of gene expression has been recognized as an alternative to genetic mutation for the conversion of environmental stressors, such as the presence of parasites, into heritable phenotypic changes. The activation of immune responses in insects involves the orchestrated expression of genes that mediate pathogen recognition and immunity-related signalling, which in turn induces the synthesis of effector molecules such as antimicrobial peptides. This transcriptional reprogramming is regulated by DNA methylation and the acetylation and deacetylation of histones, which operate before transcription begins, and by microRNAs, which control protein synthesis posttranscriptionally. Therefore, research on epigenetic regulation at the molecular, cellular, tissue, organ and organism levels in insects represents an emerging field to understand the regulation of complex parameters such as longevity, fecundity and reproduction. Microbial parasites and parasitic wasps have evolved strategies to interfere with the epigenetic mechanisms of their host insects to favour their own development. The impact of parasites on host insect epigenetics is a growing area of research because it influences phenomena such as host-parasite coevolution, the transmission of diseases by vector insects, and the control of endogenous symbionts. This research field could also pave the way for the development of novel strategies to control pest and vector insects