High throughput sequencing in the diagnosis and surveillance of tick-borne diseases: A narrative review

Ticks are blood-feeding arthropods that can transmit a wide variety of microorganisms (bacteria, viruses, protozoa, and filarial nematodes) when they feed on various vertebrate hosts. In the recent years, high-throughput sequencing (HTS), also called next-generation sequencing, has become a key tool for detecting and characterizing microorganisms, whether they are pathogens or part of the tick's own microbiota. This narrative review summarizes current applications of HTS for the surveillance and diagnosis of tick-borne diseases within a One Health framework. From nucleic acids extracted from a tick sample, HTS enables the possibility of simultaneous detection of multiple microorganisms, and provides valuable information on potential reservoir hosts through blood meal analysis. It has revealed a vast diversity of bacterial, viral, protozoan agents and filarial nematodes in various tick species worldwide, including unexpected or novel pathogens. HTS has also improved our understanding of the tick microbiota and how it interacts with pathogens, which could have an impact on vector competence. In the field of microbiological diagnosis, HTS provides a complementary or alternative approach to traditional diagnostic tests, particularly in cases with non-specific symptoms or when the etiology is unknown. HTS has proven to be effective in detecting rare or novel pathogens, including some transmitted by ticks. It has also enabled the reconstruction of whole genomes of microorganisms from clinical samples or ticks, thereby improving our understanding of the molecular epidemiology of these agents. By bridging the vector, its pathogens, the reservoir host, and human or animal clinical outcomes, HTS represents a cornerstone technology for future integrated surveillance systems of TBDs within a One Health perspective.