Tick-borne viruses: discovery, clinical aspects, influencing factors and control.

Ticks are highly competent arthropod vectors, capable of transmitting a great variety of viral, bacterial and protozoan pathogens. The continuous identification of tick-borne viruses (TBVs), especially those pathogenic to humans and animals, poses an increasing threat to public and veterinary health worldwide. Following an incubation phase, the clinical course of human TBV infections often starts with non-specific symptoms (such as fever) that can be followed by distinct clinical manifestations (such as haemorrhage, encephalitis or multi-organ failure). Importantly, a lack of specific diagnostic tests, clinician awareness and effective targeted therapeutics has constrained early diagnosis and clinical management. Climate change, natural ecological factors and intensified human activity might have contributed to the expansion of ticks and TBVs. Very few vaccines are currently available for TBVs, therefore the disruption of a complex transmission chain involving vertebrate hosts, ticks and ecological environments is challenging for the control and prevention of TBV infections. This Review summarizes tick virome diversity, outlines the growing threat of TBVs to humans and animals, and describes the clinical features of TBV infections in humans. In addition, we review the factors contributing to the increasing tick density and expanding geographic distribution, and their role as vectors in further facilitating the spread of TBVs, and we highlight the need for integrated One Health strategies to control ticks and TBVs.