Heartland Virus: An Evolving Story of an Emerging Zoonotic and Vector-Borne Disease

Abstract

Heartland virus (HRTV) is an emerging tick-borne bandavirus that is capable of causing severe disease characterized by acute thrombocytopenia and lymphopenia. The virus is endemic to the eastern United States and is carried by the Lone Star tick (Amblyomma americanum). Since its discovery in 2009, at least 60 human infections have been recorded across this area, with an overall 5–10% estimated mortality rate. All infections reported thus far have occurred following a known tick bite or exposure to tick-infested areas, but the possibility of nosocomial transmission has not been ruled out. Despite relatively high rates of seroprevalence among certain wildlife species such as white-tailed deer, the reservoir species for HRTV remains unknown, as the virus has never been isolated from any mammalian wildlife species. Furthermore, how the virus is transmitted to its vector species in nature remains unknown, though laboratory studies have confirmed both horizontal and vertical transmission of HRTV in A. americanum. In addition, the recent 2017 introduction of the Asian longhorned tick (Haemaphysalis longicornis) to the US has raised concerns about possible spillover of HRTV into a new tick species that has been confirmed to be a competent vector for HRTV in the laboratory. Thus, an increased awareness of its clinical presentation is needed, and further research is urgently required to establish the natural transmission cycle and develop new countermeasures for this novel zoonotic pathogen.