Vector competence of the invasive Asian longhorned tick, Haemaphysalis longicornis, in transmitting heartland virus under laboratory conditions

The Haemaphysalis longicornis tick is native to eastern Asia but recently established populations in the United States where it continues to expand its geographic range. In Asia, H. longicornis transmits a bandavirus that is genetically closely related to the North American tick-borne virus, Heartland virus (HRTV). As the current geographic range and the predicted range expansion of invasive H. longicornis overlap considerably with human cases of HRTV, the objective for this study was to assess the ability of H. longicornis to maintain and transmit the endemic tick-borne virus, HRTV. We microinjected female H. longicornis with HRTV or media. HRTV RNA was detected via qRT-PCR in tick salivary glands and midguts at multiple time points ranging from 14 to 40 days post-injection. Infectious virions were also detected in individual ticks screened at each time point. To evaluate horizontal transmission of HRTV from tick to mammalian host, we infested mice with HRTV-injected H. longicornis females (1 tick per mouse). 80% of the mice seroconverted, demonstrating host exposure to HRTV during tick feeding. The engorged female H. longicornis were maintained for oviposition. Transovarial and transstadial transmission of HRTV was demonstrated by detection of HRTV RNA and infectious virions in 100% of egg pools and larval pools, respectively. Together, these findings show that H. longicornis is a competent vector of HRTV. On-going studies are investigating whether non-viremic transmission of HRTV occurs between co-feeding invasive H. longicornis and native Amblyomma americanum ticks, as this could amplify transmission of HRTV in natural foci.