PROJECT SUMMARY & ABSTRACT The invasive Asian Longhorned tick, Haemaphysalis longicornis, is native to eastern Asia but recently established populations in the United States and continues to expand its geographic range. This is a public health threat, because in its native range, H. longicornis is an established vector of viruses closely related to Heartland virus (HRTV) and Deer tick virus (DTV), which are the two main North American tick-borne viruses. The capacity of H. longicornis to transmit North American tick-borne phleboviruses (HRTV) and flaviviruses (DTV) is unknown, leaving us unaware of the epidemiologic impact of this invasive tick species. The overall objective for this application is to assess the ability of H. longicornis to acquire, maintain, and transmit North American tick-borne phleboviruses and flaviviruses. The central hypothesis is that H. longicornis is a competent vector for HRTV and DTV, and co-feeding transmission of HRTV or DTV between infected native ticks and uninfected H. longicornis ticks can occur in the absence of host viremia. The rationale for this project is that if H. longicornis is capable of maintaining HRTV and DTV in tick populations and transmitting these viruses to mammalian hosts, we can begin to forecast evolving epidemiologic and transmission dynamics of these viruses in North America. The central hypothesis will be tested by pursuing two specific aims: 1) Assess the vector competence of H. longicornis ticks for HRTV and DTV; and, 2) Investigate whether non-viremic transmission of HRTV or DTV occurs between infected native ticks (Amblyomma americanum or Ixodes scapularis) co-feeding on the same host with uninfected H. longicornis. Under the first aim, H. longicornis will be infected with HRTV or DTV, and viral replication kinetics in the tick will be examined. To assess horizontal transmission of HRTV and DTV, infected H. longicornis will receive a bloodmeal and exposed hosts will undergo serology and viremia screening. After molting to the next life stage, ticks will be tested for the presence of virus to evaluate vertical transmission. For the second aim, uninfected H. longicornis nymphs will be co-fed on the same host with HRTV- infected A. americanum or DTV-infected I. scapularis adults. The H. longicornis nymphs will be tested for the presence of virus at different feeding proximities on the host. The proposed research is conceptually innovative because it is the first to evaluate H. longicornis’ vector competency for the North American viruses, HRTV and DTV, which circulate in regions where invasive H. longicornis populations recently established. This contribution will be significant because it frames the basic biology of this invasive tick species in relation to North American tick-borne viruses, which is extremely important as we seek to understand the public health implications of H. longicornis establishment in regions of North America where these viruses are endemic.