Characterization of Transstadial Transmission of Rickettsia Amblyommatis in Haemaphysalis Longicornis Using Optimized Artificial Membrane Feeding System

Ticks are blood-feeding arthropods and serve as vectors and reservoirs for diverse pathogens. Recent environmental changes have triggered the invasion of ticks into new geographical areas, prompting a public health alert for increased risk of tick-borne diseases. Amblyomma (A.) americanum (lone star tick) has emerged as the most common human-biting tick species in the eastern United States. Amblyomma americanum transmits multiple pathogens, including Rickettsia (R.) amblyommatis, the suspected cause of mild spotted fever rickettsiosis. As an invasive tick species, Haemaphysalis (H.) longicornis (longhorned tick) has rapidly invaded and expanded to high densities in the eastern United States. Haemaphysalis longicornis and A. americanum often share the habitat with preferential feeding on mid- to large-sized animals, such as white-tailed deer. This sympatric association of H. longicornis with A. americanum raises the potential for H. longicornis to acquire pathogens native to A. americanum during blood-feeding on the same host. In its native ranges, H. longicornis transmits R. japonica and R. heilongjiangensis. However, it remains unclear whether H. longicornis can transmit R. amblyommatis abundantly present in A. americanum in the United States. Using artificial membrane feeding, we establish that R. amblyommatis can stably colonize H. longicornis without altering feeding and molting behaviors. Transovarial transmission of R. amblyommatis did not occur in parthenogenetic H. longicornis. However, R. amblyommatis successfully invaded the midgut and salivary glands of H. longicornis, key organ tissues of rickettsial replication and horizontal transmission. Our results suggest that H. longicornis may serve as a vector, but not as a reservoir, for R. amblyommatis transmission.