Mycobacterium leprae Infection in Ticks and Tick-Derived Cells

Abstract

Leprosy is a zoonosis in the southern United States involving humans and wild armadillos. The majority of patients presenting with zoonotic strains of <i>Mycobacterium leprae</i> note extensive outdoor activity but only rarely report any history of direct contact with wild armadillos. Whether <i>M. leprae</i> is transmitted to new vertebrate hosts through the environment independently or with the aid of other organisms, e.g., arthropod vectors, is a fundamental question in leprosy transmission. The objectives of this study were to assess the potential for ticks to transmit <i>M. leprae</i> and to test if viable <i>M. leprae</i> can be maintained in tick-derived cells. To evaluate tick transmission, nymphal <i>Amblyomma maculatum</i> ticks were injected with isolated <i>M. leprae.</i> Infection and transmission were assessed by qPCR. Ticks infected as nymphs harbored <i>M. leprae</i> through vertical transmission events (nymph to adult and adult to progeny); and, horizontal transmission of <i>M. leprae</i> to a vertebrate host was observed. <i>Mycobacterium leprae</i> DNA was detected in multiple tick life cycle stages. Likewise, freshly isolated <i>M. leprae</i> (Thai-53) was used to infect a tick-derived cell line, and enumeration and bacterial viability were assessed at individual time points for up to 49 days. Evaluations of the viability of long-term cultured <i>M. leprae</i> (Thai-53 and Br4923) were also assessed in a mouse model. Tick-derived cells were able to maintain viable <i>M. leprae</i> over the 49-day course of infection and <i>M. leprae</i> remained infectious within tick cells for at least 300 days. The results of this study suggest that ticks themselves might serve as a vector for the transmission of <i>M. leprae</i> and that tick cells are suitable for maintenance of viable <i>M. leprae</i> for an extended period of time.