Transstadial and transovarial transmission of Orientia tsutsugamushi in Leptotrombidium imphalum and Leptotrombidium chiangraiensis (Acari: Trombiculidae).

Transovarial transmission of Orientia tsutsugamushi (Hayashi) in laboratory colonies of Leptotrombidium chiangraiensis Tanskul & Linthicum and Leptotrombidium imphalum (Vercammen-Grandjean & Langston) (Acari: Trombiculidae) was studied for two generations. In L. chiangraiensis, the transovarial and filial infection rate was 100% in each generation. Only infected females were produced. In L. imphalum, the transovarial infection rate of the parental generation was 100% but declined to 93.3% in the F1 generation. The overall filial infection rate was 100% in the F1 but was only 62.3% in the F2 generation. In infected lines, only infected females were produced in the F1 generation, but 1.5% of the F2 progeny were infected males. Lower rates of transovarial transmission in L. imphalum may be the cause of the lower natural infection rates found in nature.