Transovarial and trans-stadial transmission of Rickettsiae africae in Amblyomma variegatum ticks

Abstract

Rickettsia africae, a spotted fever group rickettsia, is the causative agent of African tick bite fever, transmitted by hard ticks of the Amblyomma genus [1]. Whereas Amblyomma hebraeum, a tick found in large ruminants and wildlife species, is the most common vector of R. africae in southern Africa, epidemiological evidence indicates that Amblyomma variegatum is the predominant vector for the rest of sub-Saharan Africa, and theWest Indies [1]. R. africae has also been detected in Amblyomma lepidum from the Sudan and from Djibouti [2]. The rates of R. africae infection in ticks in endemic area are typically high, and may reach 100% [3]. Cattle, wild game and other ungulates constitute the principal hosts of the Amblyomma vectors, although larvae and nymphs may also parasitize birds and rodents. These ticks are known to readily bite humans. In 1991, Kelly and Mason demonstrated that A. hebraeum ticks collected in Zimbabwe and naturally infected by R. africae were capable of maintaining the rickettsia through trans-stadial and transovarial transmission over two generations [4]. The objective of this work was to establish laboratory colonies of A. variegatum ticks infected by R. africae to examine the vertical transmission of the rickettsia in ticks.