Disease transmission

Transovarial transmission

Transovarial transmission (i.e. from parent to the progeny via the ovaries) occurs in the case of Babesia bovis and B. bigemina transmitted by Rhipicephalus (Boophilus) spp. Although both parasites seem to be transmitted in the same way, large differences exist between acquiring the protozoan and transmitting it. The difference might be a result of the different characteristics of the Babesia’s. Only Rhipicephalus microplus is able to transmit Babesia bovis in southern Africa. In West and equatorial Africa R. annulatus is also capable of transmitting the pathogen. B. bovis is acquired by adult ticks while they are feeding and transmission to the host occurs through the larvae of the following generation, and not by nymphs or adults. After feeding, the larvae are no longer infected and the tick needs to re-infect itself in the adult stage (no vertical transmission). Babesia bigemina is transmitted by both R. (Boophilus) decoloratus and R. microplus. Although the pathogen is also transmitted transovarially and acquired during the engorgement of adult ticks, transmission is via engorging nymphs and/or adults of the next generation. Vertical transmission occurs as well, infection from one generation to another without necessarily reinfection having taken place.