Disease transmission

Intrastadial transmission

Intrastadial (within the same life stage, by males) in the case of heartwater, caused by the parasite Ehrlichia ruminantium, mainly transmitted by Amblyomma variegatum and A. hebraeum althoughother Amblyomma spp. like A. pomposum, A. lepidum , A. cohaerens and A. gemma are of lesser importance. Amblyomma male ticks produce a pheromone during feeding that attracts nymphs and adult Amblyomma ticks to the same animal and to area where the male tick is feeding. As a consequence, clustering occurs on some animals, a phenomenon which is often observed. It is important to notice that during the process of clustering mainly male ticks first start a blood meal, during which phase the ticks can acquire infection with E. ruminantium, and after clustering some may detach and continue their blood meal on another animal. Ehrlichia ruminandium can easily be transferred from one host to another during this process and are transmitted by the same tick in the same stage, a process that is known as intrastadial transmission. The same method of transmission is also observed in the case of Anaplasma marginale and A. centrale, by their main vector R. microplus and by Rhipicephalus simus. To be able to transmit pathogens intrastadially, the pathogens needs to be infective for the host in the same lifecycle stage in which it was acquired. If not, the pathogen cannot infect the host (i.e. Theileria parva is acquired as piroplasms in the larval or nymphal stage of the tick and the parasite undergoes a sexual reproduction in the tick and only becomes infective to cattle again in the following tick stage).