Transovarial transmission of African swine fever virus in the argasid tick Ornithodoros moubata

The aim of this study was to determine filial infection prevalence of experimentally infected colony Ornithodoros moubata Walton (Ixodoidea: Argasidae) ticks for African swine fever virus (ASFV). Three groups of ticks were used: an uninfected control group, one group orally infected with the VIC T90/1 isolate and another group orally infected with the LIV 13/33 isolate of ASFV. The results show that filial infection prevalences were not constant but were highly variable between egg batches from different ticks and between successive egg batches from the same tick. Filial infection prevalences ranged from 1.8% to 31.8% for ticks infected with the VICT90/1 isolate and from 1.2% to 35.5% for ticks infected with the LIV 13/33 isolate. A similar pattern was noted after the third feed. Immunohistochemisty showed that virus replicates in the developing larval cells and not in the yolk sac cells or within the outer layers of the eggs. The results show that ASFV can replicate to a high titre (10(5.1)log10HAD50) within the larval cells of the developing egg.