Viral interference in the tick, Rhipicephalus appendiculatus. I. Interference to oral superinfection by Thogoto virus

Interference between arboviruses in a naturally infected tick vector is reported for the first time. Rhipicephalus appendiculatus nymphs were dually infected with Thogoto (THO) virus, a tick-borne virus, similar to members of the family Orthomyxoviridae. In the first series of experiments examining 'inter-stadial' interference, larvae were orally infected with a temperature-sensitive (ts) mutant, and after moulting the nymphs were superinfected with the wild-type (wt) virus. In the second series of experiments examining 'intra-stadial' interference, nymphs were dually infected by interrupted feeding; the time interval between infective feeds was either shorter than 24 h or lasted for 10 days. Interference was demonstrated by the inability of wt virus to replicate in ticks previously infected with ts virus. Both inter- and intra-stadial interference were observed and complete interference was detected in 78% of dually infected nymphs. A pool of dually infected ticks, in which intra-stadial interference had been detected, failed to transmit the superinfecting virus after moulting.