Experimental studies on the replication and dissemination of Qalyub virus (Bunyaviridae: Nairovirus) in the putative tick vector, Ornithodoros (Pavlovskyella) erraticus.

A study was undertaken to determine if the argasid tick, Ornithodoros (Pavlovskyella) erraticus, can serve as a biological vector of Qalyub (QYB) virus. The suckling mice used as viremic vertebrate hosts were acceptable hosts for all feeding stages of this tick and developed relatively high titered viremias (4.4-6.5 log10PFU/ml) 24-120 hr post intracerebral inoculation. Larval, nymphal, and adult ticks became orally infected with QYB virus after ingesting 4.4-6.4 log10PFU/ml. The overall infection rate for all experiments was 67/205 and virus was recovered up to day 179 postfeeding. Incubation of known quantities of QYB virus with uninfected triturated tick tissues did not result in any appreciable virus inactivation. QYB viral antigen was detected by immunofluorescence primarily in the tick midgut posterior diverticula cells. First and second instar nymphs orally infected as larvae did not individually transmit QYB virus to suckling mice; however they successfully transmitted the virus when feeding in groups of 11-20 per mouse. Three out of fourteen of the orally-infected male and female ticks individually transmitted QYB virus orally to suckling mice. Organ titrations of ticks orally exposed to QYB virus demonstrated virus primarily in midgut tissues; dissemination to other organ systems was discovered in only 1 tick after 142 days extrinsic incubation. Vertical transmission of virus from infected female ticks to progeny was not demonstrated. Four of the 39 ticks in our colony were infected with a spirochete; presumably, Borrelia crocidurae. O. (P.) erraticus apparently satisfies the conditions that would implicate this species as a biological vector of QYB virus and is the only known arthropod from which this virus has been isolated in nature.