Enema infusion technique inappropriate for evaluating viral competence of ticks.

To determine whether anal infusion of virus simulates the natural route of infection rather than intracoelomic injection, we compared the course of Venezuelan equine encephalitis (VEE) virus infection in Amblyomma cajennense (F.) ticks that had been exposed to virus by enema infusion with that in ticks fed on a viremic host or exposed by intracoelomic inoculation. Although virus was detected in virtually all ticks 14 d after exposure, orally exposed ticks contained significantly less virus (10(1.9) plaque-forming units [PFU] per tick) than did ticks infected by enema (10(4.1) PFU per tick) or intracoelomically (10(4.2) PFU per tick). At 42 d after virus exposure, only 1% of 512 orally exposed ticks contained virus, but most enema (77%, n = 43) or intracoelomically (79%, n = 29) exposed ticks were infected. Replication of VEE virus in A. cajennense ticks exposed to virus by enema infusion, therefore, appeared more similar to that of ticks inoculated intracoelomically than to those exposed orally. Thus, because enema infusion may bypass potential midgut infection and escape barriers, this procedure may not be appropriate for determining vector competence in ixodid ticks.