Onrab® efficacy in skunks (mephitis mephitis) and raccoons (procyon lotor)

Abstract

ONRAB®, a recombinant human adenovirus type 5 vector expressing rabies glycoprotein, has been used under experimental permit in the Canadian provinces of Ontario, New Brunswick and Quebec for wildlife rabies oral vaccination programs. Prior to its use in the field, a series of trials were conducted in two terrestrial wildlife vectors to determine the rabies virus neutralizing antibody response to ONRAB®. Eighty-three % of skunks (10/12) and 75% of raccoons (8/12) seroconverted within 6 weeks after consumption of ONRAB® in an Ultralite bait (ULB) at a dose of 109.2 TCID50/ml in 1.8 mL. In the subsequent efficacy trial, all skunks (n=28) that consumed a single ONRAB®-ULB were protected from lethal rabies challenge, while 86% (12/14) of the unvaccinated controls succumbed to rabies. In addition, pre-existing neutralizing antibody to either canine adenovirus type 2 or human adenovirus type 5, achieved by intramuscular inoculation of skunks with the viruses 28 d prior to administration of ONRAB® per os at 108.4 TCID50/ml, had no effect on the antibody response to ONRAB®. These series of experiments demonstrated that ONRAB®-ULB shows promise over previous vaccine/bait combinations as it elicited a measurable immunological response in both skunks and raccoons, and provided protection against experimental lethal rabies virus exposure in skunks. Further, results of these studies suggest that its field performance is unlikely to be affected by pre-existing immunity to other adenoviruses.