An assessment of ONRAB® oral rabies vaccine persistence in free-ranging mammal populations in Ontario, Canada

• ONRAB is a recombinant human adenovirus vaccine developed to control sylvatic rabies.
• The safety and effectiveness of ONRAB requires further investigation prior to widespread use.
• We studied persistence and shedding of ONRAB in wild mammals with quantitative PCR.
• No samples contained amounts of ONRAB DNA that exceeded the quantification limit.
• Our results suggest a short replication period of ONRAB and a low risk of spread.

ONRAB® is a rabies glycoprotein recombinant human adenovirus type 5 oral vaccine developed for application in baits to control rabies in wildlife populations. Prior to widespread use of ONRAB®, both the safety and effectiveness of this vaccine required investigation. While previous research has focused on field performance and the persistence and pathogenicity of ONRAB® in captive animals, we sought to examine persistence and shedding of ONRAB® in populations of free-ranging target and non-target mammals. We collected oral and rectal swab samples from 84 red foxes, 169 striped skunks, and 116 raccoons during 2007 and 2008 in areas where ONRAB® vaccine baits were distributed. We also analyzed 930 tissue samples, 135 oral swab and 138 rectal swab samples from 155 non-target small mammals from 10 species captured during 2008 at sites treated with high densities of ONRAB® vaccine baits. Samples were screened for the presence and quantity of ONRAB® DNA using quantitative real-time PCR. None of the samples that we analyzed from target and non-target species contained quantities of ONRAB® greater than 103EU/mL of ONRAB® DNA which is a limit that has previously been applied to assess viral shedding. This study builds on similar research and suggests that replication of ONRAB® in animals is short-lived and the likelihood of horizontal transmission to other organisms is low.