Efficacy of SAG-2 oral rabies vaccine in two species of jackal ( Canis adustus and Canis mesomelas)

Abstract

Trials were carried out to test the efficacy of SAG-2 oral rabies vaccine in two species of jackals, namely the side-striped jackal ( C. adustus) and the black-backed jackal ( C. mesomelas). The first trial tested the efficacy of SAG-2 when given by direct oral administration at doses of 6.5 and 7.5 log 10 median tissue culture infectious doses (TCID 50). One side-striped jackal which had received the higher dose did not seroconvert and succumbed to challenge, while all other jackals seroconverted and resisted a lethal challenge. The second trial tested the efficacy in side-striped jackals only of the SAG-2 vaccine when given within chicken head baits. A volume of 1.8 ml of vaccine fluid with titers of 7.0 or 8.0 log 10 TCID 50/ml were placed into blisters which were stapled under the skin of the chicken heads. All jackals (5/5) which received 8.0 log 10 TCID 50/ml and 3 of 5 which received 7.0 log 10 TCID 50/ml seroconverted and resisted lethal challenge. A third trial tested the rate of vaccine virus titer loss in chicken head baits placed under field conditions. Titer loss was marked in baits which were not protected from direct sunshine, whereas under vegetation cover approximately 1 log 10 TCID 50/ml was lost every 3 days. Hence, it was concluded that a bait vaccine virus titer of 8.0 log 10 TCID 50/ml will be sufficient to immunize wild jackal populations if enough baits can be consumed by jackals within 3 days. This conclusion needs to be tested through the use of oral vaccine in field trials.