Antibody response to Raboral VR-G® oral rabies vaccine in captive and free-ranging black-backed jackals (Canis mesomelas)

Abstract

Rabies is a zoonotic disease that remains endemic in large parts of southern Africa because of its persistence in wildlife and domestic dog vectors. The black-backed jackals (Canis mesomelas) is primarily the wildlife vector responsible for rabies outbreaks in northern parts of South Africa. Two trials were carried out to investigate antibody responses to the oral rabies vaccine Raboral V-RG® in black-backed jackals under captive and free-ranging conditions. In captive jackals 10/12 (83%; 95% confidence interval [CI]: 52% - 98%), seroconverted after single oral vaccination. Nine captive jackals had protective antibody titres ( 0.5 IU/mL) at 4 weeks (median: 2.1 IU/mL; inter quartile range [IQR]: 0.6-5.7) and 10 jackals had at 12 weeks (median: 3.5 IU/mL; IQR: 1.5-8.3) and three maintained antibody titres for up to 48 weeks (median: 3.4 IU/mL; IQR: 2.0-6.3). Four sites were baited with Raboral V-RG® vaccine for wild jackals, using fishmeal polymer and chicken heads. Baits were distributed by hand or from vehicle at three sites in north-eastern South Africa, with an average baiting density of 4.4 baits/km2 and at one site in central South Africa, at 0.12 baits/km2. This resulted in protective antibody titres in 3/11 jackals (27%; 95% Cl: 6-61) trapped between 3 and 12 months after baiting in north-eastern South Africa, compared with 4/7 jackals (57%; 95% Cl: 18-90) trapped after 3-18 months in central South Africa. This study shows the potential utility of oral rabies vaccination for the control of wildlife-associated rabies in north-eastern and central South Africa, but extensive studies with wider distribution of bait are needed to assess its potential impact on rabies control in wild jackals.

Keywords: Canis mesomelas; South Africa; black-backed jackal; oral bait; rabies; vaccination.

FIGURE 1

Map showing: (a) the seven capture sites at the John Nash and Malapa Reserve, Cradle Nature Reserve and the Lion and Safari Park in Gauteng and North West province (red triangle) and (b) the five baiting and capture sites at the Golden Gate National Park, Free State province (purple triangle), South Africa. Provincial and National Parks are shown in light green (the map was constructed using QGIS 3.4 using country boundaries and protected area boundaries downloaded and used with permission from protectedplanet.net and SANParks).

FIGURE 2

Rabies antibody titres in captive black-backed jackals (n = 12) given Raboral VR-G^® oral rabies vaccine. Red reference line = adequate antibody titre (0.5 IU/mL).

FIGURE 1-A1

Comparison of rabies antibody titres at 4, 12 and 24 weeks after administration of Raboral VR-G^® rabies vaccine in food versus orally in captive black-backed jackals. Red reference line = adequate antibody titre (0.5 IU/mL).