The Oral Delivery of Rabies Vaccines to Dogs

In most developing countries the dog remains the major transmission vector of rabies to man, despite the widespread use of parenteral vaccination. Parenteral vaccination does not, in general, achieve population immunity levels high enough to inhibit rabies transmission within the dog population. Following the demonstration that oral vaccination induced levels of population immunity sufficient to interrupt the epidemiological cycle of fox rabies in Europe, research has aimed at the development of this approach for dog rabies control. Oral vaccines are likely to be easier to administer and culturally better tolerated, and therefore well adapted to overcome the logistical problems hampering rabies control in developing countries. Among several proposed rabies vaccine candidates, the attenuated rabies vaccine strain SAG-2 has been shown to induce a protective immune response to rabies in dogs when delivered by bait. Oral live vaccines must meet high safety standards due to the risk associated with the dissemination of those replicating antigens in young and/or immunodepressed individuals. SAG-2 has confirmed its safety through the absence of clinical signs, dissemination and excretion in several carnivorous target and an important number of non-target species including non-human primates. Present field research, carried out using a placebo bait specifically designed for the oral delivery of SAG-2 to dogs, is aiming at confirming the hypothesis according to which oral vaccination, alone or as a possible adjunct to injectable rabies vaccines, might increase vaccine coverage by immunising poorly supervised dogs which are both often inaccessible to parenteral vaccination and a high-risk group for rabies transmission to man.