Vaccine trial delivers rabies protection to nearly extinct Ethiopian wolves

Newly formulated baits containing the rabies vaccine Rabigen® SAG2Dog have been successfully field-tested on three endangered wolf packs (Canis simensis) in the Bale Mountains of southeastern Ethiopia. Recently published results of this trial in the journal Vaccine indicate that the baits will deliver sufficient protection from the rabies virus, providing this dwindling population of wolves with an additional defense against extinction. Rabies has been identified as a significant threat to the continued existence of this rare population of canids, and efforts to control the transmission to the wolves by vaccinating the local domestic dog population did not achieve the desired protection due to frequent incursions from unvaccinated dogs traveling into the wolves’ habitat.

During the vaccine trials, 21 wolves were trapped after consuming the bait vaccinations, with fourteen of these testing positive for the vaccine’s biomarker. Additionally, the levels of antibody in 12 of the 14 positives were high enough to proved protective immunity, and 7 of the positives had titres above 0.5 IU/mL. All of the vaccinated wolves, except one, were still alive 14 months after trapping and testing.

The wolves have been plagued by rabies in recent years, with outbreaks occurring in 1991, 2003, 2008 and 2014. Declines in their populations have left as few as 500 wolves alive in the wild, and local habitat loss, as well as increased exposure to disease, continues to threaten their survival. Settlers near the national park in the Bale Mountains, the wolves’ current habitat, have increasingly impinged on the park’s borders and expanded into the wolves’ territory, frequently bringing domestic dogs (and their diseases) into contact with the wolves.  Domestic dogs in nearby villages are often hunted and eaten by the wolves, and the dogs regularly accompany villagers who use the park to graze goats and sheep, bringing the two populations of canids into close contact with each other.

To control the virus in wolves, the Ethiopian Wolf Conservation Programme (EWCP) carried out domestic dog vaccination programs, which focused on immunizing the local dog populations on the periphery of the park. However, these efforts did not achieve a satisfactory transmission barrier due to the dynamic nature of the domestic dog populations in this area.  Researchers also embarked on a parenteral vaccination campaign, capturing and directly injecting the wolves, but found that these efforts were too expensive and time-consuming, not to mention stressful on the wolves. Conservationists then turned to an oral vaccine, only to find that the wolves did not like the liver-flavored bait that was already on the market. Scientists went on to reformulate the SAG2 vaccine so that it appealed specifically to the wolves’ taste buds—and found that wrapping the bait in goat meat garnered maximal appeal.

University of Oxford researcher Claudio Sillero-Zubiri headed the study in collaboration with various infectious disease control and wildlife conservation organizations; he and his research team have now shown that immunizing the Ethiopian wolves with baits may provide a pre-emptive and less-labor intensive way to manage and prevent rabies outbreaks in these packs of rare wolves. “We now have a safe vaccine, a suitable bait, an efficient delivery method, and trained monitoring teams in place—all crucial steps which open up the possibility for scaling up the oral vaccination and protecting the wolf populations at risk before the disease strikes again,” said Professor Sillero-Zubiri in an interview published in Science Daily.

Summarized by Laura Baker, GARC newsletter co-editor, from online reports in Science Daily, “First test of oral rabies vaccine brings hope to the world’s rarest canid” and from National Geographic, “Vaccines May Save Africa’s Rarest Wolves from Extinction”. The full paper “Feasibility and efficacy of oral rabies vaccine SAG2 in endangered Ethiopian wolves" is by Sillero-Zubiri et al., published in Vaccine, and a ProMed report is available here.