ApesInc Tests Oral Ebola Vaccine on Chimpanzees
Transfixed by the Ebola deaths of more than 10,000 people in West Africa, the world is largely oblivious to the fact that Ebola is a much larger threat to our endangered cousins, gorillas and chimpanzees. Although vaccines developed for human use would likely protect gorillas and chimps from Ebola, delivering an injectable vaccine to large numbers of wild apes is not feasible. Apes Incorporated is now leading the first-ever chimpanzee trials on an oral Ebola vaccine that could be used to protect entire populations of wild apes.
The trial tests a vaccine combining a snippet of the Ebola coat protein (glycoprotein) with an attenuated form of rabies virus. Chimpanzees will not be challenged with Ebola during the trial. Rather, the trial will establish whether oral delivery of the vaccine is safe and produces a robust immune response similar to that seen in monkeys who were injected with the vaccine then survived Ebola challenge in previous trials by the vaccine’s developer, Professor Matthias Schnell of Thomas Jefferson University. Six chimpanzees at the University of Louisiana Lafayette’s New Iberia Research Center (NIRC) have already been vaccinated orally, with four additional chimps vaccinated through intramuscular injection. Results from the trial are expected in October.
Filoviruses such as Ebola were first recognized as a threat to wild apes in 1994, when a veterinary student conducting a chimpanzee necropsy nearly died when infected with what is now referred to as Ivory Coast virus. Large die-offs of chimpanzees and, particularly, gorillas from Ebola virus (previously Ebola Zaire) then followed in Central Africa during the late 1990’s and 2000’s. Survey data suggest these outbreaks killed about one third of the world gorilla population, leading the International Union for the Conservation of Nature to upgrade the western gorilla species to Critically Endangered on its Red List of Threatened Species. More recently, human filovirus outbreaks have occurred within tens of kilometers of important chimpanzee populations in Guinea and Uganda and the largest remaining population of bonobos in Democratic Republic of Congo. Unfortunately, wildlife management capacity in most of the affected areas is so low that we have no data on wild ape population impact.
The current trial is part of an ongoing Apes Incorporated vaccine program which has included the trial of an injectable Ebola vaccine on chimps at NIRC, a darted measles vaccine trial on wild gorillas in Central African Republic, development of non-invasive methods for assaying vaccine safety and immunogenicity, and field testing of oral baits. “Should oral delivery prove safe and immunogenic in these captive chimps, the next step will be to orally vaccinate wild gorillas at the Ngaga site in Republic of Congo”, said Ape Incorporated President Peter Walsh, also a Lecturer at the University of Cambridge. “This will be the first oral vaccine trial on any wild primate.” Walsh added that the long term objective is not just to protect against Ebola but to develop oral vaccination and non-invasive safety and immunogenicity diagnostics as cost-effective tools for protecting against the many other diseases that increasingly threaten the survival of apes and other wildlife.
The distribution of vaccine-laced oral baits has virtually eradicated fox rabies from Western Europe. However, the wildlife conservation community has been slow to embrace oral vaccination because of safety concerns. A very small amount of orally delivered vaccine passes across the mucosal barrier into the blood stream. Therefore, oral vaccines typically use live viruses that replicate within the host to invoke a robust immune response. The fear that viral replication would produce pathogenic effects has blocked the use of oral vaccination in wildlife.
Schnell’s “filorab1” vaccine was chosen for the chimpanzee trial precisely because of the high safety level of the rabies vaccine on which it is based. The rabies vaccine has been serially passaged and genetically engineered to reduce virulence, tested extensively on captive animals, then distributed in millions of baits across Europe: all with an excellent safety record. “I developed the live attenuated form of the filorab1 vaccine specifically with wild apes in mind”, said Schnell. “The parent rabies vaccine’s outstanding performance in Europe gives us strong reason to believe that the offspring filorab1 vaccine will be equally safe and effective in Africa.”
Not only is Schnell supplying vaccine and diagnostic tests for the chimpanzee trial, NIRC has donated all the animal housing, personnel, and analysis costs for conducting the trial. “This kind of applied research falls in a funding dead zone,” said Walsh. “Basic research funders such as NIH or NSF see it at as too applied while conservation donors see it as not applied enough. We operate on a shoestring, relying on the generosity of people like Matthias and NIRC to get things done.”