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In March 2014, West Africa became ground zero for the largest Ebola outbreak in history. Sierra Leone, Liberia and Guinea experienced thousands of cases of the haemorrhagic fever, with countries across the world recording similar cases of the often fatal virus. It is estimated that the outbreak claimed in excess of 11,000 lives.
Initial transmission of the virus occurs through contact with infected wildlife and then spreads from person to person. Now, a vaccine trial on a small number of captive apes in the United States shows promise in addressing the dangers of Ebola virus disease (EVD) within this vector.
The study, published in the journal Scientific Reports, used an oral Filorab1 vaccine on a group of ten captive chimpanzees at the University of Louisiana Lafayette in the US. The Filorab1 vaccine inserts the gene encoding the Ebola glycoprotein (GP) into a replication of a previously tested rabies (RABV) vaccine. This was due to the high safety and effectiveness of the parent rabies vaccine in previous oral trials. Six of the apes were given the drug combination orally and four intramuscularly.
In the past, human outbreaks of the Ebola virus have occurred through contact with infected apes. The transmission of the 2014 outbreak is suspected to have occurred through the consumption of tainted bushmeat - spreading from the fruit bat to the human population with devastating consequences. However, protecting wildlife that is susceptible to the virus could not only protect endangered primate populations, but could also help to control the spread from various animal vectors. In 2015, in the midst of the last outbreak, ecologist Ria Ghai wrote an article for the Jane Goodall Institute claiming that a third of the world’s chimpanzee and gorilla population had been killed by the virus since the 90s.
In chimps and gorillas, once infected with the disease, there is a 90-98 per cent chance they will die. In humans, this fatality rate differs between outbreak strands - ranging from 25 per cent to 90 per cent depending on the strain. The strain in 2014 had a fatality rate of 50 per cent - but before the spread of Ebola through the human population, the virus had already reached pandemic levels within the primate population of West Africa.
The lead researcher in the vaccine trial, Peter Walsh, from the University of Cambridge, considers the vaccination of apes to be a 'moral imperative'. In an interview with the BBC, Walsh describes the stark level of devastation Ebola causes on the great ape population in West Africa: "There are whole areas, hundreds of kilometres in every direction, that have just been wiped out of gorillas," he says.
The vaccine was first used on captive apes so as to test its safety before releasing it into a population of wild gorillas. The method of oral vaccination delivery was chosen in response to the challenges of traditional hypodermic dart methods of inoculation. The density of forests in which gorillas and chimpanzees live often make it difficult to track and treat them in the wild. The promise of non-invasive vaccinations is not only practical, but also means less stress for the animal. Stress can be known to trigger a strong immunosuppressant reaction, thus hindering the effectiveness of the drug post-inoculation.
Through the trial, Walsh concluded that: "Blood chemistry, hematologic, and body mass correlates of psychological stress suggested that, although sedation induced acute stress, experimental housing conditions did not induce traumatic levels of chronic stress."
While the control group of apes was relatively small and the long-term effects of the vaccine are yet to be seen, initial findings indicate a high level of immunogenicity for the Filorab1 vaccine.
Walsh noted a "lack of side-effects in captive chimpanzees [that bodes] well for its use to protect wild chimpanzees and gorillas endangered by EBOV," and that "Filorab1 produced immune responses comparable to those observed in the only previous EBOV vaccine trial on captive chimpanzees using a virus-like particle (VLP) vaccine."
However, the vaccine trials have caused ethical contention. Zoos are no longer willing to vaccinate captive gorillas in case of public backlash. Similarly, institutional change has brought about questions relating to the ethics of testing on captive apes. Walsh's vaccination trial was cut short when, in 2015, a ban on the use of chimpanzees in medical research was declared in the United States.
Furthermore, the Pan African Sanctuary Alliance also recently voted to oppose biomedical research on chimpanzees at its member institutions. Many biomedical facilities once harbouring chimpanzees are now transferring them to sanctuaries as a result.
Entitled, 'The Final (Oral Ebola) Vaccine Trial on Captive Chimpanzees?' the restrictions on biomedical research on captive apes could make this vaccine trial one of the last. As Walsh surmises, "The ban on chimpanzee research effectively precludes [further] trials as a part of our ape conservation program."
This article was originally published by WIRED UK
