Animal testing law halts Ebola vax trial

In what may be the last US biomedical research trial on captive chimpanzees, food laced with a new vaccine has been shown to be an effective way to protect chimpanzees from the Ebola virus, a new study reports.

Estimates suggest that as many as one-third of Africa’s wild great apes have been wiped out by Ebola in the past 30 years. With the aim of protecting the remaining populations, a team of scientists in the US and UK have concluded safety trials of a vaccine made from a modified rabies treatment. Their findings were published in Scientific Reports.

“It’s in our vested interest as human beings to make sure Ebola is controlled in the primate population, and of course, that benefits the poor primates because a lot of these Ebola outbreaks wipe out whole populations,” says Sanjaya Senanayake, an Australian National University medicine and infectious diseases specialist who was not involved in the study, says.

Led by University of Cambridge’s Peter Walsh, the scientists monitored the immune response of 10 chimps given the oral vaccine. The apes were resident at the University of Louisiana Lafayette’s New Iberia Research Centre.

But the work was cut short after 28 days when a new version of the federal Endangered Species Act came into force, banning research on chimpanzees.

“I definitely understand why people would think it’s cruel to have animals in captivity, but this article is all about improving animal health,” Senanayake says.

The Ebola vaccine, called Filorab1, had already been  tested in a previous study, but only in injectable form and wild animals aren’t easy to inject. To do so requires shooting them with darts – a laborious method not suited to animals which fear humans, or live in the thick understory of a forest.

Oral vaccinations, on the other hand, have already proven effective, eradicating rabies in foxes in continental Europe. The idea is that edible baits would be placed in wild ape territories, vaccinating the chimps on a large scale and over a long time frame.

Walsh’s team set out to conduct a final clinical trial to ensure the vaccine produced no serious side effects, an essential step before any large-scale roll-out. And while in theory the new law allows biomedical research on captive chimps when it benefits wildlife conservation, the reality is somewhat different.

“In practice, all of the biomedical facilities that held chimpanzees have or are in the process of ‘retiring’ their populations to sanctuaries: sanctuaries which are philosophically opposed to invasive biomedical research,” they write.

Zoos, they add, are highly unlikely to permit safe, non-invasive research on apes, for fear of a public backlash.

They note, “This really may be the final vaccine trial on captive chimpanzees: a serious setback for efforts to protect our closest relatives from the pathogens that push them ever closer to extinction in the wild.”

But how does this Ebola vaccine work?

The team inserted a weakened version of rabies, containing a similarly weakened Ebola virus, into the chimps, priming the immune system to create antibodies – proteins designed to counteract specific pathogens – for both diseases.

In the captive chimps side effects were minimal, and included “relatively mild” stress and slight weight loss while the vaccine took effect.

“If you’ve got good immune responses after 28 days and you haven’t seen any major side effects, it probably would be a reasonable vaccine to release into the wild,” Senanayake says.

But he adds that 10 chimps may not be a large enough sample size. The study authors also acknowledge this, as well the need to test the vaccine in chimps exposed to higher tropical temperatures.

However, the current global move away from biomedical testing on chimps is likely to prevent further trials.

The scientists also only used the Zaire strain of the Ebola virus, which is very different from the Sudan strain that also circulates in Africa, comments University of Queensland virologist Dr Yin Xiang Setoh. “These two strains are very different, one vaccine can’t protect the chimps from the other,” he says.