Trials to vaccinate wild apes due to start next month

Posted on March 26, 2011


Makumba a silverback gorilla

During the last two decades scientists say the Ebola virus has killed around one-third of the world’s gorillas and tens of thousands of chimpanzees. In the next decade they predict that the death toll may rise to half of the world’s gorilla population.

One American scientist from California wants to protect these endangered primates by vaccinating them against this deadly virus in the wild. Not only is this incredibly difficult but highly controversial. Vaccinating apes in their natural habitat has never been tested.

In the next few weeks Dr Peter Walsh will travel to the Central African Republic (CAR) where he embarks on the first phase of trying to achieve this goal. He plans to inoculate two habituated groups of gorillas in Dzanga Sangha National Park with a measles vaccine. This pilot will be a pre-cursor to his long-term plans.

Walsh, a quantitative ecologist who worked until recently at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told me: “Wild apes face two major disease threats, naturally occurring diseases and diseases introduced by us. The objective is to show the conservation community that the vaccine won’t kill chimpanzees or gorillas. Vaccination is scary both in international conservation circles and to many people in Africa.

“If we want apes to survive in Ebola-infected areas, vaccination is one of the few options available to protect them from dying out. It means that vaccinating one gorilla does not protect only that gorilla, it also protects gorillas further down the transmission chain. The Ebola virus, can have a 90 per cent mortality rate.”

Dr Peter Wlash with Bayaka trackers

According to the World Health Organization (WHO) Ebola haemorrhagic fever (EHF) is a viral disease and one of the most virulent known to humankind. It was first identified in the western equatorial province of Sudan and in a nearby region of Zaire (now Democratic Republic of the Congo) in 1976 after significant epidemics in Nzara, southern Sudan and Yambuku, northern Zaire. The virus can be transmitted by direct contact with the blood, body fluids and tissues of infected people and through handling sick or dead infected wild animals (chimpanzees, gorillas, monkeys, forest antelope, fruit bats).

Walsh added,”We have to carry out the measles trial first to see what’s the best way of administering a vaccine in the wild. We’ll be studying the gorillas in a non-evasive way, examining faecal samples, so looking for antibodies in their droppings and observing their behaviour after inoculation.

“The measles vaccine is safe, it’s been used millions of times on both human children as well as in captive apes and most primates for biomedical research in the United States. We don’t want to stress out the animals we’re testing, so we’ll use either a blowgun, which may be difficult in dense forest or a pistol.”

Walsh and his team will not be testing on infant gorillas under the age of two or on pregnant females. I was very surprised to learn that there is no regulatory authority that researchers need to seek permission from. It’s a matter for each country’s government to decide whether to grant access and allow this type of research to take place. Walsh told me he’s been speaking at great length to officials in CAR and they are satisfied that the measles pilot is safe.


America is the only developed nation that still houses and tests on chimpanzees for biomedical research. Opinion is polarised in the scientific community whether apes should still be experimented on. In Africa, Gabon also uses chimps for medical testing. There are currently several different Ebola vaccines being developed around the world.

 The vaccine that Walsh is planning to use is being developed by Integrated BioTherapeutics Incorporated, in Gaithersburg, Maryland, just outside of DC together with the US Army Medical Research Institute of Infectious Diseases  (USAMRIID). The company says it hopes to develop a product to also protect people against bio-chemical warfare. Walsh says the company is prepared to donate the vaccine for free for testing.

Electron microscopic image of Ebola VLP vaccine.

The controversial vaccine contains Ebola virus proteins. Walsh tells me it is not a live vaccine, it has virus-like particles which means it cannot copy itself or cause disease. It’s being tested at the New Iberia Research Center, a branch of the University of Louisiana, Lafayette. Researchers are not testing whether the vaccine works, which would mean injecting the animals with a “challenge” dose of the Ebola virus. Instead, they are assessing the safety of the vaccine and its ability to trigger an immune response. Researchers take blood samples from the animals but they also look for Ebola antibodies triggered by the vaccine in chimp stools. The same method Walsh and this team will carry out in CAR next month with the measles trial.

Walsh has been calling for the vaccination of wild apes for several years but has faced some opposition. He believes the benefits of testing on captive chimps far outweigh the costs in the long run. He said, “The Ebola vaccine has to be tested on lab chimps because no African country is going to allow you to trial it without knowing it’s definitely safe. If you want to prevent thousands of apes from dying, then you have to test it first. I don’t like having capitve animals, but this is the only way. If you can give me another solution then I’ll take it.”

There has been some success already, on 15 November 2007 a paper was published in the Journal of Infectious Diseases which showed that five monkeys had been protected against a lethal challenge dose of Ebola virus. But monkeys are not great apes, and testing on captive chimpanzees, Walsh says is a must. If the measles trial, which starts on April 8th, is a success, he could start vaccinating wild apes from Ebola as soon as the end of the year.