Measles — Peter Walsh

Fire Storm

There were some legitimate questions about the feasibility of vaccinating wild apes, particularly logistical issues like whether it would be possible to maintain vaccine cold chain in remote areas. There were also some misconceptions about what was being proposed. No, we wouldn’t need to immobilize the animals with all the risks that entailed. We could just remotely deliver the vaccine with a hypodermic dart. But any reasoned debate about these issues was drowned out by the tsunami of venom directed at proponents of vaccination, particularly me. I was astounded. I’d been primarily a “survey and monitoring guy” up to that point and had only passing contact with either the veterinary or ape habituation worlds. I didn’t realize how many hot button issues I’d pushed.

The next seven years were hell. I gave countless lectures and organized three international vaccination workshops. But no matter how much I pointed to the mountains of data showing how safe most vaccines are and how many millions of lives they’ve saved, some anti-vaxxers and animal rights advocates were convinced that an Ebola vaccine would either kill the gorillas outright or cause immunosuppression such that they became vulnerable to other pathogens (or, maybe, give them autism?). And, surely, we couldn’t be allowed to upset the natural balance in the Garden of Eden? It didn’t seem to matter that the region was already awash in human influence, from logging to illegal poaching. There was also no doubt that gorillas would be so freaked out by being vaccinated that they’d forever flee from any humans. Tourism programs that took decades to build would be destroyed. No matter that neither a 1968 measles vaccination campaign by the Mountain Gorilla Veterinary Project nor their occasional immobilization of individuals had any detectable effect on gorilla response to tourists. Even when I pointed out that these supposed risks must surely be outweighed by the imminent death of gorillas near the front of the advancing Ebola epizootic wave, the answer from park managers was still no. I was exaggerating the risk.

Dzanga Sangha

When that Ebola wave front actually did wipe out thousands or, even, tens of thousands of gorillas, it didn’t change everything. But it did change enough minds to convince the World Wildlife Fund to vaccinate gorillas at their Bai Hoku and Mongambe gorilla tourism sites in Dzanga Sangha National Park in Central African Republic. They didn’t have the inhouse veterinary expertise to do it themselves. And they were wary of new Ebola vaccines that hadn’t yet been tested in gorillas or chimps. But after a year and half of back and forth, we came to an agreement in which I would organize everything necessary to vaccinate gorillas in their tourism program with a measles vaccine that had been used extensively in zoo gorillas and several hundred million human children. I was lucky to get funding for the trial from the Wallace Global Fund and the Paul G. Allen Family Foundation.

I was even luckier to recruit two incredibly seasoned and talented collaborators. Angelique Todd had been working for WWF on the habituation program at Dzanga for more than a decade. She knew the gorillas like her own family. Chris Whittier had been the longest serving field vet for the Mountain Gorilla Veterinary Project in Rwanda. In addition to his DVM, he’d just completed an infectious disease PhD. The three of us sat down and designed a formal field trial to scientifically evaluate all the issues that had been raised by critics. We also convinced Kat Shutt to add a stress hormone analysis of the vaccinated gorillas to her PhD work. There was concern in certain quarters that a gorilla incensed by being darted would attack Chris or one of the trackers (attacking me was never mentioned). So, we recruited a second vet, Sonja Metzger, to provide veterinary and medical backup.

Darting

In April of 2011, we set off to Dzanga Sangha to dart two gorilla groups, led by silverbacks Makumba and Mayele. We agreed to a number of safety protocols to ensure the safety of the gorillas and the project staff. We spent a two week pre-vaccination period familiarizing Chris with the gorillas and the gorillas with Chris. Then we initially vaccinated one gorilla per day to allow any tension to dissipate. We stashed Sonja nearby with medical supplies and a sat phone and had a vehicle on call in case of an emergency. The trackers and I also carried long hardwood staffs to beat back any gorilla who might attack. Given that I was 50% bigger than any of the trackers, I was placed front and center with instructions from Chris to the effect that I should “look big and give the silverback a big whack in the head if he got too aggressive. Don’t be shy about it, either.” No kidding.

To minimize both the injury risk and the startle factor, Chris delivered the vaccine darts with a blow pipe rather than the traditional CO2 rifle. Talk about up close and personal. But the first gorilla Chris darted, a subadult named named Sousa, only scampered a few meters before pulling out the dart. He was back to feeding within a minute. The next day Sousa even circled around and watched from a few meters behind us when Chris darted the next gorilla. It went similarly with the rest of the family. The youngest gorillas typically scampered 5 or 10 meters after impact. The larger subadults and adult females tended to just sit up abruptly, pull the dart out, then return to their previous business.

We saved the silverback for last. We were holding our breath when Chris planted a dart squarely in Mayele’s huge latissimus dorsi muscle from about five meters. That ramped up to heart palpitations when Mayele stared directly Chris for an excruciating five seconds then another five at me holding my video camera a couple of steps to the left. But he seemed to be reacting more to the whoosh of the blow pipe than the impact of the dart. Because he then went back to feeding for a few moments. And it wasn’t until the dart bounced along on his back as he walked away that he reached up and pulled it out without slowing his stride. A tiny hypodermic dart is just not that big a deal to a gorilla that is bitten all day every day by wasps and biting flies, and, occasionally, by other gorillas.

Things went the same way with the Makumba group. In all Chris had 17 hits on 19 attempts. Take that, Steph Curry. Chris was also able to dart all the eligible gorillas but one, an adult female who just didn’t like people. And all that time only one gorilla vocalized, a soft hoot of surprise by a juvenile when the dart hit it’s back. A lot of the credit goes to Angelique, the lead field assistant Paolo, and the Bayaka trackers. Because their incredible skill put Chris in a position in which it was hard to miss. They were also absolutely fearless in putting themselves between the gorillas in case the gorillas became aggressive.

Luckily, none of the gorillas charged us or otherwise acted aggressively. None of the gorillas subsequently became more wary of people other, of course, than vets carrying blow pipes. And none of the vaccinated gorillas showed obvious lethargy, coughing, sneezing, wheezing, runny nose, or any other symptoms commonly associated with moderate to severe respiratory virus infection.

Immunogencity

The measles vaccine we used is a live attenuated virus that causes a mild, immunizing infection that typically lasts for one to two weeks. During this period vaccinated humans continue to shed small amounts of virus or viral fragments, whereas, individuals that did not experience an immunizing infection should clear the small amount of virus in the original vaccine dose within a few days. Thus, we planned to test whether darting had caused immunizing infections by using PCR methods to amplify RNA from non-invasively collected fecal samples. I spent several weeks bouncing back and forth between groups collecting gorilla poop only to find that we were unable to amplify any measles RNA from these feces, probably because they were chock full of vegetation that bound the RNA. What a bummer to realize that you’ve run yourself ragged in the Congo heat for nothing. Luckily, I did opportunistically grab some urine samples. And from these we were able to amplify measles RNA from vaccinated gorillas but not from controls. To my knowledge, this was the first use of non-invasive methods to verify vaccine immunogenicity in any wildlife species. Thanks to Kelly Warfield and Javad Amman at Integrated Biotherapeutics and Paul Duprex at Boston University for all the lab work.

Immunosuppression

To evaluate whether being vaccinated had an immunosuppressive effect on gorillas, Elevated levels of the stress hormone cortisol is a marker of immunosuppression and is often associated with moderate to severe viral infection. Therefore, we non-invasively monitored fecal metabolites of cortisol before, during, and for two weeks after vaccination. Cortisol levels did rise significantly in the first (Mayele) group. But this appeared to be a cumulative effect of the extended close contact with the darting team during the pre-darting period, as cortisol metabolite titers dropped off almost immediately post-vaccination. The second (Makumba) group had no pre-darting habituation period and a rapid, three day darting period. It’s members did not show a significant cortisol metabolite rise. These results imply that the attenuated measles vaccine did not cause a severe enough infection in gorillas to cause serious immunosuppression. In other words, the vaccine behaved in wild gorillas much as it behaves in captive gorillas and humans.

Vaccine Cold Chain

To maintain vaccine cold chain, we paid an exorbitant sum to have the vaccine shipped from the Serum Institute of India in a special insulated shipping container. Onsite, we then stored the vaccine in a 12 volt, solar powered, constant temperature refrigerator. Data loggers showed that the vaccine in the refrigerator only left optimal temperature range for a few hours during the trial. Each day we carried vaccine doses out in insulated pouches filled with frozen blue ice.

Scorecard

Issue 1. Vaccination did not cause gorillas to become aggressive or violent.

Issue 2. Vaccination did not make gorillas subsequently avoid people.

Issue 3. Vaccination with measles vaccine did not kill gorillas or cause obvious side effects.

Issue 4. Vaccination did not cause a sustained rise in stress hormone levels.

Issue 5. It is possible to maintain vaccine cold chain in the most remote corner of the poorest country in the world.

Issue 6. It is possible to non-invasively evaluate whether vaccination has caused an immunizing infection.

Issue 7. The sky will not fall if you vaccinate wild gorillas and chimpanzees.