Gorilla Doctors

Category: Field Procedures, Orphaned Mountain Gorillas, Routine Health Checks | Date: Aug 03 2008 | By: Dr. Lucy for gorilladoctors

For the past two months, we’ve been working out ways to collect and store saliva from gorillas. In the future, we plan to test these samples for diseases, especially the viruses that cause respiratory illness. This study has been a good idea in our heads for some time. Thanks to veterinary student Tierra Wilson, it’s finally underway. Tierra not only designed the research project, she found her own funding to come to Rwanda and run it! Wild celery is often fed to the orphaned Grauer’s gorillas. We’re always looking for new ideas for screening the gorillas for various pathogens, such as herpes virus or influenza.

One of the orphaned Grauer’s gorillas eats wild celery, a favorite food.

The outbreak of respiratory disease in the Susa group, for example, reminded all of us how difficult it is to diagnose a problem without intervening. Yet when gorillas cough, they must, like humans, be swallowing some of the phlegm that builds up in their nasal and airway passages—and a recent study in chimpanzees showed that respiratory viruses could indeed be found in fecal material. That made us wonder if we can find the pathogens in saliva. Tierra’s research project is the first step.

Tierra Wilson, a third year veterinary student at Tufts University in Boston, MA, USA.

We agreed on a basic approach: the field vets would follow the gorillas, collect unfinished bits of chewed-on plant material, and bring it back to the lab for Tierra to test for saliva. If she found any, she’d store the samples for future testing. Tierra also proposed an alternative, more direct method of sample collection: straight from the gorilla’s throat. She’d researched various ways of testing for saliva, including the use of a special colorimetric test kit for the enzyme alpha amylase. She hoped to try the test on saliva samples collected from anesthetized gorillas to verify that it worked.

MGVP vets perform an annual health exam on one of the orphaned gorillas, from left, project director Dr. Mike Cranfield, Dr. Jean Felix Kinani, soon to be Dr. Tierra Wilson, and Dr. Magdalena Braum.

Before she came to Rwanda, Tierra had asked for help from vets at Zoo New England who were preparing to do some exams on their lowland gorillas. The zoo staff agreed to collect saliva, using special absorbent sponges developed to collect saliva from humans. Unfortunately, these swabs yielded very little saliva. They tested positive with the color kit, but there was no sample left to store. We repeated this part of the study here on the orphaned gorillas at Kinigi when it was time for their annual exams. The results were the same. The conclusion: there’s not a whole lot of saliva in the mouth of an anesthetized gorilla.

Tierra tested saliva collected from various methods for the enzyme, amylase; a yellow color indicated a positive result.

Tierra’s findings make sense. Since the salivary glands are stimulated by the presence of food and the act of chewing, it’s no surprise that anesthetized gorillas don’t produce saliva. As noted above, our original plan had been to follow the gorillas while they foraged and to pick up discarded mouthfuls of plant material–but we didn’t want to go forward until Tierra could establish the gold-standard test for the presence of saliva. Ideally, we’d be able to store extra samples for future testing for viruses as well as stress hormones and gorilla DNA.

Saliva samples from gorillas stored on special filter paper that preserves genetic material.

Fortunately, our star student researcher had designed her study to explore all possibilities. She’d brought some novel supplies with her that at first puzzled the rest of us. In a scientific paper describing saliva collection in chimpanzees, she’d read that chimps often chew their food into big wads and then spit out the residue, creating a perfect saliva-packed sample that can be retrieved and taken to a lab. A few minutes in a centrifuge, and the wad breaks down into food and saliva. Tierra came up with the idea of a saliva-harvesting chew toy for gorillas. She asked if we could try it out on the orphans.

The orphaned gorillas chewed on the mesh bags for five to ten minutes, long enough to soak the rope inside with saliva.

We were a bit sceptical, especially because gorillas tend to destroy their toys. Tierra tried out two versions of the saliva-chew toy. Each used thick (0.5 inch) dental rope soaked in juice. One was a plastic container with holes drilled in the lid. Tierra plugged these holes with several short bits of rope, but the gorillas promptly pulled them out. The other, a mesh bag large enough to contain a longer piece of juice-soaked rope, worked beautifully. The gorillas put the bags in their mouths and chewed on the rope, trying to extract every bit of juice. When Tierra later centrifuged the chewed-on rope, she recovered lots of amylase-positive fluid.

Tierra harvested saliva samples by swabbing the bite marks made by the gorillas as they chewed on the celery.

Next, I collected a few samples from wild gorillas as a test, picking bits of chewed-on celery and bamboo from the ground, and putting them in a vial. We were ecstatic when Tierra tested these for amylase and they came up positive! While she continued to work out the best method for harvesting the saliva from the plant material, we all began collecting more samples. In the end, Tierra’s recovery method proved to be fairly low-tech: she’d rub a Q-tip in the tooth marks, then use a tiny amount of a storage reagent to save the sample in a plastic vial or on a piece of special filter paper.

Tierra also worked in the field, collecting samples of celery and other plants eaten by mountain gorillas.

Once we knew the saliva collection and storage methods were working, we requested permission from the park authorities for Tierra to visit a several gorilla families in order to collect her own samples. She not only collected bits of discarded plant material with care and precision, she had a chance to watch her study subjects chewing—and producing saliva—at firsthand. After comparing different species of plants, she concluded that wild celery works best for harvesting saliva. Now that’s not something we would have predicted, even though it’s the most common plant species eaten by the mountain gorillas.

The silverback Muninya required veterinary treatment for severe respiratory disease during the Hirwa Group respiratory outbreak, July 2008.

Before long, Tierra’s saliva study took on added significance when both the Hirwa and Group 13 gorilla groups came down with respiratory disease. We continued collecting food samples, this time storing saliva from coughing gorillas. Since these two gorilla groups often interact, we think the same virus or bacteria may have affected both. One group became much sicker than the other, however. When Muninya, the Hirwa group silverback, suddenly fell very ill, the vet team went on high alert.

Elisabeth Nyirakaragire, ORTPN vet tech, monitors the anesthetized Muninya, the silverback of Rwanda’s Hirwa group.

The Hirwa family consists of females, babies, and only one male, the silverback. If the chief is incapacitated for any reason, the family, particularly the infants, are at high risk when the group encounters another male. When Muninya failed to leave his nest and his family wandered away, we decided to intervene. Magda anesthetized Muninya with the help of Jean Felix and Elisabeth, who treated him with antibiotics and collected a full set of samples, including saliva. Fortunately, he improved dramatically the next day and continues to recover, though the rest of his family continues to cough. We hope the combination of samples will one day shed light on the diagnosis. The next step is to secure the permits needed to ship them out for analysis.

Wild celery is not only one of the gorilla’s favorite foods,  it helps captures their saliva.  

Meanwhile, Tierra completed her stay in Rwanda. She emailed me from an airport on her way back home to thank everyone again—and to make certain I had her final list of samples, formatted exactly as needed for the shipping permits. Next she’ll pursue all options for testing the stored saliva samples for the presence of various viruses, cortisol, and gorilla DNA. I know she’d like to analyze them before school starts, but that’s not likely given the permitting process.

Before she left, we took Tierra out for dinner at a local restaurant. I asked her what she’d remember most about us. Her answer: celery… and the gorillas, of course!

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