Gorilla Doctors

Umoja after surgery to repair herniated intestines riding on his mother’s back, Kwitonda Group.

I’ll always remember the day Umoja looked at me, cried out, and then crawled swiftly toward his mother on two elbows and one knee. Five days after surgery, he no longer needed our help. Nothing in his behavior or appearance suggested that a second intervention with antibiotics would be necessary. My own feet felt light that day as I scrambled down the rocky path out of the forest—until I spoke to Elisabeth. She’d just received worrisome news from the trackers in Susa Group: four gorillas were coughing.

Chief silverback Kurira with nasal discharge and lethargy at the start of the Susa Group respiratory disease outbreak.

The next morning, Elisabeth and I spent two hours recording the first cases of upper respiratory tract disease in the 39-member Susa Group. One black back and four of five silverbacks, including the chief, Kurira, yawned, coughed, picked their noses, and generally looked uncomfortable. These big males barely moved while juveniles and sub adults played nearby. I carefully checked the youngest infants and their mothers. All appeared healthy for now. But it would be only a matter of time before the illness spread.

Susa Group silverback, Igisha, sick with respiratory disease.

Back at the office, I made a general plan with Magda, Jean Felix, and Elisabeth. We’d continue to keep an eye on Umoja, but we needed to shift our focus to Susa Group—and pace ourselves. These outbreaks take weeks to run their course, and each of us would be up and down the mountain repeatedly to check the group. I put routine health checks for the other groups on hold. One or two of us would monitor the Susa gorillas regularly and carefully document the spread of respiratory signs.

Healthy juvenile in Susa Group at the start of the respiratory disease outbreak.

We’d be looking for individuals hit hardest by the disease. Right now, since the sick gorillas were all older animals, we could probably visit every three days and check in with the trackers every afternoon. Once the younger gorillas began to show signs, we might need to visit daily. Unless this particular infection had circulated recently and the mothers had some immunity, all of the infants in the group could potentially become very sick.

Silverback Kurira in Susa Group sick with upper respiratory tract infection picking his nose.

I’ve experienced two respiratory disease outbreaks among Rwanda’s habituated mountain gorilla groups: Kwitonda Group in May 2007 and Pablo Group in November 2006. In each instance, most of the gorillas in the group came down with the illness, and at least one infant died. MGVP field vets have documented other outbreaks in the past. Magda has dealt with similar problems among habituated chimpanzee groups in Tanzania (where the mortality rates were much higher). Not only do we know what to expect here, we have a pretty good idea of where the disease comes from: us.

Wild chimpanzees eating figs in Nyungwe National Park, Rwanda where ecotourism is just beginning.

Respiratory disease in groups of chimpanzees habituated for research and tourism has recently been proved to be due to viruses of human origin. In a paper describing events in the Tai Forest, Ivory Coast, Africa (scientific paper; news story), scientists demonstrated unequivocally that chimps sickened and died from respiratory viruses introduced to them from people. The data also showed there were both local and foreign sources of these infections. When the disease originated outside of Africa, the clinical signs and death rates among the chimps were more severe.

Blackback Kiki in Susa Group coughing and lethargic, sick with signs of upper respiratory tract infection.

We have every reason to believe the same thing is true of mountain gorillas—that they can contract both local and foreign respiratory viruses from human visitors. But for clinical purposes, there’s a major difference between the two species: since many more chimps die during respiratory outbreaks than gorillas, they generate numerous samples for analysis. Our quandary with the gorillas is always whether and when to intervene for sample collection in the middle of an outbreak. Since intervention is stressful to the animals, we generally try to reserve it for the really sick gorilla that will most certainly die without treatment.

Healthy adult female, Igiti, in Susa Group before she became ill.

One of our goals is to collect data and samples whenever possible. At the same time, we know from past experience, including post-mortem exams on gorillas as well as chimps, that it’s not necessarily the virus itself that causes death but rather secondary bacterial invaders. These super infections create most of the life-threatening complications in gorillas, infecting their air sacs, airways, or lungs. We can treat these cases with antibiotics with excellent results if our timing and choice of antibiotic is correct.

Largely because of his age, Rwandarushya’s six-month-old-infant is at even greater risk of severe illness during the Susa Group respiratory outbreak.

But here again lies the difficult choice we face during such outbreaks. Bigger gorillas can be darted with antibiotics, bypassing anesthetic intervention (and thus sample collection). Babies can be treated only if we anesthetize the mother, so if we’ve already intervened in another case to collect samples, and thus disrupted the group, we may not have a chance to intervene again and save an infant. As a result, our strategy is to check, check, check—and when one individual appears very ill, to think through all the ramifications of intervening on its behalf. Susa Group has fifteen gorillas between the ages of three months and five years old. We knew we had our work cut out for us.

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This entry was posted on Sunday, May 25th, 2008 at 3:13 pm filed under Monitoring Visits and. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.