On the sixth day of the respiratory outbreak it was my turn to visit Susa Group. The coughs from the sick silverbacks reverberated through the forest. Kurira had barely moved his family from where they'd foraged the day before. Juveniles and infants played — again, as if nothing were wrong.
Kurira, the leader among the five Susa Group silverbacks, all of which
became sick with a cough and lethargy during the most recent outbreak.
On the sixth day of the respiratory outbreak it was my turn to visit Susa Group. The coughs from the sick silverbacks reverberated through the forest. Kurira had barely moved his family from where they'd foraged the day before. Juveniles and infants played — again, as if nothing were wrong.
My optimism didn't last long. I heard a gorilla cough softly and knew the sound didn't come from a male. It was Poppy, the oldest female in the group. She had watery eyes and a runny nose. At least she was eating. The trackers confirmed they'd heard her cough the day before. Two of her offspring climbed trees nearby, behaving normally. Minutes later, we found another new case, Izuru, also a female. In order to nurse, her apparently healthy 2.5-year-old had to hang on tightly as his mother's body shuddered with each cough.
Susa Group's oldest adult female, Poppy, lethargic and coughing but allowing her infant to nurse.
As expected, the animals' clinical signs were consistent with a viral-induced upper respiratory tract infection. In addition to watery eyes, runny noses, coughing and probably sore throats, I saw Poppy clasp her hands over her head, an indication of a headache or sinus congestion. The sick gorillas seemed lethargic and ate very little. The coughs were loud, but not from the lungs; the nasal discharge was clear to off-white but not green.
Based on past history, what we know about upper respiratory diseases in people and the recent studies in chimpanzees, the causative organism could be any number of viruses. The list includes respiratory syncytial virus, rhinovirus (the type that causes the common cold), flu or parainfluenza virus.
Air sacs extend under the neck and armpits in male mountain gorillas and can become infected.
I spent quite awhile aiming my binoculars at each of the males, examining the area under the neck and armpits. I remember a silverback from Pablo Group, Umurava, who died several months after the 2006 respiratory outbreak with a severe air sac infection and pneumonia — this after we thought he'd recovered completely.
In retrospect, I wonder if bacteria had been percolating in there for months, a secondary infection that settled in after the respiratory virus. I didn't see any sign of fluid-filled swellings in these areas, but it's probably too early in the outbreak for this complication to develop.
A head cold in a person rarely develops into a life-threatening bacterial infection. It can happen, of course, but most of us do not need antibiotics to survive a week of cough and congested sinuses. The medical history of the mountain gorillas shows that at least one individual per family group has either died or become severely ill, requiring treatment, during these bouts of cold-like respiratory illness. Chimpanzees are even more susceptible to life-threatening secondary bacterial infections as the Tai Forest paper showed.
Susa Group's Nyabantidore sick with respiratory illness.
We don't fully understand the reasons for these differences, but there are plenty of viruses that cause mild illness in one species and severe illness in another closely related one. Environmental factors such as weather and altitude may play a role. Our normal bacterial flora could be different enough to suppress or favor superinfections. I left the forest that day thinking about how much we have yet to learn about the health of the great apes — and ourselves. Maybe this outbreak would teach us something new.
Susa Group female Rwandarushya with her 6-month-old baby, still healthy.
Twelve days after the first reported case, I made another monitoring visit. The silverbacks were clearly improving, including the chief. Kurira ate bamboo shoots hungrily, having finally changed locations. Rwandarushya's 6-month-old baby cautiously crawled away from his mother. She pulled him right back. I tried not to think of this baby as a future patient. But the outbreak wasn't even half over.
Byishimo, one of the Susa twins, sick with a runny nose.
On this day, 18 of 39 gorillas were sick, including Byishimo, one of Nyabantidore's two 4-year-olds, the first mountain gorilla twins known to survive. Later, I replayed a short stretch of video I'd taken. The sound of multiple animals coughing made me uncomfortable, and a range of what-ifs ran through my head that night.
Though we understand a lot about respiratory illness in people, gorillas and chimpanzees, we have plenty of unanswered questions. We don't — and cannot — know precisely how far droplets of moisture-containing viruses travel after a cough or sneeze, or how long these tiny particles remain infectious. (The answers depend on the shape of the microbe, temperature, wind, humidity and the type of virus.) One thing is certain: by visiting wild animals who share susceptibility to human diseases, we introduce risk.
Many of Rwanda's younger habituated mountain gorillas frequently approach human visitors.
The risk of disease transmission is one of the main reasons there are rules in place for visiting gorillas. Unfortunately, they're not consistently observed or enforced. Some guides, researchers and tourists obey the visitation rules; others don't. We've just been through a series of workshops to restate and explain them — again. They're simple and easy to follow: only healthy people are to enter the forest with clean boots, rain gear and hands; everyone keeps the recommended distance from the animals, currently seven meters; if a visitor coughs unexpectedly, he or she should put on a mask and leave the group.
The gorillas don't know the rules, of course. In Rwanda, they've become so habituated to people that the seven-meter rule is difficult to maintain. The gorillas often walk right up to and past visitors, sometimes touching them. At MGVP, we believe the responsibility for following the rules falls on each individual person (certainly not on the gorillas!). We humans have created the risk in the first place, and we're equally capable of taking appropriate action to minimize it, like moving a step back.
View of heavily cultivated farmland near Parc National des Volcans, Rwanda.
Some scientists believe respiratory outbreaks naturally occur among free-living chimps and gorillas and that intervening to treat or confirm the diagnosis is not warranted. But when people are the primary reservoir for a virus that infects the great apes — and can kill them, as shown by the chimp researchers — I'm not sure we can call such infections natural. Humans live closer to the great apes than ever before. Our proximity to them, coupled with shrinking natural habitats, increases the risk.
When I meet eco-tourists on the trail, I introduce myself and the vet project. Most are pleased to know the gorillas have doctors, and they want to know more. Some say simply, "Thank you for doing your work," and ask how they can help. My answer: enjoy your visit and, if you have time, find us on the Web and make a donation. Just search mountain gorilla vet or gorilla doctors!
[Rwanda, 2008. Pictures: Dr. Lucy Spelman/MGVP]
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