Gorilla Doctors

Category: Monitoring Visits | Date: May 28 2008 | By: Dr. Jan Ramer for gorilladoctors

Kurira, the leader among the five Susa Group silverbacks, all of which became sick with a cough and lethargy during the May 2008 outbreak.

On the sixth day of the 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 two-and-a-half-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.

The air sacs extend under the neck and armpits in male mountain gorillas and can become infected.

I spent quite a while 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 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 to 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 adult female and mother of twins, Nyabantidore, is 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.

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