From August to December 1996 an outbreak of a debilitating skin disease occurred in mountain gorillas in Bwindi Impenetrable National Park in Uganda. All four members of one gorilla group habituated for tourism were clinically affected by the disease, with severity of clinical signs inversely related to age. An infant male gorilla was most severely affected and later died. A juvenile male showed serious manifestations of the disease but recovered following treatment. The two adult animals in the group (one female and one silverback) showed mild signs, with the female being more severely affected, and recovered following treatment. Sarcoptes scabiei mites were observed on skin scrapings and skin biopsies taken during an immobilization of the juvenile for diagnosis. All animals in the group were treated with ivermectin (Ivomec, Merck & Co., Rahway, NJ, USA), an anti-parasitic drug, with the exception of the infant who died before treatment could be administered.
The diagnosis of sarcoptic mange was confirmed in the infant with postmortem skin scrapings and skin biopsy. Treatment with a single 0.2 mg/kg IM dose of injectable ivermectin, administered to all surviving gorillas in this group, was successful, and no recurrence of clinical signs was observed within the next year. No other gorilla groups in the park were clinically affected. This is the first recorded incidence of sarcoptic mange in a free-ranging population of mountain gorillas. The source of the mange mite has not yet been confirmed, but we are concerned that it may be from contact with local people, tour groups and ranger guides because scabies is a common disease in human populations around Bwindi. If the source is found to be human, it will result in the need for serious attention to control measures to prevent re-infection of wild mountain gorillas.