Read the Spanish translation: Pián, ¿Una Zoonosis Emergente en Gorilas?
Yaws (Treponema pallidum spp. pertenue), a neglected tropical disease of humans, may be present in several populations of western lowland gorillas (Gorilla gorilla gorilla) in the Republic of Congo and Gabon. Yaws causes severe skin and skeletal deformities in humans, which can limit mobility. Gorillas with gross lesions that are similar to human yaws cases were observed in Odzala-Kokoua National Park in the Republic of Congo, where the syndrome appeared to limit reproductive success of adult male gorillas.1
Evidence for existence of treponemal diseases in nonhuman primates, particularly gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes troglodytes), has mostly been based on skeletal pathology2; however, Karesh (2000) tested four western lowland gorillas in the Odzala-Kokoua National Park which were positive for treponemal antibodies3. Treponemal diseases are morphologically identical and all four diseases (yaws, bejel, pinta, syphilis) induce seroreactivity on standard serologic tests for syphilis; thus, differentiating the causative organism based on serology alone is problematic. A treponemal isolate from a wild baboon (species not identified) was found to be closely related to human yaws.4 Experimental infections of humans with this isolate caused active infections, leading to concerns that primates may serve as reservoirs for zoonotic treponemal pathogens; studies should be completed to rule out the bushmeat trade as a potential source of transmission.5 A second study found that the simian strain from the wild baboon was indistinguishable phylogenetically from human yaws.6 Additional molecular studies are needed to differentiate cross-species transmission in great apes versus coevolution of the pathogen.
A pilot surveillance program was carried out in Langoue Bai, Ivindo National Park, Gabon, showing a prevalence rate of 50% of the 18 adult gorillas fitting the case definition for a yaws-like syndrome. A case definition of yaws in humans is a person who lives in an endemic area and presents with one or more of the following signs: ulcer with scab, papillomas, and palmar/plantar hyperkeratosis.7 Gabon, and other west and central African countries are endemic for yaws.8 Other tropical skin diseases such as Buruli ulcer may have similar lesions. Dermatopathy of some kind was visible on 16/18 adult gorillas. No lesions were visible in the juvenile and infant populations (n=10). Despite the fact that an effective cure is available for treponemal diseases, the geography of the Langoue Bai would make intervention difficult if the etiology of the disease is indeed a treponemal organism. Reinfection would be very likely even if intervention were attempted. In addition to collecting pilot data, this study involved capacity building by training Gabonese field workers in collecting data to monitor gorilla health.
The authors thank the Wildlife Conservation Society’s administrative and field staff at the Parc d’Ivindo for their expert assistance, especially Ruth Starkey. We also thank the Gabon National Park Office and the Ministry of Water and Forests for permission to do the study.
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