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Like every organism, gorillas are threatened by pathogens
and parasites, some of them species specific, some shared by
other species. Paradoxically, populations that are hunted for
Bushmeat seem less prone to Ebola outbreaks, whereas ape
populations at the highest densities (and therefore the target
of conservation attention) are at greatest risk of an epidemic.
Dramatic declines in several ape populations are attributed to
outbreaks of ebola haemorrhagic fever, and efforts are under
way to develop a method of vaccinating ape populations at risk.
The close phylogenetic relationship between humans and
great apes creates exceptionally high potential for pathogen
exchange. This has resulted in disease emergence in humans
as an unintentional affect of the hunting and butchering of
the African great apes, responsible for human outbreaks of
Ebola and the global AIDS pandemic (Hahn
et al.,
2000; Le-
roy
et al.,
2004; Plantier
et al.
, 2009), as well as high rates of
mortality in wild chimpanzee (Pan troglodytes) populations
associated with anthropozoonotic transmission of human re-
spiratory viruses (Köndgen
et al.,
2008; Kaur
et al.,
2008). In
addition to such cases where pathogenic agents responsible
for epidemics could be confirmed, epidemics of a polio-like
etiology in chimpanzees (Goodall 1986) and measles-like eti-
ology in mountain gorillas (Ferber 2000) are also suspected
to have been of human origin.
Less visible than epidemics of acute disease, but equally impor-
tant as risk factors for ape conservation are chronic pathogens,
which can compromise host immune function and reduce re-
productive capacity. Proximity between wild apes and people has
been demonstrated to promote transmission of the common gas-
trointestinal bacterium Escherichia coli. Moreover, gorillas and
chimpanzees living in proximity to humans have been shown to
harbor E. coli resistant to multiple antibiotics used by people in
the region, indicating that microbes or their genes can ‘‘diffuse’’
from humans to great apes even in the best of conservation cir-
cumstances (Goldberg
et al.,
2007; Rwego
et al.,
2008). These
studies stress that direct contact between species is not neces-
sary for interspecific disease transmission. Indeed, most trans-
mission of gastrointestinal pathogens between people, livestock,
PATHOGENIC THREATS TO GORILLA
CONSERVATION
and wild apes is probably indirect and environmental. Pathogens
such as Cryptosporidium, Giardia, and enteric bacteria (i.e., Shi-
gella, Salmonella, E. coli, etc.) readily contaminate water and soil
and may persist in wet areas (Gillespie
et al.,
2008).
These demonstrations of various human pathogens negative-
ly impacting wild apes has sparked considerable debate con-
cerning the costs and benefits to surviving ape populations of
scientific research, ecotourism, and current conservation and
management paradigms (summarized in a special issue of the
American Journal of Primatology, Garber 2008). Despite the
disease-related risks, the consensus is that both research and
tourism have contributed in overwhelmingly positive ways to
the conservation of gorillas and other apes, enhancing their
long-term survival by increasing their scientific and economic
value, respectively. Nevertheless, such activities as well as over-
lap in great ape and human habitat may have unintended con-
sequences on the health and survival of wild ape populations.
In August 2009, more than 80 experts from 17 countries rep-
resenting field and laboratory researchers, wildlife veterinar-
ians, virologists, and conservation biologists came together in
Entebbe, Uganda for a Great Ape Health Workshop to develop
best practice guidelines for great ape health. Consensus was
that “minimum preventative standards” should be required for
all people entering great ape habitat, for tourism, research, or
any other reason. Since the majority of observed diseases in
great apes of possible or proven human origin are respiratory
diseases, the primary measures proposed were wearing masks
in proximity to apes, maintaining a minimum of 7 meters dis-
tance, a zero tolerance policy on visibly ill people visiting apes,
disinfection of hands and boots before visiting apes, and proof
of vaccination for all visitors. Further measures may be site
specific and more complex. Another important point discussed
was the importance of community health programs to lower
infection risks from outside protected areas and to provide ben-
efits for people living in proximity to great ape habitat. Guide-
lines evolved from this consensus process will be published
by IUCN within the best practices for ape conservation series
(Leendertz 2010).