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Disease and other health hazards pose serious threats to the persistence of wild ape populations.
The total chimpanzee population at Gombe National Park, Tanzania, has declined from an
estimated 120 to 150 individuals in the 1960's to around 100 individuals by the end of 2013, with
death associated with observable signs of disease as the leading cause of mortality. In 2004, we
began a non-invasive health-monitoring program in the two habituated communities in the park
(Kasekela and Mitumba) with the aim of understanding the prevalence of health issues in the
population, and identifying the presence and impacts of various pathogens. Here we present
prospectively collected data on clinical signs (observable changes in health) in the chimpanzees of
the Kasekela (n=81) and Mitumba (n=32) communities over an 8-year period (2005–2012). First,
we take a population approach and analyze prevalence of clinical signs in five different categories:
gastrointestinal system (diarrhea), body condition (estimated weight loss), respiratory system
(coughing, sneezing etc.), wounds/lameness, and dermatologic issues by year, month, and
community membership. Mean monthly prevalence of each clinical sign per community varied,
but typically affected <10% of observed individuals. Secondly, we analyze the presence of clinical
signs in these categories as they relate to individual demographic and social factors (age, sex, and
dominance rank) and simian immunodeficiency virus (SIVcpz) infection status. Adults have
higher odds of being observed with diarrhea, loss of body condition, and wounds or lameness
when compared to immatures, while males have a higher probability of being observed with
wounds or lameness than females. In contrast, signs of respiratory illness appear not to be related
to chimpanzee-specific factors and skin abnormalities are very rare. For a subset of known-rank
individuals, dominance rank predicts the probability of wounding/lameness in adult males, but
does not predict any adverse clinical signs in adult females. Instead, adult females with SIVcpz
infection are more likely to be observed with diarrhea, a finding that warrants further investigation.
Comparable data are needed from other sites to determine whether the prevalence of clinical signs
we observe are relatively high or low, as well as to more fully understand the factors influencing
health of wild apes at both the population and individual level. |
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