Gastrointestinal parasites of wild Bornean orang-utans (Pongo pygmaeus) in a habitat affected by wildfire smoke

Wildfires are becoming increasingly frequent and severe in the tropical peatlands of Southern Borneo, with major consequences for both wildlife and people that inhabit them. Burning peat releases vast amounts of toxic smoke that, when inhaled, can cause a plethora of health-related issues. With some of the largest remaining populations of Bornean orang-utans (Pongo pygmaeus) being found in peatland forests, wildfires are becoming one of the greatest threats to this Critically Endangered ape, yet the effects of the toxic smoke on their health are unknown. Wildfire has long been known to influence wildlife disease by reducing populations of free-living parasites in the environment (thus altering host exposure), and there is a growing body of evidence to suggest that smoke may affect host susceptibility to such parasites by diminishing physiological condition and immune function. In this study, we investigated parasitic nematode infections in wild Bornean orang-utans inhabiting a drained peatland forest prone to fire and smoke. We identified four gastrointestinal nematode taxa that varied significantly in their prevalence and intensity. Overall prevalence of nematode infection was high, but intensity was relatively low. We present some evidence for an increase the prevalence and intensity of certain nematode taxa after the wildfire smoke event. Namely, an increase in the prevalence of Enterobius spp. and Trichuris spp., and an increase in the intensity of hookworm infections, after the smoke period. We identify the need for multi-year, multi-fire event research to increase sample sizes, along with measuring endocrinological markers of physiological condition, in tandem with parasitological monitoring, to gain a more comprehensive understanding of the impacts of environmental changes on orang-utan health.