Plasmodium pitheci malaria in Bornean orang-utans at a rehabilitation centre in West Kalimantan, Indonesia

Abstract

Background Plasmodial species naturally infecting orang-utans, Plasmodium pitheci and Plasmodium silvaticum, have been rarely described and reportedly cause relatively benign infections. Orang-utans at Rescue Rehabilitation Centres (RRC) across the orang-utan natural range suffer from malaria illness. However, the species involved and clinical pathology of this illness have not been described in a systematic manner. The objective of the present study was to identify the Plasmodium species infecting orang-utans under our care, define the frequency and character of malaria illness among the infected, and establish criteria for successful diagnosis and treatment. Methods During the period 2017–2021, prospective active surveillance of malaria among 131 orang-utans resident in a forested RRC in West Kalimantan (Indonesia) was conducted. A total of 1783 blood samples were analysed by microscopy and 219 by nucleic acid based (PCR) diagnostic testing. Medical records of inpatient orang-utans at the centre from 2010 to 2016 were also retrospectively analysed for instances of symptomatic malaria. Results Active surveillance revealed 89 of 131 orang-utans were positive for malaria at least once between 2017 and 2021 (period prevalence = 68%). During that period, 14 cases (affecting 13 orang-utans) developed clinical malaria (0.027 attacks/orang-utan-year). Three other cases were found to have occurred from 2010–2016. Sick individuals presented predominantly with fever, anaemia, thrombocytopenia, and leukopenia. All had parasitaemias in excess of 4000/μL and as high as 105,000/μL, with severity of illness correlating with parasitaemia. Illness and parasitaemia quickly resolved following administration of artemisinin-combined therapies. High levels of parasitaemia also sometimes occurred in asymptomatic cases, in which case, parasitaemia cleared spontaneously. Conclusions This study demonstrated that P. pitheci very often infected orang-utans at this RRC. In about 14% of infected orang-utans, malaria illness occurred and ranged from moderate to severe in nature. The successful clinical management of acute pitheci malaria is described. Concerns are raised about this infection potentially posing a threat to this endangered species in the wild.

Naturally acquired immunity to Plasmodium pitheci in Bornean orangutans (Pongo pygmaeus)

“…One of the illnesses diagnosed at this centre is malaria, as reported by Sánchez et al . ( 2022 ). In this publication, a malaria illness definition has been developed as follows: asymptomatic malaria; clinical (symptomatic) malaria (acute uncomplicated, chronic uncomplicated or mild malaria) and severe malaria (Sánchez et al ., 2022 ).…”

“…One of the illnesses diagnosed at this centre is malaria, as reported by Sánchez et al (2022). In this publication, a malaria illness definition has been developed as follows: asymptomatic malaria; clinical (symptomatic) malaria (acute uncomplicated, chronic uncomplicated or mild malaria) and severe malaria (Sánchez et al, 2022). Most common clinical malaria symptoms described included: fever and/or lethargy or other general symptoms, accompanied by anaemia and/or thrombocytopaenia and/ or leucopaenia.…”

“…The prevalence of these infections is often quite high (Peters et al ., 1976 ; Liu et al ., 2010 , 2017 ; De Nys et al ., 2013 , 2014 , 2017 ; Wu et al ., 2018 ), but very few published studies document the health effects of malaria in these species (Steiper et al ., 2005 ; De Nys et al ., 2017 ). In the case of orangutans, malaria illness had been reported in rare individual cases (Reid et al ., 2006 ), but never studied in detail or at the population level until very recently (Sánchez et al ., 2022 ). Utilizing extensive health data longitudinally collected at a Rescue and Rehabilitation Centre (RRC) for orangutans in West Kalimantan, Indonesia, Sánchez et al ( 2022 ) described in detail clinical and parasitological features of endemic natural infection of orangutans caused by Plasmodium pitheci , 1 of the 2 species known to naturally infect orangutans.…”

“…In the case of orangutans, malaria illness had been reported in rare individual cases (Reid et al ., 2006 ), but never studied in detail or at the population level until very recently (Sánchez et al ., 2022 ). Utilizing extensive health data longitudinally collected at a Rescue and Rehabilitation Centre (RRC) for orangutans in West Kalimantan, Indonesia, Sánchez et al ( 2022 ) described in detail clinical and parasitological features of endemic natural infection of orangutans caused by Plasmodium pitheci , 1 of the 2 species known to naturally infect orangutans. Most of those infections (86%) were asymptomatic, but illness did occur in a minority of cases, sometimes serious and life threatening in character (Sánchez et al ., 2022 ).…”

“…Populations of orangutans living at RRCs within their natural habitats and range expose them to endemic transmission of plasmodia that naturally infect them, P. pitheci and Plasmodium silvaticum (Peters et al ., 1976 ; Wolfe et al ., 2002 ; Reid et al ., 2006 ; Sánchez et al ., 2022 ). These settings provide the means to safely, easily and ethically collect blood samples from wild orangutans under rehabilitation (Wolfe et al ., 2001 ; Leendertz et al ., 2006 ).…”