Parasitology (Apr 2024)

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

  • Karmele Llano Sánchez,
  • John Kevin Baird,
  • Aileen Nielsen,
  • Andini Nurillah,
  • Fitria Agustina,
  • Komara,
  • Fina Fadilah,
  • Wendi Prameswari,
  • Raden Taufiq Purna Nugraha,
  • Sugiyono Saputra,
  • Arif Nurkanto,
  • Anik Budhi Dharmayanthi,
  • Rahadian Pratama,
  • Indra Exploitasia,
  • Alex D. Greenwood

DOI
https://doi.org/10.1017/S0031182024000155
Journal volume & issue
Vol. 151
pp. 380 – 389

Abstract

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Naturally acquired immunity to the different types of malaria in humans occurs in areas of endemic transmission and results in asymptomatic infection of peripheral blood. The current study examined the possibility of naturally acquired immunity in Bornean orangutans, Pongo pygmaeus, exposed to endemic Plasmodium pitheci malaria. A total of 2140 peripheral blood samples were collected between January 2017 and December 2022 from a cohort of 135 orangutans housed at a natural forested Rescue and Rehabilitation Centre in West Kalimantan, Indonesia. Each individual was observed for an average of 4.3 years during the study period. Blood samples were examined by microscopy and polymerase chain reaction for the presence of plasmodial parasites. Infection rates and parasitaemia levels were measured among age groups and all 20 documented clinical malaria cases were reviewed to estimate the incidence of illness and risk ratios among age groups. A case group of all 17 individuals that had experienced clinical malaria and a control group of 34 individuals having an event of >2000 parasites μL−1 blood but with no outward or clinical sign of illness were studied. Immature orangutans had higher-grade and more frequent parasitaemia events, but mature individuals were more likely to suffer from clinical malaria than juveniles. The case orangutans having patent clinical malaria were 256 times more likely to have had no parasitaemia event in the prior year relative to asymptomatic control orangutans. The findings are consistent with rapidly acquired immunity to P. pitheci illness among orangutans that wanes without re-exposure to the pathogen.

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