Abstract

Orangutans (Pongo spp.), Asia’s only great apes, are threatened in their survival due to habitat loss, hunting and infections.
Nematodes of the genus Strongyloides may represent a severe cause of death in wild and captive individuals. In order to
better understand which Strongyloides species/subspecies infect orangutans under different conditions, larvae were isolated
from fecal material collected in Indonesia from 9 captive, 2 semi-captive and 9 wild individuals, 18 captive groups of
Bornean orangutans and from 1 human working with wild orangutans. Genotyping was done at the genomic rDNA locus
(part of the 18S rRNA gene and internal transcribed spacer 1, ITS1) by sequencing amplicons. Thirty isolates, including
the one from the human, could be identified as S. fuelleborni fuelleborni with 18S rRNA gene identities of 98·5–100%, with a
corresponding published sequence. The ITS1 sequences could be determined for 17 of these isolates revealing a huge
variability and 2 main clusters without obvious pattern with regard to attributes of the hosts. The ITS1 amplicons of
2 isolates were cloned and sequenced, revealing considerable variability indicative of mixed infections. One isolate from a
captive individual was identified as S. stercoralis (18S rRNA) and showed 99% identity (ITS1) with S. stercoralis sequences
from geographically distinct locations and host species. The findings are significant with regard to the zoonotic nature of
these parasites and might contribute to the conservation of remaining orangutan populations.