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Orang-utans infected by mystery Ebola-like virus

By Debora Mackenzie

6 November 2012

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Sixty-five orang-utans had survived viruses never seen outside Africa before

(Image: David Maitland/OSF/Getty)

They are already the most endangered great apes. Now orang-utans may face an additional threat: Ebola virus, or something a lot like it. Bornean orang-utans have antibodies that recognise not just the Asian species of Ebola virus, but all four African Ebola viruses and a similar African virus called Marburg.

None of the African viruses has ever been seen outside Africa before. The discovery was discussed at a conference last week by the study’s leader, Chairul Anwar Nidom of Airlangga University in Surabaya, Indonesia.

Orang-utans are the only Asian great apes: chimpanzees, bonobos and gorillas are African. Largely due to forest clearing for palm-oil plantations, only 40,000 orang-utans are thought to survive in the wild on the islands of Sumatra and Borneo, down from 60,000 a decade ago.

As part of a survey of wild mammals for H5N1 bird flu, which is endemic in Indonesian poultry, Nidom’s team collected blood from 353 apparently healthy wild orang-utans in two reserves in eastern and central Borneo. They tested the samples for antibodies to flu and other infections to check the animals’ disease history.

Sixty-five apes, from both locations, carried antibodies that bound to proteins from one of the African Ebola species, or from Marburg (PLoS ONE, doi.org/jpk).

Ebola kills African chimpanzees and lowland gorillas, and could pose a threat to both species. However, the orang-utans had clearly survived. Five others carried antibodies to the Asian species of Ebola called Reston, which has been found in macaque monkeys and pigs in the Philippines, not far from Borneo. Nidom notes that filoviruses like Ebola can be lethal in some species but not others – Reston Ebola kills cynomolgus macaques, but not rhesus macaques or humans. The African viruses might be similarly variable.

Or perhaps whatever the orang-utans caught wasn’t quite African Ebola. “There could be filoviruses in nature that do not cause disease in primates,” notes Thomas Geisbert, an Ebola expert at the University of Texas Medical Branch in Galveston. Antibodies to African Ebola might cross-react with those viruses, and give a positive test. But without an actual virus and its genetic sequence, says Geisbert, “I don’t think you can say for sure that any virus associated with antibodies in these animals is the same as the African filoviruses”.

“We only ever look for filoviruses when they’ve killed people,” says Peter Walsh of the University of Cambridge, who tracks Ebola in chimps. “We don’t know what others are out there, or what they do.” For instance, another filovirus was discovered in Spanish bats last year. We do not know what, if anything, it does in primates.

Ayato Takada of Hokkaido University in Sapporo, Japan, a co-author of the Borneo paper, agrees that we need to detect the orang-utan virus itself before we will know more. The team plans to test domestic pigs, and wants to collect samples from bats.

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