A mysterious disease in chimpanzees now identified

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Researchers and veterinarians have recently isolated the pathogen responsible for the many deaths recorded over the past fifteen years in Western chimpanzees. However, the fight has only just begun. These works are published in the journal Nature’s communications.

Since 2005, dozens of western chimpanzees have succumbed to a mysterious disease in Tacugama Sanctuary, Sierra Leone. The symptoms are as follows: The primates gradually become lethargic, lack coordination, vomit and even seize, and eventually die. The situation is all the more worrying as these chimpanzees represent a subspecies in critical extinction danger.

The cause of this disease called “epizootic neurological and gastroenteric syndrome” (ENGS) has long remained a mystery. Research, initiated by Dr Tony Goldberg, therefore began in 2016. This work, in which the sanctuary staff, veterinarians and biologists participated, made it possible to make several observations: the disease is not contagious, it does not infect humans and did not appear in any other sanctuary. In other words, only the Tacugama chimpanzees seem to be affected.

A responsible bacterium

Thanks to years of research, the teams were finally able to isolate the culprit after thorough screening of the blood and tissue of healthy chimpanzees compared to diseased samples (genomic studies and visual examinations among other techniques). The researchers have indeed noticed the presence of a bacterium in 68% of samples from sick chimpanzees, but absent in healthy subjects. This new species has just been named Package candidate trolls.

More surprisingly, this bacterium has not only been isolated from the gastrointestinal tract of infected primates, but also from their internal organs, including the brain.

Although this bacterium is a newly identified species, other members of the genus Task are already known. They are indeed common in the soil. Other species have also been detected in the human microbiome, including S. ventriculi for example, isolated from stomach contents of people suffering from recurrent vomiting, abdominal pain, nausea and diarrhea. Typically, these patients are treated with antibiotics.

Tony Goldberg, equipped with a filter to trap microbes, samples water from a stream near Tacugama Sanctuary in 2019. Credit: Tony Goldberg

Determine the origin

The fact that this new bacterium has now been identified is excellent news. However, there is still work to be done. Indeed, it is still not clear how chimpanzees are infected with the pathogen. It is nevertheless evident that these bacteria could live in their close environment, probably in the soil. Future work will hopefully allow its origin to be traced.

In the meantime, the disease continues to emerge. The syndrome always reaches its peak in March, during the dry season. According to the researchers, keeping the chimpanzees indoors in the afternoon seems to contain the disease somewhat. Some antibiotics are also more effective than others. However, it also happens that some primates, who seem to be doing better after treatment, suddenly die off the next day despite everything.

A deeper understanding of this newly identified bacteria would also help to learn more about the genus. Task which has not been the subject of much research until now.

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