Monkeys and maladies

By Stuart Semple

In the film Outbreak, a deadly virus is unleashed in America after an infected monkey is brought into the country. It’s a film with a real basis in truth – we know that diseases with catastrophic impacts can be transmitted from (non-human) primates to our own species. Ebola is perhaps the most dramatic example in recent years, and for those working in the field of human health, such emerging infectious diseases are of huge global concern.

For primatologists, there is also a real worry about disease transmission in the opposite direction – from people to primates. Fatal outbreaks of respiratory disease in chimpanzees and gorillas, for example, have recently been linked back to human sources. In this respect, tourists that travel to visit wild primates are a particular concern, as they can bring pathogens to which the animals have not previously been exposed and to which therefore they may have no immunity.

Studying lethal disease outbreaks in wild primates – and people – is, of course, rather like shutting the stable door after the horse has bolted! Useful information to potentially mitigate the risks of such events can be provided by studies looking at how close tourists get to the animals they have come to see, and whether the humans and primates physically interact with each other. That was the aim of a recent study published in EcoHealth, led by two former CRESIDA PhD students, Dr Laetitia Marechal and Dr Charlotte Carne, and also involving myself, Prof Ann MacLarnon (formerly of CRESIDA, now at Durham University) and Dr Bino Majolo (Lincoln University).

The study was carried out at a site in the Middle Atlas Mountains of Morocco, where Moroccan and international tourists come to visit wild Barbary macaques (Macaca sylvanus). We found that the monkeys spent around a fifth of their day in close proximity to tourists (less than 10m away from them); this indicates a high risk of disease transmission – from the monkeys to people or vice versa – as a sneeze can carry airborne pathogens well over this distance. Tourists also interacted frequently with the animals, attempting to feed or touch them, and occasionally being aggressive towards them. Perhaps most alarmingly, high rates of interactions and close proximity between humans and macaques occurred also during three periods when the macaques were visibly unwell – coughing and sneezing heavily.

Tourist feeding an adult male Barbary macaque in Morocco (image credit: https://www.flickr.com/photos/axelrd/4453111694/)

The Barbary macaque is classified as an Endangered species, and tourism has been proposed as a key tool in its conservation. In the paper, we argue that if the associated risks of disease – not just to the macaques but also to people – are to be reduced, preventative measures need to be implemented. Such measures – for example, ensuring a safe distance is kept between tourists and animals, and preventing physical interactions between them – are standard at many ape tourist sites. They should now be extended to sites such as our one in Morocco, and also the many others around the world where tourists visits monkeys or lemurs in their natural habitats.

A monkey causing a fatal disease outbreak may make for a dramatic film story line. We need to do what we can to ensure that these events stay in the realm of the Hollywood blockbuster, and at the same time protect our remaining wild primate populations from the health risk we pose to them.

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