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Searching for Animal Disease Transmission

Researchers are not waiting for the next new disease to emerge. They’re studying our near and distant primate¹ relatives to try to prevent future epidemics².

HIV/AIDS is a well-known zoonotic disease, an illness transmitted from animals to humans. The disease – linked to African primates³ - has killed tens of millions and more than 30 million people are now living with the disease.

Dr. Natalie Cooper said there may be many more diseases ready to jump from animals to humans. The Trinity College Dublin assistant professor and her colleagues are focusing their research on primates.

“Investigating diseases in primates gives us a really good model of the kinds of diseases which we might expect to see in humans. Because things which are common in these primate populations are also the kind of things which end up getting passed into human populations eventually, or they’re the kind of things that we already share with primates,” she said.

There are a number of things that need to happen before an animal disease spreads among humans.

“First of all you have to contact that disease somehow. So maybe you bump into an animal that sneezes on you for example. And that’s got to happen first. But then there’s a lot of stuff that happens within the human body. So that disease then has to get through your immune system. It has to get into your cells and actually start causing some disease symptoms. And so it’s much easier for these diseases, if they’re kind of adapted to this primate model system, to come into another primate, a human,” she said. 

Researchers expected to find that humans would share diseases with primates with whom they’re mostly closely related. Cooper says immune systems are likely to be similar in primates that share a common ancestor.

“It wasn’t that long ago that humans and chimpanzees had this common ancestor. So we expect that we have these similar traits in our biology, which might make it easy for us to catch the same kinds of diseases. So we were expecting – and all the previous research has suggested – that we’d share more with our very close relatives, the great apes. So this would be gorillas⁴, chimpanzees and orangutans than we would with other species of primates,” she said.

Researchers did in fact confirm that we do share many diseases with the great apes. But Cooper said they they also found something unexpected.

“What’s more surprising is that things like old world monkeys and lemurs even – so lemurs are the very primitive⁵ kinds of monkeys that you find on Madagascar – we share an ancestor with them something like a hundred million years ago, [a]really, really long time ago. So we really weren’t expecting to see that much sharing there,” she said.

So the span of a hundred million years since we had a common ancestor does not necessarily protect us from catching⁶ a virus from a lemur. By the way, we also share diseases with macaques and baboons⁷.

Cooper said there are massive gaps in knowledge about various species of monkey. She said once those gaps are filled, scientists can determine how much of a risk monkey diseases pose to humans. That could lead to vaccines⁸ to prevent outbreaks and epidemics.

“It’s a hugely daunting⁹ task, and obviously primates are only just the first step here. So there are other kinds of animals, which we actually end up having a lot more contact with. So domesticated¹⁰ animals, cats and dogs in particular - and then things like rats and mice, which we have a lot of contact with in domestic situations. And we think that these species are very, very likely to transfer diseases across to us,” she said.

As the global population grows, people are spreading into new areas. As they do, Cooper said, they’re encountering new species of animals and possibly new diseases as well.