Image copyright Unicef Image caption There are also unique health needs that current medicine can’t address
A new disease that jumped from animals to humans has been discovered in a Neanderthal man in Russia.
The 25,000-year-old case of anaplasmosis, which targets livers, is the first of its kind, and shows how the human immune system can react to infection.
The case was reported in the Journal of Clinical Investigation.
An earlier study of samples from Neanderthals shows that diseases like measles and rubella can be passed from animals like bats and rodents.
While the risk is low, the findings suggest that far more research needs to be done to understand whether diseases like malaria can be passed to humans – another of the world’s longest-lived primates.
A vicious parasite
What is anaplasmosis?
At the heart of the discovery is a parasite called leishmaniasis, which is commonly found in bats.
Anaplasmosis causes an infection in the liver.
If it infects enough people, the disease could become fatal.
Image copyright Unicef Image caption Anaplasmosis is commonly spread by bats but is becoming more common among humans
How did it become a human disease?
In a recent study of 3944 Neanderthal and modern-day people, the scientists who investigated the new case said a mutated bacterium – thought to be responsible for an infection in European bats – may have moved over to humans after the mammals became extinct.
Some 51 people in Russia’s Volga region had the illness, which sometimes appeared as anaplasmosis mesentery (AMS), in addition to more common symptoms such as bleeding and abdominal pain.
Worse was to come for some of them, with some victims developing persistent liver failure and death.
To understand how the mutation may have transferred to humans, the scientists, led by Seth D Stokes at the University of Michigan, used computer simulations to show how a human immune system responds to the infection.
They concluded the mutation appeared to trigger the development of a pathogen called Ran1, an immune system-attacking bacterium which appears to have happened a few years after the humans died.
“This is really the first example we have,” Mr Stokes told BBC News.
“To be the first to do this in a human using a modern Neanderthal is pretty exciting.”
But he said there are many challenges ahead.
The effects of the disease on the original patient may have been lost to the modern era, he explained.
There is also evidence that it is becoming more common among humans, but many people “go through normal body processes”.
He added: “Nobody gets leishmaniasis without being exposed to the bat vector. We don’t know what we do to ourselves in the modern world that lead to us getting it.”
Analysis also shows the human immune system’s response has an effect on how closely a disease can pass from person to person.
This can lead to diseases like Lyme disease developing.
Mr Stokes pointed out that the ability to adapt to an infection also provides clues about the way the human immune system works.
It’s also why the Neanderthal disease was particularly complex, he said.
“If we thought about an immune system that is pretty mature by the time humans reached the Attica massacre, it might survive well enough to figure out how to respond.”
And with all modern organisms not only adapting to our modern-day health status, but also keeping ahead of it, “this might provide an advantage to certain pathogens”, he said.
More: Anxomma & disease timing