From the Black Death and Ebola to bird flu and SARS, many of the diseases that pose a threat to human life originally come from animals.
Yet predicting how, where and when these illnesses will make the jump from another species to our own has proved frustratingly difficult.
But now scientists have constructed a series of maps to examine the patterns of how zoonoses – diseases that pass from animals to humans – are spread.
Researchers have discovered a series of hotspots around the world where certain types of animals pose a greater risk of transmitting diseases to humans. Rodents, for example, pose a greater risk in Europe and Russia while hooved animals like ungulates pose the greatest risk in east Africa (illustrated)
WHY BATS RARELY GET SICK
They have a reputation for spreading diseases like SARS, rabies and Ebola.
But despite carrying some of the most deadly diseases on the planet, bats often remain unaffected.
Now researchers have found that bats have an overactive immune systems which are switched on all the time rather than just in response to an infection.
A recent study showed that the creatures have lower numbers of a group of signalling proteins called interferons, which play a key role in the immune system, than humans.
Yet bats also continually express one of these interferons, giving them a heightened innate immune response even when they are not infected.
It is this that is thought to suppress viruses when they are infected, keeping the animals from getting ill.
They have found that certain parts of the world have become hotspots for diseases carried by specific animal hosts.
Europe and Russia, for example, are hotspots for disease carrying rodents, while Central and South America are highest in bat spread illnesses.
The researchers say their findings could help to predict where new types of zoonotic diseases may emerge.
Dr Barbara Han, a disease ecologist at the Cary Institute of Ecosystem Studies in New York, said: ‘We also see that even though there are more species in the tropics, fewer of them carry zoonoses.
‘In contrast, more of the species living in northern latitudes, such as the Arctic Circle, carry more zoonoses.
‘Understanding the implications of this pattern in light of climate warming trends will be an important line of inquiry that should be addressed sooner rather than later.’
The research, which is published in the journal Trends in Parasitology, found that 10 per cent of rodent species – 244 of 2,220 – are zoonotic hosts carrying around 85 unique diseases capable of infecting humans.
Diseases such as the plague bacterium Yersinia pestis, which claimed more than 50 million human lives during the Black Death pandemic between 1346 and 1353, was spread by rats and their fleas.
However, the new research also found that although there are comparatively few primates, a greater proportion carry zoonotic diseases – around 21 per cent.
This is likely due to the similarities between our own species and our primate cousins, which means we are more susceptible to the same diseases.
Hunting for bush meat in parts of Africa is thought to have led to the emergence of several deadly diseases in humans, including Yellow fever and some forms of Ebola.
-
The galaxy-hunting robots: Machines that will probe secrets…
Get ready for hotter summers: Scientists warn of regular…
Is there a FIFTH fundamental force? LHC’s new particle that…
-
A bumpy ride back to reality: British astronaut Tim Peake…
The researchers examined the range of diseases carried by mammals from 27 different orders. Surprisingly the highest numbers of diseases did not correspond with regions where animal diversity was greatest, but in temperate regions where human populations tended to be denser (illustrated)
There is some evidence that HIV/AIDS may also have originated in non-human primates before is spread around the world in humans.
Surprisingly, however, bats were found to carry relatively few zoonotic diseases – just 25 compared to 61 in primates, 83 in carnivores and 59 in hooved mammals.
However bats are thought to have been responsible for the deadly outbreak of Ebola in West Africa, which has claimed more than 10,000 lives.
Camels, by comparison were thought to be responsible for carrying a disease called Middle East respiratory syndrome, which spread around the world in 2013.
Livestock such as cows are also responsible for a number of food-borne diseases that can cause localised outbreaks.
However, the researchers did not examine the spread of diseases by birds, which can carry influenza viruses over long distances, for example.
The research showed that mammals carry more bacterial zoonotic diseases followed by viruses (illustrated)
Dr Han said that by identifying the hotspots where different species of animals carry diseases, it can help authorities to prepare for them spreading into humans.
She said: ‘Understanding where animals are distributed and why may not seem applicable to our day-to-day lives.
‘But the big breakthroughs that we need as a society like forecasting where the next zoonotic disease may emerge rely on exactly this kind of basic scientific knowledge.
‘I was rather surprised to see that hotspots of zoonotic diseases didn’t match hotspots of biodiversity more closely.
‘For example, there is high species diversity in the tropics, so I expected to see a similar pattern of more zoonotic parasites and pathogens in the tropics as well.
‘We do find more zoonotic hosts in the tropics, but we find more zoonotic diseases in temperate regions, possibly because these diseases can occur in multiple host species.’
Bats (greater mouse-eared bat pictured) were found to carry relatively few zoonotic diseases – just 25 compared to 61 in primates, 83 in carnivores and 59 in hooved mammals