‘Slow-living’ animal species that breed less rapidly and live longer could be reservoirs of diseases that jump to humans, a new study reveals.
Some species ‘live fast and die young’ by devoting effort to reproduction, such as rabbits and hares, while other ‘slow-living species conserve more energy for survival, like badgers, bats and primates.
Slow-living species also host a greater diversity of parasites and pathogens, like some rodents carrying hantaviruses in parts of North America.
UK researchers say the survival traits of animal hosts – either energy conservation or reproduction – can help predict reservoirs of zoonotic diseases and the vulnerability of populations to disease-induced extinctions.
European badger (pictured) is defined as a slow-living species, which are generally more likely to act as reservoirs of infection that can spill over into other species
The experts focused on endemic diseases that co-exist with host species for long periods of time, as opposed to the current coronavirus pandemic, which spread rapidly worldwide.
The experts measured what they called demographic competence – the ability of a host species to survive in large numbers while sustaining high levels of infection.
Their study found that slow-lived species often have higher demographic competence for persistent infections.
They are therefore more likely to act as reservoirs of infection that can spill over into other species, the study suggests.
Rabbits and hares have significantly faster life histories, while bats (pictured) and primates have significantly slower life histories than expected for their body size
‘Diseases of wildlife pose a threat to the survival of endangered species worldwide, and we know there is risk of spill-over of disease between closely related species of wildlife, livestock and humans,’ said study author Professor Dave Hodgson at the University of Exeter.
‘These spill-over events are known to be influenced by similarities in immune systems, and by increasing levels of contact between humans and wildlife caused by exploitation of natural ecosystems like rainforests.
‘Our findings highlight the potential to use other, more ecological, characteristics like lifespan, reproductive capacity and population size to identify and predict the wildlife reservoirs from which new diseases could emerge.’
For their study, researchers used mathematical models to explore what kinds of animal species and diseases are likely to co-exist for long periods.
The coronavirus (pictured) has drawn attention to fast-spreading infectious diseases, but the new study – by the University of Exeter – focuses on endemic diseases that co-exist with host species for long periods of time.
They found that demographic competence is generally greater among hosts with populations regulated by survival compared to reproduction.
‘As well as finding that slow-living species may be reservoirs of infectious disease, we show a flip-side whereby species with low demographic competence may not be able to co-exist with new diseases and might therefore suffer local or complete extinction,’ said study author Dr Matthew Silk at the University of Exeter.
Dr Silk said there are some differences between species when it comes to terming them as fast- or slow-living – such as rodents.
‘For their size rodents are fairly neutral on the fast-slow continuum, perhaps more on the fast side,’ he said.
‘Obviously, many rodents are also important reservoirs of zoonotic diseases, which shows how many factors play a role.’
It’s also important to note that pace-of-life in the host species isn’t the only important factor affecting demographic competence.
‘Traits of the pathogen itself – such as how easily it is transmitted and how likely it is to kill a host – will also play a key role, as will the social behaviour of the host species,’ he said.
‘We must also consider the role of immunity – differences in immune systems that we know exist between fast and slow hosts can influence how long individuals are ill and whether they can be re-infected.’
Other relevant factors include population densities and a species’ proximity to humans.
The study has been published in the journal Nature Ecology and Evolution.
HOW BATS CAN ACT AS ‘RESERVOIRS’ FOR VIRUSES WITHOUT GETTING SICK
A study suggests molecular mechanisms allow bats to tolerate zoonotic viruses, such as coronaviruses.
Bats act as ‘reservoirs’ of numerous zoonotic viruses, including SARS-CoV, MERS-CoV, Ebola virus, and, possibly, SARS-CoV-2, the pathogen behind the ongoing coronavirus pandemic.
Aaron Irving, Wang Linfa and colleagues at the Duke-National University of Singapore claim bats adopt unique strategies to prevent overactive immune responses, which protects them against diseases caused by zoonotic viruses.
The team examined three bat species – Pteropus alecto (black fruit bat), Eonycteris spelaea (cave nectar bat) and Myotis davidii (David’s myotis bat).
They identified mechanisms that balance the activity of key proteins that play a major role in mediating immunity and inflammatory responses.
These mechanisms enable bats to harbour and transmit zoonotic pathogens without setting off the detrimental consequences of immune activation, like the symptoms coronavirus-infected humans have.
One of the mechanisms bats use is to reduce the levels of caspase-1, a protein that triggers a key inflammatory cytokine protein, interleukin-1 beta (IL-1β).
Another mechanism they employ hampers the maturation of IL-1β, through a finely-tuned balancing between caspase-1 and IL-1β.
‘Suppression of overactive inflammatory responses improves longevity and prevents age-related decline in humans,’ said Professor Wang Linfa.
‘Our findings may offer potential insights to the development of new therapeutic strategies that can control and treat human infectious diseases.’
The study has been published in Proceedings of the National Academy of Sciences.