Wild vampire bats socially distance when they are sick by spending less time in their community, a new study suggests.
In the wild, US researchers injected bats with endotoxins, which stimulate an immune response, fixed them with proximity sensors and recorded their movements.
The sick creatures associated with fewer group mates, spent less time with others, and were less socially connected to healthy group mates, they found.
The experts say sickness-induced social distancing in animals does not require cooperation from others and is probably common across species.
Vampire bats socially distance when they are sick. Sickness behaviors can slow the spread of pathogens across a social network and is likely common across species
'We tracked this unintentional "social distancing" effect hour-by-hour in a wild colony of vampire bats.
'As tracking technology improves the capacity to create dynamic animal social networks from large, high-resolution datasets, we expect researchers to gain new insights into the patterns and processes underlying the spread of pathogens, information, or behavioral states.'
The researchers captured 31 adult female vampire bats from a hollow tree in Lamanai, Belize in Central America.
The team injected half the bats with an endotoxins, also known as lipopolysaccharides, an immune-challenging substance, to make them sick, while the other half received harmless saline injections.
Wild vampire bats (pictured) that are sick spend less time near others from their community, which slows how quickly a disease will spread. The research team had previously seen this behavior in the lab, and used a field experiment to confirm it in the wild
WHAT ARE ENDOTOXINS?
Endotoxins, also known as lipopolysaccharide (LPS), are the component of the outer membrane of gram-negative bacteria.
They can induce inflammation and fever as an immune response in animals.
Their presence in the blood stream may cause septic reactions with a variety of symptoms such as fever, hypotension, nausea, shivering and shock.
The researchers then glued proximity sensors to the bats and released them back into their tree.
'The sensors gave us an amazing new window into how the social behaviour of these bats changed from hour to hour and even minute to minute during the course of the day and night, even while they are hidden in the darkness of a hollow tree,' said study lead author Simon Ripperger at the Ohio State University.
'We've gone from collecting data every day to every few seconds.'
The team tracked changes over time in the associations among the 16 sick bats that had received endotoxin injections and the 15 control bats.
In the six hours after injection, a sick bat associated on average with four fewer associates than a bat that had been injected with saline.
On average a control bat had a 49 per cent chance of associating with each control bat, but only a 35 per cent chance of associating with a sick bat.
During the treatment period, sick bats also spent 25 fewer minutes associating with another partner.
These differences declined after the treatment period and when the bats were sleeping or foraging outside the roost.
Scientists had previously seen social distancing behaviour in lab conditions, but wanted to find out if it occurred in the wild.
These studies had revealed that endotoxin-injected bats were physiologically immune-challenged, slept more, moved less, engaged in social grooming with fewer partners in a cage and even produced fewer vocal calls to their fellow mates.
'In this field experiment, we showed that these effects of sickness behavior extend to proximity-based association durations and social network connectivity in the natural environment,' the team say.
'Sickness behavior can therefore slow the spread of a pathogen that is transmitted at higher probability with higher rates of physical contact (e.g., grooming) or closer proximity.'
In another study this week, researchers in Singapore claim that bats excel as carriers of viruses such as coronaviruses without getting as sick as humans do, by adopting multiple strategies to reduce pro-inflammatory responses.
Bats act as reservoirs of numerous zoonotic viruses, including SARS-CoV, MERS CoV and the Ebola virus.
It's been thought the SARS-CoV-2 virus, which causes Covid-19, originated from bats, although the exact origin of Covid-19 not yet been officially confirmed.
It is likely to have its ancestral origins in a bat species but may have reached humans through an intermediary species, such as pangolins – a scaly mammal often confused for a reptile.
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.'