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A multi-institution team designed this study, including behavioral ecologists, immunologists, virologists and statisticians.

Researchers observed that when bats  lost access to their habitat and natural food sources, they sought food on agricultural lands. And when the animals' diets changed, they shed more virus, increasing the virus' spread to horses, as well as the risk to people.

A new study,  published in the Proceedings of the Royal Society B: Biological Sciences, begins to explain why and how the bats' non-native diets increased viral shedding.

Working with Jamaican fruit bats as models, the team found that a low-protein suboptimal diet, like the mandarins or cocos-palm fruit bats consume after loss of native habitat, causes the bats to shed more virus for a longer duration. The researchers also found that the bats ate more food on these suboptimal diets, behavior that may correlate to more foraging, greater movement and increased spillover of virus into other hosts.

Broadly, the research warns of the impact of climate change and land development on the behavior and health of bats—animals known to carry and spread deadly viruses and the increasing risk of spillover, outbreaks and pandemics. 

Some of these viruses are incredibly lethal, yet we continue to clear the land, change the climate and disrupt ecosystems—stressing these animals, removing their food sources and creating new interfaces between wildlife and humans. All of this increases the risk of spillover.

The researchers fed the captive Jamaican fruit bats three distinct diets: a diet high in sugar and protein that is similar to what the bats would standardly eat; a diet low in protein, analogous to eating fruit such as mandarins; and a diet high in fat, analogous to consuming high-fat fruits like cocos-palm. They then tracked, in metabolic detail, how the bats responded when infected with a strain of influenza endemic in bats.

The bats on the low-protein diet shed more virus for longer while, surprisingly, the bats on the high-fat diet shed less virus for a shorter duration than even the standard diet.

While the bats on the high-fat diet shed less virus, that advantage, in terms of spillover, might be offset by increased foraging and any long-term health effects.

So maybe they shed virus for less time, but because they need to eat more food, the exposure risk might be higher because the bats are moving around the landscape. We also don't know what this means for their longer-term health or immune response

They found evidence that the diets altered the gut metabolites of the bats and made them more or less prepared to fend off the influenza virus. In the case of the high-fat diet, the amino acid citrulline seemed to play an important role in boosting immune function, but further studies are needed to understand the mechanisms.

This work is a first step in showing how sensitive the bats are to a change in their diets, and that different diets can change viral shedding patterns.

We must protect the world's remaining intact wild areas, restore ecosystems where possible and take proactive measures to stop these viruses from spilling over into humans in the first place, say the researchers.

 Caylee A. Falvo et al, Diet-induced changes in metabolism influence immune response and viral shedding in Jamaican fruit bats, Proceedings of the Royal Society B: Biological Sciences (2025). DOI: 10.1098/rspb.2024.2482