Secrets of the night – what lies hidden in Sweden’s bats?

Early one night, a group of researchers gathers to stretch a net across the opening beneath a bridge. In the silence of the darkness, they stand ready at either end of the fine-meshed net. Suddenly, a creature of the night glides through the air – and, if the researchers are lucky, straight into the net. With gloved hands, they carefully disentangle the bat and place it in a small cloth bag.

At a table set up a short distance away, test tubes, a computer and equipment for ring marking are ready for recording information and collecting samples from the tiny animals. The research team’s bat expert, Johnny de Jong, carefully lifts out the bats one by one while saliva samples are collected using oral swabs.

While the animal bites on the swab and being ring marked, its faeces can also be collected from the cloth bag in which it has been kept – before the bat is released and flies off into the night once again.

From bats in the night to experiments in the laboratory

Bats can become infected with and carry a wide range of viruses, and interestingly, they seem to be able to tolerate certain viral infections without becoming ill themselves, even though the same or closely related viruses can cause severe disease in other animals or humans.

Until now, very little has been known about which viruses Swedish bats actually carry – and whether these viruses can also infect other animals, or us humans.

Starting in autumn 2026, a new research project is commencing. The research team includes a veterinarian, virologists and a bat expert. The latter, Johnny de Jong, has already begun locating bat colonies. In summer 2027, he will lead the sampling in Uppland. The sampling will then be repeated the following year, this time in Skåne.

Once oral swabs and faecal samples have been collected from the bats, the research team in Uppsala takes over. The samples are studied using advanced laboratory and data analyses in a technique known as viral metagenomics. This will ultimately produce a list of all the viruses genetically detected in every individual sample.

Her colleague adds:

This requires high-containment laboratories, which fortunately are available both at SLU and at the Swedish Veterinary Agency (SVA). In these laboratories, cells from humans and various animal species are cultured. The researchers will then experimentally attempt to infect them with the different viruses.

Blood-eating vampires or misunderstood allies?

The frightening tale of Dracula, the blood-sucking vampire of Transylvania, admittedly has some basis in reality – but it is far from telling the whole story about bats.

Do bats eat blood? Yes and no. In Central and South America, there are a small number of species that do indeed feed on the blood of mammals and birds.

However, these three blood-feeding species make up only a tiny fraction of the world’s more than 1,400 bat species. The rest do not feed on blood, but on insects, fruit or nectar. All 19 bat species found in Sweden are insectivorous.

Bats play an essential role in ecosystems, not least by helping to keep populations of mosquitoes and insect pests under control, thereby also benefiting vegetation and crops. A single bat can eat several thousand insects in one night.

Preparedness as humans move closer to bats

The research project forms part of Sweden’s preparedness for infectious diseases. But the researchers want to make one thing clear:

The researchers emphasise that being able to rule out which viruses do not pose a threat to animals or humans in Sweden is equally important. And that may well turn out to be the case for most of them.

There are also broader plans for future research into bats and their unique characteristics.

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