Bats have received a lot of negative attention, but the chances are slim that the virus that causes COVID-19 was transmitted from bats to humans. The world needs bats – in ecosystems, for pollination and for seed dispersal. On top of that, they keep harmful insects in check around our homes, on farms and in cities.
The coronavirus Sars-CoV-2 has marked the media and everyday life of millions of people since the beginning of this year. New research articles and daily media reports on possible causes of the ongoing pandemic fill the airwaves.
In times of crisis like this, it’s natural to look for causes. A somewhat biased media coverage has led many people to regard bats as the cause of the pandemic. But is this true?
Sars-CoV-2 is one of many different coronaviruses
The term “coronavirus” is often used by the media. But Sars-CoV-2 (severe acute respiratory syndrome coronavirus 2), which is the virus that causes the infectious disease COVID-19, is just one of many viral strains in the large family of coronaviruses.
The coronavirus family is widespread in mammals and birds. Several hundred – and possibly thousands – of different coronavirus strains have been described. Seven different coronaviruses are already known to have been transmitted to humans from animals or between humans.
Common colds in humans are caused by various viruses, including assorted coronaviruses. Coronavirus has also been detected in European and Norwegian bats. However, these are of a completely different type than Sars-CoV-2 and are not dangerous to humans.
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Sars-CoV-2 not transmitted by bats
The exact origin of Sars-CoV-2 is still unknown. A coronavirus (designated as RaTG13) has been found in a bat species (Rhinolophus affinis) of the horseshoe bat family.
In laboratory experiments, this virus has not been able to infect human cells due to different binding capabilities of surface proteins. The virus is 96 per cent genetically similar to Sars-CoV-2, that is, it has the same degree of genetic similarity as between humans and chimpanzees.
It is therefore highly unlikely that the virus has been transmitted directly from bats to humans.
Experiments in Germany have recently been carried out where Egyptian fruit bats (Rousettus aegyptiacus) were artificially infected with Sars-Cov-2. The animals showed no symptoms and were unable to transmit the virus to other bats. It has not been shown that bats have Sars-CoV-2 or that the virus can be transmitted from bats to humans.
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Are bats a significant source of zoonoses?
Zoonosis is a viral or bacterial disease transmitted to humans from other animals. In the media, bats are sometimes portrayed as carriers of more zoonoses than other animals. This is not correct.
A recent review shows that rodents are carriers for 61 per cent of transmissions, while bats account for 30 per cent. It turns out that the number of zoonotic diseases is proportional to the number of species within an animal group. Rodents and bats have the greatest number of species among mammals, but they do not produce a relatively larger number of zoonoses than would be expected from the number of species found.
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Domesticated animals overrepresented as source of zoonoses
People’s pets and farm animals are the group of animals that are strongly overrepresented as carriers of zoonoses.
Domesticated animals have been carriers of 50 per cent of the zoonoses we know about today, and involve only 12 different animal species. Close contact between domesticated animals and humans makes the risk of infection much greater than it is between wild animals and humans.
Studies have shown that domestic cats and dogs can be carriers of Sars-CoV-2. High antibody levels have been found in cats that live with humans infected with the virus. In laboratory experiments, cats infected each other with Sars-CoV-2. Whether cats or dogs can infect humans is unknown so far.
Humans themselves the cause of most zoonosis cases
Close contact is required for animals to infect humans with viruses. Intensive animal farming and markets selling wild animals for food and traditional medicine have previously proven to provide ideal conditions for virus outbreaks caused by zoonoses like swine flu and SARS.
Close contact between different species and the exchange of bodily fluids between dead, living or injured wild animals increases the possibility of disease-causing organisms jumping onto new host animals, mutating, and spreading at a high rate.
This is how SARS-CoV-1 developed and possibly also SARS-CoV-2.
Studies that investigate causes of zoonoses show that the likelihood of disease transmission from wild animals does not hinge on whether animals are aggressive toward humans, but rather that humans are increasingly encroaching on animals’ habitats, causing them to deteriorate or disappear altogether.
This results in increased contact between humans and wild animals, which in turn can lead to outbreaks of new zoonotic diseases.
When animal-to-human infection occurs, in most cases the animals are not responsible for causing the further spread of an epidemic. This also applies to the COVID-19 pandemic, which is not being transmitted to humans from wild animals, but from human to human, and which is rapidly gaining a global reach because humans are a highly mobile species that continuously travels between continents.
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Is it dangerous to have bats in the house?
In industrialized societies, many bat species locate their breeding colonies in man-made structures such as bridges, churches, barns and, not least, residential houses. This is the case for most of the bat species in Norway.
Unlike mice, bats do not chew on insulation or wood, nor do they bring in any nesting materials.
Under normal air conditions, faeces (which mostly consist of insect shells) and urine dry very quickly, and annoying odours or sounds are usually not a problem for people who have bats in their homes. Problematic situations tend to be of a more psychological nature – some individuals perceive bats as nasty or creepy and don’t want them in the house. But having bats in the home – from a public health perspective – only rarely poses a problem.
In northern Europe, rabies is the only viral disease transmitted by bats that can be dangerous to humans. Infection occurs only through close contact with bats and can be easily avoided by not handling live or weakened bats. The animals themselves will never attack humans.
If you find yourself in a situation where you handle a bat with rabies without gloves and are bitten by it, a quick treatment with vaccine and rabies immunoglobulin would be sufficient to avoid getting sick. The risk of infection is considered very low, but scientists who handle bats get the rabies vaccination to be on the safe side.
So it is not dangerous to have bats living with us in our house or cottage.
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The world needs bats
Bats, of the order Chiroptera, consist of over 1400 different species and make up about 20 per cent of all the world’s mammal species. Bats are found in almost all ecosystems except the Arctic regions. Various bat species feed on pollen, nectar, fruit, small vertebrates, insects and other invertebrates.
Bats play an important role in maintaining the functioning and health of ecosystems and contribute to important ecosystem services, such as pollination and seed dispersal. They also control the populations of troublesome and directly harmful insects around our homes, in the agricultural landscape and in cities (see Fact box below ).
Examples of ecosystem services:
Seed dispersal: 100 species of various leaf bat species are responsible for seed dispersal in 24 per cent of the rainforest trees in South and Central America. It has been estimated that on average, the straw-coloured fruit bat (Eidolon helvum) disperses at least 150 million seeds every night on the African continent. For small seeds, distances range from a few metres to over 80 km, which far exceeds the seed dispersal carried out by monkeys and birds.
Pollination: 500 different plant species are pollinated by bats in South and Central America. The agave plant, which is used to produce tequila, is pollinated by the leafy species Leptonycteris curasoeae, for example.
Biological control of harmful insects: In southern parts of the United States, it has been estimated that Mexican free-tailed bats (Tadarida brasiliensis) alone eat so many insects that the cotton plantations save almost 11 million Euro annually in insecticides they don’t need to use. Similar studies in Kenya have emphasized that coffee plantations would produce 25 per cent fewer coffee beans if bats vanished.
The same has also been found on cocoa plantations in Indonesia. In northern Spain, researchers have estimated that soprano pipistrelle bats (Pipistrellus pygmaeus), which are also widespread in southern Norway, on their own consume enough pest insects so that farmers can spend 23 Euro less in pesticides per hectare of rice paddies.
Various species of bat eat large quantities of insects that are vectors for human diseases, such as dengue fever, yellow fever and chikungunya fever.
It is estimated that a colony of 150 North American big brown bats (Eptesicus fuscus), which is closely related to Norway’s most common bat, the northern bat (Eptesicus nilssonii), can consume close to 1.3 million insects annually.
A lot to learn from bats
Bats are fascinating animals for those of us who study them and their relationship to their surroundings. Just think – these animals have been on Earth for 55 million years and have been using echolocation to navigate for that long!
Humans, on the other hand, discovered ultrasound just before World War II. The flying skills of bats already inspired Leonardo Da Vinci, and now the first drones that mimic the bats’ efficient and elegant flight technique are being developed.
The active substance in saliva of the vampire bat counteracts blood coagulation. This active ingredient can be used effectively in the treatment of stroke and heart attack. The fact that bats have a unique and well-functioning immune system has become known in recent years. Their immune system is effective against viral diseases and in fighting cancer.
Their strong immune system is probably also the reason why bats can grow unusually old despite their modest body size. A lot is happening in all of these fields of research, and new knowledge can benefit humans both in the fight against dangerous viral diseases and help increase our understanding of age-related diseases.
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Human activity threatens bats
Worldwide, more than 20 per cent of all bats studied are endangered by human activity. Loss and degradation of habitats, disturbance, targeted persecution, overuse of common food resources and lack of information are all considered serious threats to bats. In Europe, many bat species have experienced a sharp decline in the second half of the 20th century.
All bats are therefore protected throughout Europe, including Norway, by the EUROBATS agreement. All Norwegian bats are also protected by national law. The widespread notion that COVID-19 was caused due to infection by bats has led to a rapidly growing negativity towards these animals globally, and in some places this has had catastrophic consequences.
The Indonesian authorities, for example, have been actively working to eradicate bats found in markets, even though the animals belong to a different family of bats than the alleged source.
Fact-based knowledge and collaboration
Both bat aficionados from volunteer organizations and bat researchers spend a great deal of time, dedication and effort investigating the bats’ secrets. Fact-based knowledge is important. In Norway and in many other countries, the bat community works in cooperation with both animal and public health authorities and with public nature management authorities. This ensures effective, knowledge-based management of our bat species, and a good coexistence between humans and bats.
For more fact-based and up-to-date information, we recommend the UNEP/EUROBATS page.
More about bats
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For information on where in the Viewpoints article the sources refer to, please contact the article authors.