As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
As the World Health Organization reaches its findings on the zoonotic origin of the new coronavirus, we explain why bats are such ideal hosts for virus-causing viruses.
Scientists have long suspected that the rate of new infectious diseases could accelerate, especially in developing countries where human-animal interaction is on the rise.
Changes in the environment drive displaced animal species into new habitats, enabling them to mix with other species or potential hosts.
These shifts, combined with greater human interaction with animals as humans move deeper into forests, increase the chances of a virulent virus jumping.
This type of spill, when a pathogen in one species can start circulating in another species and possibly create a new disease, is what apparently happened in China with the virus that causes COVID-19. Like many infectious viruses so introduced, the outbreak started with bats.
Chinese auburn
horseshoe bat
Among the largest bat species with a wingspan of up to 1.5 m
Chinese auburn
horseshoe butt
Among the largest bat species with a wingspan of up to 1.5 m
Chinese auburn
horseshoe butt
Among the largest bat species with a wingspan of up to 1.5 m
Chinese auburn
horseshoe butt
The Malay fruit bat is one of the largest species of bats. Its wingspan can reach up to 1.5 m
Chinese auburn
horseshoe butt
The Malay fruit bat is one of the largest species of bats. Its wingspan can reach up to 1.5 m
Zoonotic diseases, caused by pathogens that spread between animals and humans, can be problematic because the human immune system has not evolved to fight this type of invasion.
The host species often show no symptoms, even though they carry the pathogen, because the hosts and germs are often well adapted to each other. However, if these pathogens – viruses, bacteria or other disease-causing microorganisms – jump from animals to humans, the consequences can be devastating.
Bats have been pushed back into the spotlight as they are considered to be the original host of the SARS-CoV-2 virus that causes COVID-19. Molecular studies have shown that bats are natural reservoirs for many other viruses, some of which have already led to disease outbreaks.
94
Old world
bats
New Zealand
short-tailed bats
BIRTH ZOONOTIC VIRUSES
POSSIBLE INTERMEDIARIES
New Zealand
short-tailed bats
94
Old world leafy nose bats
POSSIBLE
BETWEEN
GASE
New Zealand
short-tailed bats
POSSIBLE
BETWEEN
GASE
94
Old world
bats
New Zealand
short-tailed bats
BIRTH ZOONOTIC VIRUSES
POSSIBLE INTERMEDIARIES
New Zealand
short-tailed bats
POSSIBLE
BETWEEN
GASE
Many deadly viruses in the past have originated from bats, including the deadly Ebola outbreak in West Africa. Nipah, which is also carried by bats, has already caused people in South and Southeast Asia and has a ‘serious epidemic potential’ according to global health and infectious disease specialists.
The coronavirus family of viruses also contains diseases such as severe acute respiratory syndrome (SARS) and Middle Eastern respiratory syndrome (MERS). Scientists have discovered that SARS and MERS are caused by viruses that originate in bats, while other animals act as intermediate hosts.
Why bats?
Bats are a group of flying mammals, according to IUCN, with more than 1,300 species in 20 families. They make up about 20% of all mammal species and are found all over the world, except the Arctic, the Antarctic and some ocean islands.
Bats appeared in the fossil record about 50 million years ago and represent the third group of flying vertebrates in Earth’s history, after the flying reptiles called pterosaurs and birds.
The only other group that comes close to viruses are rodents, the most diverse group of mammals. There are about 2300 species of rodents in 33 families, which make up about 40% of all mammals. Rodents are believed to contain more viruses than group, but bats contain more viruses per species.
The diversity of both groups is seen by scientists as a possible mechanism to drive virus diversity, as the greater number of species could create more potential niches for viruses.
Some bats lie in forests while others in caves. Most bats eat insects such as beetles, moths and mosquitoes. Some bats eat fruits, nectar, seeds and pollen from flowers, while others eat small animals such as birds, fish, frogs and lizards. A small number of bats consume blood.
The smallest bats are the Kitty’s pig nose bat of about 3 cm (1.2 inches) and the largest, known as a flying fox, can grow up to about 45 cm (18 inches).
Studies have shown that bats are unique when it comes to presenting zoonotic viruses, not even as rodents, because bats present more zoonotic viruses per species than rodents. Here are some factors that may help.
Longevity
Apart from diversity, the characteristics that bats are suitable as virus hosts include their size and longevity.
Bats have a relatively long lifespan for their body size, which can make it easier for viruses to persist, as chronic infections are more common.
Live longer than
similar size animals
Live longer than
similar size animals
Tends to live longer than others
animals of similar body weight
Tends to live longer than other animals
with similar body weight
Tends to live longer than other animals
with similar body weight
Sympathy & hibernation
When bat species migrate with large variations or use seasonal sleeping places for hibernation, it increases exposure to pathogens. In addition, members of some bat species live together in large communities with colonies within a quarter of an hour in places such as caves.
Flight
Bats are the only mammals that are capable of flying. There is a high energy and metabolic demand for flight, leading to elevated body temperatures in bats, which is similar to the effects of human fever that occur during immune response. This means that some viruses they carry have been adapted to be more tolerant of higher temperatures, which may be bad news for other animals if they become infected.
Why Bats Are Important
Bats provide many beneficial ecosystem services. Some bats play important roles such as pollinating plants and spreading seeds. Bats can pollinate more than 500 species of plants, including avocados, bananas, dates and mangoes.
In Southeast Asia, durian, a valued crop, can only be effectively pollinated by the Dawn Bat. In this sense, bats are economically important to humans. Some bats can also play critical roles in seed dispersal and forest regrowth.
The insectivorous bats also serve as natural biological control of insects, consuming millions of them at night, including some large crop pests.
Conservation
More than 200 bat species (~ 15%) in 60 countries are considered endangered and more than 20 are critically endangered. In addition, it has been documented that eight bat species have become extinct in the recent past. Decrease in bat population is not a regional issue, but rather a global one.
Nearly 30% of all bat species are endangered.
Criticism threatened,
threatened, vulnerable,
or near threatened
Nearly 30% of all bat species are endangered.
Criticism threatened,
threatened, vulnerable,
or near threatened
Nearly 30% of the judged species with sufficient data are threatened, almost threatened with extinction or extinction
Nearly 30% of the judged species with sufficient data are threatened, almost threatened with extinction or extinction
Nearly 30% of the judged species with sufficient data are threatened, almost threatened with extinction or extinction
There are almost 250 bat species classified as data deficient (~ 19%), a relatively large percentage compared to other mammals in general (~ 13%) or birds (~ 1%), which shows that for many bat species not known enough to even judge their status.
Threats such as habitat loss, climate change and wildlife trade are global phenomena leading to the loss of massive biodiversity. Tens of thousands of flying foxes in Australia and South Asia, for example, have died due to extreme heat waves.
Bats are also used for food or traditional medicine, as it is recorded that about 170 species of bats are hunted. Because of their larger size, Old World fruit bats are excessively affected by hunting, and about half of the species in the family are hunted.
By
Julia Janicki and Simon Scarr
Illustrations by
Catherine Tai
Additional work by
Marco Hernandez
Editing by
Will Dunham
Sources
The IUCN Red List of Threatened Species Data; AnAge: The database for longevity of animals; Research articles, Fleming et al. (2009), Turmelle et Olival (2009), Luis et al. (2013), O’Shea et al. (2014), Voigt & Kingston (2016), Hayman (2016), Frick et al. (2020), Gorbunova et al. (2020), Letko et al. (2020).