As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
As the World Health Organization reaches its discoveries about the zoonotic origins of the new coronavirus, we explain why bats are ideal hosts for disease-causing viruses.
Scientists have long suspected that the rate of new infectious diseases may accelerate, especially in developing countries, where human and animal interaction is increasing.
Changes in the environment are taking displaced animal species into new habitats, allowing them to mix with other species or potential hosts.
These changes, combined with greater human interaction with animals as people move to the depths of forests, increase the chances of a virulent virus spreading through species.
This type of overflow, when a pathogen in one species could start to circulate in another and potentially create a new disease – is what seems to have happened in China with the virus that causes COVID-19. Like many infectious viruses introduced in this way, the outbreak started with bats.
Chinese redhead
horseshoe bat
Among the largest species of bat with wingspan of up to 1.5 m
Chinese redhead
horseshoe bat
Among the largest species of bat with wingspan of up to 1.5 m
Chinese redhead
horseshoe bat
Among the largest species of bat with wingspan of up to 1.5 m
Chinese redhead
horseshoe bat
The Malaysian frugivorous bat is among the largest bat species. Its wingspan can reach up to 1.5 m
Chinese redhead
horseshoe bat
The Malaysian frugivorous bat is among the largest bat species. Its wingspan can reach up to 1.5 m
Zoonotic diseases, those caused by pathogens that spread between animals and people, can be problematic because the human immune system has not evolved to fight this type of invasion.
The reservoir host species often has no symptoms, despite carrying the pathogen, as hosts and germs are often well adapted to each other. However, when these pathogens – viruses, bacteria or other disease-causing microorganisms – jump from animals to humans, the effects can be devastating.
The bats were again highlighted because they are considered 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 caused disease outbreaks.
94
Old world
leaf-nosed bats
New Zealand
short-tailed bats
HARBORED ZOONOTIC VIRUSES
POSSIBLE INTERMEDIATE HOSTS
New Zealand
short-tailed bats
94
Old-world leaf-nosed bats
POSSIBLE
INTERMEDIARY
HOSTS
New Zealand
short-tailed bats
POSSIBLE
INTERMEDIARY
HOSTS
94
Old world
leaf-nosed bats
New Zealand
short-tailed bats
HARBORED ZOONOTIC VIRUSES
POSSIBLE INTERMEDIATE HOSTS
New Zealand
short-tailed bats
POSSIBLE
INTERMEDIARY
HOSTS
Many deadly viruses in the past originated from bats, including the lethal Ebola outbreaks in West Africa. Nipah, also carried by bats, has already caused human outbreaks in South and Southeast Asia and has “serious epidemic potential,” according to experts in global health and infectious diseases.
The family of coronavirus viruses also includes diseases such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). The scientists found that SARS and MERS were caused by viruses originating from bats, with other animals serving as intermediate hosts.
Why bats?
Bats are a group of flying mammals, with more than 1,300 species in 20 families, according to IUCN. They make up approximately 20% of all mammalian species and are found worldwide, except in the Arctic, Antarctica and some oceanic islands.
Bats first appeared in the fossil record about 50 million years ago and represent the third group of flying vertebrates in Earth’s history, after flying reptiles called pterosaurs and birds.
The only other group that comes close to harboring so many viruses are rodents, the most diverse group of mammals. There are approximately 2,300 rodent species in 33 families, representing about 40% of all mammals. Rodents are believed to harbor more viruses as a group, but bats harbor more viruses per species.
The diversity of both groups was seen by scientists as a possible mechanism to boost the diversity of viruses, since the greater number of species can create more potential niches for viruses.
Some bats perch in forests, while others in caves. Most bats eat insects such as beetles, moths and mosquitoes. Some bats eat fruit, 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 Kitti pig nose bats, about 3 cm (1.2 inches) and the largest, known as the flying fox, can reach about 45 cm (18 inches).
Studies have shown that bats are unique when it comes to hosting zoonotic viruses, even when compared to rodents, as bats host more zoonotic viruses by species than rodents. Here are some factors that can help with this.
Longevity
In addition to diversity, other characteristics that make bats suitable as hosts for viruses include their size and longevity.
Bats have a relatively long life expectancy for body size, which can facilitate the persistence of viruses, as chronic infections are more common.
Live longer than
similar size animals
Live longer than
similar size animals
Tend to live longer than others
animals with similar body weight
Tend to live longer than other animals
with similar body weight
Tend to live longer than other animals
with similar body weight
Sympathy and hibernation
When bat species with large extensions migrate or use seasonal resting places for hibernation, this increases the potential exposure to pathogens. In addition, members of some bat species live together in large communities with nearby colonies in places like caves.
Fly
Bats are the only mammals capable of motorized flying. There is a high energy and metabolic demand for flight, leading to high body temperatures in bats, which is similar to the effects of human fever that occurs during the immune response. This means that some viruses they carry have adapted to be more tolerant of higher temperatures, which can be bad news for other animals, if infected.
Why bats are important
Bats provide many beneficial ecosystem services. Some bats play important roles, such as plant pollination and seed dispersal. Bats can pollinate more than 500 species of plants, including avocados, bananas, dates and mangoes.
In Southeast Asia, the durian, a highly prized crop, can be pollinated effectively only by the dawn bat. In that sense, bats are economically important to people. Some bats can also play a critical role in spreading seeds and regenerating forests.
Insect-eating bats also serve as natural biological controls for insects, consuming millions of them at night, including some of the main plantation pests.
Conservation
More than 200 species of bats (~ 15%) in 60 countries are considered endangered and more than 20 are critically endangered. In addition, eight species of bats have been documented as extinct in the recent past. The decline in the bat population is not a regional issue, but a global one.
Almost 30% of all bat species face some level of threat.
In critical danger,
endangered, vulnerable,
or almost threatened
Almost 30% of all bat species face some level of threat.
In critical danger,
endangered, vulnerable,
or almost threatened
Almost 30% of the species evaluated with sufficient data are threatened, almost threatened with extinction or extinct
Almost 30% of the species evaluated with sufficient data are threatened, almost threatened with extinction or extinct
Almost 30% of the species evaluated with sufficient data are threatened, almost threatened with extinction or extinct
There are about 250 species of bats classified as Data Deficient (~ 19%), a relatively high proportion when compared to other mammals in general (~ 13%) or birds (~ 1%), showing that for many species of bats they do not. he is known enough to even assess his status.
Threats such as habitat loss, climate change and wildlife trade are global phenomena that lead to massive loss of biodiversity. For example, tens of thousands of flying foxes in Australia and South Asia have died from extreme heat waves.
Bats are also exploited as food or traditional medicine, as around 170 species of bats have been hunted. Due to their larger size, Old World fruit bats are disproportionately affected by hunting, with about half of the species in this family being hunted.
In
Julia Janicki and Simon Scarr
Illustrations by
Catherine Tai
Additional work of
Marco Hernandez
Edited by
Will Dunham
Origins
IUCN Red List of Threatened Species data; AnAge: The animal longevity database; 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).