Bats and the origin of outbreaks

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

BATS

and the

ORIGIN of OUTBREAKS

As the World Health Organization reaches its findings on the zoonotic origins of the novel coronavirus, we explain why bats make such ideal hosts for disease-causing viruses.

Scientists have long suspected that the rate of new infectious diseases could accelerate, especially in developing countries where human and animal interaction is increasing.

Changes in the environment are driving displaced species of animals into new habitats, allowing them to mix with other species or potential hosts.

Those shifts, combined with greater human interaction with animals as people move deeper into forests, increases the chances of a virulent virus jumping species.

This kind of spillover, when a pathogen in one species could start circulating in another and potentially create a new disease – is what appears to have happened in China with the virus that causes COVID-19. Like many infectious viruses introduced this way, the outbreak is believed to have started with bats.

Data shows that the closest known relative of the novel coronavirus is a virus discovered in horseshoe bats in southwest China.

11cm

Chinese rufous

horseshoe bat

15cm

23cm

head-body

Egyptian

rousette bat

Hammer-headed bat

Malayan fruit bat

Among the largest species of bat with a wingspan of up to 1.5 m

11cm

15cm

head-body

Chinese rufous

horseshoe bat

23cm

head-body

Egyptian

rousette bat

Hammer-headed bat

Malayan fruit bat

Among the largest species of bat with a wingspan of up to 1.5 m

Egyptian

rousette bat

Chinese rufous

horseshoe bat

11cm

15cm

head-body

23cm

head-body

Hammer-headed bat

Among the largest species of bat with a wingspan of up to 1.5 m

Malayan fruit bat

Egyptian

rousette bat

11cm

15cm

head-body

Chinese rufous

horseshoe bat

23cm

head-body

The Malayan fruit bat is among the largest species of bat. Its wingspan can reach up to 1.5 m

Hammer-headed bat

Malayan fruit bat

Egyptian

rousette bat

11cm

Chinese rufous

horseshoe bat

15cm

head-body

23cm

head-body

The Malayan fruit bat is among the largest species of bat. Its wingspan can reach up to 1.5 m

Hammer-headed bat

Malayan

fruit bat

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 against this type of invasion.

The reservoir host species often displays no symptoms despite carrying the pathogen, as the 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.

Bats were again thrust into the spotlight as they were thought to be the original host of the SARS-CoV-2 virus that causes COVID-19. Molecular studies have demonstrated that bats are natural reservoirs to many other viruses, some of which have already led to disease outbreaks.

THE UNIVERSE OF BATS

Bat family

Genus group

Species

205

Leaf-nosed bats

Disc-winged

bats

94

Old world

leaf-nosed bats

Ghost-faced bats

Smoky

bats

New Zealand

short-tailed bats

Funnel-eared

bats

Hog-nosed

bats

118

Free-tailed bats

Mouse-tailed

bats

Hairy

bats

False

vampire bats

Sucked-footed

bats

30

Bent-winged

bats

450

Simple-nosed bats

195

Old world

fruit bats

54

Sac-winged

bats

Bulldog

bats

92

Horseshoe

bats

Not all species in a family may host the virus

Slit-faced

bats

HARBORED ZOONOTIC VIRUSES

Some species in a family may not host the virus

Hantaviruses

Filoviruses

Paramyxoviruses

Moussa

Magboi

Marburg

Menagle

Coronaviruses

Ebola

Nipah

Hendra

MERS

SARS

SARS-CoV-2

Australian

bat lyssavirus

POSSIBLE INTERMEDIATE HOSTS

?

?

PASSED TO

HUMANS

THE UNIVERSE OF BATS

Bat family

Genus group

Species

205

Leaf-nosed bats

Hog-nosed bats

Bulldog bats

New Zealand

short-tailed bats

Mouse-tailed bats

118

Free-tailed bats

Disc-winged bats

Smoky bats

Sucked-footed bats

94

Old world leaf-nosed bats

Funnel-eared bats

450

Simple-nosed bats

11

Ghost-faced bats

Hairy bats

False vampire bats

54

Sac-winged bats

195

Old world fruit bats

92

Horseshoe bats

Slit-faced

bats

30

Bent-winged bats

Not all species in a family may host the virus

HARBORED

ZOONOTIC

VIRUSES

Coronaviruses

Filoviruses

Paramyxoviruses

Hantaviruses

Australian bat

lyssavirus

Ebola

Marburg

Nipah

Hendra

Menagle

Magboi

Moussa

SARS-CoV-2

MERS

SARS

POSSIBLE

INTERMEDIATE

HOSTS

?

PASSED TO

HUMANS

THE UNIVERSE OF BATS

Bat family

Genus group

Species

205

Leaf-nosed bats

New Zealand

short-tailed bats

118

Free-tailed bats

Bulldog bats

Hog-nosed bats

Sucked-footed bats

Disc-winged bats

Mouse-tailed bats

Old world

leaf-nosed bats

Smoky bats

Hairy bats

Funnel-eared bats

Ghost-faced bats

450

Simple-nosed bats

False vampire bats

195

Old world fruit bats

54

Sac-winged bats

92

Horseshoe bats

30

Bent-winged bats

16

Slit-faced bats

Not all species in a family may host the virus

Coronaviruses

Filoviruses

Paramyxoviruses

Hantaviruses

HARBORED

ZOONOTIC

VIRUSES

Australian bat

lyssavirus

Ebola

Marburg

Nipah

Hendra

Menagle

MERS

SARS

SARS-CoV-2

Magboi

Moussa

POSSIBLE

INTERMEDIATE

HOSTS

?

PASSED TO

HUMANS

THE UNIVERSE OF BATS

Bat family

Genus group

Species

205

Leaf-nosed bats

94

Old world

leaf-nosed bats

Disc-winged

bats

Ghost-faced bats

Smoky

bats

New Zealand

short-tailed bats

Funnel-eared

bats

Hog-nosed

bats

118

Free-tailed bats

Mouse-tailed

bats

Hairy

bats

False

vampire bats

Sucked-footed

bats

450

Simple-nosed bats

Bent-winged

bats

195

Old world

fruit bats

54

Sac-winged

bats

Bulldog

bats

92

Horseshoe

bats

Slit-faced

bats

HARBORED ZOONOTIC VIRUSES

Some species in a family may not host the virus

Hantaviruses

Filoviruses

Paramyxoviruses

Moussa

Magboi

Marburg

Menagle

Coronaviruses

Ebola

Nipah

Hendra

MERS

SARS

SARS-

CoV-2

Australian

bat lyssavirus

POSSIBLE INTERMEDIATE HOSTS

?

?

PASSED TO

HUMANS

THE UNIVERSE OF BATS

Bat family

Genus group

Species

205

Leaf-nosed bats

New Zealand

short-tailed bats

118

Free-tailed bats

Bulldog bats

Hog-nosed bats

Sucked-footed bats

Disc-winged bats

Mouse-tailed bats

Old world

leaf-nosed bats

Smoky bats

Hairy bats

Funnel-eared bats

Ghost-faced bats

450

Simple-nosed bats

False vampire bats

195

Old world fruit bats

54

Sac-winged bats

92

Horseshoe bats

30

Bent-winged bats

16

Slit-faced bats

Not all species in a family may host the virus

Coronaviruses

Filoviruses

Paramyxoviruses

Hantaviruses

HARBORED

ZOONOTIC

VIRUSES

Marburg

Hendra

SARS

SARS-CoV-2

MERS

Australian bat

lyssavirus

Ebola

Nipah

Menagle

Magboi

Moussa

POSSIBLE

INTERMEDIATE

HOSTS

?

PASSED TO

HUMANS

Many deadly viruses in the past have originated from bats including the deadly Ebola outbreaks in Western Africa. Nipah, also carried by bats, has already caused human outbreaks across South and South East Asia and has “serious epidemic potential”, according to global health and infectious disease specialists.

The coronavirus family of viruses also includes diseases such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). Scientists have discovered that SARS and MERS were caused by viruses that originated in 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 mammal species and are found all over the world except for the Arctic, the Antarctic and a few oceanic islands.

Bats first appear in the fossil record roughly 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 coming close to harbouring as many viruses are rodents, the most diverse group of mammals. There are approximately 2,300 species of rodents in 33 families, making up about 40% of all mammals. Rodents are believed to harbour more viruses as a group but bats harbour more viruses per species.

The diversity of both groups has been seen by scientists as a possible mechanism for driving virus diversity, as the greater number of species can create more potential niches for viruses.

Some bats roost 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’s hog-nosed bat at about 3cm (1.2 inches) and the biggest, known as a flying fox, can grow to around 45cm (18 inches).

Flying fox

Kitti’s hog-nosed bat

Flying fox

Kitti’s hog-nosed bat

Flying fox

Kitti’s hog-nosed bat

Flying fox

Kitti’s hog-nosed bat

Flying fox

Kitti’s hog-nosed bat

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 per species than rodents do. Here are some factors that could potentially aid this.

Longevity

Apart from diversity, other traits that make bats suitable as virus hosts include their size and longevity.

Bats have relatively long life spans for their body size, which can make it easier for viruses to persist as chronic infections are more common.

Bowhead whale

BATS

Shown in black

200

Human

Fin whale

Live longer than

similar sized animals

100

Gorilla

African bush

elephant

Brandt's bat

Indian flying fox

Giraffe

30

20

10

Lifespan

(years)

3

Bennett's chinchilla rat

2

Forest shrew

1

10g

100g

1kg

10kg

100kg

1,000kg

100,000kg

Mass

300

Bowhead whale

BATS

Shown in black

200

Human

Fin whale

Live longer than

similar sized animals

Humpback whale

100

Gorilla

Horse

African bush

elephant

Indian flying fox

Brandt's bat

Giraffe

30

20

10

Lifespan

(years)

3

Bennett's chinchilla rat

2

Forest shrew

1

10g

100g

1kg

10kg

100kg

1,000kg

100,000kg

Mass

300

Bowhead whale

BATS

Shown in black

200

Human

Fin whale

Tend to live longer than other

animals with similar body weight

100

Humpback whale

Gorilla

Horse

African bush elephant

Polar bear

Brandt's bat

Indian flying fox

Giraffe

30

20

10

Lifespan

(years)

3

2

Bennett's chinchilla rat

Forest shrew

1

10g

100g

1kg

10kg

100kg

1,000kg

10,000kg

100,000kg

Mass

300

Bowhead whale

200

BATS

Shown in black

Human

Fin whale

Tend to live longer than other animals

with similar body weight

Blue whale

100

Humpback whale

Gorilla

Horse

African bush elephant

Polar bear

Indian flying fox

Brandt's bat

Mouse-eared bat

Giraffe

30

20

10

Lifespan

(years)

3

2

Bennett's chinchilla rat

Forest shrew

1

10g

100g

1kg

10kg

100kg

1,000kg

10,000kg

100,000kg

Mass

300

Bowhead whale

200

BATS

Shown in black

Human

Fin whale

Tend to live longer than other animals

with similar body weight

Blue whale

100

Humpback whale

Gorilla

Horse

African bush elephant

Polar bear

Indian flying fox

Brandt's bat

Mouse-eared bat

Giraffe

30

20

10

Lifespan

(years)

3

2

Bennett's chinchilla rat

Forest shrew

1

10g

100g

1kg

10kg

100kg

1,000kg

10,000kg

100,000kg

Mass

Sympatry & hibernation

When bat species with large ranges migrate or use seasonal roosting sites for hibernation, this increases potential exposure to pathogens. Moreover, members of some bat species live together in large communities with close-quarter colonies in locations such as caves.

Flight

Bats are the only mammals capable of powered flight. 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 occurs during immune response. This means some viruses they carry have adapted to be more tolerant to higher temperatures, potentially 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, durian, a highly valued crop, can be effectively pollinated by the Dawn Bat. In this sense, bats are important economically for people. Some bats can also play critical roles in spreading seeds and regrowing forests.

The insect-eating bats also serve as natural biological controls of insects, consuming millions of them at night, including some major crop pests.

Conservation

More than 200 bat species (~15%) in 60 countries are considered threatened with extinction and more than 20 are critically endangered. In addition, eight bat species have been documented as having gone extinct in the recent past. Bat population decline is not a regional issue but rather a global one.

Almost 30% of all bat species face some level of threat.

1,304

Bat species

assessed

Extinct

Critically endangered,

endangered, vulnerable,

or near threatened

30%

1,000

815

500

Least

concern

147

153

Data

deficient

0

2008

2010

2012

2014

2016

2018

2020

1,304

Almost 30% of all bat species face some level of threat.

Extinct

Bat species

assessed

Critically endangered,

endangered, vulnerable,

or near threatened

~30%

1,000

815

500

Least

concern

147

153

Data

deficient

0

2008

2010

2012

2014

2016

2018

2020

1,304

8

Extinct

Nearly 30% of the assessed species with sufficient data are threatened, near threatened with extinction or extinct

Bat species

assessed

22

Critically endangered

78

Endangered

~30%

107

Vulnerable

88

Near Threatened

1,000

815

757

Least Concern

500

147

153

244

Data Deficient

0

2008

2010

2012

2014

2016

2018

2020

1,304

8

Extinct

Bat species

assessed

Nearly 30% of the assessed species with sufficient data are threatened, near threatened with extinction or extinct

22

Critically Endangered

78

Endangered

Around

30%

107

Vulnerable

88

Near Threatened

1,000

815

757

Least Concern

500

147

153

244

Data Deficient

0

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

1,304

8

Extinct

Nearly 30% of the assessed species with sufficient data are threatened, near threatened with extinction or extinct

22

Critically Endangered

78

Endangered

Around

30%

107

Vulnerable

88

Near Threatened

Bat species

assessed

1,000

815

757

Least Concern

500

147

153

244

Data Deficient

0

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

There are nearly 250 bat species classified as Data Deficient (~19%), a relatively high proportion when compared to other mammals in general (~13%) or birds (~1%), showing that for many bat species not enough is known to even assess their status.

Threats such as habitat loss, climate change and the wildlife trade are global phenomena leading to mass biodiversity loss. For example, tens of thousands of flying foxes in Australia and South Asia have died because of extreme heat waves.

Bats are also exploited for food or traditional medicine, as around 170 of bat species have been recorded to be hunted. Given their larger size, Old World fruit bats are disproportionately affected by hunting, with roughly half of the species in that family 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 animal longevity database; Research papers, 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).

Note

Paragraphs 4 and 5 of this story were updated to make clear that bats are suspected to be the source of the novel coronavirus but not proven.

The closest known relative of SARS-CoV-2 is a coronavirus circulating in Horseshoe Bats but so far there is not enough evidence to identify the specific source.