BBC Bats a 'likely source' of Sars

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>BBC DAILY E-MAIL: UK EDITION

>Friday, 30 September, 2005, 8:00 GMT 01:00 -07:00:US/Pacific

>

> * Bats a 'likely source' of Sars *

>A new study finds a virus very like Sars in

>Chinese bats, indicating they were the likely

>source of the 2002 outbreak.

>Full story:

>http://news.bbc.co.uk/go/em/-/1/hi/sci/tech/4291386.stm

>

Bats a 'likely source' of Sars

By Richard Black

Environment Correspondent, BBC News website

 

 

The likely source of the respiratory disease

Sars is the horseshoe bat, a new study suggests.

 

Researchers found a virus closely related to the

Sars coronavirus in bats from three regions of

China.

 

Writing in the journal Science, they say the

virus may have needed to infect another animal

such as the civet before it could transmit to

humans.

 

They suggest that live horseshoe bats are kept

out of markets until the transmission path is

fully understood.

 

The Sars (Severe Acute Respiratory Syndrome)

outbreak in 2002/3 caused about 770 deaths, and

economic damage estimated in billions of dollars;

centred on east Asia with origins in southern

China, fatalities occurred as far afield as

Canada.

 

The virus we found is 92% similar to the human Sars virus

Zhengli Shi, Chinese Academy of Sciences

Schools and businesses closed, international

trade and travel were restricted; and for a time,

until basic public health measures curtailed the

outbreak, it seemed as though the next major

global disease of humanity had emerged.

 

But emerged from where? In May 2003, the

suggestion emerged that the virus responsible had

entered the human population from civets, animals

eaten in wildlife restaurants and butchered in

live animal markets in southern China.

 

The World Health Organisation (WHO) endorsed

this link early in 2004, an announcement which

led authorities in China to embark on a culling

programme which saw an estimated 10,000 civets

killed, as well as other animals suspected of

harbouring Sars, such as badgers and raccoons.

 

Immunity clue

 

But for some time, the prevailing theory among

scientists has been that civets were not the

original source, or reservoir, of infection.

 

One clue is that they appear to have little

immunity, and become seriously ill; whereas

species which harbour pathogens for a long period

of history usually adapt to them.

 

So where did the Sars virus, labelled Sars-CoV, come from?

 

One theory named birds; but earlier this month,

researchers at Hong Kong University found cause

to suspect bats. In a Hong Kong bat species they

found a virus closely related to that found in

Sars patients.

 

Now an international collaboration between

scientists in China, Australia and the US has

gone further, and identified a Sars-like virus in

three species of bats from mainland China.

 

" The virus we found is 92% similar to the human

Sars virus, " said Zhengli Shi from the Institute

of Zoology at the Chinese Academy of Sciences in

Beijing.

 

" Why it is there in these bats, why it can

infect just these species, we are not sure - it

is a story we want to discuss, " she told the BBC

News website.

 

All three species of bat in which Dr Shi's group

found the Sars-like coronavirus, dubbed SL-CoV,

are horseshoe bats of the genus Rhinolophus ,

as does the species identified in the Hong Kong

study.

 

Civets still implicated?

 

Genomic analysis suggests that the bat

coronaviruses found by this group and by the Hong

Kong team are very alike, and that both are

closely related to the human and civet forms. The

major differences lie in genes which relate to

the binding of virus particle and host cell.

 

" This virus, we are sure, cannot infect humans, " said Zhengli Shi.

 

One of the big questions is, then, how the virus

jumped from bats to humans - and whether in the

body of an intermediary, such as the civet, it

can adapt in such a way that it can then infect a

human.

 

" At the moment we don't know, " said Peter

Daszak, Director of the Consortium for

Conservation Medicine in New York, who was also

involved in the study.

 

" But we can make a comparison with other viruses

- for example, we don't know what the original

host is for Ebola, but it appears to get into

chimpanzees first, and then into humans.

 

" Nipah virus, which emerged in Malaysia in 1998

and 99, we believe has fruit bats as the

reservoir, but it had to go into pigs before it

could infect humans. "

 

So civets could be an " amplifier host " for Sars.

If they are, one suggestion, according to Peter

Daszak, is to keep them away from horseshoe bats.

 

" In the east Asian region, we need to face up to

high-risk behaviours, " he said, " and in this

situation, bringing these species into live

markets, butchering and eating them and using

them in medicines, is a high-risk behaviour. "

 

Solving the jigsaw

 

WHO spokesperson Dick Thompson told the BBC News

website: " We see this as another piece of the

Sars jigsaw.

 

" There's an unfinished agenda for Sars, and

clearly we need to understand the disease ecology

better. "

 

The Chinese team plans to examine the possible

transmission path of the virus more closely.

 

" We will change some amino-acid sequences in the

virus we have identified, " said Zhengli Shi, " and

see if can infect humans. "

 

Confirming horseshoe bats as the source of Sars

would carry implications for future public health

research and policy.

 

" These bats have a wide distribution in Europe

and Asia, " said Peter Daszak, " and what we don't

know, and need to know urgently, is the

distribution of the Sars-like virus in these bats.

 

" On a wider scale, we need surveillance of

wildlife to look for possible new diseases, and

to identify changes in the environment, human

behaviour and demography which drive the

emergence of these diseases; because almost every

new disease which has emerged recently has been

driven by changes in land use.

 

" The last thing we should do is to take it out

on the bats, because the evidence suggests that

they have carried this coronavirus for thousands,

perhaps millions of years; only recently has it

emerged in a big way, and it was human behaviours

that made the difference. "

Story from BBC NEWS:

http://news.bbc.co.uk/go/pr/fr/-/1/hi/sci/tech/4291386.stm

 

Published: 2005/09/29 18:02:28 GMT

 

© BBC MMV

 

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