Bats, Not Civets, Identified as Wildlife Reservoir for SARS

GEELONG, Australia, October 5, 2005 (ENS) - Horseshoe bats from the central Chinese province of Hubei are likely to be the wildlife reservoir for the virus responsible for severe acute respiratory syndrome (SARS), a scientific team from Australia, China and the United States has concluded. Earlier studies indicated a cat-sized Asian mammal, the civet - could be a natural host of SARS, but no widespread SARS infection was ever found in wild or farmed civets.

In a paper published on Thursday in Sciencexpress, the online edition of the journal "Science" the researchers describe how they found a high antibody prevalence for SARS when they sampled more than 400 bats from four locations in China.

Caused by a previously unrecorded coronavirus, SARS emerged in the southern China province of Guangdong in 2002. By July 2003 it had spread worldwide, killing 774 people and infecting at least 8,000 others.

Zoonotic viruses, capable of infecting both animals and people, have been linked to bats in the past, said Dr. Linfa Wang, the SARS research team leader at the Australian government's CSIRO Livestock Industries' Australian Animal Health Laboratory in Geelong.

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A horseshoe bat from Hubei, China of the species found to be most infected with the SARS virus. (Photo courtesy Consortium for Conservation Medicine)
The scientists also knew that horseshoe bats are sold at live animal markets in China as a food item or for use in traditional Chinese medicine, raising their suspicions that bats might harbor the SARS coronavirus.

"Bats are known reservoir hosts of an increasing number of zoonotic viruses but they rarely display clinical signs of infection," Wang says. "It was these characteristics and the fact that bats are present in Asian food markets that led us to survey them."

The study sampled more than 400 bats in their native habitat from four locations in China. Bats were trapped in their native habitat at four locations - in Guangdong, Guangxi, Hubei and Tianjin.

From March, 2004 through December, 2004, investigators collected data from 408 bats representing six genera. Blood, faecal and respiratory swabs were collected and independently analyzed at the Australian Animal Health Laboratory and the Chinese Academy of Sciences' Wuhan Institute of Virology.

From the Queensland Department of Primary Industries and Fisheries, research team member Dr. Hume Field said, "Among the six genera of bats surveyed, three species from the genus Rhinolophus [horseshoe bats] showed high antibody prevalence."

More than 70 percent of Rhinolophus macrotis bats from the Chinese province of Hubei had SARS coronavirus antibodies in their blood, Field said.

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Researchers analyze bat samples at CSIRO's Australian Animal Health Laboratory. (Photo courtesy CSIRO)
Complete gene sequencing of the virus, named SARS-like coronavirus isolate Rp3 (SL-CoV Rp3), revealed that the genome organization of this virus is essentially identical to the SARS virus associated with the 2003 outbreak.

"The viruses detected from bats show greater genetic variation than those SARS coronaviruses which cause disease in humans and other animals. This variation suggests it's highly likely that the 2002/3 SARS outbreak originated from bats," Dr. Wang says.

"Now we need to find out how these viruses jump from bats to other animals and people. This is crucial if we are to manage the risk of future outbreaks," Dr. Field says.

The probability that there are still more SARS-related coronaviruses to be discovered in bats is high, said researchers from the Consortium for Conservation Medicine of New York, a member of the research team.

Further studies in field epidemiology, laboratory infection, and receptor distribution and usage are being conducted to assess potential roles played by different bat species in the SARS emergence.

This work is part of a collaboration between the Consortium for Conservation Medicine and the Australian Biosecurity Cooperative Research Center for Emerging Infectious Diseases.

Another research team, including Professor Yeun Kwok-Yung, microbiologist at the University of Hong Kong, published similar findings in the Proceedings of the National Academy of Sciences on September 27.