Interspecies transmissions of animal viruses to humans are permanent threats to human health. The recent transmissions of SARS-CoV (8
), West Nile virus (13
), Nipah virus (17
), and avian influenza virus (15
) from animals to humans have highlighted the importance of surveillance of viruses in wildlife. In order to obtain a better understanding of the prevalence of coronaviruses in this geographical region, we collected more than 300 animal samples from 44 animal species. Using a pair of consensus primers for RdRp of coronaviruses, a novel group 1 virus was identified in three Miniopterus
Of 12 bat species examined, the novel Bat-CoV was identified in three different bat species from the same genus. Interestingly, Myotis chinensis and Myotis ricketti, which frequently cohabit with M. pusillus (K. Y. Suen, personal communication), were negative in this investigation. These results demonstrate that this virus has a narrow host range. As the viral sequences in Miniopterus spp. are highly similar, our data imply that there are frequent interspecies transmissions between these species. It is not certain which Miniopterus species is the natural host of the virus. However, the majority of M. pusillus bats were found to be infected by this virus. In addition, the detection rates of this virus in M. pusillus in the summer of 2003 and 2004 were similar (57% in 2003 and 67% in 2004). These observations suggest that M. pusillus is likely to be the major reservoir of this virus. As the majority of M. pusillus bats in Hong Kong are known to migrate to tropical areas to overwinter (K. Y. Suen, personal communication), we do not know the prevalence of Bat-CoV in this species in winter. Further work on the ecology and behavior of these three bat species in Hong Kong is required to better understand the dynamic of this virus in these animals.
Although all of the infected bats were shown to be healthy upon physical examination, it is not known whether this novel virus is pathogenic in bats. Both fecal and respiratory samples were positive for the virus. However, more than 50% of fecal samples from M. pusillus contained this novel virus compared to 26% of respiratory specimens from the same bats, implying that this virus may have a predominantly enteric tropism. Further work is required to elucidate the persistence of the infection, tissue tropism, and possible pathogenicity of this virus.
The deduced Bat-CoV sequences have the typical features of coronaviruses. The virus has the highest sequence identity to group 1 coronaviruses but is clearly distinct from previously known group 1 viruses. Our phylogenic analyses of these viral sequences also suggest that the virus is a group 1 virus. These findings are further supported by the fact that the S protein of Bat-CoV contains the unique signature of group 1 coronaviruses (i.e., the unique 14 amino acids in HR1 and HR2) (2
). Recombination is common in coronaviruses and is thought to contribute to the emergence of new coronaviruses (9
). Our limited sequencing results do not allow us to draw any conclusions of the origin of this virus. However, the low sequence homology between Bat-CoV sequences and other coronavirus sequences at least suggest that this novel virus is not a recent recombinant from existing coronaviruses. We are currently attempting to sequence the rest of the viral genome for a full sequence characterization of this virus. However, these efforts are hampered by the inability to culture the virus in vitro.
Apart from the Bat-CoV, we did not identify other coronaviruses in our samples. However, one should note that our results could not reveal a complete picture of the prevalence of coronaviruses in this geographical region. First, our test relies on the detection of viral sequence. Animals with a past coronavirus infection would be negative in our assay. Second, due to the limited sample sizes of each animal species, we might miss the viruses which are circulating in low frequency. Besides, the conserved primers used in this study were based on available coronavirus sequences, and these primers might not be able to detect coronaviruses that are genetically more divergent from previously known coronaviruses.
We previously reported that SARS-CoV could be isolated from Himalayan palm civets (8
). It should be noted that the SARS-CoV-positive animals in our previous study were obtained from wild animal markets and not captured in the wild. None of the civets examined in our current study (n
= 21) was positive for SARS-CoV by both serological and molecular tests. The results from our present study do not exclude the possibility that the civet is the natural host of SARS-CoV, but our results at least indicate that SARS-CoV is not broadly circulating in wild civets. Further investigations are required to elucidate the natural reservoir of SARS-CoV, especially in mainland China.
In conclusion, we reported that a novel coronavirus was identified from bats. The virus has the highest homology to group 1 coronaviruses. Bats are the reservoir for lyssaviruses and henipaviruses and are responsible for emerging diseases in humans. It is not known whether this virus would cause zoonotic disease in humans or other animals. Further investigations are needed to understand the ecology and pathogenicity of this virus. In addition, this study also highlighted our poor understanding of viruses in wild animals. Given the catastrophic consequences of SARS, further surveillance work on viruses in wildlife should be encouraged.