Despite extensive laboratory investigations in patients with respiratory tract infections, no microbiological cause can be identified in a significant proportion of patients. In the past 3 years, several novel respiratory viruses, including human metapneumovirus, severe acute respiratory syndrome (SARS) coronavirus (SARSCoV), and human coronavirus NL63, were discovered. Here we report the discovery of another novel coronavirus, coronavirus HKU1 (CoV-HKU1), from a 71-year-old man with pneumonia who had just returned from Shenzhen, China. Quantitative reverse transcription-PCR showed that the amount of CoV-HKU1 RNA was 8.5 to 9.6 ؋ 10 6 copies per ml in his nasopharyngeal aspirates (NPAs) during the first week of the illness and dropped progressively to undetectable levels in subsequent weeks. He developed increasing serum levels of specific antibodies against the recombinant nucleocapsid protein of CoV-HKU1, with immunoglobulin M (IgM) titers of 1:20, 1:40, and 1:80 and IgG titers of <1:1,000, 1:2,000, and 1:8,000 in the first, second and fourth weeks of the illness, respectively. Isolation of the virus by using various cell lines, mixed neuron-glia culture, and intracerebral inoculation of suckling mice was unsuccessful. The complete genome sequence of CoV-HKU1 is a 29,926-nucleotide, polyadenylated RNA, with G؉C content of 32%, the lowest among all known coronaviruses with available genome sequence. Phylogenetic analysis reveals that CoV-HKU1 is a new group 2 coronavirus. Screening of 400 NPAs, negative for SARS-CoV, from patients with respiratory illness during the SARS period identified the presence of CoV-HKU1 RNA in an additional specimen, with a viral load of 1.13 ؋ 10 6 copies per ml, from a 35-year-old woman with pneumonia. Our data support the existence of a novel group 2 coronavirus associated with pneumonia in humans.Since no microbiological cause can be identified for a significant proportion of patients with respiratory tract infections (18, 29), research has been conducted to identify novel agents. Of the three novel agents identified in recent 3 years, including human metapneumovirus (36), severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) (25), and human coronavirus NL63 (HCoV-NL63) (6, 37), two were coronaviruses. Coronaviruses possess the largest genomes of all RNA viruses, consisting of about 30 kb. As a result of their unique mechanism of viral replication, coronaviruses have a high frequency of recombination.Based on genotypic and serological characterization, coronaviruses were divided into three distinct groups, with human coronavirus 229E (HCoV-229E) being a group 1 coronavirus and human coronavirus OC43 (HCoV-OC43) being a group 2 coronavirus (16). They account for 5 to 30% of human respiratory tract infections. In late 2002 and 2003, the epidemic caused by SARS-CoV affected more than 8,000 people with 750 deaths (23-25, 44, 45, 51). We have also reported the isolation of SARS-CoV-like viruses from Himalayan palm civets, which suggested that animals could be the reservoir fo...

Amongst the 60 viral species reported to be associated with bats, 59 are RNA viruses, which are potentially important in the generation of emerging and re-emerging infections in humans. The prime examples of these are the lyssaviruses and Henipavirus. The transmission of Nipah, Hendra and perhaps SARS coronavirus and Ebola virus to humans may involve intermediate amplification hosts such as pigs, horses, civets and primates, respectively. Understanding of the natural reservoir or introductory host, the amplifying host, the epidemic centre and at-risk human populations are crucial in the control of emerging zoonosis. The association between the bat coronaviruses and certain lyssaviruses with particular bat species implies co-evolution between specific viruses and bat hosts. Cross-infection between the huge number of bat species may generate new viruses which are able to jump the trans-mammalian species barrier more efficiently. The currently known viruses that have been found in bats are reviewed and the risks of transmission to humans are highlighted. Certain families of bats including the Pteropodidae, Molossidae, Phyllostomidae, and Vespertilionidae are most frequently associated with known human pathogens. A systematic survey of bats is warranted to better understand the ecology of these viruses.

IMPORTANCEAlthough horseshoe bats are the primary reservoir of SARS-related coronaviruses (SARSr-CoVs), it is still unclear how these bat viruses have evolved to cross the species barrier to infect civets and humans. Most human SARS-CoV epidemic strains contain a signature 29-nucleotide deletion in ORF8, compared to civet SARSr-CoVs, suggesting that ORF8 may be important for interspecies transmission. However, the origin of SARS-CoV ORF8 remains obscure. In particular, SARSr-Rs-BatCoVs from Chinese horseshoe bats (Rhinolophus sinicus) exhibited <40% amino acid identities to human/civet SARS-CoV in the ORF8 protein. We detected diverse alphacoronaviruses and betacoronaviruses among various bat species in Yunnan, China, including two SARSrRf-BatCoVs from greater horseshoe bats that possessed ORF8 proteins with exceptionally high amino acid identities to that of human/civet SARSr-CoVs. We demonstrated recombination events around ORF8 between SARSr-Rf-BatCoVs and SARSr-RsBatCoVs, leading to the generation of civet SARSr-CoVs. Our findings offer insight into the evolutionary origin of SARS-CoV ORF8 protein, which was likely acquired from SARSr-CoVs of greater horseshoe bats through recombination.