After the outbreak of Nipah virus (NiV) in 1998-99, which resulted in 105 human deaths and the culling of more than one million pigs, a search was initiated for the natural host reservoir of NiV on Tioman Island off the east coast of Malaysia. Three different syncytia-forming viruses were isolated from fruit bats on the island. They were Nipah virus, Tioman virus (a novel paramyxovirus related to Menangle virus), and a reovirus, named Pulau virus (PuV), which is the subject of this study. PuV displayed the typical ultra structural morphology of a reovirus and was neutralised by serum against Nelson Bay reovirus (NBV), a reovirus isolated from a fruit bat (Pteropus poliocephalus) in Australia over 30 years ago. PuV was fusogenic and formed large syncytia in Vero cells. Comparison of dsRNA segments between PuV and NBV showed distinct mobility differences for the S1 and S2 segments. Complete sequence analysis of all four S segments revealed a close relationship between PuV and NBV, with nucleotide sequence identity varying from 88% for S3 segment to 56% for the S1 segment. Similarly phylogenetic analysis of deduced protein sequences confirmed that PuV is closely related to NBV. In this paper we discuss the similarities and differences between PuV and NBV which support the classification of PuV as a novel mammalian, fusogenic reovirus within the Nelson Bay orthoreovirus species, in the genus Orthoreovirus, family Reoviridae.
Respiratory infections constitute the most widespread human infectious disease, and a substantial proportion of them are caused by unknown etiological agents. Reoviruses (respiratory enteric orphan viruses) were first isolated from humans in the early 1950s and so named because they were not associated with any known disease. Here, we report a previously unknown reovirus (named "Melaka virus") isolated from a 39-year-old male patient in Melaka, Malaysia, who was suffering from high fever and acute respiratory disease at the time of virus isolation. Two of his family members developed similar symptoms approximately 1 week later and had serological evidence of infection with the same virus. Epidemiological tracing revealed that the family was exposed to a bat in the house approximately 1 week before the onset of the father's clinical symptoms. Genome sequence analysis indicated a close genetic relationship between Melaka virus and Pulau virus, a reovirus isolated in 1999 from fruit bats in Tioman Island, Malaysia. Screening of sera collected from human volunteers on the island revealed that 14 of 109 (13%) were positive for both Pulau and Melaka viruses. This is the first report of an orthoreovirus in association with acute human respiratory diseases. Melaka virus is serologically not related to the different types of mammalian reoviruses that were known to infect humans asymptomatically. These data indicate that bat-borne reoviruses can be transmitted to and cause clinical diseases in humans.