Decades of research into the potential reservoir host

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decades of research into the potential reservoir host of filoviruses, recent data indicated that bats could be the potential natural hosts of Ebola and Marburg viruses in Africa (4, 29, 30). Filovirus RNA has been identified in a number of fruit bat species from Gabon and the Democratic Republic of Congo. It has also been shown that the incidence of Marburg haemorrhagic fever in mine workers in southern Uganda could be attributed to possible transmission from infected bats ( Rousettus aegyptiacus ) that had colonised the mine. Genetic analysis demonstrated that the Marburg virus isolated from the infected mine workers was highly similar to those circulating in the R. aegyptiacus population (30). Ebola Reston virus was first identified in the United States of America (USA) in macaques which were imported from the Philippines. This virus has recently emerged in the pig population in the Philippines, posing a significant potential threat to public health and the livestock industry in the region (31). The discovery of Ebola Reston was made during a disease outbreak in pig farms in the Philippines, but further investigation revealed that at least six people were infected by Ebola Reston, as indicated by the presence of virus-specific antibodies in their serum samples (31). Since the diseased pigs were also co-infected with porcine circovirus 2, experimental inoculation of Ebola Reston in pigs was conducted to assess its pathogenic potential. It was shown that Ebola Reston challenge resulted in asymptomatic infection in pigs. But virus shedding was observed in infected pigs, demonstrating a potential risk for farm and abattoir workers (32). Detection of Ebola-Reston- specific antibodies in R. amplexicudatus bats suggests that bats may also be the natural host of Ebola Reston virus (33). Other bat-borne viruses In addition to those ‘high-profile’ bat zoonotic viruses discussed above, there have been a large number of previously unknown viruses discovered in the last two decades. These include viruses of known zoonotic transmission, such as the Menangle virus in Australia and the related Tioman and Melaka viruses in Malaysia, and many other related bat reoviruses (34, 35). Bat viruses related to known human pathogens have also been detected in large numbers, including bat lyssaviruses, parainfluenza viruses, hantaviruses, hepaciviruses and pegiviruses (36, 37). In addition, a large number of other paramyxoviruses, coronaviruses, astroviruses, adenoviruses and herpesviruses have been reported (38, 39, 40). The public health threat of these viruses is unknown, but it would be prudent to place these viruses under a close watch for potential spillover. Emerging zoonotic viruses from other sources It should be emphasised that, while bat viruses represent one of the most important sources of recent emergence, there are many other important zoonotic viruses with a significant impact on public health that have emerged or re-emerged. As shown in Figure 1, the frequency of major zoonotic virus outbreaks in the last decade is very high.

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