Hendra and Nipah viruses: new zoonotically-acquired human pathogens.

Some of the key features of Hendra and Nipah viruses are summarized in Table 1. The appearance of these new viruses over the last 10 years emphasizes a number of issues. (1) Epidemics of human infectious diseases can occur unexpectedly and with high impact in terms of morbidity and mortality. (2) We do not know what epidemiologic factors conspire to allow these viruses to stray out of their bat reservoirs into the two different intermediate hosts (horses and pigs) and then into humans. (3) We do not know how long these viruses have been present in the bat population, where they originated from, or if they are present in other parts of the world. (4)There may be other viruses waiting for similar opportunities to cross species.(5) It is unlikely that we have seen the last of these and related viruses.