Emerging Viruses in Human Populations

Nipah and Hendra viruses are two zoonotic paramyxoviruses with an ability to cause fatal encephalitic and respiratory diseases in humans. Hendra virus was first identified in humans in Australia in 1994, with horses as the intermediate host. Nipah virus emerged in humans in 1998 in Malaysia, with pigs as the intermediate host. Nipah virus was later also identified in India and Bangladesh in 2001, with the flying fox (Pteropus spp.) as the natural host, although no intermediary animal host was found in more recent outbreaks there. A third zoonotic paramyxovirus, Menangle virus, was first identified in pigs, and will be discussed only briefly. Of the zoonotic paramyxoviruses, Nipah virus is responsible for the greatest number of human cases, with several hundred cases and at least 215 deaths reported, compared to Hendra virus, which has caused a handful of cases and 2 deaths, and Menangle, which has only caused self-limited illness in 2 individuals.