Nipah Virus Infection

Nipah virus infection is an emerging disease endemic in Southeast Asia. This virus is carried in fruit bats of the genus Pteropus, a host to which it seems well adapted. It emerges periodically to affect humans, pigs and occasionally other domesticated animals. Nipah virus infections were first described during widespread outbreaks that occurred in Malaysia in 1998-1999. The virus had apparently circulated in domesticated swine since 1996, but because the mortality rate was low and the disease resembled other porcine infections, it was not identified immediately as a new disease. The epidemic was recognized when Nipah virus spread to pig farmers and abattoir workers in Malaysia and Singapore, causing severe, often fatal encephalitis in approximately 260 people. Some other species, including cats and dogs, were also affected. The Malaysian outbreaks were controlled in both domesticated animals and humans by culling more than one million pigs. In addition, pig farming was permanently banned in some high-risk areas. Since 2001, human outbreaks and clusters of cases have been reported periodically in Bangladesh and a neighboring region of northern India. In some of these outbreaks, Nipah virus seems to have been transmitted directly from bats to humans, with person-to-person transmission the most significant means of spread. Why Nipah virus periodically emerges into humans and domesticated animals is not known; however, fruit bat populations in Southeast Asia are being disrupted by various factors that may alter their foraging patterns and behavior, and bring them into closer contact with domesticated animals and humans.