Nipah virus (NiV) emerged in Malaysia in 1998 as a respiratory and neurologic disease in pigs and caused a severe febrile encephalitis in humans, carrying a 40% mortality rate (n = 265). Bats of the genus Pteropus are considered a natural reservoir for Nipah virus and other related henipaviruses. We proposed two hypotheses for NiV emergence: 1) Nipah virus is endemic and circulating in pteropid bats throughout Malaysia and these bats normally occurred in the area of the index farm where Nipah virus emerged; and 2) the intensification of pig farms in Malaysia enabled sustained NiV epidemics to occur in pigs, facilitating NiV emergence in humans. We performed cross-sectional serological surveys of Pteropus vampyrus and P. hypomelanus from spatially disparate colonies across Peninsular Malaysia. A longitudinal sero-survey of P. hypomelanus from a single population on Tioman Island was conducted between October 2003 and November 2006. Bat population counts and satellite telemetry were used to assess abundance and long-range movements of P. vampyrus. We also analyzed livestock production data from the index farm and modeled within-farm infection dynamics.
Serological studies showed a widespread distribution of Nipah virus antibodies in both species of Pteropus bats in Peninsular Malaysia and provided evidence for continued viral circulation in bats. Results from the pig farm analyses suggest that repeated introduction of NiV from the wildlife reservoir into this intensively managed pig population led to changes in infection dynamics in the pigs. Long-term within-farm persistence permitted regional spread of the virus, ultimately producing widespread human infection. Thus, while pteropid bats have likely been the reservoir for Nipah virus for a long time, the cause of emergence of NiV can be essentially characterized as due to agricultural intensification. Targeted surveillance of these farms in areas where flying fox distributions overlap commercial pig farms is therefore important to detect spillover events early-on and prevent widespread infection.
Published online: November 19, 2008
© 2008 Published by Elsevier Inc.