No abstract

Emerging zoonoses threaten global health, yet the processes by which they emerge are complex and poorly understood. Nipah virus (NiV) is an important threat owing to its broad host and geographical range, high case fatality, potential for human-to-human transmission and lack of effective prevention or therapies. Here, we investigate the origin of the first identified outbreak of NiV encephalitis in Malaysia and Singapore. We analyse data on livestock production from the index site (a commercial pig farm in Malaysia) prior to and during the outbreak, on Malaysian agricultural production, and from surveys of NiV's wildlife reservoir (flying foxes). Our analyses suggest that repeated introduction of NiV from wildlife changed infection dynamics in pigs. Initial viral introduction produced an explosive epizootic that drove itself to extinction but primed the population for enzootic persistence upon reintroduction of the virus. The resultant within-farm persistence permitted regional spread and increased the number of human infections. This study refutes an earlier hypothesis that anomalous El Niño Southern Oscillation-related climatic conditions drove emergence and suggests that priming for persistence drove the emergence of a novel zoonotic pathogen. Thus, we provide empirical evidence for a causative mechanism previously proposed as a precursor to widespread infection with H5N1 avian influenza and other emerging pathogens.

Nipah virus, family Paramyxoviridae, caused disease in pigs and humans in peninsular Malaysia in 1998-99. Because Nipah virus appears closely related to Hendra virus, wildlife surveillance focused primarily on pteropid bats (suborder Megachiroptera), a natural host of Hendra virus in Australia. We collected 324 bats from 14 species on peninsular Malaysia. Neutralizing antibodies to Nipah virus were demonstrated in five species, suggesting widespread infection in bat populations in peninsular Malaysia.

Infection rates may be higher during pregnancy and lactation.

Abstract.A descriptive study was undertaken on 595 dairy cattle abortion submissions to the California Veterinary Diagnostic Laboratory System from July 1, 1987, to December 31, 1989, to determine the etiologic nature and distribution (seasonal and geographical) of dairy cattle abortion in California as reflected by laboratory submissions. Univariate analysis was performed to characterize abortion-related submissions by farm and laboratory variables, and logistic regression analysis was performed to determine factors that may influence success of abortion diagnosis in the laboratory. The proportions of dairies that submitted abortion-related specimens from northern, central, and southern milksheds during the 2.5-year period were 20.3%, 15.7%, and 13.1%, respectively, and 60% of submissions were from medium-sized (200-999 cows) dairies. Submissions consisted of fetus (58%), placenta (2%), fetus and placenta (12%), and fetus, placenta, and maternal blood (0.84%); fetal tissues and uterine fluid constituted the rest. An apparent pattern in abortion submissions was indicated by a peak in submissions during the winter and summer of 1988 and 1989. Infectious agents were associated with 37.1% of submissions; noninfectious causes, 5.5%, and undetermined etiology, 57.3%. Bacterial abortion accounted for 18% of etiologic diagnoses; protozoal, 14.6%; viral, 3.2%; and fungal, 1.3%. Submissions comprising fetus, placenta, maternal blood, or their combinations were associated with a higher likelihood of definitive diagnosis for abortion than tissues, as were fresher specimens and submissions associated with the second trimester of fetal gestation.Abortion in dairy cattle is a serious problem that results in considerable economic losses to the dairy industry from reduced production efficiency. 5,11,22,24 Effective control measures require not only prompt and accurate diagnosis of abortion but also understanding of the multicausal factors involved in this disease. Prospective field studies of abortion have involved onfarm surveillance programs for detection and prediction of changes in abortion risk. 12,24,25 Unfortunately, this approach is very expensive and not routinely applicable in the field. Retrospective use of laboratorybased abortion data has not been vigorously attempted because of several major shortcomings inherent in such data. Retrospective surveys using diagnostic data usually describe abortion by category of etiologic diagnosis, with few farm and laboratory variables taken into account. 1,12,14 Traditionally collected veterinary laboratory data can provide useful information for unFrom the Department of Veterinary Sevices, Ministry of Agriculture,