Centers for Disease Control and Prevention, Division of Viral and RickettsialDiseases, Measles Virus Section, Atlanta, GA, USA. wjb{at}cdc.gov
Nipah virus emerged approximately two years ago as the causative agent of fatal febrile encephalitis in humans in Peninsular Malaysia leaving 105 people dead.123 Necessary control measures left the pig farming industry in ruin, since almost 50% of the stock was destroyed to prevent spread of the disease. Nipah virus along with Hendra virus are among the most recently discovered paramyxoviruses, and share some uncommon traits that may serve to aid in defining a new genus within the Paramyxoviridae family.4 In terms of genomic structure and phylogenetic analysis, Nipah and Hendra viruses appear most closely related to the morbillivirus genus.5 The members of that genus contain viruses of a highly contagious nature including measles among humans, rinderpest among cattle, and canine distemper virus among dogs. In contrast, both Nipah and Hendra viruses have expanded host ranges, which include man, albeit as a dead-end host.
Limited experience with Hendra virus outbreaks suggested that close contact with horse saliva and perhaps urine were major risk factors for humans contracting the illness.6 Moreover, there was precedence for persistent infection, since one man died from encephalitis 13 months after assisting with an autopsy of an infected horse, his only known exposure.7 Preliminary investigations of the Nipah virus outbreak indicated that close contact with pigs was the major risk factor associated with human disease.8 The pathology in pigs, the amplifying host, involved the respiratory tract and lungs with neurological disease and death occurring only infrequently. In contrast, neurological involvement was most common in the human cases and resulted in death in 40% of those infected. Coincident with the outbreak in Malaysia, a second outbreak of Nipah virus occurred among abattoir workers in Singapore.9 However, only a single death was reported among the 11 individuals who contracted the illness.
The epidemiological investigation undertaken by Sahani and others10 was designed to examine the risk factors associated with Nipah virus infection of abattoir workers in Malaysia. A positive serology was interpreted as a sign of infection. Enrolment was extended to abattoir workers in 11 states and not just limited to those with a history of disease symptoms consistent with Nipah infection. This potentially would have permitted a measure of possible asymptomatic infection. Only seven IgG seropositive (six of seven were also IgM positive) workers were identified, and all were from regions that reported infected pig farms. Six of the workers reported close contact with infected pigs or body fluids. The paucity of seropositive workers helped allay fears that Nipah virus infections had been occurring long before the outbreak was recognized, and were more widespread involving areas where Nipah virus infected pigs had not been reported. The reason(s) for the lower mortality rate in this and the Singapore investigation remains unknown, but factors such as infectious dose and route of infection, and intensity of exposure have been proposed. To date, no recrudescence of disease in previously infected individuals has been confirmed.
References
1
Anonymous. From the Centers for Disease Control and Prevention. Outbreak of Hendra-like virusMalaysia and Singapore, 19981999. JAMA 1999;281:178788.
2 Anonymous. Outbreak of Hendra-like virusMalaysia and Singapore, 19981999 [published erratum appears in MMWR 1999;48:339]. MMWR 1999;48:26569.[Medline]
3 Anonymous. Update: outbreak of Nipah virusMalaysia and Singapore, 1999. MMWR 1999;48:33537.[Medline]
4
Chua KB, Bellini WJ, Rota PA et al. Nipah virus: a newly emergent deadly paramyxovirus.. Science 2000;288:143235.
5 Harcourt BH, Tamin A, Ksiazek TG et al. Molecular characterization of Nipah virus, a newly emergent paramyxovirus. Virology 2000;271:33449.[ISI][Medline]
6 McCormick JG, Allworth AM, Sehvey LA, Sellek PW. Transmissibility from horses to humans of a novel paramyxovirus, equine-morbillivirus (EMV). J Infect 1999;38:2223.[ISI][Medline]
7 O'Sullivan JD, Allworth AM, Paterson DL et al. Fatal encephalitis due to novel paramyxovirus transmitted from horses. Lancet 1997;349: 9395.[ISI][Medline]
8 Parashar UD, Sunn LM, Ong F et al. Case-control study of risk factors for human infection with a new zoonotic paramyxovirus, Nipah virus, during a 19981999 outbreak of severe encephalitis in Malaysia. J Infect Dis 2000;181:175559.[ISI][Medline]
9 Paton NI, LeoYS, Zaki SR et al. Outbreak of Nipah-virus infection among abattoir workers in Singapore. Lancet 1999;354:125356.[ISI][Medline]
10
Sahani M, Parashar UD, Ali R et al. Nipah virus infection among abattoir workers in Malaysia, 19981999. Int J Epidemiol 2001; 30:101720.
|