Commentary: Paramyxoviruses, pigs and abattoirs

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.