Another New Human Pathogen: The Nipah Virus
Abstract & Commentary
Source: Enserink M. New virus fingered in Malaysian epidemic. Science 1999;284:407-410.
In march of this year, the entire population of sungai Nipah, a village 62 miles south of Kuala Lumpur, abandoned their homes and their 800 pigs. They were fleeing an epidemic of infection that to date has claimed the lives of more than 100 Malaysians and led to the slaughter of more than a million pigs.
The epidemic is believed to have begun in September 1998, near the city of Ipoh in the northern state of Perak where several pig farmers developed fever, encephalitis, and, in some cases, death.1,2 After the occurrence of additional cases and spread to other areas of pig farming, the Malaysian government, based on the detection of antibody to the Japanese B encephalitis (JBE) virus in some victims, concluded that JBE was the cause of the outbreak. The initial response was insecticide fogging of pig farms and adjacent dwellings as well as vaccinating humans against JBE. Later, there were plans to vaccinate all approximately 2.4 million pigs in the country against this infection.
However, doubts were almost immediately raised to the diagnosis. These objections were the result of the close clustering of cases, all of whom had apparently had pig contact, the fact that pigs also were dying (not characteristic of JBE), the inability to recover JBE virus from affected individuals, and the failure of JBE vaccination to stem the epidemic. As nongovernment scientists in Malaysia continued to air their doubts, the government began calling the epidemic a mixed one, consisting of cases of JBE and another unknown virus.
In early March, Drs. Lam Kai Sit and Chua Kaw Bing recovered a virus from an affected patient and brought it to the CDC laboratories in Fort Collins, Colo. Examination of the virus led to the conclusion that not only was it not the agent of JBE, it was an entirely novel organism. After this observation, the Malaysian government, on March 19, officially asked the CDC for help. The following day thousands of soldiers were sent to work slaughtering pigs.
With continued spread of the virus to other pig farming areas of Malaysia (and Singapore, where at least 11 abbatoir workers are believed to have been infected and at least 1 has died) and events such as the evacuation of Sungai Nipah, the government became increasingly apprehensive. The infection was detected in two dogs, leading to the wholesale slaughter of unlicensed dogs. Just to be certain, stray cats are also being killed.
On April 29, it was reported that two horses at the Iskandar Polo Club had been destroyed because of Nipah infection and that the club was placed under quarantine. The Polo Club is located 2 km from a pig farming area. There had been previous recent equine fatalities at the club, which were apparently attributed to JBE. On May 1, it was reported that the virus had reached Seelong, in the southernmost Malaysian state, Johor, bringing the total number of states involved to four (the other 3: Negri Sembilan, Perak, and Selangor).
The Nipah organism is phenotypically and antigenically similar to the Hendra virus, but its genome has only 80% homology to the latter. The Hendra virus, a member of the subfamily, Paramyxoviridae, and previously known as equine morbilliform virus, was first identified after an outbreak involving horses and humans in Hendra, a suburb of Brisbane, Australia, in 1994 and 1995.3-5 Two of the three infected humans died. The cycle of infection involved fruit bats and to be acquired by humans as a result of exposure to blood and other body fluids.
Most, if not all cases of Nipah virus infection, appear to have resulted from direct contact with pigs; there is, to date, no evidence of human-to-human transmission. The illness is reported to be characterized by fever, myalgia, lethargy, and other symptoms of encephalitis and, eventually, coma, sometimes followed by death. No treatment is available.
References
1. http://www.cdc.gov/travel/malaysia.htm
2. ProMED archives: http://www.fas.org/promed
3. Selvey LA, et al. Infection of humans and horses by a newly described morbillivirus. Med J Aust 1995;162: 642-645.
4. http://www.cdc.gov/ncidod/eid/vol2no1/equine.htm
5. Paterson DL, Murray PK, McCormack JG. Zoonotic disease in Australia caused by a novel member of the paramyxoviridae. Clin Infect Dis 1998;27:112-118.
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