Viral Encephalitis in Malaysia and Singapore

News release

The outbreak of viral encephalitis in Malaysia is continuing. As at 7 April 1999, a total of 234 cases and 90 deaths had been reported by the Malaysian Ministry of Health. Both Japanese encephalitis virus and a newly identified paramyxovirus are implicated in the outbreak. The newly identified virus has been called a Hendra-like virus due to its similarities to a virus first isolated in Australia in 1994. Recent evidence indicates that most of the cases and deaths in Malaysia have been due to the Hendra-like virus. This virus infects both humans and pigs, causing encephalitis in humans. Deaths among infected pigs have been associated with convulsions, cyanosis, lung congestion and brain oedema.

Transmission of the virus appears to take place from pigs and to humans through direct contact with body fluids of pigs. Based on human cases currently under treatment, the incubation period ranges from 4 to 18 days with the first symptom being a severe headache. Severe cases result in coma and death. Those most at risk include workers in piggeries and abattoirs. There is so far no evidence that transmission takes place from person to person or from eating cooked pork.

The Malaysian Ministry of Health has acted promptly to control the outbreak. It appears that the disease has been contained within a small area around Bukit Pelandok in Negri Sembilan. The movement of pigs out of the area to slaughterhouses or other farms has been banned. All pigs in the area are being systematically culled. To date over 610 000 have been killed out of an estimated 850 000 targeted in the culling campaign. Residents of the most severely affected area have been evacuated and are being housed in temporary quarters, pending the completion of the culling and clean-up operations.

The Malaysian Ministry of Health is carrying out an investigation of the outbreak, supported by a team from the Centers for Disease Prevention and Control in Atlanta, United States of America, Commonwealth Scientific Industrial Research Organization (CSIRO) Australia, and other countries. WHO staff have also been dispatched to Malaysia. Laboratories in Malaysia at the Institute of Medical Research, and the WHO Collaborating Centre Laboratory at the University of Malaya have been involved. Further laboratory support has been provided by the WHO Collaborating Centre at the Institute for Tropical Medicine, Nagasaki University, Japan, and the Centers for Disease Prevention and Control.

In Singapore there have been 11 confirmed cases including 1 death due to the new virus. All were abattoir workers who had had contact with pigs imported from Malaysia. Since these cases, Singapore has stopped all imports of pigs and instituted clean up operations in affected areas. Following the imposition of the import ban and clean-up operations no further cases have been reported from Singapore.

Other countries, including the Philippines and Thailand, have temporarily halted the importation of pigs from Malaysia and are maintaining surveillance for any sign of viral encephalitis.

There are many questions still to be answered about the outbreak, but the link between pigs and man has been established. In order to prevent the disease from spreading to other pig farming areas within Malaysia and to neighbouring countries the movement of all pigs in Malaysia is being strictly controlled or totally halted. Farmers are being advised to report all unusual deaths among pigs. Since detergents destroy the virus, farmers and those handling pigs are being advised to wash up regularly and maintain sanitary conditions when working with pigs. Countries in the Region are advised to conduct surveillance of piggeries and import centres for unusual deaths among pigs.

For more information, contact Mr Charles Raby, Public Information Officer at (632) 528 9983 or email:

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