From September, 1998 and through early 1999, at least 265 people in Malaysia developed febrile encephalitis and 111 people died. Although initially attributed entirely to Japanese encephalitis virus infections, most of these people are now known to have died because of infection with a new paramyxovirus called "Nipah virus," named after the village of Sungai Nipah where the virus was first recognized.

• 93% of human patients had direct contact with pigs. Symptoms most commonly included fever, headache, dizziness and vomiting. 55% of patients manifest a reduced level of consciousness and brainstem involvement. 32% of patients rapidly deteriorated and died. 15% of patients had persistent neurologic deficits even after recovery.

The initial consideration of Japanese encephalitis virus was based on the nature of the clinical signs in the affected people as well as the strong epidemiological connection between infections in humans and contact with pigs.

Because of the epidemiological link to pigs, a massive effort was undertaken in Malaysia to euthanize all infected or possibly infected pigs so as to reduce the proposed reservoir of infection.

• Infection of pigs with Nipah virus was associated with neurologic disease in sows and boars, while weanling and feeder pigs more commonly manifest respiratory signs. In addition, results of serologic studies and experimental infections provide evidence for subclinical infections. Experimental infection studies also confirm that pigs shed the virus in their nasopharyngeal secretions.
  • In addition to pigs, Nipah virus infections have also been detected serologically in dogs, cats, goats and horses.

One additional person died on Jan. 27, 2000, and in June 2000, additional human cases of Nipah virus-induced encephalitis were diagnosed in Malaysia, leading to renewed (but smaller scale) pig depopulation efforts. Additionally, outbreaks of encephalitis disease in people in Bangladesh (with high case fatality rates) occurred in 2001 and 2003. The source of infection for these people was not cleared identified, but the infections were due to a Nipah/Hendra-like virus.

Nipah virus is genetically most closely related to Hendra virus, another recently discovered novel paramyxovirus, but the two are distinct viruses. Hendra virus, Nipah virus and Menangle virus are all novel paramyxoviruses that appear to have emerged from a fruit bat reservoir over the past decade. Most recently, another novel paramyxovirus (Tioman virus) closely realted to Menangle virus has been isolated from fruit bats in Malaysia. This virus has not yet been associated with clinical disease in terestrial mammals.

References:

Baker, M. 1999. New virus fingered in Malaysian epidemic. Science 284:407-410.

Bunning, M. et al. 2000. Epidemiological trace-back studies of the Nipah virus outbreak in pig farms in the Ipoh district of Malaysia, 1997-1999. Proceedings of the 16th Congress of the International Pig Veterinary Society, Melbourne, Australia, September 17-20:551.

Enserink, M. 1999. New virus fingered in Malaysian epidemic. Science 284:407-410.

Goh, K.J. et al. 2000. Clinical features of Nipah virus encephalitis among pig farmers in Malaysia. N. Eng. J. Med. 342:1229-1253.

Johara, M.Y. et al. 2001. Nipah virus infection in bats (Order Chiroptera) in peninsular Malaysia. Emerg. Infect. Dis. 7:439-441.

Middleton, D. et al. 2000. Experimental Nipah virus disease in pigs: clinical features, virus excretion and subclinical infection. Proceedings of the 16th Congress of the International Pig Veterinary Society, Melbourne, Australia, September 17-20:548-552.

Nor, M.N. and B.L. Ong. 2000. The Nipah virus outbreak and the effect on the pig industry in Malaysia. Proceedings of the 16th Congress of the International Pig Veterinary Society, Melbourne, Australia, September 17-20:548-550.

Watts J. 1999. Hendra-like virus responsible for epidemic in Malaysia. Lancet 353:1335.

Wong, K.T. et al. 2002. Nipah virus infection, an emerging paramyxoviral zoonosis. Springer Semin. Immunopathol. 24:215-228.