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Isolation of Nipah virus from the Island flying fox

by 5m Editor
15 August 2000, at 12:00am

Researchers in Malaysia have confirmed a link between fruit bats and Nipah virus, the recently discovered novel paramyxovirus that killed more than 100 people last year and compelled authorities to slaughter roughly a million pigs.

By Prof. Kenneth Lam Sai Kit, of the Department of Microbiology at the University of Malaya, confirmed that his research team had successfully isolated Nipah virus from urine samples collected from colonies of the Island flying fox, one of the many species of fruit bats that live throughout Southeast Asia. Professor John S. Mackenzie, of the Department of Microbiology and Parasitology at Australia's University of Queensland stated that this finding confirms that bats are carriers or reservoirs for the virus, which last year crossed over to pigs and then to humans. Professor Lam's findings constitute a breakthrough in understanding the virus.

Professor Lam's finding came just after an outbreak of Nipah virus in June in Northern Malaysia. Health authorities in Northern Perak killed more than 1 700 pigs to prevent the disease from spreading after a woman living nearby was found to have the virus. While it remains unclear exactly how the virus is transmitted from fruit bats to pigs, numerous opportunities exist for the rare crossover to occur, Professor Lam said. Fruit trees in which bats forage for food are often near pigsties, he said, and Malaysia's pig farmers tend to live very close to their pigs. Malaysia is considering measures to protect its $400-million-a-year pig farming industry, which was crippled by last year's outbreak.

Nipah virus infection first appeared as a pandemic early last year when it hit pig farms in Malaysia and slaughterhouses in nearby Singapore. Health workers initially believed they were dealing with an outbreak of Japanese encephalitis, which is transmitted from pigs to humans by mosquitoes. The symptoms were similar: high fever, aches and coma. Roughly 4 of every 10 sufferers died. Confounding this early diagnosis was the fact that some victims had been inoculated against Japanese encephalitis and that most lived near or worked on pig farms. The virus was also killing some pigs, and Japanese encephalitis virus is not associated with mortality in pigs.

After a Malaysian microbiologist isolated the virus from the brain and spinal fluid of Nipah victims, scientists at the Centers for Disease Control (CDC) in Atlanta determined that the virus was not Japanese encephalitis virus but a novel virus belonging to the family Paramyxoviridae. Its closest relative is another recently discovered paramyxovirus called Hendra virus, which was isolated in 1994 after killing 14 horses and their trainer in Australia. Hendra virus was carried by fruit bats, so researchers began searching for a similar link between Nipah virus and bats. Scientists from the CDC, Taiwan, Japan and Australia flew to Malaysia, scouring pig farms and villages and trapping bats. Tissue samples from roughly 300 fruit bats revealed antibodies against Nipah virus.

A year later, Professor Lam and his team set out to search themselves. In early June, he said, they spent 3 nights laying plastic sheets under trees full of flying foxes, collecting urine samples. Back in the lab, they found isolates of Nipah virus that matched those recovered from humans. Professor Lam said that only 3 of his 1,000-odd samples contained the virus, which indicated that bats were by no means infested by the virus. Professor Mackenzie, who researched the Hendra virus's transmission from bats to horses and to humans, said infections took place only under very rare circumstances, usually by direct contact with infected blood. In Nipah's case, no transmission between people appears to have occurred. Professor Lam said that because Nipah can also be found in saliva, it was possible that pigs may have become infected by eating fruit that the bats had nibbled on.

How the virus moves from pigs to humans remains unclear, but researchers believe one possibility is that people inhale infected particles of saliva coughed up by Nipah virus-infected pigs. Professor Lam's findings raise concern about the possibility that the bats, which are migratory, could carry the disease beyond Malaysia. Southeast Asia is home to several species of fruit bat, many of which are considered delicacies and have been hunted nearly to extinction. In Malaysia, for example, fruit bats are now protected by law. Professor Lam said antibodies against Nipah virus had been found in other species of fruit bat. Moreover, Nipah is also known to infect dogs, cats and horses, presenting the possibility that pig farms may not be the only venues for crossover.

New York Times - 15th August 2000