Scientists are racing to uncover the origin of a highly virulent new virus that erupted in Australia, killing 14 horses and a horse trainer, to determine where it might strike again.
Although Australia's outbreak appears to be over, scientists have no idea what made the still-unnamed virus suddenly appear in animals and then jump to humans - or how big a threat it poses.They do know it's part of the family that includes measles and canine distemper, but it's the first in this viral family to kill more than one species.
Until researchers know the source of the virus, such as a bird or an insect that doesn't itself become sick but spreads the pathogen to susceptible animals, they don't know what countries are at risk or how to fight back.
"Investigations are now under way to . . . establish whether the virus remains a threat," Dr. Keith Murray of the Australian Animal Health Laboratory reported Friday in the journal Science.
"It's not at all clear what's going on here," agreed Dr. Brian Mahy, viral director at the U.S. Centers for Disease Control and Prevention.
In September, 21 horses on several Queens-land farms suddenly came down with severe respiratory disease and 14 died. Vic Rail, 49, one of Australia's leading horse trainers, died after a week of similar symptoms, and a 40-year-old stablehand who also cared for the ill animals was sickened but survived.
Frustrated veterinarians ruled out every known culprit.
Then Murray and fellow researchers successfully isolated the mystery virus from the lungs of dead horses. They proved it was responsible by infecting additional horses, who quickly died. They then isolated the virus from a kidney of the late horse trainer. His virus was identical to the horses', Murray reported.
The virus killed by creating holes in blood vessels that leaked into lungs until the victims basically drowned. Veterinarians reported horses dying with blood gushing from their noses and mouths.
Genetic testing showed the pathogen is a morbillivirus, the viral family that includes measles. The family includes canine distemper, cattle plague and newly discovered versions that recently killed North Atlantic seals and African sheep.
But it's more deadly, it's the first known morbillivirus to afflict more than one mammal species and it's the first discovered in humans since measles in the 10th century. Even its genetic appearance is different from its cousins.
"Analyses suggest that the virus has not resulted from a single mutation or a few key point mutations, but most likely is a virus that has emerged from its natural host," Murray said.
The Australians are testing animals that live near the horse farms to try to uncover the natural host. They're confident the outbreak is over because tests of 1,600 horses and 90 people show no evidence of further infection.
Murray urged doctors and veterinarians worldwide to review their records of respiratory disease to see if the virus has appeared before. He will visit the CDC in Atlanta next week to discuss the new virus.