January 24, 2004

Blind Roo

Mysterious Blindness

The scenes were so pathetic that even hardened men-of-the-land went to their aid: blind, disoriented kangaroos hopping into trees, stumbling into fences, bumping into each other, starving. The first reports came from central New South Wales in 1994. The next year, blind animals turned up in the southern states of Victoria and South Australia. And at the beginning of 1996, the blindness had spread across the desert to western Australia. By then, news of kangaroo blindness had traveled around the world.

In Australia, the concern broadened. Was the phenomenon simply a nasty eye disease or something worse? Could the disease be passed on to livestock--or to humans? Was it new, or had it existed before? Was a carrier involved?

These and other questions stimulated a collaboration between agricultural, veterinary, health and wildlife agencies on a scale rarely seen before in Australia. Finally, at Australian Animal Health Laboratories (AAHL) in Geelong, near Melbourne, researchers identified two viruses, using genetic-typing techniques developed by molecular biologist Allan Gould and colleagues.

Gould also was able to test a slide of tissue taken about 20 years previously from a kangaroo with similar symptoms. Kangaroo blindness, it turned out, was not a new disease. And when the AAHL research team tested insects taken from areas where the disease was rife, the viruses turned up particularly in two species of small biting midges (sandflies). That gave the researchers a candidate carrier for the disease.

Meanwhile, veterinarians screening kangaroo populations found that although most kangaroos in areas of disease outbreak showed signs of exposure to the virus, less than three percent went on to develop blindness. And although sheep showed signs of exposure to the virus, they did not become blind. No effect of the virus has ever been detected in humans.

In 1995, heavy rains created ideal conditions for the spread of midges. The disease spread as far south as Victoria and southeastern South Australia, and it swept across the central Australian deserts to Western Australia. There have been few reports of the disease from those parts in the past year, but blind kangaroos are still being found in western New South Wales. As the outbreak has died down, many animal-health scientists have been left pondering the impact of climate change on diseases carried by insects.

Posted by Madfish Willie at January 24, 2004 12:01 AM | TrackBack
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