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Objective To determine the cause of an epidemic of blindness in kangaroos. Design and procedures Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences. Sample population For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically. Results Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975. Conclusion Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes.

Original publication

DOI

10.1111/j.1751-0813.1999.tb12126.x

Type

Journal article

Journal

Australian veterinary journal

Publication Date

08/1999

Volume

77

Pages

529 - 536

Addresses

CSIRO Australian Animal Health Laboratory, PO Bag 24, Geelong, Victoria 3220NSW Agriculture, Elizabeth Macarthur Agricultural Institute, PMB 8, Camden, New South Wales 2570VETLAB SA, Department of Primary Industries, GPO Box 1671, Adelaide, South Australia 5001NSW Agriculture Horticultural Research and Advisory Station, PO Box 581, Gosford, New South Wales 2250VIAS Attwood, Agriculture Victoria, 475/485 Mickleham Road, Attwood, Victoria 3049.