Experimental reproduction of viral chorioretinitis in kangaroos

Objective To investigate whether preparations containing Wallal and/or Warr ego viruses could cause disease when inoculated subcutaneously into captive kangaroos. Design and procedure Four groups of two kangaroos, seronegative to both Wal lal and Warrego virus, were each inoculated with wild Wallal virus, culture d Wallal virus, wild Warrego virus, or wild Warrego virus followed by wild Wallal virus after 3 weeks. A single uninoculated animal served as a contro l. Animals were monitored weekly under anaesthesia, examined ophthalmoscopi cally (including fundic photography), and samples collected for haematologi cal and serum biochemical analysis, virus isolation, PCR and serological ex amination for antibodies against Wallal and Warrego viruses. Animals inocul ated with cultured Wallal virus were killed at week 10, and remaining kanga roos were reinoculated with cultured Wallal virus at week 12. Results Virus was isolated from the blood of two kangaroos 2 weeks after in oculation with Wallal virus preparations, and from a third kangaroo 2 weeks after reinoculation. By 3 weeks after inoculation, all kangaroos given Wal lal virus preparations had seroconverted to Wallal virus and one had seroco nverted to Warrego virus. Fundic changes were detected in the three viraemi c kangaroos 4 or more weeks after inoculation, and lesions were present in the eye and brain typical of those seen in field cases of chorioretinitis. No other kangaroos had lesions. Wallal virus was identified by PCR and immu nohistochemical analysis in the retina of one affected animal and orbivirus -like particles were seen by electron microscopy in the remains of retinal cells. Conclusion The condition of chorioretinitis was reproduced in three of eigh t kangaroos by inoculation with preparations containing Wallal virus.