A guinea-pig model of Hendra virus encephalitis.

Subcutaneous inoculation, but not intradermal (footpad) or intranasal inoculation, with high doses of Hendra virus (HeV) consistently produced disease in guinea-pigs. Of 15 subcutaneously inoculated animals, 14 developed vascular disease with positive HeV immunohistochemical labelling in a range of tissues. A new observation was the presence of lesions, including syncytial cells, with immunolabelling in the transitional epithelium of the bladder. Virus isolation from the urine rather than from nasal, oral, rectal or conjunctival swabs, the other external sites, was consistent with previous epidemiological work in horses, indicating a limited possibility of transmission. The dose used (30 000 to 50 000 TCID(50)), which was higher than in previous studies, produced microscopical lesions of encephalitis in eight of the 15 subcutaneously inoculated guinea-pigs, with positive immunolabelling in blood vessels and neurons, especially in the medulla, cerebellum and thalamus. The virus was recovered from six of the encephalitic brains. Severe vascular degeneration in the centres of encephalitic lesions in six of the eight encephalitic guinea-pigs and positive immunolabelling in the choroid plexus of a further animal indicated that the virus entered the brain following virus-induced vascular injury and choroid plexus invasion. Guinea-pigs would appear to be suitable for the study of HeV encephalitis.