To investigate whether BD may cause degeneration of photoreceptors and possibly of other neuronal cells at least at later stages of the disease, we performed a detailed quantitative morphologic study of retinal tissue from Borna-diseased horses.
BD was diagnosed by detection of pathognomonic Joest-Degen inclusion bodies in the postmortem brains.
Paraffin sections of paraformaldehyde-fixed retinae were used for histologic and immunohistochemical stainings.
Numbers of neurons and Müller glial cells were counted, and neuron-to-Müller cell ratios were calculated. Among tissues from 9 horses with BD, we found retinae with strongly altered histologic appearance as well as retinae with only minor changes.
The neuron-to-Müller cell ratio for the whole retina was significantly smaller in diseased animals (8.5 ± 0.4; P < .01) as compared with controls (17.6 ± 0.8).
It can be concluded that BD in horses causes alterations of the retinal histology of a variable degree.
The study provides new data about the pathogenesis of BD concerning the retina and demonstrates that a loss of photoreceptors may explain the observed blindness in infected horses.
Source: J. Dietzel, H. Kuhrt, T. Stahl, J. Kacza, J. Seeger, M. Weber, A. Uhlig, A. Reichenbach, A. Grosche and T. Pannicke (2007): Morphometric Analysis of the Retina from Horses Infected with the Borna Disease Virus. In: Vet Pathol 44:57-63 (2007)
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