Morphometric analysis of the retina from horses infected with the Borna disease virus.

The research studies the impact of Borna disease (BD), a fatal disorder, on the retina of infected horses, suggesting that the disease may cause degeneration of photoreceptors and other neuronal cells, potentially explaining the incidence of blindness in these horses.

Study Objective and Methodology

• The main aim of the research was to investigate if Borna disease causes degeneration of photoreceptors and other neuronal cells in the horse’s retina. This was done through a detailed quantitative morphologic study of retinal tissue in Borna-diseased horses.
• The disease was diagnosed by identifying distinctive Joest-Degen inclusion bodies in the postmortem brains of the horses. To study the effect on retinal tissue, paraffin sections of paraformaldehyde-fixed retinae were used for histologic and immunohistochemical staining.
• The researchers counted the number of neurons and Müller glial cells, a type of retinal cell, in the studied tissue. After this, the neuron-to-Müller cell ratios were calculated to compare the values with those of uninfected control horses.

Results and Findings

• The researchers found a wide range of effects on the retinal tissues from the nine horses infected with Borna disease. Some retinae showed significant changes in their histologic appearance, while others displayed minor changes. The variation indicates that the impact of Borna disease on retinal tissue might differ from one individual to another.
• Significantly, the neuron-to-Müller cell ratio for the whole retina was substantially smaller in the infected horses (an average of 8.5) as compared to the control horses (an average of 17.6). The reduction in this ratio in the diseased animals was significant, with a P-value of less than 0.01, indicating a statistically significant difference.
• The decreased neuron-to-Müller cell ratio in the diseased animals implies that Borna disease in horses likely causes alterations in the retinal histology. In other words, the disease may cause a shift in the cellular structure and composition of the retina.

Conclusion

• The research provides new insights into the pathogenesis of Borna disease and its impact on the retina, suggesting that the loss of photoreceptors might explain the occurrence of blindness in infected horses.
• Given the significant alterations in retinal histology observed in the diseased animals, it can be concluded that Borna disease does impact the retinal cells at some degree. However, the extent of this impact can vary among horses.