Exophthalmos and Buphthalmos in Broiler Breeders Associated with Marek's Disease Virus

This study investigated blindness accompanied by unilateral or bilateral exophthalmos in four broiler breeder flocks. Histopathologic examination revealed keratitis, corneal edema, cataracts, uveitis, and pectenitis. In addition, retinal degeneration and occasional intranuclear inclusion bodies, consistent with herpesvirus, were observed in the ganglion layer. Immunohistochemical analysis of the ocular sections revealed a mixture of T cells (CD3+) and B cells (Pax5). Marek's disease virus type 1 (MDV-1) DNA was detected in all samples of optic nerve, vitreous fluid, retina, cornea, iris, and lens, at similar or higher levels than it was found in the spleen. Even though the MDV-1 DNA load was compatible with latency levels in all samples, it was highest in those eye structures with evident gross and microscopic lesions. The level of DNA detected was compatible with latency of Marek's disease virus (MDV) in the spleens and eyes; however, the <i>pp38</i> gene from oncogenic MDV was not detected. Similar lesions have been reported in chickens vaccinated for herpesvirus of turkey when challenged with a very virulent plus (vv+) MDV. This is the first report suggesting a potential association with MDV-induced eye lesions in CVI988-vaccinated chickens that were properly protected against tumor development induced by MDV.