Age-Dependent Invasion of Pseudorabies Virus into Porcine Central Nervous System via Maxillary Nerve

Pseudorabies virus (PRV) is the causative agent for Aujeszky's disease, a disease that mainly affects pigs and incidentally other domestic and wild animals. While PRV is almost always fatal, causing neurological disease independently of the age in non-porcine species, the development of neurological manifestation in its host species, the pig, highly depends on the age. In this study, an attempt was made to investigate the effect of nerve development on the outcome of virus infection and the effect of virus infection on the structure of nerves in piglets of various ages. For that reason, 42 pigs at the age of one (n = 14), three (n = 14) and five (n = 14) weeks were inoculated with 10⁷ TCID₅₀ of PRV Kaplan strain and euthanized at one- or four-days post inoculation (DPI). The tissues of the trigeminal nervous pathway were collected and examined for virus replication (titration) in cell cultures for nerve morphology by light and transmission electron microscopy, and for viral antigen visualization by immunohistochemistry. The results showed that as the age of the pig increases, virus titers and clinical manifestations reduced, while, at the same time, myelin and axon development ceased. Following infection, the nerve structure was disrupted at all ages examined, being more prominent in one-week-old pigs compared to five-week-old pigs. In conclusion, the age-dependent PRV neuroinvasion in pigs seems to correlate with the morphological changes of neurons.