Abstract
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.
Highlights
Suid herpesvirus 1, known as Aujeszky’s disease virus or pseudorabies virus (PRV), has been classified in the genus Varicellovirus, subfamily Alphaherpesvirinae and family Herpesviridae [1]
Pigs euthanized at four Days Post Inoculation (DPI) showed clinical signs, the severity of which was dependent on their age: (i) the one-week-old piglets showed diminished appetite, nasal secretion, depression and unbalanced stepping, while they were continuously keeping their heads down sniffing at the floor; (ii) the three-week-old piglets showed less severe symptoms, e.g., diminished appetite and nasal secretion, while only two of them were depressed; (iii) the five-week-old pigs were in a good condition showing only a small decrease in their appetite
At four DPI, the virus had been detected in all neuronal levels of the pigs of all age groups, with virus quantities being reduced with increasing age and neuronal level (Table 1)
Summary
Suid herpesvirus 1, known as Aujeszky’s disease virus or pseudorabies virus (PRV), has been classified in the genus Varicellovirus, subfamily Alphaherpesvirinae and family Herpesviridae [1]. PRV is the causative agent for pseudorabies, a disease that mainly affects pigs and incidentally other domestic and wild animals. PRV has been eliminated from the domestic pigs of several countries in Europe and around the world due to the implementation of national eradication programs [6,7,8]. While PRV is almost always fatal, causing neurological disease independently of the age in non-porcine species, the severity of neurological manifestation in its host species, the pig, decreases as the age increases [14,15,16]. After primary replication in the nasopharyngeal mucosa, the virus spreads via nerves towards the central nervous system (CNS), where it causes non-suppurative meningoencephalitis. The neurons of the trigeminal ganglion represent the first neuronal level; the neurons of the pontine and spinal nucleus of the trigeminal nerve, which are located in the pons and the medulla oblongata, respectively, represent the second neuronal level; the neurons of thalamus and the Purkinje cells of the cerebellum represent the third neuronal level
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