Age- and strain-dependent differences in the outcome of experimental infections of domestic pigs with wild boar pseudorabies virus isolates

Abstract

Although pseudorabies virus (PRV) has been eradicated in domestic swine in many countries, its presence in wild boars remains a threat for a reintroduction into the currently unprotected swine population. To assess the possible impact of such a reintroduction in a naive herd, an in vivo infection study using two genetically characterized wild boar PRV isolates (BEL24043 and BEL20075) representative for wild boar strains circulating in south-western and central Europe and the virulent NIA3 reference strain was performed in 2-and 15-week-old domestic pigs. Our study revealed an attenuated nature of both wild boar strains in 15-week-old pigs. In contrast, it showed the capacity of strain BEL24043 to induce severe clinical symptoms and mortality in young piglets, thereby confirming that the known age dependency of disease outcome after PRV infection also holds for wild boar isolates. Despite the absence of clinical disease in 15-week-old sows, both wild boar PRV strains were able to induce seroconversion, but to a different extent. Importantly, differences in infection and transmission capacity of both strains were observed in 15-week-old sows. Strain BEL24043 induced a more prolonged and disseminated infection than strain BEL20075 and was able to spread efficiently to contact animals, indicative of its capacity to induce a sustained infection. In conclusion, it was shown that a reintroduction of a wild boar isolate into the domestic swine population could have serious economic consequences due to the induction of clinical symptoms in piglets and by jeopardizing the PRV-negative status.

Genetic Diversity among Pseudorabies Viruses Isolated from Dogs in France from 2006 to 2018

“…Many other variations in amino acid residues were observed between the various PRV strains, as for example, at positions 16, 25, 38, or 39. Many of them have also been observed in previous studies conducted in other countries [10,13,35], but these differences in gC did not seem to relate to biological differences in vitro [12]. In vivo, it was demonstrated that two Belgian PRV strains differing from each other by the amino acid at position 18 presented attenuated clinical signs in adult pigs, but only one of them induced a major respiratory and neurological disease in young piglets [36]. Sequencing the partial UL44 gene, which is only a small part of the PRV genome, is not sufficient to assume a possible difference in the pathogenicity of PRV strains.…”

Pseudorabies virus isolates from domestic pigs and wild boars show no apparent in vitro differences in replication kinetics and sensitivity to interferon-induced antiviral status

“…Phylogenetic analysis of a part of the gC gene, performed in accordance with literature standards (Goldberg et al, 2001;Hahn et al, 2010;Müller et al, 2010), showed that these isolates cluster together with other wild boar isolates from south-western Europe in clade B and can therefore be considered as representative strains (Verpoest et al, 2014). The virulence of two of these wild boar strains, BEL20075 and BEL24043, was tested in vivo in 2-and 15-week-old domestic pigs, and indicated the attenuated nature of these strains in adult pigs (Verpoest et al, 2016). Domestic swine strains were directly obtained from domestic swine that were euthanized after experiencing important clinical symptoms typical for Aujeszky's disease.…”

Reduced virulence of a pseudorabies virus isolate from wild boar origin in domestic pigs correlates with hampered visceral spread and age-dependent reduced neuroinvasive capacity

“…In this report, we present a study of the pathogenesis and associated cytokine mRNA expression in 2- and 15-week-old domestic pigs after infection with the previously characterized wild boar PRV isolate BEL24043. 7 In addition, we compare and contrast these results to our previous study with the virulent domestic NIA3 strain 8 and from this suggest mechanistic explanations for the age-dependence of infection and the overall reduced virulence of the BEL24043 strain.…”

“…While two Belgian wild boar strains were attenuated in adult pigs (BEL24043 and BEL20075), only one induced important respiratory and neurological disease in 2-week-old piglets (BEL24043). 7 Overall, cell biological and molecular explanations for the observed differences in virulence between PRV strains, and particularly wild boar strains, are lacking.…”