Virulent Pseudorabies Virus Infection Induces a Specific and Lethal Systemic Inflammatory Response in Mice

Abstract

Pseudorabies virus (PRV) is an alphaherpesvirus that infects the peripheral nervous system (PNS). The natural host of PRV is the swine, but it can infect most mammals, including cattle, rodents, and dogs. In these nonnatural hosts, PRV always causes a severe acute and lethal neuropathy called the "mad itch," which is uncommon in swine. Thus far, the pathophysiological and immunological processes leading to the development of the neuropathic itch and the death of the animal are unclear. Using a footpad inoculation model, we established that mice inoculated with PRV-Becker (virulent strain) develop a severe pruritus in the foot and become moribund at 82 h postinoculation (hpi). We found necrosis and inflammation with a massive neutrophil infiltration only in the footpad and dorsal root ganglia (DRGs) by hematoxylin and eosin staining. PRV load was detected in the foot, PNS, and central nervous system tissues by quantitative reverse transcription-PCR. Infected mice had elevated plasma levels of proinflammatory cytokines (interleukin-6 [IL-6] and granulocyte colony-stimulating factor [G-CSF]) and chemokines (Gro-1 and monocyte chemoattractant protein 1). Significant IL-6 and G-CSF levels were detected in several tissues at 82 hpi. High plasma levels of C-reactive protein confirmed the acute inflammatory response to PRV-Becker infection. Moreover, mice inoculated with PRV-Bartha (attenuated, live vaccine strain) did not develop pruritus at 82 hpi. PRV-Bartha also replicated in the PNS, and the infection spread further in the brain than PRV-Becker. PRV-Bartha infection did not induce the specific and lethal systemic inflammatory response seen with PRV-Becker. Overall, we demonstrated the importance of inflammation in the clinical outcome of PRV infection in mice and provide new insights into the process of PRV-induced neuroinflammation.IMPORTANCE Pseudorabies virus (PRV) is an alphaherpesvirus related to human pathogens such as herpes simplex virus 1 and varicella-zoster virus (VZV). The natural host of PRV is the swine, but it can infect most mammals. In susceptible animals other than pigs, PRV infection always causes a characteristic lethal pruritus known as the "mad itch." The role of the immune response in the clinical outcome of PRV infection is still poorly understood. Here, we show that a systemic host inflammatory response is responsible for the severe pruritus and acute death of mice infected with virulent PRV-Becker but not mice infected with attenuated strain PRV-Bartha. In addition, we identified IL-6 and G-CSF as two main cytokines that play crucial roles in the regulation of this process. Our findings give new insights into neuroinflammatory diseases and strengthen further the similarities between VZV and PRV infections at the level of innate immunity. Citation Laval K, Vernejoul JB, Van Cleemput J, Koyuncu OO, Enquist LW. 2018. Virulent pseudorabies virus infection induces a specific and lethal systemic inflammatory response in mice. J Virol 92:e01614-18. https://doi.org/10 .1128/JVI.01614-18. Editor Ric...

An improved animal model for herpesvirus encephalitis in humans

“…Histopathological changes including viral antigen detection and inflammatory response in mice infected with PrV-ΔUL21/US3Δkin were mainly observed unilateral in FL, MTL and PIR as well as in HIP as reported for patients who died of HSE [74,76,77]. Apoptotic cells were identified mainly in areas without inflammatory reaction indicating increased neuronal death in the context of virus-induced neuronal damage [78][79][80]. So far, PrV-ΔUL21/US3Δkin is the only PrV mutant that establishes a productive infection in mice, which the animals are able to control and survive despite widespread neuroinvasion towards the cerebral cortex and a concomitant severe inflammatory response particularly in the frontal and mesiotemporal lobes.…”

The Neuropathic Itch Caused by Pseudorabies Virus

“…So far, no evidence exists for cell-free or cell-associated viremia in non-natural hosts. No infectious virus was detected in tissues other than the nervous system of infected dogs and mice [30,33,81]. In addition, intravenous inoculation of cattle with PRV failed to disseminate the virus throughout the body.…”

“…Likely, it resulted from virus particles that originally infected the DRG, replicated and went back to the footpad rather than from local viral replication in the footpad. Indeed, the inoculated footpad, which exhibited epidermal necrosis accompanied by immune cell infiltrates, did not have time to regenerate and support efficient viral replication [81].…”

“…Using the footpad inoculation model, it was later shown that virulent PRV-Becker, but not attenuated PRV-Bartha, infection induces a specific and lethal systemic inflammatory response in mice. High levels of IL-6 and granulocyte colony-stimulating factor (G-CSF) were measured in both tissues and plasma of infected animals, including the footpad and DRG at moribund stage [81]. Furthermore, a strong correlation was found between the level of infectious virus detected in the DRG and footpad and the production of pro-inflammatory cytokines.…”

Acute phase protein response to viral infection and vaccination

“…Aujeszky's disease (pseudorabies) is a pathology of pigs caused by a herpes virus resulting in neurological signs that can be fatal [63]. The clinical outcome of pseudorabies virus infection in a mouse model is determined by the acute inflammatory response after infection, with high levels of CRP and il6 produced in several tissues [47].…”