This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
T. T. Arunsiripate, R. de Paiva, M. Almeida, C. L. Davis, M. Vincent, K. Saeng-Chuto, B. Guo, JQ. Zhang, and P. E. Piñeyro from Iowa State University take a fresh look at PHEV in today’s Science Page.
Key Points:
- PHEV infection has been associated with necrotizing bronchitis and bronchiolitis in positive lungs
- Historical and contemporary PHEV strains showed similar pathogenicity, both inducing seroconversion and mild epithelial damage
- Limited surveillance highlights the need to better understand PHEV’s role in respiratory disease complexes
Introduction
Porcine hemagglutinating encephalomyelitis virus (PHEV) is a member of the genus Betacoronavirus, and has been historically associated with neurological disease in neonatal pigs. This betacoronavirus presents a neurologic tropism in preweaned piglets causing vomiting and wasting disease due to neuritis of the Meissner plexus and an encephalitis [1, 2]. Although serologic studies indicate global dissemination, the prevalence of PHEV remains unclear due to sporadic reporting and lack of active surveillance. Neonatal pigs are particularly vulnerable, with outbreaks resulting in high morbidity and mortality. Histopathological findings typically include non-suppurative encephalomyelitis and lymphoplasmacytic perivascular cuffs, gliosis, and neuronal degeneration [3, 4]. Recently, PHEV has been detected in a case of influenza-like respiratory disease of show pigs in Michigan, US. During 2020, three diagnostic cases from pigs with reported respiratory clinical signs were received at ISU-VDL. The presence of the virus was confirmed by qPCR, in-situ hybridization and virus isolation in cases of necrotizing bronchitis and bronchiolitis. Therefore the objective of this study is to compare the pathogenic role of the historical PHEV Mengeling strain and a contemporary PHEV field isolate.
Methods
Twenty seven, 12-week-old pigs were inoculated intratracheal and intranasal with 5 and 2 ml respectively with 106 TCID50/ml of Mengeling strain (n=9), contemporary ISU-PHEV isolate strain (n=9) and growth media (n=9). Serum samples were collected on days 0, 2, 5, 10, and 14 for antibody detection, and three pigs per group were euthanized on days 2, 5, and 14 to evaluate gross and histological lesions and molecular detection of PHEV nucleic acid in turbinates, trachea, and lung.
Results
No significant clinical signs (sneezing, coughing, or dyspnea) were observed in the control group or in either of the challenged groups. The control group remained seronegative and no viral nucleic acid was detected by qPCR through the study. The presence of specific IgG PHEV antibodies was confirmed in both challenged groups by 5 DPI with the higher S/P by 10 DPI. Common gross findings in both groups were found in the lung characterized by mild multifocal depressions were suggestive of lobular atelectasis. PHEV nucleic acid was detected by qPCR nasal turbinates and trachea in the Mengeling group while animals in contemporary ISU-PHEV group were positive in the nasal turbinates and lung. Histological evaluation showed mild epithelial attenuation of the mucosal upper respiratory epithelium in both groups.
Discussion
These findings suggest that this model induced a subclinical upper respiratory infection, with the virus being shed in nasal secretions and causing mild gross and histological lesions. However, no significant differences were observed between the historical and contemporary strains. Additionally, PHEV tracheal and nasal inoculation can induce seroconversion. The importance of this finding is that it adds to the understanding of PHEV as a predisposing factor in the porcine respiratory disease complex, potentially allowing infection by other respiratory pathogens due to damage to the mucosal respiratory barriers.
This study was presented at the 2024 NAPRRS/NC229: International Conference of Swine Viral Diseases, the proceeding of this study can be find at: https://vetmed.illinois.edu/wp-content/uploads/2024/12/NAPRRS-NC229-ICSVD_2024-Proceedings_small.pdf
References
[1] Cutlip RC, Mengeling WL. Lesions induced by hemagglutinating encephalomyelitis virus strain 67N in pigs. Am J Vet Res. 1972;33:2003-9.
[2] Cartwright SF, Lucas M, Cavill JP, Gush AF, Blandford TB. Vomiting and wasting disease of piglets. Vet Rec. 1969;84:175-6
[3] Meyvisch C, Hoorens J. An electron microscopic study of experimentally-induced HEV encephalitis. Vet Pathol. 1978;15:102-13.
[4] Li Z, He W, Lan Y, Zhao K, Lv X, Lu H, et al. The evidence of porcine hemagglutinating encephalomyelitis virus induced nonsuppurative encephalitis as the cause of death in piglets. PeerJ. 2016;4:e2443