A Neonatal Murine Model For Caprine Enterovirus Infection And The Viral Tissue Tropism

Enterovirus is a non-enveloped,positive single-stranded RNA virus belonging to the genus Enterovirus within the family of Picornaviridae.As the major causative agents,enterovirus leads to digestive,neurological,and respiratory diseases.According to the latest virus taxonomy,Enterovirus are divided into 12 species enterovirus and 3 species rhinovirus.Enterovirus A-D mainly lead to infections to humans.Enterovirus E and Enterovirus F are causative agents of bovine enterovirus infection in cattle showing clinical signs from respiratory to enteric diseases.Enterovirus G,named porcine enterovirus B previously,is the causative pathogen of enterovirus infections in swine.Enterovirus H and Enterovirus J mainly infect Monkeys.Enterovirus I,Enterovirus K,and Enterovirus L are recently identified new enterovirus species.In 2014,CEV-JL14 was isolated from a goat herd characterized by respiratory and digestive diseases with morbidity and mortality up to 50-80%.As an emerging infection,the pathogenicity and viral pathogenesis remains largely unknown.In this study,we have employed CEV-JL14 viruses to infect different suckling mice to establish a murine model for Caprine enterovirus infection.The susceptible mouse strain,the minimal infective does,the infection route,the virus shedding pattern were determined,separately using different approaches.Out of Kunming,BALB/C and ICR mouse strains,the ICR mouse strain was determined as the most susceptible mouse strain.Results of RT-PCR detection and virus recovery isolation from mice infected with CEV showed that ICR mice were infected by CEV-JL14 via all infection routes,including intraperitoneal injection,intramuscular injection,subcutaneous injection,intragastric administration and nasal administration.The minimal infective dose for CEV virus infection was determined as 2×10⁶ TCID₅₀.The virus was detectable even after 16 dpi in the tissue of the infected mice,suggesting that CEV can persist in mice at least 16 days after they were infected.Histopathological observations revealed that heart typically showed oedema in interstitium and lymphohistiocytic inflammatory infiltration.In liver,cells exhibited granular degeneration and vacuolar degeneration.A huge amounts of inflammation cells infiltrated to the lung and resulted in the disruption and replacement of normal alveolar structure.The epithelial cells in the kidney and small intestine were severely disrupted.There are different degrees of vacuolar degeneration and necrosis in brain neurons.Interstitial edema,lymphocytic infiltration and fibrous tissue were observed in muscle of infected mice.Simultaneously,CEV viral antigen were detected in tissues including heart,liver,spleen,lung,kidney,intestine,brain and muscle by immunohistochemistry assay.The virus was significantly higher in the myocardium,muscle,liver and lung than in other tissues.In summary,we have successfully established CEV suckling mouse model and determined the most susceptible mouse strain,the minimal infective dose,the infection routes,the pathological lesions,and viral tissue tropism.These results will lay the foundation for further study of the pathogenic mechanism of the CEV.