Attenuation of duck Tembusu virus ZJSBL01 strain following serial passage in BHK-21 cells supplied with 5-Fluorouracil.

Duck Tembusu virus (DTMUV) is a new pathogen that produces an acute and potent disease in ducks which has caused serious economic losses in China. In this study, a virulent strain of DTMUV, designated as ZJSBL01, was attenuated by serial passages in BHK-21 cells supplied with 5-Fluorouracil (5-FU) for 50 passages to induce mutation and attenuation. Growth kinetics of different passages of ZJSBL01 strain in BHK-21 cells show that these viruses have similar replication characteristics. The virus was highly attenuated after 40 passages in BHK-21 cells supplied with 5-FU, based on mortality, morbidity, and viral load in inoculated Sheldrake ducklings. In addition, all of the ducklings immunized with ZJSBL01-P40, the virus obtained at passage 40 of ZJSBL01, showed seroconversion on day 14 post inoculation. Moreover, P40 did not cause clinical symptom for layding ducks. Immunization with ZJSBL01-P40 could provide effective protection against the virulent parental ZJSBL01 strain. Seventeen amino acid substitutions were observed in the polyprotein of ZJSBL01-P40 compared with parental ZJSBL01. These results indicate that ZJSBL01-P40 may be a live vaccine candidate for prevention of DTMUV-disease.

Porcine deltacoronavirus induces TLR3, IL-12, IFN-α, IFN-ß and PKR mRNA expression in infected Peyer's patches in vivo.

Porcine deltacoronavirus (PDCoV) is a newly identified swine enteropathogenic coronavirus that causes watery diarrhea in piglets and results in significant economic losses to the pig industry. Currently there are no effective treatments or vaccines for PDCoV. In particular, the pathogenesis of PDCoV infection is still largely unknown. In this study, we reported that inoculating conventional weaned piglets with 1 × 109 TCID50 of the PDCoV CHN-GD-2016 strain by oral feeding could cause severe diarrhea. Virus RNA was detected in rectal swabs from 1 to 7 days post inoculation. In addition, microscopic lesions in small intestine were observed, and viral antigen also detected in the small intestines with PDCoV immunohistochemical staining. Importantly, PDCoV significantly induced mRNA expression of TLR3, IL-12, IFN-α, IFN-ß, and PKR, the genes involved in modulation of the host immune responses, in infected Peyer's patches at 3 d.p.i., indicating that Peyer's patches play an important role in PDCoV immune responses in vivo. Collectively, our findings suggest that the observed gene expression profile might help explain immunological and pathological changes associated with PDCoV infection.

Rapid development and evaluation of a live-attenuated QX-like infectious bronchitis virus vaccine.

Infectious bronchitis (IB) is an acute, highly contagious disease, which causes economic losses to the poultry industry worldwide. To control the disease, biosecurity and vaccination are required. In the current research, we rapidly attenuated a QX-like IBV field strain ZYY-2014 using passage in embryos at limiting dilution and tested the safety and efficacy of the attenuated Chinese QX-like IBV strain ZYYR-2014 in 1-day-old specific-pathogen-free (SPF) chickens through spray route. Our result revealed that the attenuated strain presented a decreased pathogenicity in 1-day-old chickens. The strain ZYY-2014 inoculated birds presented typical IBV clinical signs with a mortality of 43%, while the attenuated strain ZYYR-2014 inoculated birds remained healthy. The strain ZYYR-2014 also presented stronger antibody responses and lower viral loads in tracheas, lungs and kidneys. When vaccinated through spray route into 1-day-old SPF chickens, our data suggest a potential of the attenuated ZYYR-2014 strain as a vaccine candidate applied in hatchery, which can contribute in preventing the QX-like IBV infections. Furthermore, attenuation by passage at limiting dilution could be applied for rapid vaccine development against emerging strains.