Background: Pasteurella multocida (P. multocida) infection can cause a series of diseases in different animals and cause huge economic losses to the breeding industry. P. multocida is considered to be one of the most significant pathogens in rabbits. In order to elucidate the pathogenic mechanism and innate immune response of P. multocida, an infection experiment was carried out in this study. Results: Our results showed that the clinical symptoms of rabbits were severe dyspnoea and serous nasal fluid. During the course of the disease, the deaths peaked at 2 days post infection (dpi) and mortality rate was 60%. The pathological changes of the lung, trachea, and thymus were observed. In particular, consolidation and abscesses appeared in lung. Histopathologic changes in rabbits showed edema, hemorrhage, and neutrophil infiltration in the lung. P. multocida can rapidly replicate in a variety of tissues, and the colonization in most of the tested tissues reached the maximum at 2 dpi and then decreased at 3 dpi. The number of P. multocida in lung and thymus remained high level at 3 dpi. Toll-like receptors 2 and 4 signaling pathways were activated after P. multocida infection. The expression of Il1β, Il6, Il8, and Tnf-α was significantly increased. The expression of most proinflammatory cytokines peaked at 2 dpi and decreased at 3 dpi, and the expression trend of cytokines was consistent with the colonization of P. multocida in rabbit tissues. Conclusions: The P. multocida can rapidly replicate in various tissues of rabbit and cause bacteremia after infection. TLRs signaling pathways were activated after P. multocida infection, significantly inducing the expression of proinflammatory cytokines, which is might the main cause of respiratory inflammation and septicemia.

Commercial inactivated vaccines against H9N2 avian influenza (AI) have been developed in China since 1990s and show excellent immunogenicity with strong HI antibodies. However, currently approved vaccines cannot meet the clinical demand for a live-vectored vaccine. Newcastle disease virus (NDV) vectored vaccines have shown effective protection in chickens against H9N2 virus. However, preexisting NDV antibodies may affect protective efficacy of the vaccine in the field. Here, we explored avian paramyxovirus serotype 2 (APMV-2) as a vector for developing an H9N2 vaccine via intranasal delivery. APMV-2 belongs to the same genus as NDV, distantly related to NDV in the phylogenetic tree, based on the sequences of Fusion (F) and hemagglutinin-neuraminidase (HN) gene, and has low cross-reactivity with anti-NDV antisera. We incorporated hemagglutinin (HA) of H9N2 into the junction of P and M gene in the APMV-2 genome by being flanked with the gene start, gene end, and UTR of each gene of APMV-2-T4 to generate seven recombinant APMV-2 viruses rAPMV-2/HAs, rAPMV-2-NPUTR-HA, rAPMV-2-PUTR-HA, rAPMV-2-FUTR-HA, rAPMV-2-HNUTR-HA, rAPMV-2-LUTR-HA, and rAPMV-2-MUTR-HA, expressing HA. The rAPMV-2/HAs displayed similar pathogenicity compared with the parental APMV-2-T4 virus and expressed HA protein in infected CEF cells. The NP-UTR facilitated the expression and secretion of HA protein in cells infected with rAPMV-2-NPUTR-HA. Animal studies demonstrated that immunization with rAPMV-2-NPUTR-HA elicited effective H9N2-specific antibody (6.14 ± 1.2 log2) responses and conferred complete immune protection to prevent viral shedding in the oropharyngeal and cloacal swabs from chickens challenged with H9N2 virus. This study suggests that our recombinant APMV-2 virus is safe and immunogenic and can be a useful tool in the combat of H9N2 outbreaks in chicken.

Avian influenza viruses can cross species barriers and adapt to mammals. The H7N9 subtype AIV that emerged in China in 2013 caused 1568 human infections, with a mortality rate of nearly 40%. We conducted a retrospective analysis of H7N9 viruses that were isolated in live poultry markets in 2013. We found that two avian-origin H7N9 isolates, A/chicken/Eastern China/JTC4/2013 and A/chicken/Eastern China/JTC11/2013, have a similar genetic background but exhibit different pathogenicity in mice. Whole-genome alignment of the two H7N9 viruses was carried out, and only six amino acid differences mapped in five genes, including the well-known virulence molecular marker PB2-E627K. Our retrospective analysis highlighted the importance of monitoring the adaptive mutations in avian influenza viruses with zoonotic potential.