Safety and protective effects of an avirulent Salmonella Gallinarum isolate as a vaccine candidate against Salmonella Gallinarum infections in young chickens.

Fowl typhoid is an important disease of chickens and turkeys, which is caused by Salmonella Gallinarum (S. Gallinarum). Vaccines with high levels of protective effects against fowl typhoid need to be developed for the poultry industry. In this study, a S. Gallinarum strain, named SG01, was isolated from a poultry farm in Mashan region of Wuxi City, China, and identified through biochemical tests and specific PCR amplifications. Then, safety evaluations of the SG01 strain were performed in young chickens. No clinical symptom including depression and diarrhea and gross lesion involved in the cardiac nodule, hepatic necrotic lesion and splenic necrotic lesion, was determined on fifteen-day-old chickens after immunization with 1 × 1010 CFU of the SG01 strain through the oral route. However, diarrhea symptoms and hepatic lesions were identified from chickens immunized with the commercial vaccine strain SG9R by the same dose and route. At 14 days post inoculation, SG01 strain was eliminated in the liver and spleen from SG01-immunized chickens, while the SG9R strain still could be identified from SG9R-immunized chickens. After challenge with the virulent S. Gallinarum strain, significant reduction of the morbidity rate was found in the SG01 immunized group (20 %) compared to the challenge group (100 %) according to signs scoring systems for clinical symptoms and gross lesions. Additionally, immunization with the SG01 strain could provide more than 8 weeks of protection periods against fowl typhoid. These results demonstrate the SG01 strain is avirulent to young chickens and might be safer compared to the SG9R strain. In addition, SG01 strain is a potential vaccine candidate against fowl typhoid in young chickens.

Immunogenicity and protective efficacy of an EB66® cell culture-derived duck Tembusu virus vaccine.

The avian EB66® cell line, derived from duck embryonic stem cells, has been widely used for producing human and animal therapeutic proteins and vaccines. In current study we evaluated the potential use of EB66® cell line in a cell culture-derived duck Tembusu virus (DTMUV) vaccine development. After optimizing the growth conditions of DTMUV HB strain in EB66® cells, we successfully generated three batches of viruses with ELD50 titres of 105.9/0.1 ml, 105.3/0.1 ml and 105.5/0.1 ml, respectively, for using in the preparation of inactivated vaccines. The immunogenicity and protective efficacy of these EB66® cells-derived inactivated vaccines were examined in ducks. Results indicated that all three batches of vaccines induced haemagglutination-inhibition (HI) antibody response in immunized birds at 2 weeks after a single immunization. Immunized ducks and ducklings were protected against a virulent challenge at 4 weeks after a booster immunization. The duration of immunity was for 3-4 months after a booster immunization. These results demonstrated the feasibility of using EB66® cell line to grow up DTMUV for vaccine preparation. RESEARCH HIGHLIGHTS Duck Tembusu virus can be propagated in EB66® cells. EB66® cell-derived inactivated DTMUV vaccines are immunogenic and can provide protection against a virulent challenge. A long-lasting immunity is induced after a booster immunization.

Efficacy Evaluation of an Inactivated Duck Tembusu Virus Vaccine.

To evaluate the potential use of an inactivated virus-based vaccine for the control and prevention of the newly emerged duck Tembusu virus infection in China, a duck Tembusu virus isolate, Tembusu-HB, was propagated in 12-day-old duck embryos and inactivated by treatment with formaldehyde. The inactivated viral antigen was emulsified with mineral oil, and five batches of the vaccine were manufactured. The immunogenicity and protection efficacy of the vaccine were evaluated in Beijing ducks and Beijing white geese. Results showed that more than 80% of immunized ducks were protected against virulent virus challenge after two intramuscular or subcutaneous injections of the inactivated vaccine, as evidenced by the negative virus isolation results. The protection is also correlated with a positive virus-specific antibody response as detected by ELISA. In contrast, none of the control ducks and geese had any detectable antibody response. Virus was isolated from all control ducks and geese after virulent virus challenge. Interestingly, a variable level of protection (20%-80%) was observed in Beijing white geese immunized twice with the same batches of vaccine, suggesting a species-specific effect of the vaccine. Overall, the results clearly suggest that the inactivated duck Tembusu virus vaccine is immunogenic and provides protection against virulent virus challenge.

[Advances in research and development of universal influenza vaccines].

Vaccination is the primary strategy for the prevention and control of pandemic influenza. Because influenza virus is highly variable across strains, universal influenza vaccines need to be developed to address this problem. This review describes the research progress in conserved epitopes of influenza virus, the advances in the research and development of universal influenza vaccines based on the relatively conserved sequences of NP, M2e, HA2, and headless HA, the mechanisms of cross-protection, and the methods to improve cross-protection.

Emergence of a highly pathogenic porcine reproductive and respiratory syndrome virus in the Mid-Eastern region of China.

Herds of pigs in the Mid-Eastern region of China have experienced recent outbreaks of a severe form of porcine reproductive and respiratory syndrome (PRRS) characterised by high fever and morbidity and mortality in animals of different ages. Eighty-one herds were diagnosed with PRRS virus (PRRSV) infection from June to December 2006 on the basis of clinical signs, pathological findings and reverse transcriptase polymerase chain reaction (RT-PCR). Twenty strains of PRRSV were isolated from 20 herds in six provinces. Following experimental inoculation, one isolate, designated SY0608, caused 100% morbidity and 25-50% mortality in 30-, 65- and 105-day-old pigs and the birth of stillborn and weak piglets from affected sows. The ORF5 gene had 99.5-99.8% nucleotide and 99-100% derived amino acid sequence identities among SY0608 and five other field isolates, but only 89.4% and 88.6% identities, respectively, with VR-2332, the prototypic North American isolate. The 2850bp Nsp2 gene of SY0608 had 79.4% nucleotide and 74.9% derived amino acid sequence identities with VR-2332; deletions of 1 and 29 amino acids corresponded to positions 480 and 531-559 of strain VR-2332, respectively. These findings demonstrated that a new highly pathogenic Northern American type PRRSV has spread widely in the Mid-Eastern region of China.