Development of a highly immunogenic Newcastle disease virus chicken vaccine strain of duck origin.

Newcastle disease virus (NDV) strain NDRL0901 was developed as a live vaccine candidate for control of Newcastle disease. NDV isolate KR/duck/13/07 (DK1307) of duck origin was used as the selected vaccine strain. DK1307 was passaged 6 times in chickens. Then a single clone from the chicken-adapted virus (DK1307C) was finally selected, and the vaccine strain was named NDRL0901. DK1307C and the clone NDRL0901 viruses showed enhanced immunogenicity compared to the DK1307 virus. Principal component analysis based on fusion and hemagglutinin-neuraminidase genes revealed the codon usage pattern in the dataset is distinct separating duck viral sequences and avian sequences, and passage of the duck origin virus into the chicken host causes deviation in the codon usage pattern. The NDRL0901 virus was avirulent and did not acquire viral virulence even after 7 back passages in chickens. When day-old chicks were vaccinated with the NDRL0901 virus via spray, eye drops, and drinking water, the vaccinated birds showed no clinical signs and had significant protection efficacy (>80%) against very virulent NDV (Kr005 strain) infection regardless of the administration route employed. The results indicate that the NDRL0901 strain is safe in chickens and can offer protective immunity.

Development and field application of a competitive enzyme-linked immunosorbent assay for detection of Newcastle disease virus antibodies in chickens and ducks.

A competitive enzyme-linked immunosorbent assay (C-ELISA) using a baculovirus-expressed recombinant nucleocapsid protein antigen (rNDV-N) and an rNDV-N-specific monoclonal antibody (5B3) was developed for the detection of Newcastle disease virus (NDV) antibodies, and its diagnostic performance was evaluated. The specificity and sensitivity of the C-ELISA was found to be 98.4 and 98.9%, respectively, for chickens, and 98.2 and 97.9% for ducks. However, the C-ELISA showed weak cross-reaction with hyperimmune antisera to some other avian paramyxovirus serotypes. In all experimentally vaccinated chickens, seroconversion rates at 7 d postinoculation were 100 and 40% when measured by C-ELISA and hemagglutination inhibition (HI), respectively. In field trials, the C-ELISA showed positive results in 98.9% of HI-positive sera and 40.8% of HI-negative sera from NDV-vaccinated chickens (n = 705). In domestic ducks (n = 158) from NDV-positive duck farms (n = 8), the positive rates according to C-ELISA were significantly higher than those according to the HI test. At the same time, 98.1% of ducks (n = 209) from NDV-negative duck farms (n = 11) were also negative by C-ELISA. Our results indicate that C-ELISA could be a useful alternative to HI testing for detecting NDV antibodies in different avian species such as chickens and ducks.

Epidemiological investigation of outbreaks of fowl adenovirus infection in commercial chickens in Korea.

In total, 39 clinical cases of fowl adenoviruses (FAdV) infection in chickens (28 broiler, 7 native, and 4 layer chickens) between 2007 and 2010 in Korea were investigated. The FAdV types 4, 8b, and 11 comprised 18, 9, and 12 clinical cases, respectively. All FAdV type 4 cases showed clinical hydropericardium (HPS) lesions as well as inclusion body hepatitis (IBH), whereas all FAdV types 8b and 11 cases exhibited IBH lesions without HPS. All 3 types were detected in broiler (9-30 d old) and layer chickens (23-112 d old), whereas most native chickens (14-65 d old) were affected only by FAdV type 4. Infectious bursal disease virus and chicken infectious anemia virus were complications in 51.3% of FAdV cases, with mortalities of 55% to <0.1%. Chicken infectious anemia virus was detected in all native chicken cases. These results indicate that preventive measures against FAdV infection and immunosuppressive diseases on poultry farms should be implemented.

Vaccination as a control measure during the outbreak of foot-and-mouth disease in 2000 in Korea.

The Republic of Korea had been free from foot-and-mouth disease (FMD) for 66 years until 15 cases were confirmed between 24 March and 15 April in 2000. The FMD virus isolated in Korea was an O Pan Asia type, which was also responsible for the recent outbreaks in Japan and the U.K. Control measures including the stamping-out of infected animals on neighbouring farms, movement restrictions and emergency vaccination were implemented. The decision to vaccinate was made because the cattle affected were showing severe FMD lesions, there was significant possibility that a large amount of virus had already been shed and conditions at the time seemed to favour wind-borne spread. Also, because the spread was limited to cattle, it was assumed that the use of vaccinations would be more effective than if pigs had been affected. All susceptible animals within 10 km radius of the infected farms were vaccinated with inactivated, double-oil emulsion vaccines. Totals of 860,700 and 661,770 animals were vaccinated during the first and second round of booster vaccinations, and were completed within five months of the first outbreak. The government decided to adopt a let-live policy so that the vaccinated animals were not slaughtered. However, they were placed under movement restrictions and had to be identified and registered. Although there were concerns about the vaccinated animals becoming carriers, extensive serological surveillance using NSP ELISA found no evidence of FMD in the remaining vaccinated population. The use of emergency vaccinations in 2000 is regarded as being a major factor in limiting the spread of FMD and containing the outbreak within a month.