Immunogenicity and safety of a live Riemerella anatipestifer vaccine and the contribution of IgA to protective efficacy in Pekin ducks.

Riemerella anatipestifer (RA) infections cause major economic losses in the duck industry. In this study, we developed an RA vaccine to control virulent serotype 1 and 2 RA, which predominate in worldwide prevalence. We established a strategy for vaccine candidate screening, and selected strains D15-RDA-92 (serotype 1) and D14-RDA-8 (serotype 2). These strains were characterized by ≤50% embryo mortality and <3.0 serum resistance assay values in in vitro screening. We evaluated the protective efficacy of live bivalent RA vaccines against virulent homologous serotype RA. Ducklings received two oral immunizations with the bivalent vaccine and showed significant protection against two virulent strains (serotypes 1 and 2) at 21 days post-immunization. No death or clinical signs of diarrhea, tremors, or limb swelling were observed in the immunized ducks. In a safety evaluation, ducks immunized with 100 times higher doses showed no clinical signs, mortality, gross lesions, or histological lesions, and body weight of the ducks showed no significant difference compared to that of negative controls. In addition, IgA analysis showed a significant increase in secretory IgA antibodies generated in the trachea and duodenum of orally immunized ducks at 28 days of age. The IgA might be involved in one of the major immune responses to RA and contributes to protecting against virulent RA. In this study, we developed monovalent and bivalent RA vaccines that were safe in ducks and provided significant protective efficacy against virulent homologous RA strains.

Effects of Various LED Light Colors on Growth and Immune Response in Broilers.

We evaluated the effects of different light-emitting diode (LED) colors between blue and green on growth performance and the immune response in broilers. A total of 1,200 1-day-old Ross broilers were divided randomly into six groups and exposed to pure blue (PB), bright blue (BB), sky blue (SB), greenish blue (GB), pure green (PG), or white (W) using LEDs for 6 weeks. Consequently, body weights were higher in chickens reared under PB and GB on day (d) 7 and SB on d 21 than the other groups. Chickens in the PB group on d 42 were the heaviest among the groups, followed by the BB group and were significantly heavier than the W group. Splenocyte proliferation was significantly enhanced in chickens reared under PB followed by BB on d 42 and proliferation of peripheral blood mononuclear cells was significantly enhanced in chickens reared under BB on d 42. In addition, chickens in the BB group showed significantly elevated nitric oxide production on d 42, indicating activation of macrophages. These results suggest that immune function and growth of broilers can be improved at the later stage by rearing under shorter wavelength LEDs such as PB and BB.

Surveillance and characterization of Riemerella anatipestifer from wild birds in South Korea.

We conducted surveillance for Riemerella anatipestifer (RA) in wild birds along the East Asian-Australasian flyway in South Korea. Detected RA were characterized by serotype, antibiotic susceptibility, and sequence analysis of the 16S rRNA gene. We collected 944 wild birds of 34 species from 19 of South Korea's major migratory wild bird habitats between 2011 and 2012. We identified RA by PCR and rRNA gene sequence in 71/102 (69.6%) pharyngeal swabs and 19/944 (2.0%) cloacal swabs of wild birds. Most RA positives (71/75 [95%] pharyngeal and 19/704 [(2.6%] cloacal) were from three duck species (family Anatidae): Mallard Duck (Anas platyrhynchos), Northern Pintail (Anas acuta), and Spot-billed Duck (Anas poecilorhyncha). Thirty-three RA isolates obtained and examined were highly resistant to aminoglycosides: kanamycin (100%), gentamicin (94%), amikacin (91%), neomycin (88%), and streptomycin (82%). Six isolates were identified as serotype 4 by agar gel precipitation. Serotypes 1 and 7, which are known virulent serotypes, were also identified in three isolates from wild duck species.

Antimicrobial susceptibility profiles and molecular typing of Campylobacter jejuni and Campylobacter coli isolates from ducks in South Korea.

Campylobacter is a food-borne zoonotic pathogen that causes human gastroenteritis worldwide. Campylobacter bacteria are commensal in the intestines of many food production animals, including ducks and chickens. The objective of the study was to determine the prevalence of Campylobacter species in domestic ducks, and the agar dilution method was used to determine resistance of the isolates to eight antibiotics. In addition, multilocus sequence typing (MLST) was performed to determine the sequence types (STs) of selected Campylobacter isolates. Between May and September 2012, 58 duck farms were analyzed, and 56 (96.6%) were positive for Campylobacter. Among the isolates, 82.1% were Campylobacter jejuni, 16.1% were C. coli, and one was unidentified by PCR. Of the 46 C. jejuni isolates, 87.0%, 10.9%, and 21.7% were resistant to ciprofloxacin, erythromycin, and azithromycin, respectively. Among the C. coli isolates, all 9 strains were resistant to ampicillin, and 77.8% and 33.3% were resistant to ciprofloxacin and azithromycin, respectively. The majority of the Campylobacter isolates were classified as multidrug resistant. Twenty-eight STs were identified, including 20 STs for C. jejuni and 8 STs for C. coli. The most common clonal complexes in C. jejuni were the ST-21 complex and the ST-45 complex, while the ST-828 complex predominated in C. coli. The majority of isolates were of STs noted in ducks and humans from earlier studies, along with seven STs previously associated only with human disease. These STs overlapped between duck and human isolates, indicating that Campylobacter isolates from ducks should be considered potential sources of human infection.

Prevalence of Salmonella isolates and antimicrobial resistance in poultry meat from South Korea.

Contamination of Salmonella was assessed in duck and chicken meat collected from supermarkets, traditional markets, internet shopping malls, and wholesale markets in Jeonlado, South Korea, in 2013. Salmonella contamination was found in 51.3% of duck meat samples and 3.7% of chicken meat samples. Salmonella contamination of duck meat samples differed by meat type, i.e., 69.8% of samples of whole ducks and 33.9% of samples of duck pieces. Six serotypes were identified from 64 Salmonella isolates in duck meat: Salmonella Typhimurium (37.5%), Salmonella Enteritidis (21.8%), Salmonella Stanley (3.1%), Salmonella Regent (1.6%), Salmonella Winterthur (3.1%), and Salmonella Westhampton (1.6%). All isolates were resistant to one or more antibiotics. Resistance to sulfisoxazole was most common (93.8% of isolates), followed by resistance to nalidixic acid (59.4%), ceftazidime (26.6%), and ampicillin (26.6%). To our knowledge, this study is the first to report Salmonella contamination in duck meat from Korea. Duck meat should be considered an important source of foodborne pathogens.

Prevalence of duck circovirus infection of subclinical pekin ducks in South Korea.

An investigation was carried out to determine the prevalence and infection pattern of duck circovirus (DuCV) in subclinical Pekin ducks on South Korean duck farms. A total of 147 samples collected from 92 duck farms in five provinces were examined from 2011 to 2012. The overall prevalence of DuCV PCR-positive pooled bursa of Fabricius and liver samples was 21.8% (32/147). The prevalence of DuCV PCR-positive samples increased significantly in 3-week-old ducks compared with that in 1-week-old ducks (P<0.05). DuCV in association with Riemerella and Salmonella infections (10.9%; 16/147) occurred at the same level as infection with DuCV alone (10.9%; 16/147). In comparison of the relationship between bacterial diseases (salmonellosis, Riemerella infection) and morbidity in farms with and without DuCV, morbidity was higher in circovirus-positive farms (50%; 16/32) than in circovirus-negative farms (26.1%; 30/115). Our findings provide baseline information on the degree of DuCV infection and distribution and pattern of DuCV in ducks, and it is evident that DuCV can be associated with subclinical diseases and that subclinical infection could be economically important.

Chicken embryo lethality assay for determining the virulence of Riemerella anatipestifer isolates.

Riemerella anatipestifer is the causative agent of polyserositis and septicaemia in waterfowl. Twenty-one serotypes have been reported, and there is a strong variation in virulence between strains according to serotype or strain. However, little information is available to assess virulence, such as virulence-associated genes; thus, it is difficult to estimate the risk from field strains. Hence, we established a chicken embryo lethality assay (ELA) model to determine the virulence of R. anatipestifer strains. Three virulent strains (RA T1, RA T7, and V-1) and three avirulent strains (Av-1, Av-2, and Av-3), which were confirmed by duck challenge, were used to perform the ELA. Inoculating 10(2) to 10(4) colony-forming units into the allantoic cavity of 10-day-old embryos discriminated between virulent and avirulent strains based on mortality. Differences in invasion rates into embryonic tissues were found between the RA T1 and Av-1 strains. The maximum colony-forming units of the RA T1 strain were about 1000 times higher than those of the Av-1 strain in the tissue invasion rate for 4 days. We found that the virulent strains killed embryos at mortality rates ≥ 50% during the first 3 days after inoculation and that the avirulent strains had death rates of ≤ 20% over 5 days. These results obtained by repeated testing suggest that the ELA could be used as a first-line screening method to determine the virulence of R. anatipestifer strains.

Serologic survey for antibodies to canine parvovirus and influenza virus in wild raccoon dogs (Nyctereutes procyonoides) in South Korea.

Sera from 102 wild raccoon dogs (Nyctereutes procyonoides) were screened for antibodies to canine parvovirus (CPV) and influenza A virus (IAV) in South Korea. Sixteen samples were antibody positive for CPV and all samples were negative for IAV antibodies.