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In order to replace the antibiotic treatment for control of Vibrio harveyi, a causal agent of luminous disease in Black tiger shrimp, anti-V. harveyi IgY was produced and showed its potential in our preliminary study. However, for further use as feed additive, the IgY stability should be evaluated. The titre of specific IgY was enhanced with an immunostimulant, C-phosphate guanosine oligodeoxynucleotide (CpG-ODN). IgY was stable at natural pH while the activity was decreased below pH 4 or above pH 10. The supplementation of 30% sorbitol significantly enhanced the IgY stability at tested temperatures in excess of 70°C. The activity of IgY remained at 9 and 94% after 4 h incubation in simulated gastric and intestinal fluids, respectively. A storage temperature at −20°C was found to be the best condition. IgY at the concentrations of 1, 5 and 10 mg/ml efficiently inhibited V. harveyi in vitro within 24 h after exposure.

Sugarcane disease surveys were conducted from 2010 to 2014 at major sugarcane growing areas in 5 provinces (Nakhon Pathom, Kanchanaburi, Udon Thani, Khon Kaen, Nakhon Ratchasima) and germplasm collection fields. Random samples of the virus-like sugarcane leaves obtained from the surveyed areas suggested yellow streak mosaic symptoms. Direct antigen coating ELISA using locally produced SCSMV antiserum, revealed widespread incidence of SCSMV in the major sugarcane growing areas and the germplasm collection fields, ranging from 43.48-90.91% and 54.17-100% respectively. The virus isolate from sugarcane in Kamphaeng Saen, Nakhon Pathom, designated as THA-NP3, was characterized by genomic sequencing. Complete genome of THA-NP3 (JN163911) contained 9,781 nucleotides, excluding 3¢ Poly (A) tail which encoded a polyprotein of 3,130 amino acid residues comprising 10 functional proteins, namely P1, HC-Pro, P3, 6K1, CI, 6K2, NIa-VPg, NIa-Pro, NIb and CP. Sequence comparisons revealed that THA-NP3 showed 97.84% nucleotide identity to JP2 (JF488065) from China and 81.39-97.78% nucleotide identities to other recorded SCSMV sequences. Detection for the presence of CP gene by RT-PCR indicated 1094 bp containing 846 bp of the CP coding region. Analysis of the CP gene revealed genetic variation of 58 Thai SCSMV isolates, 86.17-100% nucleotide identities among them and 85.70-99.29% nucleotide identities to SCSMV isolates from other countries. Recombination events existed in the CP coding regions between two distinct sub-populations, the germplasm isolates and the farmers’ field isolates. These results suggested the incidence of SCSMV variants between the farmers’ fields and the germplasm collection fields.

Egg yolk immunoglobulin (IgY) is an alternative treatment for the prevention of gastrointestinal infections in pigs, cows, chickens and fish. In our previous report, we preliminarily proved that anti-V. harveyi IgY had effective potential to control luminous disease in black tiger shrimp. However,IgY activity may be reduced or destroyed by gastric conditions, particularly low pH and digestive enzymes. Therefore, it is necessary to find an effective method to preserve the therapeutic function of IgY antibodies during gastric passage. Chitosan-alginate microcapsules have been developed to protect IgY from gastric inactivation. The processing factors included different forms of chitosan and alginate, while a CaCl2 concentration and encapsulation medium was investigated. The optimum results were obtained under the following conditions: High Mw chitosan concentration 0.2% (w/v), medium viscosity alginate concentration 2% (w/v), CaCl2 concentration 0.5% (w/v). The stability of IgY in simulated gastric fluid (SGF, pH 1.2) was greatly improved by encapsulation in chitosan-alginate microcapsules, and retained greater than 90% activity after 2 h exposure to SGF. Less than 10% IgY was released upon the microcapsules’ exposure to SGF for 2 h, and more than 80% IgY was released upon the microcapsules’ exposure to simulated intestinal fluid (SIF, pH 6.8) for 16 h.