Studies on control strategy for iridoviral infection in grouper (Epinephelus sp.)

• Main Authors: chien-chun Ku, 顧倩君
• Other Authors: Hsin-Yiu Chou
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/94043567497812767436

碩士 === 國立海洋大學 === 水產養殖學系 === 90 === This paper is the study of control strategy on grouper iridovirus of Taiwan (TGIV); first we did the deactivation tests of TGIV. Physical factors include heat, pH and UV irradiation. For the heat treatment, the result shows 5 minutes under 70℃ completely inactivation of TGIV can be achieved. This virus is also vulnerable to extreme acid and alkal environment, its resistance to acidity is even weaker than to the alkalinity. After 72 hours put into the pH11 solution, its titer indicator has been reduced to 103.33 TCID50/ml, but it only took 1 hour in pH3 solution to completely inactivate the virus. The TGIV has stronger resistance to UV irradiation. After 1 hour exposure to 910 µW/cm2 UV, the virus still has some residue titer. As far as the chemical treatment part, chloride can completely inactivate TGIV, either 25 ppm 20min or 50 ppm 10 min can reach the result; the virus are even more sensitive to iodine, 25 ppm 15 min or 50 ppm 5 min can inactivate the virus. For Formalin, it would take more time to reach the complete inactivation of TGIV, i.e., 4% formalin would take 24 hours to completely inactivate TGIV. ß-propiolactone (BPL) has the similar effect, 4% BPL need 12 hours to inactivate the TGIV. The survival test for TGIV at different environments show that the virus can last more than 10 days in distilled water, in Hank’s balanced salt solution (HBSS buffer), has added serum or not, all survived more than 40 days. TGIV has excellent tolerance to dry condition; its infection ability can keep up for more than 40 days. The test of water temperature to TGIV infection of grouper, the result reveals that TGIV infection definitely related with water temperature. This agrees with the higher occurrences of TGIV infection at high temperature season in south Taiwan. Artificial infection TGIV groupers feed at 25℃ or 30℃, mortality rate reach 100% at the 9th day; but feed at 18℃, mortality would not start until the 7th day. After 2 weeks, mortality rate only reach 20%. Using PCR detection, all infection groupers have virus positive, so low temperature 18℃ inhibit TGIV burst. The part of development for TGIV inactivation vaccine, three kind of concentrations (1:200, 1:400, 1:800) of Formalin and BPL treatment at 4℃, 20℃,37℃ has been conducted. After three times blind passage tests to identify the conditions of complete loss of the virus infection capability, the selected inactivation vaccine prepare conditions are Formalin and BPL treatment at 4℃ and 20℃ for 4 days. The vaccination methods used for groupers were injection, immersion, and feeding. For Formalin 1:400 and 1:800 concentration vaccine with 30-days and 40-days immunization periods, TGIV challenge test result shows that the protection effect for all groups are 100%. But further virus re-isolation of the sample groupers shows that both 1:400 concentration groups has detect virus rate 0%; so Formalin treatment with 1:400 concentration has the best protection effect. After 30 days vaccination with BPL- treatment vaccine, the immunization effect was way below expectation, only the 1:800 concentration group has 40% protection rate. Although BPL-treatment vaccine with 40 days vaccination period has worse protection rate than the Formalin groups, but 1:200 and 1:400 concentration groups has better effect than 30 days vaccination period groups, their survival rates are 70% and 50%. For the immersion experiment cases, BPL treatment microcapsule vaccine with 1 hour immunization period has the best survival rate 80%, better than the Formalin treatment cases 50%. For the feeding experiment cases, both microcapsule vaccines with 20-days and 30-days immunization periods have zero protection effect.