Viral hemorrhagic septicemia virus (VHSV) is one of the most serious
infectious pathogen of juvenile olive flounder in terms of its wide host-range,
pathogenicity, disease course, and mortality rates. VHSV can cause cumulative
mortality as high as 90%, resulting in serious economic losse...
Viral hemorrhagic septicemia virus (VHSV) is one of the most serious
infectious pathogen of juvenile olive flounder in terms of its wide host-range,
pathogenicity, disease course, and mortality rates. VHSV can cause cumulative
mortality as high as 90%, resulting in serious economic losses to olive flounder
(Paralichthys olivaceus) aquaculture in Korea. It occurs in winter and spring season
when water temperature is low (at 8 to 15°C).
For the controlling VHS, fish immune response is essential factor to recognize
virus and evoking initial anti-viral responses.
In the Chapter I, background and literature review were briefly reviewed. In the
Chapter II, VHSV infectivity dynamic at 10 and 13°C by intramuscular injection and
immersion challenge route were performed for investigating the differences of VHS
progression within VHSV susceptible temperature. Cumulative mortality was initiated
x
earlier at 10°C than 13°C. The higher cumulative mortality by IM injection was
observed than by immersion challenge route in same water temperature. In the Chapter
III, dynamics of VHSV infectivity and quantification analysis with regard to virus
exposure concentration and challenge routes. VHSV infectivity was estimated by cell
culture (TCID50) method and VHSV distribution was quantified by qRT-PCR technique.
The survived and dead flounder by VHSV infection, different patterns of their
infectivity and distribution was shown in this study. Based on cumulative mortality, the
virulence of VHSV was found to highly different depending on challenge routes and
viral exposure doses. VHSV infectivity was constantly estimated in all the tested organs
from dead flounder. However, VHSV infectivity was under the detection limt,
meanwhile VHSV-N gene was detected in all the tested organs from flounder survivind
VHSV infection. It was indicated that VHSV exist in organs even in flounder surviving
VHSV infection, however, it was not pathogen in flounder. In the Chapter IV, it was
performed to determine the infectivity and distribution of VHSV in blood from VHSVinfected
flounder. Results of TCID50 and qRT-PCR analysis, viral RNA was present in
the blood at very early time point of VHSV-infection. It suggested that blood is one of
important factor to transfer the virus in fish body, moreover it was proposed that the
blood could be utilized in the diagnosis of VHS.
For the controlling and prevention of VHS, in the Chapter V, flounder immune
response was stimulated on various conditions including VHSV concentration, pretreatment
methods and large-scale treatment condition. Olive flounder were exposed
with VHSV at doses of 102.5, 105.5 and 107.5 TCID50/mL at 17°C. Prior to exposure, fish
were divided three experimental groups for investingating pre-treatment methods 1)
non-treated group, 2) 1 min tap water exposure; 3) fish body was wiped with cotton
xi
swap. Also in this chapter, expression profiles of immune response gene in juvenile
olive flounder after immune response stimulation by immersion was performed. The
profiled expression level of immune response was estimated in spleen, head kidney and
blood. Different expression patterns were observed and VHSV-specific antibody was
detected in flounder. However, the particular gene expression and/or VHSV-specific
antibody detection was not observed in juvenile olive flounder proposed that fish
immune response against VHSV is still unclear even though the cumulative mortality
was not highly occurred in immune response stimulated flounder.
Finally, in the Chapter VI concluded the present research on VHSV infection
and immune response against VHSV in juvenile olive flounder.
Viral hemorrhagic septicemia virus (VHSV) is one of the most serious
infectious pathogen of juvenile olive flounder in terms of its wide host-range,
pathogenicity, disease course, and mortality rates. VHSV can cause cumulative
mortality as high as 90%, resulting in serious economic losses to olive flounder
(Paralichthys olivaceus) aquaculture in Korea. It occurs in winter and spring season
when water temperature is low (at 8 to 15°C).
For the controlling VHS, fish immune response is essential factor to recognize
virus and evoking initial anti-viral responses.
In the Chapter I, background and literature review were briefly reviewed. In the
Chapter II, VHSV infectivity dynamic at 10 and 13°C by intramuscular injection and
immersion challenge route were performed for investigating the differences of VHS
progression within VHSV susceptible temperature. Cumulative mortality was initiated
x
earlier at 10°C than 13°C. The higher cumulative mortality by IM injection was
observed than by immersion challenge route in same water temperature. In the Chapter
III, dynamics of VHSV infectivity and quantification analysis with regard to virus
exposure concentration and challenge routes. VHSV infectivity was estimated by cell
culture (TCID50) method and VHSV distribution was quantified by qRT-PCR technique.
The survived and dead flounder by VHSV infection, different patterns of their
infectivity and distribution was shown in this study. Based on cumulative mortality, the
virulence of VHSV was found to highly different depending on challenge routes and
viral exposure doses. VHSV infectivity was constantly estimated in all the tested organs
from dead flounder. However, VHSV infectivity was under the detection limt,
meanwhile VHSV-N gene was detected in all the tested organs from flounder survivind
VHSV infection. It was indicated that VHSV exist in organs even in flounder surviving
VHSV infection, however, it was not pathogen in flounder. In the Chapter IV, it was
performed to determine the infectivity and distribution of VHSV in blood from VHSVinfected
flounder. Results of TCID50 and qRT-PCR analysis, viral RNA was present in
the blood at very early time point of VHSV-infection. It suggested that blood is one of
important factor to transfer the virus in fish body, moreover it was proposed that the
blood could be utilized in the diagnosis of VHS.
For the controlling and prevention of VHS, in the Chapter V, flounder immune
response was stimulated on various conditions including VHSV concentration, pretreatment
methods and large-scale treatment condition. Olive flounder were exposed
with VHSV at doses of 102.5, 105.5 and 107.5 TCID50/mL at 17°C. Prior to exposure, fish
were divided three experimental groups for investingating pre-treatment methods 1)
non-treated group, 2) 1 min tap water exposure; 3) fish body was wiped with cotton
xi
swap. Also in this chapter, expression profiles of immune response gene in juvenile
olive flounder after immune response stimulation by immersion was performed. The
profiled expression level of immune response was estimated in spleen, head kidney and
blood. Different expression patterns were observed and VHSV-specific antibody was
detected in flounder. However, the particular gene expression and/or VHSV-specific
antibody detection was not observed in juvenile olive flounder proposed that fish
immune response against VHSV is still unclear even though the cumulative mortality
was not highly occurred in immune response stimulated flounder.
Finally, in the Chapter VI concluded the present research on VHSV infection
and immune response against VHSV in juvenile olive flounder.
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