Immunolocalisation of nervous necrosis virus indicates vertical transmission in hatchery produced Asian sea bass (Lates calcarifer Bloch)—A case study
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Abstract
A probable vertical mode of piscine nodavirus transmission is reported in the present investigation based on a case of nodavirus associated larval mortalities in hatchery produced Asian sea bass. Polyclonal rabbit anti-SJNNV antibodies (SGWak97) detected the viral antigens in the tissue sections from the eggs and the larvae at different time intervals from − 1 to 42 days post hatch (dph). Immunopositive ovarian connective tissue associated with the oocytes along with the progressive localization of the viral antigens in the brain, spinal cord, liver, stomach and dermal musculature during the larval development indicates a probable vertical transmission of nodavirus in the Asian sea bass. The surviving larger larvae, from the batch suffering mass mortalities, produced very intense immunofluorescent positivity in the liver, stomach and dermal musculature. Results of this investigation demonstrating a possibility of vertical transmission of the nodavirus emphasize the need for screening of eggs and larvae for evolving suitable preventive and prophylactic health management strategies.
Suggested Citation
Azad, I. S., Jithendran, K. P., Shekhar, M. S., Thirunavukkarasu, A. R., & de la Pena, L. D. (2006). Immunolocalisation of nervous necrosis virus indicates vertical transmission in hatchery produced Asian sea bass (Lates calcarifer Bloch)—A case study. Aquaculture , 255(1-4), 39-47. https://doi.org/10.1016/j.aquaculture.2005.04.076
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Immunization regimen in Asian sea bass (Lates calcarifer) broodfish: A practical strategy to control vertical transmission of nervous necrosis virus during seed production
Pakingking, Rolando V., Jr.
; ; ; (Elsevier, 2018-08)
Outbreaks of viral nervous necrosis (VNN) in Asian sea bass (Lates calcarifer) at the larval stages via vertical transmission of nervous necrosis virus (NNV) from asymptomatic broodfish remain as a major deterrent during seed production. A five-year study was conducted to produce NNV-specific-free sea bass broodfish reared in land-based tanks through an annual immunization regimen with the formalin-inactivated NNV. We primarily immunized (intraperitoneal injection) sea bass juveniles (5 g) and monitored the neutralizing antibody (Nab) titers in the sera of these fish at scheduled intervals post-immunization. Nab titers in the sera of immunized fish peaked at Month 2 (titer: 1:4480 ± 1185) but thereafter gradually declined and significantly dropped (1:260 ± 83) at Month 12 post-primary immunization. Booster immunization of these fish at Month 12 post-immunization led to abrupt increases in Nab titers in booster immunized (B-Im) fish at Month 1 (1:12800 ± 6704) but thereafter declined and dropped at Month 12 (1:480 ± 165) post-booster immunization. The annual booster injections with the inactivated vaccine or L-15 (Unimmunized [U-Im]) were consecutively conducted for 4 years until the fish became sexually mature. Mature fish from both groups were successively induced to spawn twice (1-month interval) via intramuscular injection with luteinizing hormone-releasing hormone analogue (LHRH-a; 100 µg/kg BW). NNV was not detected by RT-PCR in oocytes and milts, and spawned eggs of B-Im fish. In contrast, oocytes and milts, and spawned eggs of U-Im fish were NNV positive. Spawned eggs of B-Im broodfish exhibited Nab titers ranging from 1:192 ± 34 to 1:240 while such was not detected (<1:40) in eggs of U-Im fish. Taken together, current data clearly demonstrate that annual immunization regimen with inactivated NNV vaccine is a pragmatic approach for sustaining immunocompetent sea bass broodfish reared in land-based tanks and circumvent the risk of vertical transmission of NNV from asymptomatic broodfish to their offspring under stress of repetitive spawning. -
Establishment of preventive measures against viral nervous necrosis (VNN) in finfish hatcheries
; ; ; ; ; Tendencia, Eleonor; (Aquaculture Department, Southeast Asian Fisheries Development Center, 2005-03)
The establishment of preventive measures against viral nervous necrosis (VNN) at the finfish hatcheries of SEAFDEC Aquaculture Department in Iloilo, Philippines, was instituted primarily to minimize the impact of the viral infection in cultured stocks. Selection of VNN-negative broodstocks was conducted and the detection rate ranged from 25-56%. It was confirmed that all species of broodstocks are already contaminated with the virus with varying percentages. The combination of cell culture and RT-PCR in the detection of the virus proved to be more sensitive than the RT-PCR alone. The trash fish food was suspected as a main source of contamination and tests prove that most of the trash fish species were contaminated with the virus. The effect of chemical treatment was tested and a good result was obtained by using 5 and 7 ppm iodine. Several recommendations were formulated in the prevention and control of VNN in the hatchery phase: VNN-negative broodstocks should be selected by using cell culture and PCR; spawning of the selected broodstocks should be limited to only six times and these fertilized eggs should be used for larval productions; fertilized eggs should be washed and disinfected with iodine; and commercial broodstock feeds should be used instead of trash fish. -
Mass mortalities associated with viral nervous necrosis in hatchery-reared sea bass Lates calcarifer in the Philippines
(Ministry of Tropical Agricultural Research Centre, 2004)Viral nervous necrosis (VNN), also known as viral encephalopathy and retinopathy (VER), is an emerging disease affecting larvae and juveniles of many farmed marine fish species in Asia, Australia, Europe and North America. Mass mortality occurred in 14-day old larval sea bass Lates calcarifer at a hatchery in the Philippines associated with clinical signs such as abnormal swimming behavior and pale-gray discoloration of the body. Histological investigations in moribund fish revealed marked vacuolation in the retina and brain. Cytopathic effects (CPE) were observed in SSN-1 cells inoculated with the tissue filtrate of affected sea bass. A piscine nodavirus, the causative agent of VNN, was detected in the affected tissues and SSN-1 cells inoculated with the tissue filtrate of affected fish by RT-PCR. Electron microscopy revealed non-enveloped viral particles, 22-28 nm in diameter, in the cytoplasm of the brain and retina of affected fish and in the cytoplasm of VNN-infected SSN-1 cells after CPE appeared. These results indicate that mass mortality of sea bass larvae in the Philippines was caused by a piscine nodavirus.
