| Crucian carp hematopoietic necrosis(Cc HN)caused by Cyprinid herpesvirus 2(Cy HV-2)spreads widely with high morbidity and mortality,leading huge economic losses to the crusian carp aquaculture industry.The environmental factors such as temperature,ammonia nitrogen,and dissolved oxygen,etc,are important for the induction of Cc HN outbreaking.The temperature will affect the infectivity and pathogenicity of Cy HV-2 to Carassius auratus gibelio.In this study,the detection and surveillance of Cy HV-2 pathogen was conducted by PCR.during the fry and fingerlings breeding process,meanwhile,the quantitative analysis of Cy HV-2 both in healthy C.auratus gibelio and in diseased C.auratus gibelio at different temperatures were carried out,finally,the dynamic changes of Cy HV-2 loading in C.auratus gibelio at different temperatures were assayed,etc.The results were obtained as follows:(1)Cutting off the transmission route is the most effective way to control viral diseases.Through the monitoring of Cy HV-2 in the whole process of the artificial production of C.auratus gibelio fry and fingerlings by PCR detection and gene sequence analysisthe route of vertical transmission of Cy HV-2 in C.auratus gibelio was revealed.It was confirmed that Cy HV-2 could be passed from parent fish to offsprings under suitable temperature while the parent fish that carried Cy HV-2 were used in artificial breeding experiment.Cy HV-2 was distributed in multiple tissues of the parents,with the highest viral load in kidney tissue.(2)Under natural conditions,the Cy HV-2 loading in healthy C.auratus gibelio varies greatly among individuals at different temperatures,but it is generally at a low level.Cy HV-2 can be in a latent state for a long time in healthy C.auratus gibelio,and even at a suitable temperature,thecopy number of virus is low,the hosts do not show disease.(3)Cy HV-2 could be detected in all tissues of naturally infected C.auratus gibelio,among these tissues the highest viral loading was observed in mesonephros,reaching4.91±0.56×10~9copies/mg tissue.The viral load in brain tissue was the lowest,which was9.70±0.50×10~5copies/mg tissue.The naturally diseased C.auratus gibelio had significant pathological changes in many tissues and organs throughout the body,and a large number of virus particles could be observed in the tissues by transmission electron microscopy.(4)The viral loading in the diseased C.auratus gibelio and in the asymptomatic fish in the same pond is quite different.The viral loading in diseased C.auratus gibelio were:mesonephric 1.44±0.24×10~8copies/mg tissue,brain 5.11±0.89×10~5 copies/mg tissue.The viral loading in the asymptomatic C.auratus gibelio was much lower than that in diseased C.auratus gibelio and were:mesonephric 3.76±0.24×10~3copies/mg,brain55±7.50 copies/mg.(5)The artificially acute infection experiment showed that the pathogenicity of Cy HV-2 was different under different temperature conditions.When the temperature was13±1℃,25±1℃,and 31±1℃,the cumulative survival rates of the experimental fish were 100%,0%,and 90±2.69%,respectively.Cy HV-2 could quickly lead to the death of C.auratus gibelio under suitable temperature condition,with a mortality rate of 100%,and the mortality rate is significantly reduced at unsuitable temperature.Cy HV-2proliferated rapidly in C.auratus gibelio at 25℃,but slowed down significantly at 13℃and 31℃.This study confirmed that Cy HV-2 could be transmitted vertically through fish eggs,clarified its distribution and viral loading in C.auratus gibelio,and revealed the difference in infection characteristics of Cy HV-2 in C.auratus gibelio under temperature and its changes.The results provide a bsae for further elucidating the prevalence,the pathogenic mechanism of Cy HV-2 and investigating on the prevention methods of the disease. |
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