Further observations on the epidemiology and spread of epizootic haematopoietic necrosis virus (EHNV) in farmed rainbow trout Oncorhynchus mykiss in southeastern Australia and a recommended sampling strategy for surveillance

Diseases of Aquatic Organisms

I. Marsh¹  Z. Zupanovic¹  L. A. Reddacliff¹  C. Kearns¹  R. B. Callinan¹  R. J. Whittington¹ 

关键词: Epizootic haematopoietic necrosis virus;    Iridovirus;    Certification;    Rainbow trout;    Oncorhynchus mykiss;    ELISA;   

DOI  :  10.3354/dao035125

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Epizootic haematopoietic necrosis virus (EHNV) is an iridovirus confined to Australia and is known only from rainbow trout Oncorhynchus mykiss and redfin perch Perca fluviatilis. Outbreaks of disease caused by EHNV in troutpopulations have invariably been of low severity, affecting only 0+ post-hatchery phase fingerlings <125 mm in length. To date the virus has been demonstrated in very few live in-contact fish, and anti-EHNV antibodies have not been found in survivorsof outbreaks, suggesting low infectivity but high case fatality rates in trout. During an on-going study on an endemically infected farm (Farm A) in the Murrumbidgee River catchment of southeastern New South Wales, EHNV infection was demonstrated in 4 to6 wk old trout fingerlings in the hatchery as well as in 1+ to 2+ grower fish. During a separate investigation of mortalities in 1+ to 2+ trout on Farm B in the Shoalhaven River catchment in southeastern New South Wales, EHNV infection was demonstrated inboth fingerlings and adult fish in association with nocardiosis. A 0.7% prevalence of antibodies against EHNV was detected by ELISA in the serum of grower fish at this time, providing the first evidence that EHNV might not kill all infected trout. EHNVinfection on Farm B occurred after transfer of fingerlings from Farm C in the Murrumbidgee river catchment. When investigated, there were no obvious signs of diseases on Farm C. 'Routine' mortalities were collected over 10 d on Farm C and EHNV wasdetected in 2.1% of 190 fish. Tracing investigations of sources of supply of fingerlings to Farm B also led to investigation of Farm D in Victoria, where the prevalence of anti-EHNV antibodies in 3+ to 4+ fish was 1.3%. The results of this study indicatethat EHNV may be found in trout in all age classes, need not be associated with clinically detectable disease in the population, can be transferred with shipments of live fish, can be detected in a small proportion of 'routine' mortalities and may beassociated with specific antibodies in a small proportion of older fish. Sampling to detect EHNV for certification purposes should be based on examination of 'routine' mortalities rather than random samples of live fish. Antigen-capture ELISA can be usedas a cost effective screening test to detect EHNV on a farm provided that sampling rates conform with statistical principles.

【 授权许可】

Unknown