Monitoring the prevalence of the parasitic dinoflagellate Hematodinium sp. in snow crabs Chionoecetes opilio from Conception Bay, Newfoundland

Diseases of Aquatic Organisms

Gottfried P. Pestal¹  David M. Taylor¹  Jeffrey D. Shields¹  Roger Pickavance¹  John M. Hoenig¹ 

关键词: Sensitivity;    Specificity;    Cluster sampling;    Disease;    Diagnosis;   

DOI  :  10.3354/dao053067

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Bitter crab disease (BCD) of snow crabs Chionoecetes opilio is caused by a parasitic dinoflagellate, Hematodinium sp. In Newfoundland¹s commercial fishery, infected snow crabs are identified using visual, macroscopic signs ofdisease for separation prior to processing. We estimated the sensitivity and specificity of gross, macroscopic diagnosis of Hematodinium sp. by comparing these results with microscopic examination of prepared hemolymph smears. The sensitivity of adiagnostic test is the probability that the test will yield a positive result given that the animal has the disease. The specificity is the probability of a negative result given the animal is not diseased. In October 1998, we conducted a design-basedsurvey using cluster sampling in 2 strata. Over 10000 snow crabs from pot and trawl surveys were examined macroscopically for BCD. In addition, over 350 crabs were randomly examined microscopically for disease. The double sampling resulted in an estimatedsensitivity of 52.7% and an estimated specificity of 100%. That is, a positive result from macroscopic examination is definitive, if the observer is well trained, but macroscopic examination will fail to detect infections in crabs with borderlineclinical signs of disease. The prevalence estimated from macroscopic observations (p�?_st = 2.24%) was corrected for misclassification by dividing p�?_st by the estimated sensitivity (0.527), giving acorrected estimate of 4.25%. The use of double sampling provides for efficient estimation of prevalence in that large numbers of crabs can be quickly examined for gross signs of infection and the results corrected for misclassification based on a limitednumber of observations with a better, but time-consuming test. In addition, the prevalence of macroscopically infected male crabs was lower in a trap survey (0.57%) compared to a trawl survey (1.59%). In the trawl survey, female crabs had a significantlyhigher prevalence of macroscopically diagnosed infections than males (6.34%). The prevalence of BCD has shown an alarming increase since it was first detected in Newfoundland during the early 1990s. Transmission and mortality studies are warranted tobetter understand the effect of the disease on its commercially important host.

【 授权许可】

Unknown