Dorjee S, Heuer C, Jackson R, West D M, Collins-Emerson J M, Midwinter A C, Ridler A L
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
N Z Vet J. 2009 Feb;57(1):28-33. doi: 10.1080/00480169.2009.36865.
To determine the association between white-spot lesions in kidneys and serological and cultural prevalence of leptospirosis in sheep, and to evaluate the diagnostic value of these lesions in individual sheep and lines of sheep at slaughter as indicators of past or current episodes of leptospirosis.
Lines of lambs were randomly selected, and within lines individual lambs were randomly selected at slaughter. Blood samples and entire kidneys were collected. Serum was tested using the microscopic agglutination test (MAT) for antibody against Leptospira borgpetersenii serovar Hardjobovis or Leptospira interrogans serovar Pomona. Kidneys were cultured for the presence of Leptospira spp. The association between grossly visible white-spotted kidneys (WSK) and the serological status, and between WSK and culture status was evaluated at both line and individual levels. A fixed-effect multivariable logistic regression model was fitted to the line-level data, and included within-line prevalence of carcasses with WSK and line size. A random-effect multivariable logistic regression model was fitted to the individual-level data. This model included WSK lesion score and a random line effect.
White-spot lesions in kidneys were significantly associated with the serological status for Leptospira spp. in individual sheep. A strong positive dose-response relationship between sero-status and the number of white spots on kidneys was observed. However, the sensitivity of WSK to detect seropositive carcasses was low (51 (95% CI=43-59)%), and specificity was moderately low (86 (95% CI=84-87)%). Due to a low observed seroprevalence of 5.2 (95% CI=3.9-7.1)% to serovar Hardjo or Pomona, the positive predictive value (PPV) of WSK for serology was only 18 (95% CI=14-22)%, and the negative predictive value (NPV) was 96 (95% CI=96-97)%. Carcasses with high WSK lesion scores (more than five white spots or white mottling on one or both kidneys) were 6.1 (95% CI=4.3-8.3) times more likely to be seropositive to either serovar than were carcasses with low scores (one to five white spots on one or both kidneys). However, the test sensitivity and PPV for these criteria were regarded unacceptably low (27 (95% CI=20-34)% and 27 (95% CI=21-35)%, respectively). Consideration of lesion status of lines rather than individual animals resulted in a high sensitivity of 98 (95% CI=87-100)%, but very low specificity of 15 (95% CI=8-27)% and a PPV of 48 (95% CI=37-59)%. Due to the low sensitivity of WSK and low prevalence of culture- positive carcasses, the PPV for WSK was as low as 4 (95% CI=2-12)%.
Whereas highly significant associations, including a strong dose-response effect, were observed between WSK and MAT serology, WSK was a poor predictor for the antibody and pathogen status of sheep carcasses with respect to leptospirosis.
确定绵羊肾脏白点病变与钩端螺旋体病血清学及培养患病率之间的关联，并评估这些病变在屠宰时对个体绵羊及绵羊品系作为既往或当前钩端螺旋体病发作指标的诊断价值。
随机选择羔羊品系，在品系内随机选择个体羔羊进行屠宰。采集血样和整个肾脏。血清采用显微镜凝集试验（MAT）检测针对波摩那钩端螺旋体血清型波摩那或博氏钩端螺旋体血清型哈德乔博维斯的抗体。肾脏培养钩端螺旋体属细菌。在品系和个体水平评估肉眼可见的白点肾（WSK）与血清学状态以及WSK与培养状态之间的关联。对品系水平数据拟合固定效应多变量逻辑回归模型，模型包括品系内有WSK的胴体患病率和品系规模。对个体水平数据拟合随机效应多变量逻辑回归模型。该模型包括WSK病变评分和随机品系效应。
个体绵羊肾脏白点病变与钩端螺旋体属细菌的血清学状态显著相关。观察到血清学状态与肾脏白点数量之间存在强阳性剂量反应关系。然而，WSK检测血清阳性胴体的敏感性较低（51（95%CI = 43 - 59）%），特异性中等偏低（86（95%CI = 84 - 87）%）。由于观察到针对哈德乔或波摩那血清型的血清患病率较低，为5.2（95%CI = 3.9 - 7.1）%，WSK对血清学的阳性预测值（PPV）仅为18（95%CI = 14 - 22）%，阴性预测值（NPV）为96（95%CI = 96 - 97）%。WSK病变评分高（一个或两个肾脏上有超过五个白点或白色斑纹）的胴体对任一血清型血清阳性的可能性是评分低（一个或两个肾脏上有一至五个白点）的胴体的6.1（95%CI = 4.3 - 8.3）倍。然而，这些标准的检测敏感性和PPV被认为低得不可接受（分别为27（95%CI = 20 - 34）%和27（95%CI = 21 - 35）%）。考虑品系而非个体动物的病变状态导致敏感性较高，为98（95%CI = 87 - 100）%，但特异性非常低，为15（95%CI = 8 - 27）%，PPV为48（95%CI = 37 - 59）%。由于WSK敏感性低且培养阳性胴体患病率低，WSK的PPV低至4（95%CI = 2 - 12）%。
虽然在WSK与MAT血清学之间观察到高度显著的关联，包括强剂量反应效应，但就钩端螺旋体病而言，WSK对绵羊胴体的抗体和病原体状态是一个较差的预测指标。
