Serology as an aid to diagnosis: uses and abuses

The importance of correct interpretation of serological test results, common sources of error and problems associated with tests are discussed. In bovine brucellosis, a disease which is ideally suited to serological diagnosis, foetal contact with infection may cause the calf to be a serologically negative carrier. The immune tolerant animal resulting from foetal contact with virus is a major problem in the serological detection of border disease. In Johnes' disease and to a lesser extent in Brucella ovis and leptospiral infections, problems associated with sensitivity and specificity of the tests are stressed. Serovar specificity, cumbersome test procedures and negative tests in the incubation period cause difficulty in the interpretation of serological test results for leptospirosis. The importance of clinical examination, herd histories and alternative diagnostic procedures is important in all diseases. Wherever possible, flocks or herds should be maintained in specific disease-free state. Selection of stock from accredited herds or flocks is the most certain method of buying non-infected animals.     

Serology and semen culture for the diagnosis of Brucella ovis infection in chronically infected rams

The serological response to Brucella ovis and the shedding of the organism in semen was followed for a period of 13-14 months in 42 naturally infected rams. Most rams remained chronically infected and excreted the organism in their semen throughout the investigation. B. ovis was isolated from 87.9% of the semen samples from the infected rams. The most common sites from which B. ovis could be isolated at necropsy were the epididymides and accessory sexual glands. In one ram the organism was isolated from lung, spleen, kidney and iliac lymph nodes. Three rams ceased to shed B. ovis in their semen during the course of the investigation. Seventy-five (11%) of 686 sera from infected rams were negative in the complement fixation test (CFT) although 76% and 77% of CFT-negative sera were positive in the gel diffusion precipitin test (GDT) and enzyme labelled immunosorbent assay (ELISA) respectively. The high incidence of CFT-negative infected rams was due to the selection for the investigation of many rams with histories of negative or vacillating CFT titres. Sera from five rams which never shed B. ovis in their semen reacted erratically in the three serological tests. The five rams were from heavily infected flocks and were kept in contact with infected rams throughout the investigation.     

影响鱼类分布的生态水文因子建模及分析

人类活动干扰下河流自然水势改变,导致鱼类栖息地环境变化。为准确分析影响鱼类分布的生态水文环境,该文以美国阿肯色河流域的国家级濒危小型鱼类:产漂流性卵鲤鱼(Arkansas River Shiner,Notropis girardi,ARS)为例,根据其繁殖期特有的水文条件需求,选取流域40个水文站点的日径流数据,分别计算历史时期(1950-1962年)和当前时期(1990-2010年)的3个繁殖期生态水文因子:高流量,较高流量历时及断流历时。每个生态水文因子分别结合其他25个环境因子,基于最大熵理论(MaxEnt)构建物种分布模型。运用经典受试者工作曲线(receiver operating characteristic,ROC)及Parolo等提出的模型转移前后预测结果的Spearman’s rho相关系数,评价模型的自适应性(model fit)和转移能力(transferability)。3个模型在两个时期的ROC曲线与横坐标围成的面积均大于0.95,模型转移前后预测结果的Spearman’s rho相关系数均大于0.6。研究分析表明,模型具有较好的自适应性及转移性。3个生态水文因子中,高流量对模型的贡献率最大,对该种鱼类在两个时期的潜在分布影响最显著。不同的历史时期,物种的潜在适生概率随同一生态水文因子的变化呈现出了不一致的变化趋势。3个模型均预测出ARS的潜在生境有相同的空间变化趋势。该研究结果能够为中国保护河流生态系统与濒危鱼类提供借鉴经验。