PubMed · 10920772
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P Bartlett. 2000. Penstrep clarification.. https://doi.org/10.1111/j.1751-0813.2000.tb11818.x
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Single-locus disorders in domesticated animals were among the first Mendelian traits to be documented after the rediscovery of Mendelism, and to be included in early linkage maps. The use of linkage maps and (increasingly) comparative genomics has been central to the identification of the causative gene for single-locus disorders of considerable practical importance. The 'score-card' in domestic animals is now more than 100 disorders for which the molecular lesion has been identified and hence for which a DNA test is available. Because of the limited lifespan of any such test, a cost-effective and hence popular means of protecting the intellectual property inherent in a DNA test is not to publish the discovery. While understandable, this practice creates a disconcerting precedent. For multifactorial disorders that are scored on an all-or-none basis or into many classes, the effectiveness of control schemes could be greatly enhanced by selection on estimated breeding values for liability. Genetic variation for resistance to pathogens and parasites is ubiquitous. Selection for resistance can therefore be successful. Because of the technical and welfare challenges inherent in the requirement to expose animals to pathogens or parasites in order to be able to select for resistance, there is a very active search for DNA markers for resistance. The first practical fruits of this research were seen in 2002, with the launch of a national scrapie control programme in the UK.
In this study five parasitological methods and a polymerase chain reaction (PCR) were compared for the diagnostic sensitivity for Trypanosoma evansi in experimentally infected water buffaloes over a period of 15 weeks. The combined estimates of sensitivity (CE(se)) of the PCR proved to be highest at 78.2%, closely followed by the mouse inoculation (MI), the micro-haematocrite centrifugation technique (MHCT) and the mini-anion-exchange centrifugation technique (MAECT) with CE(se) of, respectively, 74.0, 69.6 and 62.4%. The CE(se) of the buffy-coat technique (BCT) at 38.6% and the sodium dodecyl sulfate (SDS) clarification technique at 25.1% were considerably lower. PCR detected consistently all buffaloes infected from week 3 post-infection (PI) onwards. For MI this occurred after 5 weeks PI while for MHCT and MAECT these sustainable high levels were reached in the 7th week PI. BCT and SDS never detected all buffaloes infected. The influence of time and temperature on the viability of T. evansi in heparinized blood from water buffalo was also studied. In general we observed that the survival time tends to be longer when blood is kept at 4 degrees C. In samples kept in direct sunlight parasites became undetectable with the MHCT after 30min. After treatment of the water buffaloes with diminazene aceturate, the PCR signal disappeared within 24h.
Designing a survey to detect the presence of a disease is complicated if the test used to detect the disease has non-perfect sensitivity and specificity. This paper gives two new approximations that simplify such a task. The first gives the cumulative probability distribution of the number of apparently diseased animals detected in the survey and the second gives the probability that no diseased animals are detected if the test used has 100% specificity. Both approximations can be used to determine confidence limits for the true prevalence. The main purpose of the approximations is to determine the number of animals that need to be tested to be confident that a herd is free of disease, and then to determine the number of herds that need to be tested to demonstrate area freedom. One approach to such an area survey has been to classify each herd as diseased or not based on the number of reactors found in the herd, and then to use the number of herds classified as diseased to determine the area's status. The paper points out that basing the decision simply on the magnitude of the maximum observed within-herd reactor proportion results in a more accurate survey for the same number of animals and herds tested.