Technological advances in veterinary diagnostics: opportunities to deploy rapid decentralised tests to detect pathogens affecting livestock.

Sustainable food production capable of feeding a growing human population is a significant global challenge, and is a priority encompassed within the United Nations Millennium Development Goal to 'eradicate extreme poverty and hunger'. Infectious diseases reduce the productivity of farm animals, and the globalised trade of animals and their products increases the threat of disease incursion. Accurate and rapid diagnostic tests are an essential component of contingency plans to detect, control and eradicate such diseases. Diagnosis involves a 'pipeline' that normally starts with clinical suspicion, followed by collecting samples, transporting specimens to a centralised laboratory setting (e.g. national/international Reference Laboratories), analysing these samples using a range of diagnostic tests and reporting the results. However, the transport of specimens from the field to the laboratory can be a lengthy process that can delay critical decision-making and severely affect the quality of the samples. This important limitation of centralised diagnostic testing has motivated the development of tools for the rapid, simple detection of livestock pathogens. Recent advances in the development of technologies for personalised human medicine have motivated the development of prototype diagnostic tests for a wide selection of diseases of livestock. However, many of these tests are not yet routinely used or commercially available. This paper critically reviews the most promising examples of such assays, and highlights the challenges that remain to transition these tests from applied research and development into routine use.

La production durable de denrées alimentaires pour nourrir une population humaine en constante augmentation constitue un vaste enjeu planétaire ainsi que l'une des priorités définies par les Nations Unies dans le cadre des Objectifs du Millénaire pour le développement visant à « éradiquer l'extrême pauvreté et la faim dans le monde ¼. D'une part, les maladies animales réduisent la productivité des animaux d'élevage ; d'autre part, la mondialisation des échanges d'animaux et de produits d'origine animale intensifie les risques d'incursion de maladies. L'utilisation de tests de diagnostic rapides et fiables est une composante essentielle des plans d'urgence visant à détecter, contrôler et éradiquer ces maladies. Une procédure de diagnostic est généralement constituée de plusieurs opérations, depuis la suspicion clinique, la collecte d'échantillons, leur transport vers un laboratoire central (par exemple un laboratoire de référence national/international), jusqu'à l'analyse de ces échantillons au moyen d'une série de tests diagnostiques et la notification des résultats. Néanmoins, le transport des échantillons depuis le terrain jusqu'au laboratoire est parfois un processus très long qui peut retarder la prise de décisions cruciales, voire compromettre gravement la qualité des échantillons. Cette limitation importante des procédures diagnostiques centralisées a incité à mettre au point des outils permettant une détection rapide et aisée des agents pathogènes affectant le bétail. Les progrès récents accomplis dans les technologies relevant de la médecine humaine personnalisée ont encouragé le développement de prototypes d'épreuves de diagnostic pour nombre de maladies du bétail. Toutefois, plusieurs de ces tests ne sont pas encore utilisés en routine ni disponibles commercialement. Les auteurs font le point sur les exemples les plus prometteurs de ces tests et soulignent les difficultés restant à résoudre pour que ces tests puissent évoluer d'une application en recherche et développement à une utilisation en routine.

El logro de una producción sostenible de alimentos en cantidad suficiente para abastecer a una población humana cada vez más numerosa es una difícil empresa que el mundo tiene ante sí, que además entronca con una de las prioridades plasmadas en los Objetivos de Desarrollo del Milenio de las Naciones Unidas: «erradicar la pobreza extrema y el hambre¼. Las enfermedades infecciosas merman la productividad de los animales de granja, al tiempo que el comercio mundializado de animales y sus derivados amplifica la amenaza de incursiones infecciosas. La existencia de pruebas de diagnóstico rápidas y exactas es un elemento básico de todo plan de emergencia encaminado a detectar, controlar y erradicar esas enfermedades. Las labores de diagnóstico entrañan un «circuito¼ que normalmente empieza con la sospecha clínica, sigue con la obtención de muestras, su transporte a un laboratorio central (como un laboratorio de referencia nacional o internacional) y su análisis mediante diversas pruebas de diagnóstico y culmina con la notificación de los resultados. Sin embargo, el transporte hasta un laboratorio de las muestras obtenidas sobre el terreno es a veces un proceso lento, que puede retrasar la adopción de decisiones cruciales y mermar sensiblemente la calidad de las muestras. Este importante inconveniente derivado de la realización centralizada de pruebas ha llevado a concebir herramientas que permitan detectar de forma rápida y sencilla patógenos presentes en el ganado. Los avances registrados últimamente en la obtención de tecnologías destinadas a la medicina humana personalizada han propiciado también la elaboración de prototipos de pruebas para diagnosticar numerosas enfermedades del ganado, aunque muchas de ellas todavía no se utilizan sistemáticamente ni están comercializadas. Los autores, tras examinar en clave crítica los más prometedores ejemplos de estos nuevos ensayos, señalan las dificultades que aún subsisten para que estas pruebas puedan pasar del ámbito de la investigación aplicada y el desarrollo al de su utilización sistemática.

Validation of a foot-and-mouth disease antibody screening solid-phase competition ELISA (SPCE).

This paper describes the validation of a solid-phase competition enzyme-linked immunosorbent assay (SPCE) for the serological detection of antibody to serotype O foot-and-mouth disease (FMD) in sheep, cattle and pigs. The specificity of the SPCE was calculated from the results of testing known negative sera from sheep, cattle and pigs (n=3030, 1418 and 1495, respectively). The mean percentage inhibition (PI) for known negative sheep, cattle and pig sera were 19.3, 24.1 and 20.8%, respectively. The specificity of the SPCE at a cut-off point (COP) of 60 PI was 99.50% for sheep sera, 99.44% for cattle sera and 100% for pig sera. The analytical sensitivity of the SPCE was examined by testing sera from sheep, cattle and pigs. Based on the testing of serial bleeds from experimentally infected animals, seroconversion at the 60 PI COP occurred between 4 and 9 days post-infection or -exposure, similar to that observed using the virus neutralisation test (VNT) with a COP of 1/45. When applied to 267 sheep and 143 pig samples, that were obtained in Great Britain (GB) during the 2001 FMD UK outbreak, the SPCE identified more positive samples than did the VNT. Estimates of the accuracy, repeatability and reproducibility of the SPCE were verified during the large-scale serosurveillance necessitated by the 2001 outbreak. Results from field and experimental sera showed that when compared against the VNT, the sensitivity of the SPCE was less affected by the choice of virus strain used in the test. Using the O(1) UKG 2001 FMD virus in the VNT with samples representative of the uninfected GB sheep population, the test specificity was 100% at a COP of 1/45.

Rabies antibody testing and the UK Pet Travel Scheme.

The Pet Travel Scheme (PETS) commenced on February 28, 2000, allowing pet dogs and cats from named countries to enter the UK without spending six months in quarantine as long as they met specific criteria. Since the start of the scheme to the end of February 2002, more than 45,000 animals have successfully entered the UK under PETS. In this article, Dr Tony Fooks and colleagues consider the results of serological testing under the scheme at the Veterinary Laboratories Agency and look to future developments.

Albizia versicolor poisoning of sheep and goats in Malawi.

A report is given of the 1st confirmed outbreak of Albizia versicolor poisoning in Malawi and the 1st natural outbreak reported in sheep and goats. Approximately 800 animals are estimated to have died over a 9-year period on a government farm near Lake Malawi. Deaths occurred exclusively from August to December when ripe dry pods that fell to the ground were ingested. The major clinical signs were hyperaesthesia, wild running, lateral recumbency with rapid leg movements, nystagmus and rapid blinking. Approximately 75% of clinical cases made a full and rapid recovery. Sheep more often showed signs of poisoning than goats which was attributed to inherent susceptibility rather than selective feeding. The majority of animals affected were under 1 year of age. A series of experiments was conducted and all animals dosed with 6.4 g/kg or more of dry pods died with typical clinical signs. Although A. versicolor is well known to the local population there appeared to be no appreciation of its toxicity. Poisonings are probably rare under traditional management systems.

Seroconversion to Cowdria ruminantium of Malawi zebu calves, reared under different tick control strategies.

The seroconversion by indirect ELISA to Cowdria ruminantium over the first year of life of sixty-six Malawi zebu calves born into groups which were dipped 17 times per year was compared to seroconversion of 32 calves born into non-dipped groups. Amblyomma variegatum tick counts and clinical disease in each group of cattle were monitored throughout the study period. No cases of heartwater were seen in either group of calves over the first 22 months of life. Only one case of heartwater was observed, in an 8 year old cow, in the 1,800 intensively monitored cattle over the same period. By 12 months of age almost all undipped calves had seroconverted and 50% of seroconversions were attributed to nymphal challenge. In contrast, only 41% of calves had become seropositive by 12 months of age in the dipped groups. The dipping regime used therefore significantly decreased seroconversion rates to C. ruminantium in these calves. 73% of calves had detectable levels of maternal antibodies to C. ruminantium in the first 4 weeks of life. Antibody levels in each of the calves in dipped groups had waned to below the cut off point for the ELISA by 8-12 weeks. Seroconversion did not occur in the first 8-12 weeks of life in dipped herds. The indirect ELISA test results were not significantly different in the proportion positive in single tests at 12 months of age, or by cumulative test results of the previous 9 months, and therefore the test may be of value as a test of herd immunity.(ABSTRACT TRUNCATED AT 250 WORDS)