Selection and use of reference panels: a case study highlighting current gaps in the materials available for foot and mouth disease.

The World Organisation for Animal Health (OIE) Manual of Diagnostic Tests and Vaccines for Terrestrial Animals describes a diverse array of assays that can be used to detect, characterise and monitor the presence of infectious agents of farmed livestock. These methods have been developed in different laboratories, at different times, and often include tests or kits provided by the commercial sector. Reference panels are essential tools that can be used during assay development and in validation exercises to compare the performance of these varied (and sometimes competing) diagnostic technologies. World Organisation for Animal Health Reference Laboratories already provide approved international standard reagents to help calibrate diagnostic tests for a range of diseases, but there remain important gaps in their availability for comparative purposes and the calibration of test results across different laboratories. Using foot and mouth disease (FMD) as an example, this review highlights four specific areas where new reference reagents are required. These are to: reduce bias in estimates of the diagnostic sensitivity and inter-serotypic specificity of tests used to detect diverse strains of FMD virus (FMDV), provide bio-safe positive controls for new point-of-care test formats that can be deployed outside high containment, harmonise FMDV antigens for post-vaccination serology, and address inter-laboratory differences in serological assays used to measure virus-specific FMD antibody responses. Since there are often limited resources to prepare and distribute these materials, sustainable progress in this arena will only be achievable if there is consensus and coordination of these activities among OIE Reference Laboratories.

Le Manuel des tests de diagnostic et des vaccins pour les animaux terrestres de l'Organisation mondiale de la santé animale (OIE) décrit une vaste panoplie d'essais utilisables pour la détection, la caractérisation et la surveillance des agents pathogènes affectant les animaux d'élevage. Ces méthodes ont été mises au point par des laboratoires différents à diverses périodes et intègrent souvent des tests ou des kits fournis par le secteur privé. Les panels de référence sont des outils essentiels aussi bien lors de la conception d'un essai que lors d'exercices de validation, leur but étant alors de comparer les performances de technologies diagnostiques variées (et parfois concurrentes). Les Laboratoires de référence de l'OIE fournissent des réactifs de référence internationaux validés afin d'aider à calibrer les tests de diagnostic pour un certain nombre de maladies animales ; toutefois, on constate que nombre de ces réactifs ne sont pas disponibles pour la comparaison et le calibrage interlaboratoires des résultats de tests. À partir de l'exemple de la fièvre aphteuse, les auteurs soulignent quatre domaines spécifiques pour lesquels il conviendrait de disposer de nouveaux réactifs de référence. Il s'agit des réactifs nécessaires pour : (1) réduire les biais dans l'estimation de la sensibilité diagnostique et de la spécificité pour différents sérotypes des tests utilisés pour détecter diverses souches du virus de la fièvre aphteuse ; (2) fournir des contrôles positifs sûrs au plan biologique pour les nouveaux formats de tests utilisables sur le lieu d'intervention et non plus dans des laboratoires de confinement à haute sécurité ; (3) harmoniser les antigènes du virus de la fièvre aphteuse pour la sérologie post-vaccinale ; (4) résoudre le problème des différences obtenues entre laboratoires lors d'essais sérologiques visant à mesurer la réponse en anticorps spécifiques du virus de la fièvre aphteuse. Compte tenu des ressources souvent limitées consacrées à la préparation et à la distribution de ces réactifs, des progrès durables ne seront obtenus que s'il existe un consensus en la matière et une coordination de ces activités parmi les Laboratoires de référence de l'OIE.

En el Manual de pruebas de diagnóstico y vacunas para los animales terrestres de la Organización Mundial de Sanidad Animal (OIE) se describe todo un conjunto de ensayos que se pueden emplear para detectar y caracterizar agentes infecciosos del ganado doméstico y hacer así controles sistemáticos de su eventual presencia. Estos métodos, concebidos en distintos laboratorios en distintos momentos, suelen acompañarse de pruebas o estuches analíticos que proporcionan empresas privadas. Los paneles de referencia son una herramienta esencial, que se puede emplear durante la concepción de ensayos y en los procesos de validación para comparar el funcionamiento de estas diferentes técnicas de diagnóstico, que a veces compiten unas con otras. Los laboratorios de referencia de la OIE ya facilitan reactivos de referencia internacional aprobados que ayudan a calibrar las pruebas de diagnóstico de una serie de enfermedades, pero todavía hay importantes carencias por lo que respecta a la posibilidad de procurárselos con fines de comparación y a la calibración de los resultados que obtienen diferentes laboratorios. Sirviéndose del ejemplo de la fiebre aftosa, los autores destacan cuatro aspectos específicos para los que hacen falta nuevos reactivos de referencia. Se trata de los siguientes: reducir el sesgo a la hora de calcular la sensibilidad de diagnóstico y la especificidad interserotípica de las pruebas empleadas para detectar diversas cepas del virus de la fiebre aftosa; proporcionar controles positivos que ofrezcan seguridad biológica para nuevos modalidades de ensayo utilizables en el lugar de consulta, esto es, en condiciones que no sean de alta contención; armonizar los antígenos víricos para la práctica de análisis serológicos tras la vacunación; y solventar las diferencias entre laboratorios por lo que respecta a los ensayos serológicos empleados para medir la respuesta de anticuerpos específicos contra el virus de la fiebre aftosa. Dado que suele haber escasos recursos para preparar y distribuir este tipo de material, solo será posible avanzar duraderamente en la materia si los laboratorios de referencia de la OIE consensúan y coordinan estas actividades.

Outbreak investigations and molecular characterization of foot-and-mouth disease viruses circulating in south-west Niger.

In Niger, the epidemiological situation regarding foot-and-mouth disease is unclear as many outbreaks are unreported. This study aimed (i) to identify Foot-and-mouth disease virus (FMDV) strains currently circulating in cattle herds, and (ii) to identify risk factors associated with Foot-and-mouth disease (FMD)-seropositive animals in clinical outbreaks. Epithelial tissues (n = 25) and sera (n = 227) were collected from cattle in eight districts of the south-western part of Niger. Testing of clinical material revealed the presence of FMDV serotype O that was characterized within the O/WEST AFRICA topotype. The antigenic relationship between one of the FMDV isolates from Niger (O/NGR/4/2015) and three reference vaccine strains was determined by the two-dimensional virus neutralization test (2dmVNT), revealing a close antigenic match between the field isolate from Niger and three FMDV serotype O vaccine strains. Serological analyses using a non-structural protein (NSP) test provided evidence for previous FMDV infection in 70% (158/227) of the sera tested. Multivariate logistic regression analysis revealed that only the herd composition (presence of both cattle and small ruminants) was significantly associated with FMDV seropositivity as defined by NSP-positive results (p-value = .006). Of these positive sera, subsequent testing by liquid-phase blocking ELISA (LPBE) showed that 86% (136/158) were positive for one (or more) of four FMDV serotypes (A, O, Southern African Territories (SAT) 1 and SAT 2). This study provides epidemiological information about FMD in the south-western part of Niger and highlights the complex transboundary nature of FMD in Africa. These findings may help to develop effective control and preventive strategies for FMD in Niger as well, as other countries in West Africa.

Antigenic variation of foot-and-mouth disease virus serotype A.

The current measures to control foot-and-mouth disease (FMD) include vaccination, movement control and slaughter of infected or susceptible animals. One of the difficulties in controlling FMD by vaccination arises due to the substantial diversity found among the seven serotypes of FMD virus (FMDV) and the strains within these serotypes. Therefore, vaccination using a single vaccine strain may not fully cross-protect against all strains within that serotype, and therefore selection of appropriate vaccines requires serological comparison of the field virus and potential vaccine viruses using relationship coefficients (r1 values). Limitations of this approach are that antigenic relationships among field viruses are not addressed, as comparisons are only with potential vaccine virus. Furthermore, inherent variation among vaccine sera may impair reproducibility of one-way relationship scores. Here, we used antigenic cartography to quantify and visualize the antigenic relationships among FMD serotype A viruses, aiming to improve the understanding of FMDV antigenic evolution and the scope and reliability of vaccine matching. Our results suggest that predicting antigenic difference using genetic sequence alone or by geographical location is not currently reliable. We found co-circulating lineages in one region that were genetically similar but antigenically distinct. Nevertheless, by comparing antigenic distances measured from the antigenic maps with the full capsid (P1) sequence, we identified a specific amino acid substitution associated with an antigenic mismatch among field viruses and a commonly used prototype vaccine strain, A22/IRQ/24/64.