Vaccination: foot-and-mouth disease experience in South America.

Vaccination against foot-and-mouth disease (FMD) constitutes an important component of the policy for its control and eradication in South America. Considering that immunization may not impair subclinical infection, it became advisable to ally to vaccination campaigns a surveillance instrument to monitor silent viral circulation. Novel approaches for the evaluation of antibodies to FMD non-capsid proteins (NCPs), developed and validated at PANAFTOSA proved valuable for assessing viral circulation in immunized populations. The extensive and coordinated application in South America of vaccination together with this serosurvey tool indicated the effectiveness of systematic vaccination to prevent FMD spread and to restrain silent viral circulation intra- and inter- herds, and gave input to an old controversy related to the real epidemiological significance, if any, of carrier animals under the vaccination conditions in South America. The fitness of NCP tests to assess viral circulation in a population supported the incorporation into the OIE code of the "free of FMD with vaccination" category as a step prior to the recognition of the "free of FMD without vaccination" category. Likewise it released the path to allow animals, vaccinated for protective purposes during emergencies, to live for the term of their productive lives.

Vaccines and companion diagnostic tests for foot-and-mouth disease virus. An overview of the experience in South America.

Vaccination constitutes an important control policy for foot-and-mouth disease (FMD) in affected areas with advanced eradication programmes, as well as in free regions that decide to use immunization as a control measure after a recent introduction of the disease. However, considering that vaccinated animals exposed to FMD virus can establish sub-clinical infection and eventually remain persistently infected, availability of tools to identify sub-clinical infection and its silent transmission within and between herds, regardless of their vaccination state, is of utmost importance. In response to the need for new diagnostic tools to support the eradication campaigns implemented in 1988 in South America, during the past decade we have developed, validated and applied a highly sensitive and specific immuno-enzymatic system for recognition of persistence at a herd level. The system is based on the detection of antibodies against non-capsid proteins required for viral replication. These proteins, in principle, are removed from the viral suspensions destined for production of BEI inactivated vaccines. Within the validation steps, evaluation of potential induction of antibodies to non-capsid proteins caused by traces of these proteins eventually remaining in the vaccines was a major concern. This report presents a review on the experience gathered through the application of the system to various experimental and field immunization conditions. It was concluded that vaccination is not expected to induce antibody responses to non-capsid proteins that could lead to misinterpretation of serological investigations. Progress on the development of approaches towards vaccine certification to guarantee absence of interference will be discussed.

Rapid serological profiling by enzyme-linked immunosorbent assay and its use as an epidemiological indicator of foot-and-mouth disease viral activity.

Frequency distribution of reactivity levels of foot-and-mouth disease infection-specific antibodies in livestock populations was analysed. Specific antibody responses against non-capsid polyprotein 3ABC were assessed through a highly sensitive indirect enzyme-linked immonosorbent assay (I-ELISA 3ABC). A graphic display of data was designed based on three negative and three positive categories to illustrate reactivity patterns. The resulting patterns were correlated to the epidemiological status. On this basis, results of over 100,000 sera derived from cattle populations in regions with various well-documented epidemiological situations were compiled and are exemplified in this paper.Distinct distributions of antibody reactivity patterns reflecting the various epidemiological situations were attained. Whereas non-affected areas presented a rather homogenous negative pattern with very limited test-positive reactions, affected regions revealed quite heterogeneous profiles, including positive and negative categories, with distributions that varied according to the region. The use of graphic prints encompassing I-ELISA 3ABC antibody profile responses constituted an adequate epidemiological indicator of the risk of foot-and-mouth disease viral activity, providing immediate visualization for a rapid inference of the epidemiological situation of a region. Moreover, such profiles allowed for convenient follow-up of infection after a focus as a function of time and geographical spread.

Review of the status of foot and mouth disease in countries of South America and approaches to control and eradication.

Since the signing in 1987 of the Hemispheric Plan for the Eradication of Foot-and-Mouth Disease (PHEFA) by the countries of South America, clinical cases of foot and mouth disease (FMD) have decreased significantly throughout the continent. During the early 1990s, national laboratories diagnosed an average of 766 cases per year in South America. By the late 1990s, this continent-wide average had fallen to 130. By the end of the 1990s, the international community recognised Argentina, Chile, Guyana and Uruguay as free of FMD without vaccination. In 1999, clinical signs of FMD were absent in 60% of all cattle of the continent. These cattle represented 41% of all herds in South America and extended over 60% of the geographical area of the continent. However, in the spring of 2001, FMD re-appeared in certain countries of the Southern Cone. This widespread re-occurrence of the disease in Argentina, Uruguay and the State of Rio Grande do Sul in Brazil called into question the basic premise of the PHEFA--that countries in South America can achieve and maintain FMD-free status, with or without vaccination. The authors suggest that these countries can regain their FMD-free status by supporting the PHEFA. A successful disease eradication strategy relies on high levels of vaccination, effectiveness of outbreak responses, and control of animal movement. This strategy must have a regional, not national, focus and must be based on risk analysis methodology. The multilateral administration of vaccination campaigns and field activities to ensure wide and simultaneous vaccine application, along with primary prevention and joint border activities, is the key to eradicating FMD and maintaining areas free of the disease.

Control of foot and mouth disease: the experience of the Americas.

Foot and mouth disease (FMD) was first recognised in South America in 1870, almost simultaneously in the province of Buenos Aires (Argentina), in the central region of Chile, in Uruguay, in southern Brazil and coincidentally, on the northeastern coast of the United States of America. The epidemiology of the disease was unknown and no government action was taken following the initial outbreaks. This resulted in the disease spreading to other areas of Chile, as well as to Peru, Bolivia and Paraguay, reaching Venezuela and Colombia in the 1950s, and Ecuador in 1961. The entire continent was affected in the 1960s when national FMD control programmes were initiated, with the exception of Guyana, Surinam, French Guiana and Patagonia. In the 1970s, steps were taken to implement a regional control and eradication strategy in view of the impact of production and trade on the persistence of the virus. The Plan Hemisférico de Erradicación de la Fiebre Aftosa (PHEFA: Hemispheric FMD Eradication Plan), public- and private-sector policies, new diagnostic tools, the oil-adjuvanted FMD vaccine and regional strategies played a part in improving the epidemiological situation during the 1990s. A setback was encountered in 2000 and 2001, with outbreaks due to virus types A and 0 recorded in Argentina, Uruguay and Brazil.