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Title: Factors associated with within-herd transmission of serotype A foot-and-mouth disease virus during the 2001 outbreak in Argentina: a protective effect of vaccination

Author
item BRITO, B - University Of California
item PEREZ, A - University Of California
item KONIG, G - Instituto Nacional Tecnologia Agropecuaria
item COSENTINO, B - National Health Service And Food Quality (SENASA)
item Rodriguez, Luis

Submitted to: Transboundary and Emerging Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2011
Publication Date: 3/28/2011
Citation: Brito, B.P., Perez, A.M., Konig, G.A., Cosentino, B., Rodriguez, L.L. 2011. Factors associated with within-herd transmission of serotype A foot-and-mouth disease virus during the 2001 outbreak in Argentina: a protective effect of vaccination. Transboundary and Emerging Diseases. 58(5):387-393.

Interpretive Summary: Foot-and-Mouth Disease (FMD) is one of the most important animal diseases in terms of the economic impact that it inflicts to regions affected by the disease. Argentina, recognized by the World Organisation for Animal Health (OIE) as a FMD-free-without vaccination country, was affected by a major FMD epidemic in 2001. The epidemic was caused by serotype A virus strains and was controlled by application of systematic vaccination. Here, we quantified the protective effect that emergency vaccination had in reducing the within-herd transmission rate of the disease through the epidemic. This information will contribute to estimate the impact that vaccination may have in the event of a FMD epidemic in the United States.

Technical Abstract: Argentina suffered an extensive foot-and-mouth disease (FMD) epidemic in 2001, shortly after obtaining the official FMD-free without vaccination status conferred by the World Organisation for Animal Health (OIE). This epidemic affected at least 2,519 herds and it is one of the largest FMD epidemics controlled by the implementation of a systematic mass vaccination campaign ever reported in an FMD-free country. Estimates of FMD transmission are important to understand the dynamics of the disease and to use them for the parameterization of disease transmission models to predict its spread, assess and design control strategies, conduct economic analyses, and ultimately, support the decision making process in the face of an epidemic. Here, the within-herd coefficient of transmission Beta, was computed for the FMD epidemic that affected Argentina in 2001. A probability distribution for Beta was fitted for vaccinated and unvaccinated herds. Within-herd FMD transmission was categorized as low or high based on the median value of Beta calculated for the epidemic, and a logistic regression model was fitted to identify factors significantly associated with high values of Beta. Results suggest that the odds of having a high value of Beta were significantly associated with time-length between initial infection in the herd and disease detection, date of report, vaccination and time-length between initial infection in the herd and vaccination. This study will be useful for the parameterization of epidemiological models aimed at quantifying the impact of vaccination in the face of an FMD epidemic. Results presented here demonstrate a positive impact of vaccination by reducing FMD transmission in infected herds.