Serological survey of Salmonella spp. infection in finishing pigs from northeastern Spain and associated risk factors

Abstract

The results of a serological survey carried out in northeastern Spain to estimate the seroprevalence to Salmonella spp. and to determine potential risk factors are presented. Sera were obtained from farms submitting serum samples to the Regional Diagnostic Laboratory (RDL) for the diagnosis of other infectious diseases included within official eradication/surveillance programs, and farm data collected through a questionnaire. Out of 6,182 pig sera (217 farms) analyzed 1,219 (19.7%) were positive (optical density, OD ≥ 40%). More than 70% of the herds presented ≥ 1 seropositive animal indicating that salmonellosis was widespread. In a multivariable logistic mixed regression model seroprevalence was associated with farms where birds were visible inside the fattening units (OR = 2.1; 95% CI: 1.3-3.2) or that shared workers with other pig farms (OR = 2.5; 95% CI: 1.4-4.7). Seropositivity also increased when farmers used footwear exclusive for the farm (OR = 3.1; 95% CI: 1.3-7.3) or pigs were fed mostly with pellets (OR = 1.7; 95% CI: 1.1-2.6). It was also higher during the fall and winter months. The presence of a changing room and shower in the farm was negatively associated with it (OR = 0.5; 95% CI: 0.3-0.8). Most risk factors could be mitigated through strict hygiene and biosecurity measures, but the high (> 40%) within-herd seroprevalence observed in many herds may challenge the capacity of intervention of animal health authorities.Additional key words: ELISA test; risk factors; salmonellosis; seroprevalence; swine. ResumenEstudio serológico de la infección por Salmonella spp. en cerdos de engorde del Noreste de España y factores de riesgo asociados Se presentan los resultados de un estudio serológico realizado en explotaciones porcinas del Noreste de España para estimar la seroprevalencia frente a Salmonella spp. y determinar posibles factores de riesgo asociados. Los sueros se obtuvieron a partir de aquellos enviados por las explotaciones al Laboratorio Regional de Diagnóstico para el diagnóstico de otras enfermedades infecciosas sometidas a erradicación/vigilancia oficial, y los datos sobre las explotaciones se recogieron mediante un cuestionario. De un total de 6.182 sueros de cerdo (217 granjas) analizados 1.219 (19,7%) resultaron positivos (densidad óptica, DO ≥ 40%). Más del 70% de los rebaños presentaron al menos un animal positivo, indicando que la salmonelosis está ampliamente distribuida en la región. Según un modelo multivariable mixto de regresión logística, la seroprevalencia se asoció con granjas en las cuales se veían aves en el interior de las naves (OR = 2,1; IC 95%: 1,3-3,2) y también con granjas que compartían trabajadores (OR = 2,5; IC 95%: 1,4-4,7). Se observó que la seropositividad se incrementaba cuando los trabajadores usaban botas exclusivas en la explotación (OR = 3,1; IC 95%: 1,3-7,3) o al alimentar a los cerdos principalmente con alimento granulado (OR = 1,7; IC 95%: 1,1-2,6). La seroprevalencia también fue superior durante los meses de otoño e invierno. La existencia en las...

Longitudinal study describing time to Salmonella seroconversion in piglets on three farrow‐to‐finish farms

“…Detection of antibodies against Salmonella is not the best indicator of infection at the pig level because neither the infection of lymph nodes nor the shedding of Salmonella organism in faeces is necessarily related to the presence of antibodies in pigs 23. Despite that, ELISA is useful to detect prior exposure to the bacteria at the herd level, and some national programmes against pig salmonellosis are based on serology 14. Serology at the farm level is considered as a good solution to categorise livestock.…”

“…They give an indication of previous exposure to Salmonella and are not necessarily correlated with Salmonella shedding by pigs at the time of testing 13. However, serology is considered to be one of the better alternatives for establishing the level of a herd's Salmonella exposure14 and may help to predict the risk of Salmonella shedding at slaughter 15 16. To follow the dynamics of Salmonella infection in pig herds over time, longitudinal studies on the bacteriological and serological status of pigs need to be performed 17.…”

Identifying Active Salmonella Infections in Swine Nurseries Using Serology and Bacterial Culture and Evaluating Associated Risk Factors

“…By understanding the Salmonella status at the cohort level, it can help veterinarians and producers better target the control and prevention methods in the nursery barn. Previous studies have used different methods and classification schemes for identifying Salmonella status in pig herds or scoring them as low, moderate and high-risk, using serological (based on different OD values/S/P ratios) and/or bacteriological testing methods [7,[22][23][24][25]. Various studies have solely relied on either bacteriology or serology to identify Salmonella status in pigs and on farms [11,25,26].…”