0
The objectives of this study were to determine the sample size adequate to establish a PMWS diagnosis in individual pigs and to analyze the evolution of mortality before and after a PMWS outbreak.
To determine the sample size adequate to establish a PMWS diagnosis in individual pigs, data from two previously published studies were used. Those studies were performed in a total of 56 PMWS-affected herds in Denmark (n = 8), Spain (n = 3), and Italy (n = 45). A total of 330 wasted pigs (91 from Denmark, 79 from Spain, and 160 from Italy) were necropsied and lymphoid tissues were examined histopathologically and by IHC or ISH for PCV2 detection. The percentages of suspected pigs that fulfilled PMWS diagnosis in Italy, Denmark, and Spain were 69%, 56%, and 46%, respectively. Results showed that to diagnose at least one PMWS-affected pig with a probability > 95%, it is necessary to study a minimum of three, four, and five pigs, considering Italian, Danish, and Spanish data, respectively.
In order to analyze the evolution of mortality before and after a PMWS outbreak, three different herds per country in Denmark (Dk-1, Dk-2, and Dk-3), France (Fr-1, Fr-2, and Fr-3), and Spain (Sp-1, Sp-2, and Sp-3), and one in Sweden (Sw-1), were retrospectively selected, taking into account the fulfillment of two conditions: firstly, availability of a PMWS diagnosis in at least one pig; and, secondly, longitudinal mortality data available during a period before PMWS occurred (between 9 and 35 months, depending on the herd) and during the time when PMWS was occurring. Longitudinally collected data showed that when > 20 data points were available, a significant increase in mortality was always detected at close to the time of PMWS diagnosis. When < 10 points were available, a significant increase in mortality was detected in four of six studied herds, although mortality percentages were always higher at the time of PMWS diagnosis than before diagnosis.
These results suggest that two conditions must be fulfilled to diagnose PMWS in a herd. Firstly, a significant increase in postweaning mortality, compared to the historical background in the herd, must be observed in association with clinical signs compatible with PMWS. Secondly, PMWS must be diagnosed in at least one of three to five necropsied pigs concurrently with the increase in mortality. Ruling out other potential causes of increased mortality is also necessary.
Grau-Roma L, Baekbo P, Rose N, et al. Clinical and laboratory studies on herds affected with postweaning multisystemic wasting syndrome in Denmark, France, Spain, and Sweden: Disease progression and a proposal for herd case definition. J Swine Health Prod. 2012;20(3):129–136.