Selected Swine Viral Pathogens in Indoor Pigs in Spain. Seroprevalence and Farm-Level Characteristics. Lopez-Soria S, Maldonado J, Riera P, Nofrarias M, Espinal A, Valero O, Blanchard P, Jestin A, Casal J, Domingo M, Artigas C, Segales J. Transbound Emerg Dis. 2010 Jun;57(3):171-9
What are they studying?
The seroprevalence against PRRSV, SIV, PCV2, ADV and PPV in sow, fattening and boar herds in Spain from 2003 to 2005, as well as their relationship on production parameters.
How is it done?
A retrospective study was carried out with blood samples submitted in 2003, 2004 and 2005. The samples were screened for several pathogens (PRRSV, SIV, ADV PPV and PCV2). Table 1 shows the number of herds and samples that were investigated for PRRSV.
Table 1. Number of herds and animals tested for PRRSV
|no. tested herds||no. tested samples|
In order to eliminate some of the bias due to the fact that the samples were sent for routine analyses, not for the purpose of this study, 44 non vaccinated farms (for PRRS, PCV2 and SIV) were studied to provide information on seroprevalences and co-seropositivity to PRRSV, SIV, ADV and PCV2, and to study their relationship with farm characteristics and productive parameters.
What are the results?
High seroprevalences were observed for PRRSV in sow and fattening pig herds, the sow farm prevalence for PRRSV was between 85 and 89% and for fattening farms it was between 78% and 83%. For SIV, the seropositivity went from 87% to 95% in sows farms, and from 68% to 82% in fattening farms. Table 2 shows the full results.
Table 2. Seropositivity results for the main pathogens studied
|% of positive herds||PRRS||SIV||PPV|
On the 44 “non-biased” farms a high prevalence was still detected: PRRS was found in 91% of sow herds and 86% of fattening herds, SIV was found in 96% and 73% of sow and fattening herds respectively, and PCV2 was present in all the samples. The following figures show the co-seropositivity on the different farms.
Graphic 1. Co-seropositivity to PRRSV, SIV, ADV and PCV2 in sow and fattening herds.
No relationship could be found in this study between seroprevalences and farm characteristics, management and productive parameters. However, the authors don’t rule out the possibility of an effect of any of the studied variables since the number of farms studied was low.
What implications does this paper have?
All the monitored pathogens were found in most of the herds and the seroprevalence of PCV2, PRRSV, and SIV is still very high in sow and fattening farms. The main microorganisms associated with respiratory diseases are widespread in Spain and are probably interacting.
The field view by Enric Marco
The high prevalence found confirms the feeling you get from the field: these diseases are widespread in our farms. But not just that; the fact that the prevalences found in a large number of farms involve several of the various infections investigated, highlights the possibility of mixed infections on the farms, worsening and complicating the clinical picture observed.
Based on these results, especially those relating to PRRS, influenza and PCV2, the study also shows the need to implement control measures on pig farms, especially in high density areas. Taking into account the wide distribution of these infections in the aforementioned areas and their airborne transmission (among other routes), the possibility of undertaking elimination plans does not seem advisable due to risk of reinfection.
Furthermore, and in the absence of marker vaccines that limit viral excretion, as in the case of Aujeszky's disease, efforts to reduce prevalence are neither advisable in light of the risk of leaving some subpopulations unprotected, which would in turn increase the risk of clinical problems. For these reasons, immunization of the whole pig stock (actions designed to adapt herd replacement and maintain an homogeneous immune status of the sows) should help achieve improvements at production level.
The high prevalence of these pathogens in areas of high concentration of farms raises the need for coordinated control measures in these areas, given that different production systems (one or more phases) or management measures that could be implemented individually (all in-all out, solid partitions or stocking densities) do not seem (at least in this study), to be very effective in reducing prevalence. By "coordinated control measures" we understand all those measures which are directed to contain viral spread, such as: biosecurity, control of the health status of the source herds, coordinated (both in product and time of application) vaccination plans, etc. A positive example of this is Aujeszky's disease, where a coordinated plan has been able to reduce the prevalence (as the work shows) to 0 at this present time.