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Author(s): Desrosiers, Robert
Publication Date: January 1, 2007
Country: Canada


Starting at the end of 2004, and particularly since the beginning of 2005, cases of post-weaning multi-systemic wasting syndrome (PMWS) in Quebec increased dramatically. Simultaneously in Ontario and a little later in North Carolina, the same phenomenon of dramatic increase in PMWS cases was observed. This paper tries to shed some light on the possible reasons why this may have occurred and on what can be done to control the losses. This paper also briefly looks at some of the conditions, other than PMWS, that might be associated with porcine circovirus type 2 (PCV2), and at a few similarities and differences that may exist between the European situation and the one we have to deal with in Eastern Canada and the US. The acronym PMWS is gradually being replaced in Europe by PCVD (porcine circovirus disease) and in North America by PCVAD, (porcine circovirus associated disease). Reasons for this switch include: 1) wasting is not specific to PCV2; 2) PCV2 has been associated with conditions in pigs other than PMWS; 3) the word wasting might have a negative impact on public perceptions of the swine industry, and of the safety of pork. Two main positions are currently debated. There are those who believe that PCV2 is the cause of PCVD, although other factors or agents may contribute significantly to the losses associated with it in the field, and that another as-yet-unidentified agent, often called agent X, might be the real culprit. The virus can be transmitted in various ways, it has been reported to be excreted through nasal and ocular secretions, urine, feces and colostrums, it is also present in semen and some boars have been found to shed it for at least 24 weeks (McIntosh et al, 2005); it is very persistent in the environment, and pigs from herds with no clinical signs can contract the disease if placed in contact with sick pigs, or if placed in close proximity (Kristensen et al, 2004). Many other ways that PCV2 can be transmitted are also summarized in this paper. The best chances of success or improvement when PCVD is a problem are genetic changes, vaccination, management changes, serotherapy, the control of other diseases, like PRRS, that can trigger the condition or increase its severity and depopulation/repopulation. Strategies that have been suggested to help control PCVD include: reduce the number of weaned or feeder pig sources; reevaluate the vaccines and vaccination programs used; use disinfectants (e.g. Virkon S) that have good activity against PCV2; batch farrowing every 2, 3, 4 or even 5 weeks; partial depopulation of the nursery; bioflavonoids, vitamin E and Se, antioxidants, mash feed, feeds with larger particle size, restricted feeding, no feed changes after moving pigs, richer diets; no hospital pens, either euthanize sick pigs or move them elsewhere; increase weaning age; acetaminophen, acetylsalicylic acid, florfenicol, tilmicosin; closing the herd; use measures to improve colostrum intake; all piglets to suckle their natural mothers for the first 24 hours. The list seems almost endless and one must admit that the results obtained have been very variable, and quite frequently disappointing. There are, however, situations showing that management strategies and infection pressure may have a significant impact on the outcome. PMWS/PCVD/PCVAD has produced severe losses for pig producers in many areas of the world. While North America has to a certain extent avoided these severe losses until recently, we now have areas where losses are unacceptably high and solutions have to be found. Different control alternatives have been briefly discussed in this paper. In my opinion the two approaches most likely to make our lives easier with this condition are genetics and vaccines. Some genetic lines or combinations are clearly more resistant to PCVD than others, and the preliminary results obtained with vaccines are very encouraging. An effective and practical control of the problems associated with PCV2 now appears possible.

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