In the mid-1990s, the name Post-Weaning Multisystemic Syndrome was given to an unknown condition seen in piglet producing herds in Western Canada.
Within a short time, it became clear that PMWS also was occurring in other countries. Concentrated international research revealed the central culprit to be a porcine circovirus called Type II or PCV2.
A worldwide problem
We can say today with some confidence that PMWS is a worldwide problem, responsible for severe losses in affected herds. It is also widely accepted that the disease does not occur unless the PCV2 virus is present—and, most of us agree, the presence of other infections makes it worse.
But, a question that remains to be answered despite all the research over the past 20 years is quite simply this—why is PMWS so inconsistent? Even in apparently identical circumstances, the disease typically affects some herds far more than others, and only some of the weaned pigs in a badly affected herd.
This year, a global symposium held in Spain included many discussions about pig diseases associated with PCV2. One of the guest presenters was veterinarian Dr Poul Baekbo from the Danish Agriculture & Food Council’s Pig Research Centre. His take-home message was that even though PCV2 vaccination has been tremendously successful, there is still much that herd managers can do to beat PMWS.
A new study conducted by the British Pig Executive links environmental and management factors and PMWS severity. It suggests that other pathogens may be important co-factors for the disease. In addition, the on-farm study in England highlights the potential efficacy of biosecurity measures in the reduction or prevention of within-farm PMWS severity.
Dr Baekbo particularly mentioned that PCV2 needed one or more co-factors to be present before it could go from infection to disease. Risk factors can be identified. From a Danish perspective, these include having a larger herd (more than 400 sows) and purchasing replacement gilts in large numbers, but also being infected by the virus of PRRS in addition to PCV2.
Quite obviously, pigs will be less ill if they suffer from fewer infections. Therefore, the first line of defence must be to keep clean and to keep pathogens out. Experience says it is virtually impossible to exclude the PCV2 virus unless you are running a highly elaborate research unit, or providing organs for human transplants; but restricting secondary invaders will reduce the severity with which PMWS can strike.
Improved biosecurity was also on a checklist of management procedures proposed by Dr Baekbo to consider in support of using a PCV2 vaccination. He advised, using an all-in/all-out production routine, avoiding the mixing of pigs from different pens or units and doing less cross-fostering of piglets between litters to minimize risk factors. No less important, he emphasised, was to have hospital pens available to avoid mixing diseased and healthy pigs.