|
|
           |
Pig Wasting Disease Devastates IndustryDate: 29 Oct 2001 Post-weaning multisystemic wasting syndrome (PMWS) is an enigmatic emerging disease of early-weaned swine that is manifesting in epidemic and endemic forms in major pig-producing countries around the world. Although clearly and consistently associated with porcine circovirus 2 (PCV2) infection, PMWS cannot be reproduced by inoculation of PCV2 alone. In fact PCV2 is a common and usually non-pathogenic virus on pig farms. So what are the co-factors that allow PCV2 to become pathogenic and manifest as PMWS? Evidence is now accumulating that pathogenic PCV2 infectionmay resultfrom an overwhelming challenge to the immune system when pigs areweaned early (e.g., 3-4 weeks of age). Under typical intensive farming conditions, weaning is a time when theyoung pig's immune system faces challenge from a variety of novel infectious agents as a result of moving to rearing accommodation combined with mixing with other pigs. Porcine reproductive and respiratory disease syndrome virus (PRRSV) and porcine parvovirus(PPV) infections are often experienced, though mostly sub-clinically, in the weeks following weaning. Experimentally, PRRSV and PPV have induced PMWS in pigs inoculated with PCV2, in circumstances where PCV2 inoculation alone was ineffective. Research just published in the November (vol.48) edition of "The Pig Journal" (organ of the UK Pig Veterinary Society) draws attention to another possible co-factor of the emergence of this devastating disease -- the growing use over the last few years of a multiplicity of vaccines in young pigs. The hypothesis is that powerful antigenic challenges from modern vaccines may, in some situations,contribute toan "overwhelming" of the early-weaned pig's immune system. To test this hypothesis, the authors withdrew a _Mycoplasma hyopneumoniae_ vaccination programme from approximately 50% of the piglets born over a 4 months period. In non-vaccinated animals, losses due to PMWS were reduced in 4 out of 5 groups studied. Another paper in the same journal reports on a case-control study of PMWS in which risk factors for the disease included large farm sizeand more numerous breeding stock introductions. So it may be that a variety of management factors that have increased in recent years, a sa response to economic pressures and price competition, may bebecoming counter-productive. Further details of this new research, and a reference list, can befound at: http://www.pighealth.com/circovirus.htm Pig Disease Information Centre <pdic@btclick.com> |