PCV2d outbreaks and control
Vaccines considered the gold standard for prevention and control of PCVAD.
Clayton Johnson DVM, Carthage Veterinary Service
via National Hog Farmer - Apr 27, 2021
Porcine circovirus (PCV) is a common virus of swine, found throughout the world. The detection and emergence of a novel porcine circovirus (porcine circovirus type 2; PCV2) in the early 2000’s has led to PCV2 being an endemic pathogen of swine, by definition a pathogen that we expect all pigs to be infected with at some point during their life. PCV associated disease (PCVAD) was originally described as a postweaning multisystemic wasting syndrome (PMWS). Additional disease presentations have been described throughout the years with various disease manifestations present in all ages of swine. Vaccines have played a critical role in PCV control and are considered the gold standard for prevention and control of PCVAD.
PCV2 and associated PCVAD represent endemic pathogens of swine and their herd impact is always difficult to quantify. While we typically associate disease “outbreaks” with epidemic disease-causing agents such as PED, ASF, etc., novel introduction of heterologous endemic pathogens can absolutely manifest itself as a disease outbreak within a susceptible population, even if that population has partial immunity through heterologous PCV vaccination and/or natural exposure.
Several breed-to-wean (BTW) sow herds have observed a high incidence of PCVAD in recently weaned pigs despite the continuous use of industry standard PCV2 vaccination programs. Each of these farms represent a “closed herd” in which BTW herd replacement animals are produced internally with no outside animal introductions following the initial farm stockings. All replacement gilts and teaser boars were vaccinated with commercial PCV2 vaccine at processing, weaning and again at 20 weeks of age. The PCV2 instability resulted in dramatically increased culls and mortality in growing pigs. In most situations, early observations of PCV2 outbreaks at the sow farm level existed only in the post-weaning piglet population. Nursery aged piglets were diagnosed with PCVAD via RT-PCR and IHC from tissues of affected pigs. The majority of PCV2 outbreaks on BTW farms will go unnoticed at the BTW herd level, without obvious clinical signs or production metric impacts. Occasionally, PCV2 outbreaks will manifest clinical signs and performance impacts at the BTW herd level, with increased percentages of low viability piglets, stillborns and mummies at birth as well as the presence of “wasting” piglets in the internal GDU that fail to respond to medication. In my observations, PCV2 outbreaks at the sow farm have been much more frequent in purebred herds produced parent stock females compared to their commercial cross bred herd counterparts, but this observation is limited in scope and scale and should be taken with a heavy grain of salt...