PARTNER FEATURE ▶▶▶


No reason to worry about new PCV2 genotypes


Globally, vaccination of pigs against Porcine Circovirus (PCV) disease has been widely adopted with control of the disease and return on investment for farmers. Since the virus’ early days, research has shown a continuous evolution of the PCV2 virus at the genetic level. There is, however, no reason for concern.


BY OLIVER DURAN, GLOBAL STRATEGIC MARKETING, BOEHRINGER INGELHEIM AN- IMAL HEALTH


T PCV2-a


The most frequent genotype before the advent of PCV-2- systemic disease outbreaks


o understand how PCV2 is moving in time and ge- ographically, scientists use molecular sequencing. That has focused on sequencing one part of the virus: the ORF2 gene that encodes for the capsid,


the key protein detected by the pig’s immune system. Investigations prove that the virus has continuously evolved, from the early days of post-weaning multisystemic wasting syndrome (PMWS), to the time of PCV2 vaccine launches (2007–2010) when PCV2-b was the most common, to PCV2-d, the genotype currently found in higher frequency. This was to be expected from a virus that has a high muta- tion rate. The current genetic changes do not seem to change the structure of the capsid protein enough to evade protection from PCV2-a based vaccines. Therefore, despite the signifi- cant number of genotypes described (PCV2-a to PCV2-i), it seems one single PCV2 serotype exists so far.


Figure 1 - Predominant PCV2 genotypes detected globally.


Scientists do not fully understand what drives this rapid evolution, but it is likely due to immune pressure and a high virus population. For that reason, it is important to monitor PCV2 detected from clinical cases and the different geno- types that evolve, to confirm the continued high degree of protection from current vaccines.


Vaccination confers cross-protection Researchers Giovanni Franzo, at the University of Padova, Italy and Professor Joaquim Segalés, from CReSA-IRTA, Spain re- cently published about the subject. They stated, “So far, all vaccines in the market have shown great efficacy in reducing clinical signs associated to diseases caused by PCV2, inde- pendently of the genotype present in the farm. Moreover, ex- perimental data demonstrated the cross-protection of PCV2-a vaccines against the most widespread genotypes (PCV2-a, PCV2-b and PCV2-d).” Numerous farm and laboratory studies around the globe show clear evidence that a PCV2-a based vaccine (Ingelvac CircoFlex) provides effective protection against the most prevalent strains in the field (see Table 1).


PCV2-b


Genotype PCV2-b was the most commonly detected during the most severe clinical disease globally


(Segalés et al., 2013)


8 PCV2-c


Only occasionally detected and hardly plays a role in the field


PCV2-d


First detected in 2004. In the last five to seven years, PCV2-d has become the most prevalent genotype worldwide


(Franzo and Segalés, 2021)


Assumption of vaccine failure Certainly, at a very low frequency there are still times when PCV2 infection is suspected because producers report wast- ing and other clinical signs. However, when those cases are carefully investigated, they are mostly related to either fail- ures in the vaccination procedure, occurrence of Porcine Reproductive and Respiratory Syndrome or combinations of viral and bacterial infections. In some rare cases, very early PCV disease is seen in piglets in early nursery, despite vaccination around the time of wean- ing. Typically, what is recognised is that the PCV2 infection has happened before vaccination. The most likely reason is infection of the foetus during gesta- tion in sows or gilts that had not been fully protected by vac- cination. Diagnostic investigations have shown that in very effectively vaccinated and managed herds, gilts selected for replacements can enter the breeding herd completely naïve to PCV2. If those gilts become exposed during gestation, PCV2 can cross the placenta and infect the foetus, causing infertility or infected pigs at birth. In other cases, the sow herd immunity becomes uneven al- lowing for increased circulation of PCV2 in sows (unstable sow


▶ PIG PROGRESS | Volume 37, No. 4, 2021


PHOTO: BOEHRINGER INGELHEIM


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