There are currently four recognized species of porcine Circovirus: PCV1, PCV2, PCV3 and more recently PCV4.
PCV2 is the species of the greatest clinical importance.
PCV2 strains are currently classified into 8 genotypes (from 2a to 2h) based on differences in the capsid gene (ORF-2).
For several years, Biovet has been offering identification of genotypes 2a, 2b and 2d by means of a multiplex RT-PCR test.
Most of the samples submitted to us are serum samples whose exact origin (e.g. clinical case or not) is only rarely specified.
They come from both Western Canada and Quebec (about 40% vs. 60%)
We have compiled genotyping results for the past 35 months (from 2019-07-01 to 2021-05-31).
The distribution of the different genotypes (by farm and not by sample) is shown in Figure 1.
Figure 1. Results of PCV2 genotyping (by farm)
In 20 to 35% of farms, the genotype could not be determined.
In the very large majority, this is explained by low viral loads (Ct between 30 and 35), below the detection threshold of genotyping PCR, which is less sensitive than the screening threshold.
In the vast majority of cases, there was only one genotype.
However, there were some exceptions, such as the cases identified “2a+ 2d”, “2a+2b”, “2b+2d”, where two genotypes were present.
The distribution of the three genotypes 2a, 2b and 2d among farms with at least one genotype detected is shown in Figure 2.
Figure 2. Distribution of genotypes 2a, 2b, and 2c (by farm)
Genotype 2a has been systematically and largely the most prevalent over the past three years (51 to 63% of farms).
Genotype 2b was present in 11 to 26% of farms while genotype 2d was detected in 21 to 26% of farms.
Only a few rare cases of genotype 2d came from Quebec; the vast majority came from farms in Western Canada.
In conclusion, genotype 2a remains surprisingly the most prevalent genotype, far ahead of genotype 2d, which predominates in many countries including the USA.
Given the clinical importance of the different genotypes, our results should be interpreted with caution.
Indeed, the sample examined is probably not representative of farms with problems associated with PCV2.