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PCV2 Isolates

Molecular studies to determine the genetic variation of PCV2 found that minor branches of PCV2 were associated with geographic origin rather than with differences in viruelence (Fenaux et al., 2000; Mankertz et al., 2000). Meehan et al. (2001) investigated PCV2 isolates from cases of PDNS and abortions and found the isolates being closely related to a PMWS-associated PCV2 further establishing the apparent genetic stability of PCV2. Mahé et al. (2000) identified four dominant immunoreactive areas by PEPSCAN analysis within ORF2. Larochelle et al. (2002) sequenced 34 Eastern Canadian PCV2 isolates recovered from 5- to 20-week-old pigs with various clinical conditions such as PMWS (15 isolates), PRRS (8 isolates), generalized tremors (5 isolates), erysipelas (1 isolate), gastric ulcer (1 isolate), nervous signs (1 isolate), arthritis (1 isolate), and no clinical signs (1 isolate) and compared the obtained sequences to 36 published sequences. Sequence analysis indicated that all the isolates were closely related. Three major regions of amino acid heterogeneity were identified among PCV2 isolates, and two of the regions corresponded to two of the immunoreactive areas described by Mahé et al. (2000). Comparison of three immunodominant regions however, revealed no link between capsid protein variation and pathogenicity of isolates (Larochelle et al., 2002).

Larochelle et al. (2003) compared PCV2 from PMWS-affected herds to PCV2 from healthy pigs from herds non-affected by PMWS and found closely related strains in 6 different herds (4 with PMWS and 2 without) sharing at least 99.4% of their nucleotide-sequence identity and more than 98.7% of their amino-acid identity for the capsid protein. One strain identified in a herd without PMWS was found to be 100.0% homologous to a PCV2 from a PMWS herd (Larochelle et al., 2003). De Boisséson et al. (2004) used 31 pigs originating from 13 PMWS-affected herds and 25 pigs from 10 PMWS fee herds and sequenced 38 PCV2 isolates. All the isolates shared 94.2-100% nucleotide identity. A wider nucleotide diversity was observed in the PCV2 isolates originating from PMWS free herds compared with isolates from PMWS herds; however, residues found to be specific to non-PMWS strains were also found in PMWS strains and no molecular marker of virulence in PMWS strains could be identified (de Boisséson et al., 2004). Sequence analysis of a PCV1 associated with congenital tremor in 1960 and two PCV2 isolates associated with recent cases of congenital tremors demonstrated that the PCV2 isolates showed 99% sequence identity with each other and also with other PMWS-isolates (Choi et al., 2002). No consistent genomic differences between PMWS and recent congenital tremor isolates were found. The 1960 PCV1 isolate showed 98% similarity to other PCV1 isolates (Choi et al., 2002). In a case control study done by Pogranichniy et al. (2002) PCV2 was not only found in PMWS cases but also in 62.5% of the control cases. Sequencing and genetic comparison revealed no differences between 5 PMWS-associated PCV2 isolates and 4 PCV2 isolates recovered from cases not associated with PMWS (Pogranichniy et al., 2002).

In contrast, Wang et al. (2004) comparing the ORF2 of Taiwanese PCV2 isolates associated with PMWS (4 isolates), PDNS (2 isolates), nervous signs (1 isolate), abortion (1 isolate) found a small number of residue difference associated with the different clinical conditions. Farnham et al. (2003) further characterized 2 PCV2 isolates associated with abortions by ORF2 sequencing and found that the isolates were almost identical to each other and to other isolates associated with reproductive failure whereas there were at least 2 amino acid differences to PCV2 isolates associated with PMWS. Recently it has been demonstrated that two amino acid changes in the PCV2 capsid protein that occurred during serial in vitro passage enhanced the ability of PCV2 to grow in vitro and attenuated the virus in vivo (Fenaux et al., 2004). Furthermore, we recently compared field isolates of PCV2 recovered from a case with moderate-to-severe PCV2-associated lesions to a PCV2 isolate from a case with no PCV2-associated lesions and demonstrated significant differences in incidence and severity of PCV2-induced lesions and in amount of PCV2 virus in the serum and tissues of experimentally-inoculated SPF pigs (Opriessnig and Halbur, 2005).

Delay et al. (2005) reported on markedly increased incidence and severity of porcine circovirus type 2 (PCV2)-associated disease in eastern Canada since January 2005. PCV2 strains isolated from these outbreaks appear to be different from the resident PCV2 strains that have been in the region for the last 10-15 years. There is a dramatic increase of restriction fragment length polymorphism (RFLP) type 321 strains, whereas the most common PCV2 strain had been type 422. Sequencing and comparison of the ORF2 gene of the recent 321 strains showed high homology with French isolates (99%) but only 95% sequence identity with pre-2005 strains from eastern Canada.

 

Combining RFLP info and ORF2 sequence info - Courtesy of Dr. A. Hamel  

Dendogram based on entire PCV2 sequencing and comparison of PCV2 sequences available from the GenBank.

 
Click on the diagrams for a larger view.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References:
Choi J, Stevenson GW, Kiupel M, Harrach B, Anothayanontha L, Kanitz CL, Mittal SK: Sequence analysis of old and new strains of porcine circovirus associated with congenital tremors in pigs and their comparison with strains involved with postweaning multisystemic wasting syndrome. Can J Vet Res. 66:217-224, 2002

De Boisséson C, Béven V, Bigarré L, Thiéry R, Rose N, Eveno E, Madec F, Jestin A: Molecular characterization of porcine circovirus type 2 isolates from post-weaning multisystemic wasting syndrome-affected and non-affected pigs. J Gen Virol. 85:293-304, 2004

Delay J, McEwen B, Carman S, van Dreuel T, Fairles J: Porcine circovirus type 2-associated disease is increasing. AHL Newsletter. 9:22, 2005

Farnham MW, Choi YK, Goyal SM, Joo HS: Isolation and characterization of porcine circovirus type-2 from sera of stillborn fetuses. Can J Vet Res. 67:108-113, 2003

Fenaux M, Halbur PG, Gill M, Toth TE, Meng XJ: Genetic characterization of type 2 porcine circovirus (PCV-2) from pigs with postweaning multisystemic wasting syndrome in different geographic regions of North America and development of a differential PCR-restriction fragment length polymorphism assay to detect and differentiate between infections with PCV-1 and PCV-2. J Clin Microbiol. 38:2494-2503, 2000

Fenaux M, Opriessnig T, Halbur PG, Elvinger F, Meng XJ:Two amino acid mutations in the capsid protein of type 2 porcine circovirus (PCV2) enhanced PCV2 replication in vitro and attenuated the virus in vivo. J Virol. 78:13440-13446, 2004b

Larochelle R, Magar R, D’Allaire S: Genetic characterization and phylogenetic analysis of porcine circovirus type 2 (PCV2) strains from cases presenting various clinical conditions. Virus Res. 90:101-112, 2002

Larochelle R, Magar R, D'Allaire S: Comparative serologic and virologic study of commercial swine herds with and without postweaning multisystemic wasting syndrome. Can J Vet Res. 67:114-120, 2003

Mahé D, Blanchard P, Truong C, Arnauld C, Le Cann P, Cariolet R, Madec F, Albina E, Jestin A: Differential recognition of ORF2 protein from type 1 and type 2 porcine circoviruses and identification of immunorelevant epitopes. J Gen Virol. 81:1815-1824, 2000

Mankertz A, Domingo M, Folch JM, LeCann P, Jestin A, Segalés J, Chmielewicz B, Plana-Durán J, Soike D: Characterisation of PCV-2 isolates from Spain, Germany and France. Virus Res. 66:65-77, 2000

Meehan BM, McNeilly F, Todd D, Kennedy S, Jewhurst VA, Ellis JA, Hassard LE, Clark EG, Haines DM, Allan GM: Characterization of novel circovirus DNAs associated with wasting syndromes in pigs. J Gen Virol. 79:2171-2179, 1998

Opriessnig T., Halbur PG: Comparison of the pathogenicity of US PCV2 isolates from cases with and without the hallmark PCV2-associated lymphoid lesions. In: Proc Am Assoc Vet Lab Diag, Hershey, Pennsylvania, 48:106, 2005

Pogranichniy RM, Yoon KJ, Harms PA, Sorden SD, Daniels M: Case-control study on the association of porcine circovirus type 2 and other swine viral pathogens with postweaning multisystemic wasting syndrome. J Vet Diagn Invest. 14:449-456, 2002

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