Herd Health: PCV2 dominates the IPVS 2008 conference in Durban

Friday, October 10, 2008

Some highlights from last June's International Pig Veterinary Society Congress in South Africa last June, which attracted a record attendance and a proliferation of papers

by S. ERNEST SANFORD

Last June, the 20th IPVS (International Pig Veterinary Society) Congress was held in Durban, South Africa, the first time the IPVS has been on the African continent. The congress was a resounding success with many "firsts" and records to its name.
The total attendance of 2,146 from 52 countries was a record for an IPVS conference outside Europe. It is also the first time that attendance at an IPVS outside Europe has reached the 2,000 mark. 

Abstracts accepted for publication in the conference proceedings totalled 918 and were published in two volumes. An additional 29 papers were presented at satellite symposia put on by the nine premier sponsors of the IPVS. Some 34 referees from around the world reviewed the abstracts and there were 46 chairpersons to conduct the oral sessions.  Student bursaries amounting to $24,000 were awarded to 17 students from various countries around the world. 

PCV2 grabbed the lion's share of scientific abstracts, accounting for 124 papers, followed by PRRS with 83. Another 12 papers on Torque Teno Virus (TTV), a virus related to PCV2 brought the circovirus-related presentations to 136. Papers on Lawsonia (53), Mycoplasma (44), Salmonella (31) Actinobacillus (27) and Brachyspira (20) were also well represented.  There were 60 papers on various aspects of production. Not surprisingly, MRSA (methicillin resistant Staphylococcus aureus) abstracts (10) were also prominent at this IPVS. 

Here are synopses of a few of the oral presentations related to PCV2. More will follow in future articles:

PCV2 seroprevalence in Canadian swine herds – Cunningham G, et al. Vol. 1, Pg. 12.
A cross-sectional seroprofiling survey was conducted in herds from Quebec to Alberta. Sera were collected from 50 pigs of different ages in 40 herds – 10 herds each in Quebec, Ontario and Manitoba, and five herds each in Saskatchewan and Alberta – and tested for antibodies (Abs) to PCV2. Sera were collected from 50 pigs in each herd; 10 sera from breeders (five gilts and five sows of varying parities), five sera from weaners (3-4 weeks old), 10 sera each from end of nursery (8-10 weeks old), early finisher (13 weeks old) and mid-finisher (18 weeks old), and five sera from pigs in late finisher (22-24 weeks old). Multi-site systems and farrow-to-finish (F-F) herds were about equally represented.

Results. Pigs of varying ages were PCV2 positive in all herds tested, with 83.2 per cent of pigs in the 40 herds testing positive. Seropositivity was similar in herds across all five provinces. Pigs at end of nursery (8-10 weeks old) and in early finisher (13 weeks old) had significantly fewer positives than pigs in any other age group, consistent with a picture of waning of maternal Ab titres in late nursery followed by exposure and infection by PCV2 in the early finisher when the pigs develop active PCV2 Ab titres. This fits exactly with the time of PCVAD outbreaks (i.e. early to mid-finisher) seen across Canada.  Late finishers, gilts and sows were nearly 100 per cent positive. Findings were similar for multi-site and F-F herds.

Take home. All herds in this cross-Canada survey were positive to PCV2. Seropositivity waned in late nursery and early finisher pigs, then approached 100 per cent positive in mid- and late finishers, gilts and sows of all parities.

Identification of a new PCV2 strain – Introducing PCV2 genotype 3 (PCV2c) – Dupont K, et al. Vol. 1, Pg. 18.

Two PCV2 genotypes are currently recognized – genotypes 1 and 2 – which correspond to PCV2b (RFLP 321) and PCV2a (RFLP 422), respectively. The PCVAD epidemic which we have just gone through in North America was caused almost exclusively by PCV2b (RFLP 321). Danish researchers sequenced PCV2 viruses from archived pig samples collected between 1980 and 1996 looking for relatedness among isolates.

Results. A new genotype (PCV2 genotype 3) was identified in samples collected from 1980 to 1990. Genotype 3 showed greater nucleotide relatedness to genotype 1 (95 per cent) than to genotype 2 (91-93 per cent).

Sequence analysis suggests that genotype 3 is nonpathogenic and has poor spreading capacity and hence was quickly out-competed by the more pathogenic genotypes 1 and 2.  The above differences make genotype 3 an excellent candidate to identify amino acids (AAs) important for pathogenicity.

Further AA sequence alignment revealed 25 AAs, located in two distinct clusters (residues 21-108 and 185-213) that separated genotypes 1 and 2 from the newly identified genotype 3. Additional analysis revealed five AA positions (63, 89, 190, 206 and 210) as unique to the pathogenic genotype 1 and possibly related to genotype 1's pathogenicity.

Comment and take home. I know what many are thinking, "Does this mean we now have to deal with yet another circovirus?" Yes, a new PCV2 (PCV2 genotype 3 [PCV2c]) is now a fact, but it seems we'll not have to worry about this one. Unlike genotypes 1 and 2, PCV2, genotype 3 is nonpathogenic.

PCV2 levels in serum, blood swabs and semen after PCV2 vaccination of boars – Reicks DL, et al. Vol. 1, Pg. 14.

Previous studies identified PCV2 in boar's serum and semen from four to 55 days and five to 47 days after infection, respectively. The researchers challenged unvaccinated and Ingelvac CircoFLEX-vaccinated boars with PCV2 and tested for PCV2 levels.

Results. Boars were identified PCV2 positive on days four, seven and 14 post-challenge in serum, blood swabs and semen. Vaccinated boars had a marked reduction in quantity of virus compared with unvaccinated boars. Vaccinating 14 days after challenge had no effect on reduction of virus load.

Take home. Vaccinating boars five weeks pre-challenge with CircoFLEX vaccine significantly reduced the quantity of virus in serum, blood swabs and semen by four days after challenge. Vaccinating post-challenge or vaccinating with a second PCV2 isolate had no effect. The authors concluded that elimination of shedding, even in vaccinated boars, seems unlikely.

PCVAD in Sweden – From exotic to endemic in three years – Wallgren P, et al. Vol. 1, Pg. 27.

Sweden had its first case of PCVAD in December 2003, although PCV2 infection had been identified in stored samples retrospectively back to 1993. The workers traced the development of PCVAD from the first exotic cases in 2003/04 to the current endemic state.

Results. The number of herds diagnosed with PCVAD annually increased from 16 and 41 in 2004 and 2005, respectively to 123 by December 2006. After adjusting herds for size PCVAD was diagnosed in:

• 0.2 per cent of herds with <50 sows (n = 1,597)
• 4.4 per cent of herds with 50-100 sows (n = 459)
• 11.8 per cent of herds with 101-500 sows (n = 382)
• 13.0 per cent of herds with 501-1000 sows ( n = 23)
• 13.8 per cent of herds with >1000 sows (n = 22)

In the Swedish sow pool satellite system, PCVAD was more often diagnosed (P>0.01) in satellites using shorter cycles (nine affected out of 20 herds = 45 per cent) than the conventional 16 week cycle herds (31 affected of 264 herds = nine per  cent).

Take home. PCVAD became endemic in Sweden over a three-year period. PCVAD was usually seen in larger herds and herds with more intensive production systems.
This is a brief peek into proceedings on circovirus which I found interesting. I'll be delving into further proceedings papers on PCV2 and other topics in future issues of Better Pork. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: esanford@bur.boehringer-ingelheim.com