PCV2 and PRRS get the lion's share of attention at the Vancouver IPVS Congress
Monday, December 6, 2010
With more than 2,700 attendees from 66 countries, the 21st IPVS Congress was a smashing success. Here's a summary of some of the findings presented
by S. ERNEST SANFORD
The 21st IPVS (International Pig Veterinary Society) Congress was held in Vancouver, July 18-21, 2010, the first time this event has ever been held in Canada.
The IPVS has been in existence for 40 years and is held every even-numbered year in a country that is decided by vote by the delegates. Canada had put together unsuccessful bids to host an IPVS on two previous occasions and was finally successful at the 19th IPVS Congress in Copenhagen, when we won the bid decisively on the first ballot with Vancouver as the venue.
The Vancouver Congress was a smashing success. There were over 2,700 registered attendees from 66 countries in the new Vancouver Convention Centre, which was built in time for the Winter Olympics in Vancouver six months previously. The registered attendees and number of countries are both records for an IPVS Congress outside of Europe and the second highest (after Copenhagen) for any IPVS Congress ever.
Some 1,161 of 1,189 submitted abstracts were accepted after review by more than 100 international scientists, 274 as oral presentations and 887 as posters. Electronic posters (e-posters) were used for the first time at an IPVS.
PCV2 and PRRS, with 197 and 118 papers respectively, took the lion's share of papers at the Congress. Mycoplasma hyopneumoniae (72), swine influenza, including pandemic H1N1 (63), ileitis (38) and MRSA (methicillin resistant Staphylococcus aureus) (22) were well represented, along with public health issues, such as salmonella, welfare and behaviour, postweaning catabolic syndrome and analgesia/anesthesia with reference to castration of piglets.
The following are "take homes" from some of the oral presentations, starting with two lead speaker presentations and following with papers on PCV2.
A new PCV (PCV1/2a) in Canada – Gagnon C, et al., p. 51
Background. PCV1 ORF1 and PCV2 ORF2 were identified during examination of three cases submitted to the University of Montreal's diagnostic lab between September 2008 and January 2009. Two of the three were live infectious viruses. The PCV1/2a had five to six nucleotides (nts) different from chimeric PCV1/2 with nt identity of 99.6-99.7 per cent. All nt differences were located on ORF1.
Take Home. The authors offered two hypotheses: natural genetic recombination between PCV1 & PCV2: the chimeric "killed" PCV1-2 virus in the Suvaxyn® PCV vaccine was not inactivated.
IgG and IgM differentiation of antibodies to detect primary and secondary immune response to PCV2 – Keller C, et al., p 104
Take Homes. Field exposed pigs mounted IgM response at four weeks post-exposure (about the time of PCV2 viremia) followed by IgG. Very few (two of 20) vaccinated pigs ever mount IgM response, only IgG. IgM could be used to differentiate field versus vaccine exposure. Detection of many IgM-positives in a population indicates field PCV2 exposure.
PCV2 Disease diagnosis by serology and PCR – Larsen L, et al., p. 105
Background. A threshold of seven log10 PCV2 DNA is accepted for development of PMWS. This study described results of serological and virological (PCR) profiling of 14 Danish herds with clinical PCVD.
Results. Two profiles identified: PCV2 viremia and increased PCV2 antibodies (Abs) seen in weaners; PCV2 viremia and increased PCV2 Abs seen in older pigs (soon after placement in finisher).
Increased levels of PCV2 Abs paralleled increased PCV2 viral load. Most pigs had four to six log10 DNA copies/mL of serum. A few had seven to nine log10 DNA/mL.
Increased viral load seen concurrent with clinical disease in some herds. No such correlation in other herds.
Also, comparably high levels of viremia seen in control non-clinical PCVAD herds.
Take Home. PCV2 PCR serum profiles can be valuable to confirm PCVAD.
PCV2 in extended pooled semen from U.S. boar studs – Kauffold J, et al., p. 103
Take Home. PCV2 is still present in extended semen. The virus is likely sperm-associated rather than loose in seminal fluid.
High prevalence of PCV2 viremia in newborn piglets in five clinically normal swine breeding herds in North America – Shen H, et al., p. 56
Background. Pigs from five herds (one Mexican; four American) were studied; 128 clinically healthy sows and 504 live normal piglets were examined for intrauterine PCV2 infection, sow viremia and sow and piglet Ab levels.
Results. All 128 of the sows and 21.2 per cent of the piglets had anti-PCV2 IgG Abs;
66.4 per cent of sows were PCV2 viremic by PCR; 43.1 per cent of piglets were PCV2 viremic.
Viremia in 71.8 per cent of sows and 75.1 per cent of piglets had PCV2b; 12.9 per cent of sows and 15.1 per cent of pigs had PCV2a; 10.2 per cent of sows and 4.2 per cent of piglets had concurrent PCV2a/PCV2b infections.
Pigs born to sows with high PCV2 DNA loads had increased frequency of PCV2 viremia and elevated PCV2 DNA copy numbers in serum.
Higher amounts of PCV2 DNA were found in PCV2 seronegative piglets compared with seropositive piglets, indicating some degree of protective humoral immunity developed in utero.
PCV2 Abs in dams did not necessarily alleviate PCV2 infection in fetuses.
Take Homes. Vertical transmission is common in clinically normal herds. Dam viremia is linked to the frequency and level of PCV2 infection in piglets. Dam PCV2 Abs did not necessarily block PCV2 infection in fetuses, but PCV2 Abs in piglets could alleviate PCV2 infection, indicating that humoral immune response by the fetus might be protective.
Comparison of PCV2 viremia between heavy and lightweight pigs at marketing age in farms with routine PCV2 vaccination – Lyoo KS, et al., p. 106
Background. IFA and PCV2a/b viremia in heavy and lightweight pigs were measured in seven herds routinely using a commercial PCV2 vaccine and experiencing no clinical PCVAD problems. The researchers checked antibodies (using IFA) and viremia by PCV2a and PCV2b (using PCR) in pigs that were of market age. Although the pigs were of market age, there were pigs that were clearly lighter than market weight (lightweight pigs) and those that were truly market weight (heavyweight pigs). They tested to see if the lightweight pigs were more likely viremic with PCV2a and/or PCV2b than the market weight pigs of the same age.
Take Homes. Not always statistically significant but higher PCV2 IFA and more viremic pigs seen in lightweight pigs at marketing. Usually PCV2b viremia and not PCV2a.
Many papers were devoted to determining if there were virulence differences between PCV2a and PCV2b. They all indicated that PCV2b was more virulent than PCV2a or that the epidemic outbreaks of PCVAD seen in North America since 2004-05 were the result of PCV2b infections. Here are "Take Homes" from a few of those papers.
Mutations of PCV2 capsid motif, specific for PCV2 genogroup, attenuate virulence in vitro – Grasland B, et al., p. 52
Take Home. PCV2b strain was more virulent than PCV2a.
Clinical and virological outcome of experimental PCV2a and PCV2b infections mid-gestational porcine fetuses – Saha D, et al., p. 54
Take Home. The different PCV2 strains of PCV2a and PCV2b induced similar gross pathological lesions and replicated in similar high titres in different fetal organisms.
Singular PCV2a or PCV2b infection results in apoptosis to hepatocytes in clinically affected gnotobiotic pigs – Sinha A, et al., p. 52
Take Home. Gnotobiotic pigs experimentally infected with PCV2a or PCV2b developed clinical disease and apoptosis. Apoptosis is likely one pathway for PCV2 to cause PCVAD.
This is a very brief review of a few of the PCV2 papers among nearly 1,200 abstracts submitted for the 21 IPVS Congress. In the next issue of Better Pork, I'll tackle some of the PRRS papers and other interesting topics that caught my eye. BP
S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. E mail: ernest.sanford@ boehringer-ingelheim.com