Porcine Circovirus Type 2 Vaccines - An Update
by
David G S Burch  BVetMed DECPHM MRCVS
Veterinarian, Octagon Services Ltd

Published: Pig World, January 2008
 

In an earlier article (PW, February 2007) the new porcine circovirus type 2 (PCV2) vaccines, which had appeared in North America to protect against the rampaging outbreak of post-weaning multisystemic wasting syndrome (PMWS), were described. Now, as they are starting to appear in the UK, it was suggested an update would be helpful.

Circovac® (Merial) has been authorised for marketing in the European Union and is now available in the UK, since September, for the vaccination of sows and gilts and offers passive protection to piglets via the colostrum up to 5 weeks of age (see Table 1). It has reduced lesions in lymphoid tissues associated with PCV2 infection and PCV2-linked mortality. The PCV2 virus is grown in cell culture and then inactivated to produce the antigenic component of the vaccine.

Table 1. PCV-2 Vaccines introduced in N. America

Company

Product

Sow/Piglet

Type of vaccine

Adjuvant

No of injections

Merial

Circovac®

Sow

Killed-PCV2 virus

Mineral oil

2 + boosters

Boehringer-Ingelheim

Ingelvac
CircoFLEX®

Piglet (3wks+)

PCV2 Capsid

Aqueous polymer

1

Fort Dodge

Suvaxyn® PCV2 One Dose

Piglet (4wks +)

Killed - recombinant PCV1 & 2

SL-CD aqueous

1

Intervet

Porcilis® PCV

Piglet

PCV2 Capsid

Diluvac
Tocopherol

2

It is important to note that PCV2 (see Photo 1) is now recognized as the primary cause of PMWS, although there are a number of factors that influence the expression of the disease, its timing and severity. It is a small relatively slow growing virus. The outer capsid proteins appear to be the most antigenically important (immunity stimulating) component of the vaccine and this is produced by a genetic fraction of the virus called the open-reading frame 2 (ORF2). This is important to describe, as two of the vaccines are capsid-based sub-unit vaccines (Ingelvac CircoFLEX® - Boehringer Ingelheim and Porcilis® PCV - Schering-Plough/Intervet) and they use other faster growing viruses to produce the capsid protein. Suvaxyn® PCV2 (Fort Dodge) however, is a recombinant virus vaccine, utilising the related but non-pathogenic, faster growing PCV1 with the PCV2 ORF2 gene inserted into it to produce the immunogenic PCV2 capsid protein.

Photo 1. Porcine circovirus type 2 (PCV2) with fine outer capsid

Porcine circovirus type 2 (PCV2) with fine outer capsid

 

Currently, only the Ingelvac CircoFLEX and Suvaxyn PCV2 piglet vaccines are available via your veterinary surgeon for importation under a Special Treatment Certificate under the 'cascade guidelines' for use in herds where the clinical expression of PMWS is in older pigs, usually in the finisher sheds i.e. 10 weeks of age and over.

All of the vaccines have shown impressive reductions in mortality particularly in N. American studies. It is interesting to note that the Danes have reported a more variable response to vaccinating sows (PW, November 2007) but this might be associated with other factors, such as porcine reproductive and respiratory syndrome virus (PRRSV) infections. It may also be due to later onset of viraemic challenge, after the maternal antibodies have subsided.

A trial has been carried out under UK field conditions by Nigel Woolfenden of the Bishopton Veterinary Group in Ripon and recently reported (von Richthofen and others, 2007) using the piglet vaccine Ingelvac CircoFLEX. There was a dramatic reduction in mortality associated with PMWS from 14.3% to 4.6% (see Graph 1), in pigs that had been vaccinated at 3 weeks of age and the trial lasted for a further 20 weeks, almost to slaughter. The surviving pigs also put on an extra 6.6 kg liveweight in comparison with the unvaccinated controls. The farm did not have PRRSV or enzootic pneumonia but did have some streptococcal meningitis and pleuropneumonia problems. What was particularly impressive, the trial was a fully controlled study carried out according to good clinical practice (GCPv) and the vaccinated and placebo control pigs were kept in the same pens but identified individually, so were exposed to the same environmental conditions, stresses and virus challenge. The viraemia and mortality started at 6 weeks of age and peaked at 9 weeks. It can be considered a very severe natural challenge.

Graph 1. Mortality in vaccinated and placebo controls before and after the onset of viraemia
Mortality in vaccinated and placebo controls before and after the onset of viraemia

There are advantages to both sow vaccination and piglet vaccination programmes (see Graph 2). The PCV2 battleground for protective immunity though is usually when maternal antibodies are waning and the piglet's immunity is developing. Where there is a late onset viraemia and challenge the piglet vaccines should give more consistent protection.

Graph 2. Comparison of protection from MDAs and piglet vaccination - the PCV2 battleground

Comparison of protection from MDAs and piglet vaccination - the PCV2 battleground

However if we take the average BPEX (2006) National herd mortality figures in finishers (see Graph 3) it rose from an average of 3.3% to 6.5% with the arrival of PMWS. As it is an average, there are 50% of farms that have a higher mortality up to 9.7%. Using a financial model and putting in an average feed cost of 180/tonne, the cost of vaccinating each pig is equivalent to an additional 1.4% mortality, but above that it would be an advantage to vaccinate, possibly in 78% of farms.

Graph 3. Cost benefit for PCV2 vaccination based on finisher mortality

Cost benefit for PCV2 vaccination based on finisher mortality

I have already been asked if it is worthwhile continuing to vaccinate against enzootic pneumonia or PRRS. My answer is yes. If you had an EP or PRRS problem before PMWS, which was being controlled by these vaccines then it would be advisable to continue. Check your lung lesion scores in the Pig Health Scheme survey

These are exciting times with the prospect of controlling PMWS, especially as we are facing incredibly high feed prices in the future. It is hoped that PCV2 vaccination will help many producers improve their profitability or at least, reduce their losses.

 

References:
British Pig Executive (BPEX) (2006) Pig Yearbook 2006 pp 47-50.

Von Richthofen, I., Woolfenden, N., Lischewski, A. And Strachan, W.D. (2007) Field Efficacy study of a PCV2 vaccine in three week old piglets in the United Kingdom. Fifth Symposium on Emerging and Re-emerging Pig Diseases Krakow, Poland, p 122.

 

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*Pig Diseases & Medication:  Pig Health Reviews
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