Best practice and future challenges for vaccination against porcine circovirus type 2

Abstract

Porcine circovirus type 2 (PCV2)-systemic disease (SD) (initially named as postweaning multisystemic wasting syndrome) was discovered as an occasional disease affecting postweaning pigs in North-America by mid-1990s. Soon afterward, it was noticed as a devastating disease worldwide. Such scenario prompted to develop vaccine prototypes that worked fairly well under experimental conditions. In spite of the multifactorial nature of the PCV2-SD, the first commercialized vaccines containing inactivated or chimeric PCV2 viruses or PCV2 Cap protein represented by far the best system to control the disease under farm conditions. Moreover, vaccination of non-clinically affected pigs demonstrated a significant improvement of average daily weight gain and, in consequence, the economic importance of the PCV2-subclinical infection. In the present review, a comprehensive overview on PCV2 vaccines and best practices on PCV2 vaccination strategies are presented and discussed.

Keywords:

• age of vaccination
• immunity
• maternally derived immunity
• PCV2-subclinical infection
• PCV2-systemic disease
• pigs
• porcine circovirus diseases
• porcine circovirus type 2
• sows
• vaccine

Acknowledgements

The author wants to deeply thank all researchers, technicians, PhD students and undergraduates who have participated in the research on PCV2 and PCVDs at the Centre de Recerca en Sanitat Animal (CReSA) and the Veterinary School of the Universitat Autònoma de Barcelona (UAB) since 1997 to date. The author also thank the field veterinarians and farmers who have participated actively in all studies performed by his research group during last 17 years.

Financial & competing interests disclosure

The author is employed as associate professor at the Universitat Autònoma de Barcelona (UAB), and his research is ascribed at the Centre de Recerca en Sanitat Animal (CReSA), a Public Foundation created in 1999 by UAB and Institut de Recerca i Tecnologia Agroalimentària (IRTA). The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Porcine circovirus type 2 (PCV2)-systemic disease (SD) resulted in a devastating disease for the swine sector; subsequently, PCV2-subclinical infection (SI) has been identified as the porcine circovirus diseases representing the greatest proportion of negative economic impact.

• Several PCV2 vaccines are commercialized in the worldwide market based on inactivated wild or chimeric viruses, or Cap protein expressed in baculovirus systems.

• PCV2 vaccination is able to induce full clinical protection and to develop both humoral (total anti-PCV2 antibodies and neutralizing antibodies) and cellular (IFN-γ-SC) immunity.

• The rationale of stimulating active immunity in gilts and sows is to provide passive immunity to piglets, through colostrum intake, allowing prevention of PCV2-SD development in the offspring. However, the repeated use of sow vaccination seem to prevent effects of PCV2 on the reproductive parameters.

• The rationale of stimulating active immunity in piglets is to provide protection against PCV2 infection in the group of animals that are specifically suffering from PCV2-SD and PCV2-SI.

• The most efficient way to prevent porcine circovirus diseases in the shorter term is by means of piglet vaccination.

• A ‘vaccination window’ has been defined as the range of antibody titers at which piglets should be vaccinated to minimize interference with maternally derived antibodies and, at the same time, ensure the development of protective immunity before PCV2 infection. Vaccination of piglets around weaning in absence of sow vaccination is usually sufficient to overcome maternally derived immunity.

• Perceived vaccine failures have been described over the world; however, no definitive clue is still available in regards the existence of true vaccine escape mutants for PCV2. Continuous surveillance for new PCV2 variants will be paramount in the future.

• Future insights point out to increase the use of PCV2b-based vaccines or the putative development of polyvalent vaccines including two or more genotypes.

• PCV2 eradication or elimination at a local, regional or country basis is still far from the mind of veterinarians and producers, but apparently feasible by means of mass vaccination programs used in a continued form.