Using diagnostics to optimize PCV2 vaccination

By Don McDermid, DVM, Swine Veterinary Services Manager, Zoetis
Kirkland, Quebec, Canada

Porcine circovirus type 2 (PCV2) is one of the global pig industry’s most common and costly viral pathogens. Before the introduction of PCV2 vaccines, diseases associated with PCV2 cost producers billions of dollars globally due to mortalities, increased medical costs and reduced production.  Even today, with vaccination a standard practice, the virus remains present on the great majority of farms and is a constant threat.¹

Currently there are no treatments for PCV2, so control and prevention are crucial to keeping animals healthy and operations sustainable. Vaccines are one of the most effective tools for preventing PCV2 infection, but several factors influence a vaccination strategy’s success. By shedding light on a herd’s immune status and degree of disease challenge, routine diagnostics can help maximize both health and the economic benefits of PCV2 vaccination.

High cost, no cure

PCV2 is a ubiquitous viral pathogen that can cause both clinical and subclinical disease. Originally associated with wasting disease, it can also be involved in a range of systemic illness, particularly pneumonia. PCV2 has also been implicated in porcine dermatitis and nephropathy syndrome, as well as diarrhea and reproductive disorders.²

When other pathogens are present, such as Mycoplasma hyopneumoniae, Pasteurella multocida and the virus that causes porcine reproductive and respiratory syndrome, disease outbreaks can be especially prolonged and severe.

Clinical and subclinical PCV2 infection can take a devastating economic toll, resulting in reduced growth, poor feed efficiency, extended time to market and increased mortalities. Bacterial infections associated with PCV2 are often slow to respond to antimicrobial treatment, making control and prevention all the more important.

Diagnostic detective work

Vaccination has been shown to be an effective means of preventing PCV2 infection, but the efficacy of the vaccine — and consequently, its economic benefits — can vary based on several important factors. Diagnostic testing at strategic points in the growing cycle can help bring these factors to light so you can fine-tune your vaccination program and improve economic performance.³

One important variable is the degree of disease challenge, either late in the nursery or early in the grow-finish period. Evidence of a high PCV2 challenge may include observation of clinical symptoms of PCV2, including increased mortality, slow growth and respiratory or digestive problems, with serological confirmation. Veterinarians can also use polymerase chain reaction (PCR) testing to detect significant PCV2 viremia in blood samples.

Maternally derived antibodies

If PCV2 challenge is significant during the finishing period, despite vaccination, then maternally derived antibodies (MDA) may be to blame. Passed from sow to piglet via the colostrum, MDA neutralize PCV2 viruses before they have a chance to cause infection, providing young pigs with their earliest form of immunity. However, they can also prevent vaccine antigens from inducing the desired immune response.

At 3 weeks of age, MDA are usually low enough for successful vaccination, but PCV2 challenge in the breeding herd or the use of PCV2 vaccine in sows or gilts may result in higher and more persistent MDA levels. Performing serological testing around the time of vaccination can help determine MDA levels, while running PCR testing on the same blood samples will reveal the PCV2 viremia status of these newly weaned pigs. Viremia in piglets could indicate viral transmission in utero or through the colostrum.⁴

If MDA levels are consistently high at weaning, later vaccination may be warranted and a two-dose vaccination program may be more effective than a single dose.  Conversely, if levels are low, early protection is needed.

Highly variable MDA levels make it impossible to choose an ideal time for vaccination, so it may be worth vaccinating the breeding herd to stabilize MDA.  If significant numbers of piglets are viremic, breeding-herd vaccination may also be necessary to reduce PCV2 transmission from sow to piglet. Always consult your veterinarian before implementing a breeding-herd PCV2 vaccination program, as the piglet vaccination protocol may also need to be adjusted.

Healthy animals, healthy margins

In summary, two major factors should be taken into account prior to implementing PCV2 vaccination programs: the presence of PCV2 in the growing herd and MDA levels in weaned pigs.

If PCV2 is present in older pigs, chances are that MDA levels were too high at the time of vaccination. When MDA levels have moderated, vaccination will be more successful and the crippling costs of PCV2 infection can be reduced.

Diagnostic testing can provide valuable insights into the herd’s immune status and degree of PCV2 infection. Based on this information, producers and veterinarians can select a vaccination strategy that is more likely to keep animals healthy and margins secure.

Editor’s note: The opinions and recommendations presented in this article are the author’s and are not necessarily shared by the editors of Pig Health Today or its sponsor.

1 http://impact.ref.ac.uk/CaseStudies/CaseStudy.aspx?Id=38453
2 http://www.thepigsite.com/articles/813/pork-health-fact-sheet-circovirus-infection-in-swine/
3 Van Esch,, E. “Monitoring your PCV2 intervention leads to higher economic returns,” International Pig Topics, 30(5);21-23.
4 “PCV2 Vaccination: 1-Dose or 2-Doses?”, Zoetis