Introduction

It has not been unusual for clinical postweaning multisystemic wasting syndrome (PMWS) to be diagnosed on farms in the United States, on the basis of the case definition published by Sorden.¹ These affected farms have historically been positive for porcine circovirus type 2 (PCV2).

However, an increase in the incidence of the severe form of PMWS has been reported in the United States since the fall of 2005. Clinical signs include anorexia, rapid weight loss, enlarged lymph nodes, and respiratory signs. Postweaning multisystemic wasting syndrome, now referred to as porcine circovirus associated disease (PCVAD), is still spreading in the United States’ swine population.

Scientific researchers, veterinarians, allied industry representatives, and producers met to discuss and vote on PCVAD research priorities for the Pork Checkoff. A summary of the meeting and ranked research priorities were published in the Journal of Swine Health and Production.² The information gathered during this meeting was used to develop the 2008 PCVAD call for proposals.

Research priorities

In March, the National Pork Board posted a call for research proposals addressing five priority areas, including immunology, epidemiology, pathogenesis, diagnostics, and prevention and treatment. The call for proposals deadline was May 6. Contracts are expected to commence in September. Instructions, priority areas, and research priorities will be included in the call for proposals.

The research priorities to be addressed in this call for proposals are outlined below.

1. Immunology

a. Investigate the effect of strain variation on cross-protection and on cell-mediated immunity and humoral immunity.

b. Determine cross-protection and whether immunogenic epitopes need to be conserved among different strains.

2. Epidemiology

a. Investigate and identify factors influencing transmission: virus type, pig genetics, herd size, and production system (number of sites).

b. Molecular epidemiology: establish a PCV2-sequence database that links strain sequence with clinical disease, infectious cofactors, management practices, chronology, and geographic locale.

i. Investigate how much genetic variation there is within a genotype.

ii. Determine if that genetic variation is also reflected as antigenic variation.

c. Develop checklists of risk factors, management approaches, and roles of other agents, cofactors, and serum therapy.

d. Evaluate current practices

i. Evaluate what biosecurity practices may prevent infection of a herd.

ii. Evaluate whether injections with antibiotics, vaccines, and serum therapy transmit disease.

e. Estimate whether susceptibility, transmissibility, and persistence change with age, PCV2 strain, various cofactors, and management factors.

f. Define the role of the sow herd in an outbreak.

i. In a clean-up program.

ii. Identify the criteria for determining when an unaffected farm should begin vaccination (geospatial factors, when undertaking “risky” practices, cost-benefit in an unaffected farm).

g. Define the duration of PCV2a and PCV2b infection and the ability to be transmitted when:

i. Young pigs are infected.

ii. Older pigs are infected.

3. Pathogenesis

a. Develop tools for pathogenesis research, including source of PCV1- and PCV2-negative pigs (all ages), reproducible disease model, and technology to look for other agents.

b. Determine variability in disease expression due to host variation, for example genotype-phenotype, age-parity, management, and gender.

c. Determine the role of PCV2 in vertical transmission:

i. The frequency of vertical transmission.

ii. If it is constant or changes as a function of the PCV2 genotype and antibody status of the breeding herd.

iii. Semen transmission in PCVAD: viral loads and frequency and identification of contaminated semen.

iv. Effect of sow-gilt exposure to PCV2.

d. Characterize diseases caused by PCV2 and selected cofactors:

i. Does co-infection with specific cofactors result in a specific disease syndrome? PCVAD model systems to investigate include: porcine dermatitis and nephropathy syndrome, shaker pigs, porcine respiratory disease complex, and PMWS. Agents to investigate include: PCV2a and PCV2b, PRRS, teschovirus, parvovirus, and others.

4. Diagnostics

a. Develop standardized diagnostic tools for use in diagnostic laboratories in North America. Tools and tests include:

i. Tissue-culture-adapted PCV2a and PCV2b.

ii. Monospecific polyclonal and monoclonal antibody.

iii. Standardized immunofluorescence assay and serum neutralization serology.

iv. Develop protocols for monitoring boar studs and breeding herds, especially for the purpose of producer surveillance and import criteria.

5. Prevention and treatment

a. Investigate the relationship of maternal (passive) antibody and

i. Vaccination interference: determine whether high levels of maternal antibody interfere with vaccination;

ii. Investigate how much antibody variation exists in the breeding herd and how this might impact maternal antibody transfer:

• Determine whether that variation is a function of parity,

• Determine whether it would be beneficial to have the same level of antibodyin the breeding herd;

iii. Cross-serotype-genotype-infection. Investigate whether maternal antibody has the same “protective” effect on PCV2a and PCV2b (for example, does one virus infect baby pigs sooner than the other in pigs with the same levels of passive antibody);

iv. Determine whether passive antibody against one genotype promotes infection at a younger age with the other genotype.

b. Determine vaccine efficacy in the face of PCV2 and cofactors.

c. Determine the most effective facility decontamination procedures to reduce or eliminate PCV2 from the environment.

d. Investigate ability to produce PCV2-negative pigs from positive herds. If possible, determine ramifications of repopulating with PCV2-negative pigs.

PCVAD update

The research priorities that do not appear in this list, but that were ranked and published in previous communications, have in some form been addressed or are in the process of being addressed. The following list provides an update on these.

Under the priority area of immunology, the first research priority was “Determine the role of cell-mediated immunity and humoral immunity in the immune response to PCV2a and PCV2b infection: i. Defective immune response, or, ii. Effective immune response”.

John Butler conducts a project titled, “Is humoral immunity defective in PCV2 infected piglets?” and Dick Hesse heads a project titled, “PCVAD-induced immune dysfunction”. Both projects are ongoing and further funding research in this area awaits results from these.

In the area of epidemiology, to address the research priority, “Determine the predominant mode of transmission,” a project is being conducted at Iowa State University by Tanja Opriessnig. Her project, titled “Transmission of PCV2: Comparison of shedding patterns between PCV2a and PCV2b, evaluation of routes of transmission (fecal, oral, nasal, mechanical) and understanding the roles of spray-dried plasma and transport vehicles” is ongoing.

In the area of pathogenesis, John Harding and Bob Rowland conducted separate studies in 2006 to address the research priority “Conduct classical pathogenesis studies in conventional pigs to investigate the role of PCV2a and PCV2b in PCVAD and the role of concurrent PCV2a and PCV2b infections.”

Also in the area of pathogenesis, the research priority of semen transmission in PCVAD is being addressed by Tanja Opriessnig. Her research project was presented at the American Association of Swine Veterinarians’ annual meeting in San Diego, California. Her work studies the amount of virus needed for intrauterine transmission of PCV2. The research priority is still open, with the expectation that researchers will propose a new research project investigating viral load in porcine and commercial semen.

In the area of diagnostics, the priority of “Development of standardized differential and real-time PCR” was eliminated, as Dick Hesse of Kansas State University has developed them. Hesse also is working on delivering a test for differentiating infected and vaccinated individuals.

Also in the area of diagnostics, a project comparing shedding patterns of PCV2a and PCV2b is ongoing.

Two projects investigating vaccine efficacy are being funded under the priority area of prevention and treatment, as well as a project addressing the priority “Determine the most effective transport decontamination procedures to reduce or eliminate PCV2 from the environment.”

Other calls for proposals

The National Pork Board’s March research proposal call included a call for environment, animal welfare, and international trade research. The environment research solicited included projects in the main areas of air quality, water quality, and on-farm water conservation management practices. The animal welfare research included projects in the areas of humane euthanasia and sow housing. In the area of international trade, research priorities focused on issues that may hamper trade of fresh and cured meats with foreign markets, including issues of swine health (mainly porcine reproductive and respiratory syndrome and PCVAD) and pathogens in meat, including Salmonella, Toxoplasma, Campylobacter, and Yersinia.

The Pork Checkoff’s Demand Enhancement team announces the arrival of four new cuts

To increase the price of undervalued cuts or increase the demand for underused cuts, the Pork Checkoff’s Demand Enhancement team has worked since late 2006 in the development of four new cuts. Creating these new cuts and getting the pork chain and its customers to accept them has finally paid off. A committee of nation-wide retailers that is tasked with managing and ensuring the consistency of meat for retail purchasing has offered its support and the following names for these cuts.

• Pork shoulder breast boneless, for the pectoralis profundi muscle cut.

• Pork shoulder petite tender boneless, for the teres major muscle cut.

• Pork leg cap steak boneless, for a gracilis muscle cut.

• Pork leg sirloin tip roast boneless, for a vastus lateralis and rectus femoris cut.

These cuts have already received the support of chefs, culinary schools, and some packers. Their demand in food-service outlets will dictate their appearance in the retail meat case.

References

1. Sorden SD, Diagnostic notes. Update on porcine circovirus and postweaning multisystemic wasting syndrome (PMWS). Swine Health Prod. 2000;8:133–136.

2. News from the National Pork Board. Porcine Circovirus Associated Diseases Workshop stimulates research discussion. J Swine Health Prod. 2007;15:47–51.