As porcine circovirus type 2 (PCV2) is known to be present in blood, outbreaks of PCV2 have raised concerns about the spread of PCV2 in spray-dried plasma protein products in the field. This has resulted in some producers and practitioners withdrawing plasma protein from swine diets.
To determine whether spray-dried plasma is infectious, 12, 3-week-old, colostrum-fed, crossbred, specific-pathogen-free (SPF) pigs were divided into groups of three and placed in separate rooms. Pigs were inoculated in one of three manners: intraperitoneally (abdominal cavity) with a reconstituted spray-dried plasma product, intraperitoneally with PCV2-infected plasma or inoculated by oral gavage (stomach tube) with a reconstituted spray-dried plasma product. Blood samples were collected weekly for seven weeks following inoculation.
Results provided evidence that spray-dried plasma is indeed infectious as indicated by seroconversion and viremia (infection in the bloodstream).
With research making a stronger case for fecal-oral transmission of PCV2, producers have also become concerned about the introduction of new PCV2 strains from transport vehicles.
To determine the efficacy of various trailer disinfection methods, three model trailers were designed and manufactured by Eby Trailers, Story City, IA, with materials identical to full-size trailers. The trailers were contaminated with feces collected at the time of euthanasia from a pig exhibiting clinical signs of porcine circovirus-associated disease (PCVAD).
Trailers were disinfected (except for positive controls), power-washed and rinsed similar to commercial washing procedures. Then Synergize, Virkon, Quatricide and Virkon, followed by bleach, were used as disinfectants.
Two naïve pigs were placed into each trailer for two hours, followed by placement in rooms and tested for the presence of PCV2 for 42 days.
Study results indicated that all disinfection protocols were equally effective in preventing seroconversion and viremia in naïve animals.
To determine if PCV2b was present in the United States prior to 2005, when PCVAD outbreaks started to occur, tissue samples were collected from different Midwest farms suspected to be infected with PCVAD during 2002 and 2003. Shedding patterns were studied by inoculating four groups of 9-week-old SPF pigs with PCV2a, PCV2b, less virulent PCV2a and a negative control group. Blood samples were collected for two weeks following infection.
Differences in clinical signs in 2004 and 2005 may correspond with the emergence of PCV2b in the United States, but consistent differences between the amount of PCV2a and PCV2b shed in nasal, oral and fecal routes were not observed. PCV2b was recovered from only two of 81 samples from PCVAD cases submitted between 2002 and 2003. This data suggests that PCV2b was not the predominant strain prior to the severe PCVAD cases seen in 2005.
Funding for this research was provided by the National Pork Board.
Researcher: Tanja Opriessnig, DVM, Iowa State University. For more information, contact Opriessnig by phone (515) 294-1950, fax (515) 294-6961 or e-mail email@example.com.
Editor’s note: Iowa State University College of Veterinary Medicine (ISU CVM) and the North American Spray Dried Blood and Plasma Producers (NASDBPP) issued the following joint clarification pertaining to a research report entitled “Circovirus Shedding, Transmission, Plasma, Transport Roles Scrutinized,” published in the Dec. 15, 2009 issue of National Hog Farmer.
In the section where plasma is discussed as a potential vector for the spread of porcine circovirus type 2 (PCV2), the research summary did not include the materials and methods of the study, which provides additional specific information about the experimental spray dried porcine plasma product used in this study. There are significant differences between commercially produced spray dried porcine plasma and the experimentally produced spray dried porcine plasma product used in the study.
Although the outcome of the research raises concern about the potential for transmission of viruses in spray dried plasma and warrants conducting more research in this area, it is not appropriate to conclude that the experimentally produced plasma product represents commercially produced spray dried porcine plasma.
Some of the differences between experimentally produced product and commercially produced product include, but are not limited to, the source animal(s), pooling effects, processing temperatures, product retention time and post drying conditions. These differences are significant and are outlined in the table below.
Pooling plasma from healthy source pigs maximizes the potential for antibodies from previous pathogen exposure and vaccinations to neutralize virus in the plasma. In general, higher drying temperatures and extended dwell times reduce pathogen survival, based on work with pseudorabies, porcine reproductive and respiratory syndrome, swine vesicular disease virus, Classical Swine Fever, salmonella, E. coli K88 and K99 strains. To date, no experiment involving the feeding of commercial spray dried plasma protein has demonstrated transmission of PCV2.
In summary, it is not appropriate to conclude that the experimentally produced plasma product fully represents commercially produced spray dried porcine plasma used in the swine industry today. Collaborative research in this area is in progress.
Clarification jointly submitted by:
Assistant Professor, Veterinary Pathologist
Veterinary Diagnostic Laboratory
College of Veterinary Medicine
Iowa State University
Abby Patterson, DVM, MS
Adjunct Instructor, Graduate Student
College of Veterinary Medicine
Iowa State University
Phone: (515) 294-1950
Pat Halbur, DVM, MS, PhD
Professor and Chair
Dept of Veterinary Diagnostic & Production Animal Medicine
Executive Director - ISU Veterinary Diagnostic Laboratory
Iowa State University College of Veterinary Medicine
Phone: (515) 294-6970
Louis E. Russell, PhD
North American Spray Dried Blood & Plasma Producers
Phone: (515) 289-7607