Porcine Circovirus Shedding, Transmission, Plasma, Transport Roles Scrutinized

January 6, 2010 — 

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 tanjaopr@iastate.edu.

Source:
National Hog Farmer