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Circovirus Presents Environmental Challenge

When a Kansas hog farm struggled with porcine circovirus type 2 (PCV2) viremia (virus in the bloodstream) in vaccinated pigs, a warning bell went off in the minds of KSU researchers

When a Kansas hog farm struggled with porcine circovirus type 2 (PCV2) viremia (virus in the bloodstream) in vaccinated pigs, a warning bell went off in the minds of Kansas State University (KSU) researchers.

Circovirus vaccines had gained a strong reputation for reducing mortality and morbidity in a few short years, and recent work had shown vaccine reduces nasal and fecal shedding. Less shedding ultimately translates into less viral environmental contamination.

The question was whether vaccine failure or overwhelming environmental contamination was to blame. Porcine circovirus is a small, circular, non-enveloped DNA virus that is considered very tough to kill and is often more resistant to disinfectants than enveloped viruses, such as porcine reproductive and respiratory syndrome, states KSU swine researcher Megan Potter, DVM.

Potter says the hog operation appears to have closely followed proper procedures for PCV2 vaccination and normal cleaning and disinfecting protocols. Yet circovirus struck some of the multi-site operation’s nurseries and finishers hard.
“One of the barns was really struggling with viremia in vaccinated pigs. That was when we decided to start this environmental study,” she reports. Samples were collected with cotton swabs, and 100% of them came back positive for circovirus.

The pigs at this site were vaccinated at weaning and again 2-3 weeks later with Circumvent PCV (Intervet Schering-Plough Animal Health), and still some of the pigs became viremic or very sick with the virus. “This operation was losing quite a few pigs, particularly sudden deaths in the nursery and some death losses in the finisher,” she recalls.

Potter points out that there has been additional evidence for PCV2 spread in other vaccinated herds. In one commercial trial, a group of pigs were left unvaccinated, housed adjacent to vaccinated pigs, and the untreated group still got infected with the virus.

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Environmental Study

The objective of Potter’s study was to demonstrate the applicability of swabbing and testing using PCR (polymerase chain reaction) as a means of monitoring PCV2 viral loads on a variety of surfaces in swine production units. “Although detection by PCR does not indicate viral infectivity, this testing procedure does allow viral nucleic acid to be detected and quantified,” she says.

The team began by swabbing inside surfaces of barns at KSU’s swine teaching and research facility in Manhattan where circovirus had been identified, but clinical signs of wasting and pneumonia were not prevalent, she explains. No PCV2 was found in the environment.

Then a series of nurseries and finishers at the Kansas hog operation sites were tested. Only a couple of the sites had reported clinical problems with PCV2. But all of the rooms in both nursery and finisher sites showed detectable levels of the virus.

Potter says a key objective of the study — detecting circovirus in the environment — was achieved. “But we were surprised that we detected the virus in every room at the commercial farm,” she says. “As far as we know, this is the first time this type of testing has been done on the farm for environmental presence of this virus.”

Cleaning Protocol

Once it was determined there was environmental contamination, the next objective was to learn if cleaning and disinfection made a difference in the viral load inside the barns of the infected sites.
Previously, Synergize (Preserve International) had been used to disinfect the barns between pig groups. In the latest study, there were three cleaning protocols for nursery and finisher rooms:

1. Rooms not washed but empty;

2. Rooms washed, disinfected with Synergize, disinfected with Virkon S (Antec International) and washed again; and

3. Rooms washed, disinfected with Synergize, disinfected with Virkon S, washed again and disinfected with Synergize again.

Rooms were swabbed and tested. Results indicated that the unwashed room had higher levels of virus than did the other two rooms. Rooms in the second protocol had somewhat higher levels of virus than did the third room, Potter says.

“It appears that we are having some effect by mechanical cleaning and disinfection in lowering viral levels, but we are still able to detect presence of viral DNA regardless of protocol,” she notes.

The hardest places to clean were around fans and heaters, which when swabbed had the highest concentration of virus, Potter notes. Next in order of concentration were floor slats, gates, feeders and water sources.

“So this suggests you may want to concentrate on thorough cleaning and disinfection and focus on specific areas,” she says.

The research bears out that environmental swabbing and testing is a practical method of monitoring for circovirus in the environment. The next step in the KSU research is to determine if the virus detected in the environment with PCR is infectious, Potter concludes.

Once that is learned, researchers will better understand if more rigorous cleaning programs are warranted.