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A pig virus that exists worldwide has become more dangerous as the virushas mutated and then combined with other pathogens, according to PurdueUniversity researchers.It¹s not known why a virus that has been known to infect swine foralmost 40 years in North America in 1991 suddenly started causing disease inyoung pigs and then began mutating into more deadly forms. Evidence fromresearch being conducted at the Indiana Animal Disease Diagnostic Laboratoryon the Purdue campus, has indicated that the most recent mutation of a groupof viruses called ³porcine circoviruses,² can cause widespread acutedisease. Other pathogens can combine with the virus to increase the fatalityrate significantly.³Our goal is to help the hog industry by understanding porcinecircoviruses better,² said Roman Pogranichniy, a Purdue School of VeterinaryMedicine virologist and a scientist with the lab.In the ongoing study to determine how the mutated form of porcinecircovirus‹abbreviated PCV2-1a‹causes more deadly illness, the scientistshave studied pigs exposed to a virus combination. The viruses, PCV2 andbovine viral diarrhea virus, came from pigs that had developed the diseaseson the farm.³We think that the new co-factors, including bovine viral diarrheavirus-like pathogen and other swine viruses, work together with porcinecircovirus to attack the animals¹ systems and become more virulent,²Pogranichniy said.Studying virus-caused lesions and blood of PCV2-infected pigs providedsome indications of how the virus enters the animals¹ cells, the scientistssaid. This helps them understand the process that allows circovirus-relateddiseases to progress and become more deadly.³Results of the study also indicated that the amount of the PCV2 virusfound in the animals had a direct relationship to how sick the pigs became,²Pogranichniy said. ³There was a high correlation between the amount of PCV2viral DNA in the lesions and the severity of the disease.²During the past decade porcine circoviruses have spread to almost everyarea of the world where hogs are raised, but the mortality rate per herd isusually low. On farms infected with other viruses in addition to the newform of porcine circovirus disease, however, the mortality rate rose to 35percent to 50 percent. Porcine circoviruses do not infect people.Three commercial vaccines against PCV2 are available in the U.S. market.It was reported that a recently developed vaccine against PCV2 will reducemortality, but testing on the newest porcine circovirus form is ongoing.Scientists first identified one type of porcine circovirus in 1974 inEurope. Further study showed that it had been present in pigs since at least1969, but didn¹t cause apparent disease.In 1991 a disease appeared in 6-11-week-old nursery-age pigs in whichthey lost weight, developed lesions on their organs, and often hadrespiratory problems, diarrhea and jaundice. The disease was calledpost-weaning multi-systemic wasting syndrome.Porcine circovirus type 2 (PCV2), identified in 1996, causes lesions inthe lymph tissues, kidney, liver and lungs. A more deadly form ofpost-weaning disease now also is found in older pigs. PCV2 also contributesto other swine health problems including abortion, pneumonia and systemicinfection. In addition to those consequences, the newest porcine circovirusmutation causes enlargement of the spleen and fluid in the body cavity,lungs, abdomen and intestines.Further investigation needs to be conducted into cases of the latestporcine circovirus-mutation that are characterized by the lesions producedin the blood vessels, Pogranichniy said. A more exact determination needs tobe made of the role bovine viral diarrhea virus-like pathogen plays indevelopment of circovirus diseases.The Purdue School of Veterinary Medicine, College of Agriculture and theNational Pork Board have provided funding for the circovirus research.Collaborators on this research have included Steve Lenz, Purdue veterinarypathologist and Animal Disease Diagnostic Laboratory researcher; GregoryStevenson, formerly a Purdue and lab researcher and pathologist; IngeborgLangohr and Huiling Wei, both Purdue veterinary comparative pathologygraduate students; and Eric Nelson, a South Dakota State Universityvirologist.

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