Viral wasting syndrome of swine: Experimental reproduction of postweaning multisystemic wasting syndrome in gnotobiotic swine by coinfection with porcine circovirus 2 and porcine parvovirus

One-day-old gnotobiotic piglets were inoculated intranasally with in vitro passaged porcine circovirus 1 (PCV-1), PCV-2, and porcine parvovirus (PPV) alone or in combination (PCV-1/PCV-2, PCV-1/PPV, and PCV-2/PPV). Piglets we re evaluated for 1) the development of porcine postweaning multisystemic wa sting syndrome (PWMS), 2) distribution of viral antigens by immunochemistry , and 3) viremia and the presence of viral DNA in nasal and ocular secretio ns and feces. All single agent-infected piglets and piglets infected with P CV-1/PCV-2 or PCV-1/PPV were clinically asymptomatic. They were transiently viremic and seroconverted to homologous virus(es). At termination of the s tudy on postinfection day (PID) 35, microscopic lesions were restricted to focal inflammatory cell infiltrates in livers and myocardia. One piglet giv en PCV-1/PPV was PPV viremic for 2 weeks after infection and had lymphangie ctasia of the spiral and descending colon associated with granulomatous inf lammation. All four PCV-2/PPV-inoculated piglets developed PMWS, characteri zed by sudden onset of depression and anorexia, icterus, and submucosal ede ma. One piglet became moribund on PID 27, and the remaining three piglets w ere euthanatized between PLD 27 and PID 30 because of severe disease. Lymph nodes were small and the livers were mottled. Disseminated angiocentric gr anulomatous inflammation was present in all tissues examined except the bra in. Multiple lightly basophilic intracytoplasmic inclusion bodies were iden tified in macrophages and histiocytes. PCV-2 antigen was widely distributed within macrophages; PPV antigen was sparse. Hepatocellular necrosis and bi le retention were prominent. PCV-2 DNA was identified in ocular fecal, and nasal secretions. Terminal sera contained antibodies to PPV (4/4) and PCV-2 (3/4). Production of PMWS in gnotobiotic swine appears to require PCV-2 an d additional infectious agents such as PPV for full disease expression in g notobiotic piglets.