Postweaning Multisystemic Wasting Syndrome Induced after Experimental Inoculation of Cesarean-Derived, Colostrum-Deprived Piglets with Type 2 Porcine Circovirus

Abstract

Cesarean-derived, colostrum-deprived pigs ( n = 23) were inoculated intranasally and subcutaneously with a low cell culture passage of type 2 porcine circovirus. In 11 pigs, a persistent fever that lasted 7–17 days began 12–15 days after inoculation with virus. Additional signs of disease in those 11 pigs included depression (11 of 11 pigs), palpable enlargement of inguinal, prefemoral, and popliteal lymph nodes (11 of 11), icterus (6 of 11), and hyperpnea (2 of 11). The remaining 12 pigs had fever that occurred intermittently for 2–4 days between days 12 and 20 postinoculation. Overt signs of disease in those pigs were limited to palpable enlargement of inguinal and popliteal lymph nodes (9 of 12 pigs). When compared with control pigs of similar age, the average daily rate of weight gain for all pigs inoculated with virus was less over a 2-week period that began 2 weeks post inoculation. At postmortem examination, lymph node enlargement was seen in 14 of 14 pigs euthanized between days 20 and 28 postinoculation. Lymph node enlargement was especially prominent in pigs that developed a persistent fever. Microscopic lesions noted in pigs that developed a persistent fever included cellular depletion in lymphoid tissues; hepatic cell necrosis; and lymphogranulomatous inflammation of lymph nodes, Peyer's patches of the intestine, liver, kidney, and heart. Virus was isolated with varying frequency from nasal, rectal, or tonsil swab specimens, buffy coat, serum, urine, and lung lavage fluid obtained antemortem or postmortem. Virus was isolated from or viral DNA was detected in a variety of tissues obtained postmortem up to 125 days postinoculation. Antibody against type 2 porcine circovirus usually was detected in serum between 15 and 20 days postinoculation; however, antibody against virus was not detected in serum from 4 pigs euthanized 20–24 days postinoculation. Direct contact with pigs inoculated with virus 42 days previously resulted in transmission of virus to 3 of 3 control pigs.