Effects of Porcine Circovirus Type 2 (PCV2) Maternal Antibodies on Experimental Infection of Piglets with PCV2

摘要

To determine the effects of porcine circovirus type 2 (PCV2) maternal antibodies on and response to experimental PCV2 infection, 24 piglets were divided into four groups on the basis of the enzyme-linked immunosorbent assay titers of PCV2 maternal antibodies: group A (n = 6; sample/positive [S/P] ratio, <0.2), group B (n = 5; S/P ratio, >0.2 to <0.5), and groups C (n = 8) and D (n = 5) (S/P ratio, >0.5). Piglets in groups A, B, and C were inoculated with PCV2 at day 0 and challenged with PCV2 at day 42. Group D piglets were not exposed to PCV2 at day 0 but were challenged at day 42. Before challenge, seroconversion to PCV2 antibodies occurred in five?of?six group A piglets, and the antibody level rose above the cutoff level in one?of?five group B piglets. Viremia was detected in five?of?six, four?of?five, and two?of?eight pigs in groups A, B, and C, respectively. After challenge, PCV2 DNA was detectable from 7 to 21 days postchallenge in the sera from six?of?six, four?of?five, three?of?eight, and five?of?five pigs in groups A, B, C, and D, respectively. The results indicated that protection against PCV2 infection conferred by maternal antibodies is titer dependent: higher titers are generally protective, but low titers are not.