Viruses that replicate in the monocyte/macrophage lineage such as porcine parvovirus (PPV) (Allan et al., 1999a; Opriessnig et al., 2004) and porcine reproductive and respiratory virus (PRRSV) (Allan et al., 2000a; Harms et al., 2001; Rovira et al., 2002), have been shown to increase the replication of PCV2 in coinfected pigs and increase the incidence of PMWS. Despite the presence of PCV2 in macrophages and dentritic cells. Recent in vitro studies suggest that monocytic cells may not represent the primary target for PCV2 replication (Gilpin et al., 2003). Monocytes and macrophages were tested for the ability to support PCV2-replication in vitro. PCV2-replication in these cell types was not observed; however, PCV2 was not degraded and was stored in the cytoplasm of the cells (Gilpin et al., 2003). Similarly, no evidence of in vitro virus replication in dendritic cells was found by Vincent et al. (2003); however, PCV2 did persist in dendritic cells without loss of infectivity or the induction of cell death. It has been speculated that because of their migratory capacity, dendritic cells can provide a potent vehicle for transport of the virus throughout the host without the need for replication (Vincent et al., 2003).
Allan GM, McNeilly F, Ellis J, Krakowka S, Meehan B, McNair I, Walker I, Kennedy S: Experimental infection of colostrum deprived piglets with porcine circovirus 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) potentiates PCV2 replication. Arch Virol. 145:2421-2429, 2000a
Allan GM, McNeilly F, Kennedy S, Meehan B, Ellis J, Krakowka S: Immunostimulation, PCV-2 and PMWS. Vet Rec. 147:170-171, 2000c
Gilpin DF, McCullough K, Meehan BM, McNeilly F, McNair I, Stevenson LS, Foster JC, Ellis JA, Krakowka S, Adair BM, Allan GM: In vitro studies on the infection and replication of porcine circovirus type 2 in cells of the porcine immune system. Vet Immunol Immunopathol. 94:149-161, 2003
Harms PA, Sorden SD, Halbur PG, Bolin SR, Lager KM, Morozov I, Paul PS: Experimental reproduction of severe disease in CD/CD pigs concurrently infected with type 2 porcine circovirus and porcine reproductive and respiratory syndrome virus. Vet Pathol. 38:528-539, 2001
Opriessnig T, Fenaux M, Yu S, Evans RB, Cavanaugh D, Gallup JM, Pallares FJ, Thacker EL, Lager KM, Meng XJ, Halbur PG: Effect of porcine parvovirus vaccination on the development of PMWS in segregated early weaned pigs coinfected with type 2 porcine circovirus and porcine parvovirus. Vet Microbiol. 98:209-220, 2004a
Vincent IE, Carrasco CP, Herrmann B, Meehan BM, Allan GM, Summerfield A, McCullough KC: Dendritic cells harbor infectious porcine circovirus type 2 in the absence of apparent cell modulation or replication of the virus. J Virol. 77:13288-13300, 2003