PCV2 Associated Lymphoid Depletion

Pigs with PCVAD typically have enlarged lymph nodes

PCV2-associated lymphoid depletion is a hallmark lesion of PMWS but can also be observed in subclinically infected pigs (Quintana et al., 2001). Sanchez et al. (2004) investigated the development of PCV2-associated lymphoid lesions in pigs that had been inoculated in utero at 92 to 104 gestational days (n = 12) or at 1 day of age (n = 14) and found that high PCV2 titers in lymphoid organs may lead to the development of severe microscopic lymphoid lesions without causing clinical manifest disease. The infection appears to occur mainly in infiltrating monocytic cells and to a lesser extend in cells bearing lymphocyte markers (Sanchez et al., 2004).

Lymphoid depletion and granulomatous lymphadenitis Normal Lymph Node

Kim and Chae (2005) described seven field cases of PCV2-associated necrotizing lymphadenitis. The main lesion was follicular necrosis in the center of prominent lymphoid follicles. PCV2 was detected in all lymph nodes with necrotic foci but was absent in other lymph nodes. No other infectious cause could be found and granulomatous inflammation and intracytoplasmic inclusion bodies were not observed in these cases (Kim and Chae, 2005). In three pigs experimentally infected with PCV2, viral antigen was also associated with obliterated blood vessels in areas of granulomatous and necrotizing lymphadenitis (Opriessnig et al., 2006).

	Normal lymph nodes with lymphoid depletion score of 0 (range 0-3) and histiocytic replacement score of 0 (range 0-3). Lymph nodes from a pig experimentally-infected with PCV2 and demonstrating mild lymphoid depletion (score of 1, range 0-3) and mild histiocytic replacement (score of 1, range 0-3) of lymphoid follicles.
	Lymph nodes from a pig experimentally-infected with PCV2 and demonstrating moderate lymphoid depletion (score of 2, range 0-3) and moderate histiocytic replacement (score of 2, range 0-3) of lymphoid follicles.
	Lymph nodes from a pig experimentally-infected with PCV2 and demonstrating severe lymphoid depletion (score of 3, range 0-3) and severe histiocytic replacement (score of 3, range 0-3) of lymphoid follicles. Lymph nodes from a pig experimentally-infected with PCV2 and demonstrating severe lymphoid depletion (score of 3, range 0-3) and severe histiocytic replacement (score of 3, range 0-3) of lymphoid follicles.
	Timeline of PCV2-induced microscopic lesions and antigen distribution Click on an image to view a larger size.

References:

Kim J, Chae C: Necrotising lymphadenitis associated with porcine circovirus type 2 in pigs. Vet Rec. 156:177-178, 2005

Opriessnig T, Janke BH, Halbur PG: Cardiovascular lesions in pigs naturally or experimentally infected with porcine circovirus type 2. J Comp Pathol. 134:105-110, 2006

Quintana J, Segalés J, Rosell C, Calsamiglia M, Rodríguez-Arrioja GM, Chianini F, Folch JM, Maldonado J, Canal M, Plana-Durán J, Domingo M: Clinical and pathological observations on pigs with postweaning multisystemic wasting syndrome. Vet Rec. 149:357-361, 2001

Sanchez RE Jr, Meerts P, Nauwynck HJ, Ellis JA, Pensaert MB: Characteristics of porcine circovirus-2 replication in lymphoid organs of pigs inoculated in late gestation or postnatally and possible relation to clinical and pathological outcome of infection. J Vet Diagn Invest. 16:175-185, 2004