Clinical Disease, Macroscopic and Microscopic Lesions

Severe systemic PCV2 infection is a disease complex characterized by weight loss or decreased performance and pneumonia in pigs in the late nursery and early grower stages typically affecting pigs between 5 and 20 weeks of age (Allan and Ellis, 2000; Harding, 2004). Harding (2004) emphasizes six fundamental clinical signs of PMWS: wasting, dyspnea, enlarged lymph nodes, diarrhea, pallor, and jaundice. While all the fundamental clinical signs may not be noted in a single pig, affected farms will present with the majority of them over a period of time. Other clinical signs include coughing fever, gastric ulceration, meningitis, and sudden death (Harding et al., 2004).

Macroscopic lesions associated with PCV2 infection include generalized lymphadenopathy, non-collapsed, rubbery lungs with mottling and increased firmness, enlarged spleen, and enlarged kidneys (Clark, 1997).

Characteristic microscopic lesions associated with PCV2-infection and PMWS include lymphoid depletion and histiocytic replacement of follicles in lymphoid tissues. The lymphocellular depletion affects both, lymphoid follicles and parafollicular zones (Rosell et al., 1999). Mild-to-severe granulomatous inflammation in lymphoid and other tissues also is commonly observed (Allan and Ellis, 2000; Sorden, 2000). Syncytial cells can be seen frequently, especially in lymph nodes, Peyer’s patches, and lamina propria of the intestinal villi (Rosell et al., 1999). Macrophages in affected lymphoid tissues may contain sharply demarcated, spherical, basophilic cytoplasmic inclusion bodies (Clark, 1997; Rosell et al., 1999). The inclusions are either large and single or smaller and multiple with groups of up to 12 inclusions (Rosell et al., 1999).

 

References:

Allan GM, Ellis JA: Porcine circoviruses: a review. J Vet Diagn Invest. 12:3-14, 2000

Clark EG: Post-weaning multisystemic wasting syndrome. In: Proc Am Assoc Swine Pract, Quebec, Canada. 28:499-501, 1997

Harding JCS: The clinical expression and emergence of porcine circovirus 2. Vet Microbiol. 98:131-135, 2004

Rosell C, Segalés J, Plana-Durán J, Balasch M, Rodríguez-Arrioja GM, Kennedy S, Allan GM, McNeilly F, Latimer KS, Domingo M: Pathological, immunohistochemical, and in-situ-hybridization studies of natural cases of postweaning multisystemic wasting syndrome (PMWS) in pigs. J Comp Pathol. 120:59-78, 1999

Sorden SD: Update on porcine circovirus and postweaning multisystemic wasting syndrome (PMWS). Swine Health Prod. 8:133-136, 2000