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Pneumonia

PCV2 Associated Pneumonia

 
PCV2 antigen (brown staining) associated with bronchiolitis in a field case of PCV2-associated porcine respiratory disease complex (PRDC).
Lungs from a field case of Porcine Respiratory Disease Complex (PRDC) due to coinfection with PCV2 (brown staining) and Mycoplasma hyopneumoniae.
 
Lungs from a pig experimentally-infected with PCV2 are mottled tan and fail to collapse. Microscopic examination reveals mild bronchointerstitial pneumonia with peribronchiolar lymphohistiocytic infiltration (above right) and lymphoid depletion and histiocytic (lower right) replacement of follicles associated with PCV2 antigen (brown staining).

Recent field investigations suggest that PCV2 may be playing an important role in some cases of porcine respiratory disease complex (PRDC) (Harms et al., 2002; Kim et al., 2003). PRDC is a condition observed mainly in 8- to 26-week-old pigs and associated with multiple respiratory pathogens including PRRSV, SIV, and M. hyopneumoniae. PRDC is characterized by decreased rate of growth, decreased feed efficiency, anorexia, fever, cough, and dyspnea. There is diagnostic overlap between PMWS and PCV2-associated pneumonia. The presence of prolonged and unusually severe clinical respiratory disease, granulomatous bronchointerstitial pneumonia with bonchiolitis and bronchiolar fibrosis, and abundant PCV2 antigen associated with the lesions is suggestive of PCV2-associated pneumonia and PRDC. There is experimental evidence of unique lung lesions associated with PCV2 antigen in the literature. Interstitial pneumonia with bronchiolitis was reported in the first cases of PMWS (Clark, 1997; Ellis et al., 1998). Magar et al. (2000) reproduced bronchointerstitial pneumonia in addition to the hallmark lymphoid lesions of PMWS in conventional pigs inoculated with PCV2. Bolin et al. (2001) induced mild respiratory disease and multifocal interstitial pneumonia in CDCD pigs inoculated with PCV2. Rovira et al. (2002) induced mild interstitial pneumonia and lymphoplasmacytic rhinitis in conventional pigs inoculated with PCV2. Mild granulomatous bronchointerstitial pneumonia was reproduced in conventional pigs using an infectious DNA clone of PCV2 (Fenaux et al., 2002).

Coinfections with PCV2 and other pathogens in lung lesions have been reported. Pneumocystis carinii was reported to occur in approximately 0.5% of cases with PMWS in western Canada (Clark, 1997). Pulmonary aspergillosis was diagnosed in a pig affected by PMWS (Segalés et al., 2003). Harms et al. (2002) demonstrated a high prevalence of coinfection with PRRSV in cases of PRDC in the Midwestern United States. Coinfection with SIV and M. hyopneumoniae was also reported in this study (Harms et al., 2002a). Proliferative and necrotizing pneumonia (PNP) which is characterized microscopically by lymphohistiocytic interstitial pneumonia with marked proliferation of type 2 pneumocytes, multifocal coagulates of necrotic cells in the alveoli, hyaline membranes, intra-alveolar lymphoplasmacytic infiltrates, and bronchiolar necrosis has been implicated to be the result of coinfection with PRRSV and PCV2 (Larochelle et al., 1999). Drolet et al. (2003) did a retrospective study on 60 cases of PNP diagnosed between 1988 and 2001 and found PRRSV antigen in 55/60 PNP cases, SIV antigen in 1/60 PNP cases, and PCV2 in 25/55 PNP cases. The authors concluded that coinfection with PCV2 is not a determining factor in PNP and that PRRSV is consistently and predominately associated with PNP (Drolet et al., 2003).

References:

Bolin SR, Stoffregen WC, Nayar GPS, Hamel AL: Postweaning multisystemic wasting syndrome induced after experimental inoculation of cesarean-derived, colostrum-deprived piglets with type 2 porcine circovirus. J Vet Diagn Invest. 13:185-194, 2001

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

Drolet R, Larochelle R, Morin M, Delisle B, Magar R: Detection rates of porcine reproductive and respiratory syndrome virus, porcine circovirus type 2, and swine influenza virus in porcine proliferative and necrotizing pneumonia. Vet Pathol. 40:143-148, 2003

Ellis J, Hassard L, Clark E, Harding J, Allan G, Willson P, Strokappe J, Martin K, McNeilly F, Meehan B, Todd D, Haines D: Isolation of circovirus from lesions of pigs with postweaning multisystemic wasting syndrome. Can Vet J. 39:44-51, 1998

Fenaux M, Halbur PG, Haqshenas G, Royer R, Thomas P, Nawagitgul P, Gill M, Toth TE, Meng XJ: Cloned genomic DNA of type 2 porcine circovirus is infectious when injected directly into the liver and lymph nodes of pigs: characterization of clinical disease, virus distribution, and pathologic lesions. J Virol. 76:541-551, 2002

Harms PA, Halbur PG, Sorden SD: Three cases of porcine respiratory disease complex associated with porcine circovirus type 2 infection. J Swine Health Prod. 10:27-30, 2002

Kim J, Chae C: Optimal enhancement of in situ hybridization for the detection of porcine circovirus 2 in formalin-fixed, paraffin-wax-embedded tissues using a combined pretreatment of thermocycler and proteinase K. Res Vet Sci. 74:235-240, 2003

Larochelle R, Morin M, Antaya M, Magar R: Identification and incidence of porcine circovirus in routine field cases in Quebec as determined by PCR. Vet Rec. 145:140-142, 1999

Magar R, Larochelle R, Thibault S, Lamontagne L: Experimental transmission of porcine circovirus type 2 (PCV2) in weaned pigs: a sequential study. J Comp Pathol. 123:258-269, 2000

Rovira A, Balasch M, Segalés J, García L, Plana-Durán J, Rosell C, Ellerbrok H, Mankertz A, Domingo M: Experimental inoculation of conventional pigs with porcine reproductive and respiratory syndrome virus and porcine circovirus 2. J Virol. 76:3232-3239, 2002

Segalés J, Domingo M, Collell M, Jensen HE, Blanco JL: Pulmonary aspergillosis in a post-weaning multisystemic wasting syndrome (PMWS) affected pig. Pig J. 52:41-47, 2003

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