Histopathological and molecular findings in emaciated pigs from Mexico

Wasting of post-weaning piglets is a problem of global pig farming. The most important viral diseases linked to this problem in Mexico are porcine circovirus type 2 (PCV2)-systemic disease, porcine reproductive and respiratory syndrome (PRRS) and blue eye disease (BED); the latter, is only present in Mexico. These diseases cause great economic losses and predispose to the development of co-infections, mainly with bacteria. The objective of this work was to identify microscopic lesions and involvement of PCV2, PRRS virus (PRRSV) and porcine rubulavirus (PoRV) in emaciated piglets.

Thirty-seven necropsies of pigs with poor body condition were performed in the Bajío region of Mexico. Inclusion criteria were 6-16 week-old pigs displaying marked growth retardation (body condition scoring 1 or 2). Tissue samples of lung and lymph nodes were fixed in buffered formalin for histopathological analysis and immunohistochemistry for PCV2. Same tissue samples were taken and frozen for subsequent detection of PCV2 by PCR and PRRSV and PoRV by RT-PCRs.

Histopathologically, interstitial pneumonia was observed in 25/37 (68%) of the piglets, catarrhal-purulent bronchopneumonia was observed in 7/37 pigs, broncho-interstitial pneumonia was found in 5/37 pigs and 2/37 animals had fibrino-hemorrhagic-necrotizing pleuropneumonia. Also, a varying degree of lymphocyte depletion in lymphoid organs was found in 14/37 (38%) animals. A total of 16/37 (43%) pigs were PCV2 PCR positive, 18/37 (49%) yielded a positive RT-PCR for PRRSV (North American strain) and 1/37 (3%) pigs positive for PoRV. PCV2 and PRRSV co-infection was noticed in 7/37 (19%) piglets, while only 1/37 (3%) was positive both for PRRSV and PoRV. Finally, 10/37 (27%) animals were negative for all three viruses.

In this study, histopathological and viral detection methods showed that 73% of wasted pigs were associated with infections or co-infections with PRRSV and PCV2. It is important to highlight that 38% of pigs had pulmonary lesions suggestive of bacterial infections. It is possible that potential immunosuppression or immunomodulation of viral origin (PCV2 and/or PRRSV mainly) favored the development of these infections. In conclusion, results obtained in this study suggest that PCV2 and PRRSV are present very often (alone or in co-infection) in wasted pigs from Mexican farms. The PoRV played a relatively minimal role in the causation of emaciation in the studied pigs.

Disclosure of Interest: None Declared.