El primer reporte de enfermedad asociada con el Circovirus porcino tipo 2 (PCV2) fue descrito como Síndrome multisistémico del desmedro o adelgazamiento postdestete = “Postweaning multisystemic wasting syndrome” (PMWS) en la provincia de Saskatchewan (zona oeste de Canadá) en el año 1991. Sin embargo, es en 1996 en un congreso regional canadiense, y en marzo de 1997 en el congreso anual de la Asociación Americana de Veterinarios Especialistas en Porcino (AASP), donde es descrita como una nueva enfermedad que afectaba a cerdos de esa región (1), desde entonces un número creciente de casos ha sido diagnosticado en todo el mundo (2, 5) y en nuestro país fue diagnosticado por primera vez a finales del 2001 (3,4). Si bien muchos aspectos de la patogenia de la enfermedad permanecen sin aclarar. Las coinfecciones bacterianas suelen ser muy importantes en la presentación del PMWS (4) y Mycoplasma hyopneumoniae (Mh) podría ser importante en el PMWS (2). En este trabajo nos planteamos la detección de Mh en casos naturales de PMWS.

Detection of Mycoplasma suis in clinical cases with postweaning multisystemic wasting syndrome in swine. Mycoplasma suis is a swine erythrocyte obligatory parasite. Its presence may result in chronic or acute anaemia in different pig categories. It is considered that the postweaning multisystemic wasting syndrome (PMWS) is caused by porcine circovirus type 2, but some aspects of the pathogenesis remain unknown. PMWS signs are impaired weight gain, anaemia and jaundice in 5 to 12 week-old pigs that suffer from immunosuppression and bacterial co-infections. The pigs with signs of these diseases on three porcine farms were studied. Compatible M. suis forms in blood smears and typical PMWS lesions in tissue cuts were seen. This is the first communication of the clinical association between these two entities.

Mycoplasma hyopneumoniae (Mh) is the primary agent of porcine enzootic pneumonia (PEN), a chronic respiratory disease endemic to pig farms, and characterized histologically by infiltration of mononuclear cells in airways and prominent hyperplasia of the bronchus-associated lymphoid tissue (BALT). To gain further insight into the pathogenesis of PEN, cytokine expression in the lung, with particular attention to the BALT, was examined immunohistochemically in pigs naturally infected with Mh. An increase (P < 0.05) in proinflammatory and immunoregulatory cytokines (especially interleukin [IL]-2, IL-4 and tumour necrosis factor [TNF]-alpha, and to a lesser extent IL-1 [alpha and beta] and IL-6) was detected in the BALT, which showed intense lymphoid hyperplasia. IL-1beta and TNF-alpha were also detected in the bronchoalveolar exudate of infected pigs, and IL-6 and IL-8 were demonstrated in mononuclear cells of the alveolar septa. The results showed that in Mh infection, macrophage and lymphocyte activation results in the expression of a number of cytokines capable of inducing lung lesions and lymphoreticular hyperplasia of the BALT.

Postweaning multisystemic wasting syndrome was first described in Canada in 1991 and at present an increasing number of cases has been diagnosed worldwide. In Argentina the first cases of PMWS were reported recently. Forty eight 5 to 12 week old pigs with signs characteristic of PMWS from 19 farms were studied. Although the real distribution of the virus in our country is not known it was observed an increasing number of farms with PMWS distributed in the major producing provinces. The histopathology was an important tool in diagnosis of suspicious cases of PMWS with the observation of different degrees of lesion. In the studied animals, the secondary infections, either by opportunistic pathogens or secondary bacteria could be important.

El aparato respiratorio del cerdo, como el de otros mamiferos consta de una porcion conductora y una porcion respiratoria donde tiene lugar el intercambio gaseoso. Las estructuras que componen estas vias poseen una organizacion general, constituida por un epitelio respiratorio ?pseudoestratificado cilindrico ciliado con celulas caliciformes?, lamina propia de tejido conjuntivo, tejido de sosten representado por anillos de cartilago hialino unidos en sus extremos por fibras musculares y una adventicia de tejido conectivo. Esta organizacion basica se va modificando conforme se profundiza en el parenquima pulmonar, perdiendo el tejido cartilaginoso y disminuyendo en altura el epitelio hasta convertirse en un epitelio simple plano en las vias respiratorias. Dispone de una serie de mecanismos de defensa que actuan intentando mantener el equilibrio del sistema para cumplir su funcion principal de intercambio gaseoso: el aparato mucociliar traqueobronquial, macrofagos alveolares e intravasculares, y el sistema inmune humoral por medio de las inmunoglobulinas A, M y G, con predominio de una y otras en las diferentes porciones del aparato respiratorio, asi como el mecanismo de defensa celular, constituido por linfocitos (T y B), celulas K, celulas dendriticas, complejo de histocompatibilidad, algunas de ellas aun sin un completo conocimiento de su mecanismo de accion. Conociendo la estructura y funciones del sistema respiratorio, se esquematiza como participan, e interactuan cada una de las celulas y sus productos liberados en la respuesta inmune del aparato respiratorio.

Porcine enzootic pneumonia (PEN), caused by Mycoplasma hyopneumoniae (Mh), has been described in pigs in all geographic areas. The disease is characterized by high morbidity and low mortality rates in intensive swine production systems. A morphologic and immunohistochemical study was done to determine the cellular populations present in lung parenchyma of infected pigs, with special attention to the bronchus-associated lymphoid tissue (BALT). Polyclonal and monoclonal antibodies were used for the detection of antigens of Mh, T lymphocytes (CD3 + , CD4 + , and CD8 + ), IgG + or IgA + lymphocytes, and cells containing lysozyme, S-100 protein, major histocompatibility complex class II antigen or myeloid-histiocyte antigen. Findings in lung tissues associated with Mh infection were catarrhal bronchointerstitial pneumonia, with infiltration of inflammatory cells in the lamina propria of bronchi and bronchioles and alveolar septa. Hyperplasia of mononuclear cells in the BALT areas was the most significant histologic change. The BALT showed a high morphologic and cellular organization. Macrophages and B lymphocytes were the main cellular components of germinal centers. T lymphocytes were primarily located in perifollicular areas of the BALT, lamina propria and within the airway epithelium, and plasma cells containing IgG or IgA at the periphery of the BALT, in the lamina propria of bronchi and bronchioles, in alveolar septa, and around bronchial submucosal glands. The hyperplastic BALT in PEN cases consisted of macrophages, dendritic cells, T and B lymphocytes, and IgG + and IgA + plasma cells. CD4+ cells predominated over CD8+ cells. Local humoral immunity appears to play an important role in the infection.

The distribution of cells containing lysozyme, S-100 protein, CD3, CD4, CD8, major histocompatibility complex class II antigen and immunoglobulin G (IgG) was analysed in the bronchus-associated lymphoid tissue (BALT) of goats naturally infected with three Mycoplasma species. This study included the immunohistochemical characterization of the pneumonic lesions of 18 goats (3-5 months old) infected with one of the following Mycoplasma species: M. mycoides ssp. mycoides, Large Colony type (goats no. 1-6), M. mycoides ssp. capri (goats no. 7-12) and M. capricolum ssp. capricolum (goats no. 13-18). Microscopically, infected animals showed a moderate broncho-interstitial pneumonia, characterized by lymphoid hyperplasia of the BALT and infiltration of mononuclear cells in the alveolar walls and airways. The main cellular type in the BALT was represented by CD3+ T lymphocytes, and the ratio of CD4+:CD8+ cells was > 2. The BALT showed large germinal centres mainly composed of IgG+ B lymphocytes, with numerous S-100+ follicular dendritic cells. The presence of follicular dendritic cells confirmed the high degree of organization of this lymphoid tissue. The immunohistochemical results showed that activated T lymphocytes, particularly in the CD4 subset, and IgG+ B cells, play a major role in the immune response of the caprine lung infected with these species of mycoplasmas.

Goats aged 3 months were inoculated with a recent isolate of Mycoplasma agalactiae (five animals) or Mycoplasma bovis (five animals) by a combined (intratracheal+intranasal) route. Two control goats were inoculated by the same route with sterile mycoplasma broth. Animals were killed 14 or 21 days after infection. At necropsy, tracheal and lung tissue was taken for pathological and immunohistochemical examination to determine changes in the lymphocyte subpopulations in the bronchus-associated lymphoid tissue (BALT). Consolidation of the lungs was not observed in any animal. M. agalactiae or M. bovis was recovered from the respiratory tract and lung of all but two infected animals. Both Mycoplasma spp. induced a moderate bronchointerstitial pneumonia, characterized by lymphoid hyperplasia of the BALT and infiltration of mononuclear cells into the alveolar walls. The predominant phagocytic cell in the pulmonary parenchyma and the airways was the macrophage. The main cellular type in the BALT was the CD3(+)T lymphocyte, and the ratio of CD4(+): CD8(+)cells was >1. It is likely that cellular immune mechanisms, through the activation of CD4(+)T lymphocytes, plays a prominent role in the acute and subacute phase of these infections.