Epidemiology of mycobacterial lymphadenitis in an Idaho swine herd

Experimental infection of Eurasian wild boar with Mycobacterium avium subsp. avium

The Eurasian wild boar (Sus scrofa) is increasingly relevant as a host for several pathogenic mycobacteria. We aimed to characterize the first experimental Mycobacterium avium subsp. avium (MAA) infection in wild boar in order to describe the lesions and the immune response as compared to uninfected controls. Twelve 1-4-month-old wild boar piglets were housed in class III bio-containment facilities. Four concentrations of MAA suspension were used: 10, 10(2) and 10(4) mycobacteria (2 animals each, oropharyngeal route) and 2.5 x 10(6) mycobacteria (2 animals each by the oropharyngeal and nasal routes). No clinical signs were observed and pathology evidenced a low pathogenicity of this MAA strain for this particular host. Bacteriological and pathological evidence of successful infection after experimental inoculation was found for the group challenged with 2.5 x 10(6) mycobacteria. These four wild boar showed a positive IFN-gamma response to the avian PPD and the real-time RT-PCR data revealed that three genes, complement component C3, IFN-gamma and RANTES, were significantly down regulated in infected animals. These results were similar to those found in naturally and experimentally M. bovis-infected wild boar and may constitute biomarkers of mycobacterial infection in this species.

Comparação entre métodos de tuberculinização no diagnóstico da infecção por agentes do complexo Mycobacterium avium ou M. bovis em suínos

Avaliou-se a eficiência do teste de tuberculina intradérmico comparado, para identificar rebanhos suínos infectados com o complexo Mycobacterium avium (MAC), seu poder de discriminação entre rebanhos infectados com MAC e Mycobacterium bovis, e para estudar diferentes critérios de leitura e interpretação. Foram realizados três experimentos com rebanhos infectados naturalmente com MAC, com suínos inoculados com MAC e com suínos inoculados com M. bovis. Os testes foram comparados com a presença ou não de lesões macro e/ou microscópicas nos linfonodos de suínos em idade de abate. Verificaram-se reações cruzadas entre os testes intradérmicos, tanto com animais infectados com o MAC como com M. bovis. Reações acima de 0,5cm de diâmetro ou acima de 0,20cm no aumento da espessura da dobra da pele, entre a aplicação e a leitura, foram consideradas positivas no cálculo da média para rebanhos. Rebanhos infectados com MAC podem ser identificados por meio do teste intradérmico com PPD aviário e bovino. Tanto a medida do diâmetro quanto o aumento da espessura da dobra da pele das reações foram eficientes no diagnóstico da infecção por MAC. Recomenda-se a utilização do método da medição do diâmetro.

Identification of a chemotactic, MCP-1-like protein from Mycobacterium avium

In the immunocompetent host, Mycobacterium avium is responsible for chronic localized pulmonary disease, which is characterized by the presence of increased numbers of activated T cells and macrophages in the lungs. M. avium organisms as well as sonic extracts of M. avium were found to act as chemoattractants for THP-1 cells as well as monocytes, monocyte-derived macrophages and alveolar macrophages obtained from normal human donors in an in vitro chemotaxis assay, where a significantly higher number of cells were found in wells containing M. avium compared to control wells. Proteolytic treatment of M. avium sonicate resulted in significant loss (50%) of chemotactic activity. Monoclonal antibodies against recombinant human monocyte chemoattractant protein-1 (MCP-1) were found to cross-react with a 34-kDa protein of M. avium sonicate on Western blot and inhibit M. avium sonicate-mediated chemotaxis of THP-1 cells (47%). These data suggest the presence of an 'MCP-1 like' molecule on M. avium. Recruitment of host immune regulatory cells to the site of infection by pathogens may be involved in generating a local immune response or may be a bacterial strategy for survival within the host by recruiting the cells that they infect, i.e. macrophages.

Expression of inflammatory cytokine mRNA in lymphoid tissue from swine experimentally infected with Mycobacterium avium serovar 2

OBJECTIVE

To evaluate in situ expression of inflammatory cytokine mRNA in lymphoid tissue of swine experimentally infected with Mycobacterium avium serovar 2.

ANIMALS

7 noninfected pigs and 7 pigs infected with M. avium serovar 2.

PROCEDURE

Expression of mRNA of inflammatory cytokines such as tumor necrosis factor alpha (TNFalpha), interleukin (IL)-1beta IL-6, and IL-8 in formalin-fixed paraffin-embedded blocks of lymphoid tissue (lymph nodes and tonsil) of swine experimentally infected with M. avium serovar 2 was compared with that of noninfected pigs. Tissues were evaluated by use of morphologic localization of cytokine mRNA, using in situ hybridization at 160 days after inoculation.

RESULTS

A noticeable increase in mRNA expression for TNFalpha and mild increases in mRNA expression of IL-8 and IL-1beta were detected in mandibular lymph nodes from infected swine, compared with noninfected swine. Mild increase in mRNA expression for 1L-6 also was observed in tonsils from infected swine. Cytokine mRNA was detected in macrophages and lymphocytes, primarily within cortical follicles and adjacent mantle zones.

CONCLUSIONS AND CLINICAL RELEVANCE

Expression of mRNA for inflammatory cytokines was increased in lymphoid tissue of infected swine, possibly resulting from local factors on, or secreted by, M. avium. These results suggest that alterations in cytokine mRNA expression are important in the pathogenesis and clinical course of mycobacteriosis in swine. Modulation of the immune response by vaccines that selectively target cytokine expression and secretion in response to mycobacterial challenge may be effective in prevention of mycobacteriosis in swine.

Mycobacterium avium serotype 4 infection of swine: the attempted transmission by contact and the sequence of morphological changes in inoculated pigs

After 30 pigs were inoculated orally in groups at 4, 8, 12, 16 and 20 weeks of age with Mycobacterium avium serotype 4 and killed when approximately 210 lbs body weight, 24 pigs had gross lesions caused by M. avium and all had microscopic lesions. It was found that the group inoculated at 8 weeks of age had lesions that best reproduced those found in outbreaks of mycobacteriosis. Thirty-four contact pigs did not develop gross mycobacterial lesions and only 2 developed microscopic lesions. In a second experiment, 29 pigs were inoculated orally when 8 weeks of age and killed 6, 12, 18, 21 and 28 weeks later. Gross lesions caused by M. avium were present in 9 pigs and 17 pigs had microscopic lesions. Severe lesions were found in the pigs killed after 18 weeks. Gross lesions were enlargement or caseation of lymph nodes. Enlargement alone was not considered a reliable indicator of mycobacterial disease, as less than half the affected lymph nodes were histologically granulomatous. When a granulomatous lesion was present in enlarged lymph nodes, it was most likely to be an accumulation of epithelioid macrophages with areas of necrosis and caseation. The most common histological lesion found in grossly caseated lymph nodes was discrete granulomas with severe caseation and a thick fibrous capsule. Granulomas that consisted of epithelioid cells, or epithelioid cells and caseation were most numerous after 12 weeks or less. Multinucleate giant cells dominated the picture when the interval between inoculation and slaughter was 6 or 10.5 weeks. Encapsulated granulomas were the main type in animals inoculated 18 weeks or longer before slaughter. Caseation of epithelioid granulomas and the formation of multinucleate giant cells seemed to progress faster in the older inoculated animals. Microscopic granulomas were present in the tonsils and intestines of 8 pigs and 16 pigs, respectively, and most of these pigs were inoculated at 16 and 20 weeks of age and killed 10.5 and 6 weeks later. Lesions of the tonsil and intestine did not become encapsulated, and probably resolved. The conditions of our experiment should have allowed contact animals to be exposed to organisms shed from the tonsil and intestine of inoculated pigs, yet only a few microscopic lesions developed.