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| − | ==MAC group generalities==
| + | #redirect[[Mycobacterium avium]] |
| − | *Share many of the same properties, so often referred to as the M.avium-intracellulare complex (MAIC)
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| − | *Dogs and cats very resistant to infection with MAIC
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| − | **Siamese cats are predisposed to getting disseminated disease.
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| − | *Ubiquitous, saprophytic causing disease in immunocompromised hosts.
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| − | *Genetic susceptibility for disseminated disease in:
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| − | **Humans, rabbits, Basset hounds and mice
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| − | ***Susceptibility identified by the Bcg locus in mice.
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| − | *In most mammals infection results in granulomatous inflammation with little necrosis, calcification or fibrosis. Lymph nodes are usually involved. Dissemination by hematogenous route later.
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| − | ==Johne's disease==
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| − | *Caused by Mycobacterium avium subsp. paratuberculosis
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| − | *Faculative intracellular acid-fast bacillus
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| − | *Rule out Nocardia and Corynebacterium – also acid-fast.
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| − | *22% of the US dairy herds are infected.
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| − | *Infection can be cleared at the early stage, but if colonization takes place, and initial subclinical phase and then a chronic phase.
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| − | *Clinical signs – chronic diarrhea, progressive emaciation – diffuse granulomatous enteritis and lymphadenitis.
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| − | *Progression to clinical stages associated with reduced expression of IFNgamma at the site of infection.
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| − | *Infected at an early age, c/s not apparent until 2yrs+ old.
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| − | *Will shed the bacteria in the faeces before c/s apparent.
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| − | *Infection mediated by transport of bacteria across the Peyer’s patch by M cells and macrophages – transported inside macrophages
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| − | *CMI is mainly by αβ T cells including CD4+ T cells and CD8+ T cells.
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| − | *γδ T cells involved in protection of early infectious stage of disease of mycobacteria and other intracellular organisms
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| − | *Proliferation and activation of γδ T cells at the site of colonization is mediated by 70kd mycobacterial heat shock protein and cytokines.
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| − | *γδ T cells produce proinflammatory cytokines, activate immunoreactive macrophages, αβ T cells and NK cells.
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| − | *But much controversy of their protective role or whether they just recruit other inflammatory cells.
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| − | This study:
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| − | BALB/c mice are susceptible to M.paratuberculosis infection
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| − | γδ T cells KO mice produced fewer granulomas than controls and lower numbers of organisms in the spleen.
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| − | Therefore γδ T cells may be involved in granuloma formation
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| − | γδ T cells in bovines produce TH1 type of cytokines – IFNγ, TNFα and IL-2. May recruit macrophages via production of MCP-1.
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| − | TNFα and IFNγ act synergysticly to produce granulomas.
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| − | IL-2 induces proliferation of T cells, B cells, macrophages and NK cells, and enhances IFNγ and TNFα production from CD4+ T cells.
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| − | Bovines have relatively high proportion of γδ T cells in the GIT compared to man and mice.
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| − | [Reduced formation of granulomata in gamma-delta T cell knockout BALB/c mice inoculated with Mycobacterium avium subsp. Paratuberculosis. Tanaka S et al. Vet Path (2000) 37 415-21] | |
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| − | *Can use culture to detect the bacteria in pooled fecal samples from low-level infected herds – as sensitive as detection of Mycobacteria avium subsp. paratuberculosis from feces of an individual animal (about 70%)
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| − | [Culture of pooled bovine fecal samples as a method to screen herds for paratuberculosis. JVDI (2000) 12 547-51]
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| − | [Immunohistochemical detection of M.paraTB in formalin fixed tissues. JVDI (2000) 12 60-3]
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| − | *The subclinical form in sheep – intestinal lymphoid tissue or adjacent lamina propria.
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| − | *Numbers of organisms identifiable in macrophages seen in lesions with least CMI response.
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| − | ==M.genavense==
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| − | *Disease in birds, dogs, immunosuppressed people.
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| − | *Most common agent of mycobacteriosis in birds in Switzerland.
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| − | *Can differentiate from M.avium by PCR.
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