|
|
| Line 1: |
Line 1: |
| − | {{review}}
| + | #REDIRECT[[:Category:Mycobacteria species]] |
| − | | |
| − | {{toplink
| |
| − | |backcolour =
| |
| − | |linkpage =Bacteria
| |
| − | |linktext =BACTERIA
| |
| − | |pagetype=Bugs
| |
| − | }}
| |
| − | <br>
| |
| − | | |
| − | ===Overview===
| |
| − | | |
| − | *Mycobacterial infections are caused by bacteria belonging to the family Mycobacteriaceae, order Actinomycetales
| |
| − | *Includes obligate pathogens, opportunistic pathogens and saprophytes
| |
| − | *Cause chronic, progressive, granulomatous infections
| |
| − | *Cause tuberculosis, [[Intestines Proliferative Enteritis - Pathology#Paratuberculosis (Johnes disease)|Johne's disease]] and feline leprosy
| |
| − | *''M. bovis'', ''M. tuberculosis'' and ''M. avium'' cause [[Respiratory Bacterial Infections - Pathology#Tuberculosis|tuberculosis of cattle]], [[Respiratory Bacterial Infections - Pathology#Tuberculosis in pigs|tuberculosis of pigs]] and [[Respiratory Bacterial Infections - Pathology#Tuberculosis in dogs|tuberculosis of dogs]] respectively
| |
| − | *The 'classical' tuberculosis lesions are caused by the [[Mycobacterium tuberculosis complex]]
| |
| − | *The Johne's type lesions are caused by the [[Mycobacterium avium complex]]
| |
| − | *Environmental species are found in soil, vegetation and water
| |
| − | *''Mycobacterium leprae'' and ''M.lepraemurium'' cause human, feline/murine leprosy respectively
| |
| − | *Atypical mycobacteriosis is a localized opportunistic skin and subcutaneous infection caused by saprophytic and rapidly growing atypical mycobacteria
| |
| − | *Granulomatous lesions in [[Muscles Inflammatory - Pathology#Tuberculosis|muscle]] and [[Bacterial skin infections - Pathology#Bacterial granulomatous dermatitis|skin]]
| |
| − | *Skin tuberculosis of cattle causes nodules along the lymphatics of the limbs
| |
| − | *Bovine farcy is thought to be caused by ''M. senegalense'' and ''M. farcinogenes''
| |
| − | *Saprophytic mycobacteria cause granulomatous lesions
| |
| − | | |
| − | ===Characteristics===
| |
| − | | |
| − | *Aerobic, weakly Gram-positive acid-fast rods
| |
| − | *Non-motile, non-spore forming
| |
| − | *Cell walls contain mycolic acid
| |
| − | *Require egg-based media for growth
| |
| − | *Slow-growing colonies
| |
| − | *Resistant to disinfectants and environmental conditions; susceptible to pasteurisation
| |
| − | *Mycobacteria stain with carbol dyes and resist subsequent decolorization with inorganic acids; this characteristic which is due to the spatial arrangement of mycolic acids within the cell wall makes them acid fast
| |
| − | | |
| − | | |
| − | ===Identification===
| |
| − | | |
| − | *Identified by Ziehl-Neelson staining
| |
| − | *Differentiated by culture, biochemical tests, chromatography and molecular techniques
| |
| − | *Pathogenic species require at least three weeks for growth on egg-based media
| |
| − | | |
| − | | |
| − | ===Bovine tuberculosis===
| |
| − | | |
| − | *Epidemiology
| |
| − | **World-wide disease caused by ''M. bovis''
| |
| − | **Aerosol transmission between cattle kept in close contact
| |
| − | **Transmission to calves via ingestion od contaminated milk
| |
| − | **Wildlife reservoirs include badgers and possibly deer in the Europe
| |
| − | | |
| − | *Pathogenesis and pathogenicity
| |
| − | **The ability of mycobacteria to survive and multiply within macrophages determines whether disease will occur within the host
| |
| − | **Survival and multiplication in macrophages at primary site of infection due to prevention of phagosome-lysosome fusion
| |
| − | **Mycobacteria utilize several virulence factors including cord factor or trehalose dimycolate, surface glycolipid, sulfatides, lipoarabinomannan, heteropolysaccharide, heat shock protein, complement, and tubuloprotein
| |
| − | **The types of immune responses that are critical in responding to mycobacterial infection are cell-mediated immunity and the delayed hypersensitivity response
| |
| − | **Pathogenicity of mycobacteria depends on their ability to escape phagocytic killing, mostly imparted by the cell wall consitiutents:
| |
| − | ***Cord factor (trehalose dimycolate) – surface glycolipid responsible for serpentine growth in vitro
| |
| − | ***Suphatides – surface glycolipid containing sulphur which prevents fusion of phagosome with lysosome. cAMP secreted by the bacteria may also facilitate this.
| |
| − | ***LAM – heteropolysaccharide which inhibits macrophage activation by IFNγ and induces macrophages to secrete TNFα which induces fever and IL-10 which suppresses mycobacteria-induced T cell proliferation
| |
| − | ***The wax of the cell wall, peptidoglycans and other glycolipids are responsible for the adjuvant activity – attracts antigen presenting cells
| |
| − | ***Tubuloprotein – important antigen; purified tubuloprotein is the basis of the tuberculin test
| |
| − | **Mycobacteria are released from macrophages and also migrate within macrophages around the body
| |
| − | **Waxy cell wall contributes to the host immune response to the mycobacteria and the development of lesions
| |
| − | **Cell-mediated immune response with activated macrophages and sensitised T cells
| |
| − | **Delayed-type hypersensitivity response with granuloma formation
| |
| − | **Lesions contain macrophages, multinucleate giant cells and later a central area of caseous necrosis, giving a cheesy appearance
| |
| − | | |
| − | *Clinical signs
| |
| − | **Initially asymptomatic
| |
| − | **Loss of condition
| |
| − | **Cough and intermittent pyrexia with lung pathology
| |
| − | **Tuberculous mastitis with transmission via milk
| |
| − | | |
| − | *Diagnosis
| |
| − | **Tuberculin test - comparative intradermal test
| |
| − | **Avian and bovine tuberculin (purified protein derivative) is injected intradermally into two different clipped sites on the side of the neck
| |
| − | **Skin thickness at these sites is compared before and 72 hours after the injection of tuberculin with calipers
| |
| − | **Increases in skin thickness at the bovine PPD site of more than 4mm greater than the avian PPD site are seen as positive (reactor)
| |
| − | **Blood tests including the gamma interferon assay are being developed
| |
| − | **Laboratory examination of lesions, lymph nodes and milk
| |
| − | **Ziehl-Neelson staining of tissues
| |
| − | **Isolation requires Lowenstein-Jensen medium
| |
| − | | |
| − | *Control
| |
| − | **Eradication programs using a test and slaughter policy
| |
| − | **Reactors positive to the tuberculin test are slaughtered and restrictions applied to the affected herd
| |
| − | | |
| − | ===Avian tuberculosis===
| |
| − | | |
| − | *Caused by members of the ''M avium'' complex
| |
| − | *Depression, loss of condition and lameness in affected birds
| |
| − | *Granulomatous lesions in liver, spleen, bone marrow and intestines
| |
| − | *Diagnosis by Ziehl-Neelson staining of smears and post-mortem appearance
| |
| − | *Tuberculin testing of poultry
| |
| − | | |
| − | | |
| − | ===Feline leprosy===
| |
| − | | |
| − | *Caused by ''M. lepraemurium''
| |
| − | *Sporadic infections of cats via bites from infected rodents
| |
| − | *Subcutaneous nodules form usually on the head or limbs and can ulcerate
| |
| − | *Smears reveal Ziehl-Neelson-positive rods
| |
| − | *Diagnosis by histopathology
| |
| − | *Treatment includes excision of lesions
| |
| − | | |
| − | | |
| − | ===[[Intestines Proliferative Enteritis - Pathology#Paratuberculosis (Johnes disease)|Johne's Disease (paratuberculosis)]]===
| |
| − | | |
| − | *[[Intestines Proliferative Enteritis - Pathology#Paratuberculosis (Johnes disease)|Johne's Disease]] is a chronic, contagious enteritis of ruminants
| |
| − | *Caused by ''M avium'' subsp. ''paratuberculosis''
| |
| − | | |
| − | *Epidemiology
| |
| − | **Transmitted to young calves by ingestion of mycobacteria in faeces of infected adults
| |
| − | **Organisms viable in environment for long periods
| |
| − | **Long incubation period with clinical signs appearing in cattle over 2 years of age
| |
| − | **Subclinical carriers can occur, shedding organisms in their faeces
| |
| − | | |
| − | *Pathogenesis and pathogenicity
| |
| − | **''M avium'' subsp. ''paratuberculosis'' is an intracellular pathogen
| |
| − | **Mycobacteria are ingested by macrophages in the Peyer's patches
| |
| − | **Survival and replication of mycobacteria in macrophages initiate an immune-mediated granulomatous reaction
| |
| − | **Lymphocytes and macrophages accumulate in the lamina propria and submucosa, resulting in marked thickening and folding of the intestinal wall
| |
| − | **Mesenteric lymph nodes are enlarged
| |
| − | **A protein-losing enteropathy results, along with failure to absorb nutrients and water
| |
| − | | |
| − | *Clinical signs
| |
| − | **Diarrhoea, initially intermittent, and weight loss in cattle
| |
| − | **Weight loss in sheep and goats
| |
| − | **Rapidly fatal with weight loss and diarrhoea in some deer
| |
| − | | |
| − | *Diagnosis
| |
| − | **All diagnostic procedures have faults but include:
| |
| − | **Microscopy of rectal biopsies
| |
| − | **Faecal culture
| |
| − | **Serology of serum including complement fixation tests, agar-gel immunodiffusion test and an ELISA
| |
| − | **Histopathology of intestines and lymph nodes
| |
| − | **Isolation and identification of mycobacteria from faeces and tissues
| |
| − | **Ziehl-Neelson-positive smears
| |
| − | **Intradermal tuberculin test
| |
| − | **DNA probes for detection in faeces
| |
| − | | |
| − | *Control
| |
| − | **Slaughter of affected animals
| |
| − | **Detection and slaughter of subclinical shedders using faecal culture, DNA probes and ELISA
| |
| − | **Good hygiene to protect young calves
| |
| − | **Separation and isolation of calves from affected dams
| |
| − | **Inactivated adjuvanted vaccines are available and reduce shedding of mycobacteria but do not eliminate infection
| |