Changes

Jump to navigation Jump to search
8,410 bytes removed ,  10:44, 14 May 2010
Line 1: Line 1: −
{{review}}
+
#REDIRECT[[:Category:Mycobacterium 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 4cm 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
 
Author, Donkey, Bureaucrats, Administrators
53,803

edits

Navigation menu