Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
55 Cards in this Set
- Front
- Back
|
Mycobacteria basic info
|
-acid-fast bacilli (rod shape)
-non motile -aerobic -non spore forming |
|
|
Mycobacteria cell wall
|
-cytochemically gram positive
-however, the high lipid and mycolic acid content of their cell walls prevents uptake of the dyes employed in the gram stain -bacilli stain red in the Ziehl-Neelson staining method and is therefore called acid-fast or ZN positive |
|
|
Mycobacteria species
|
-many species in genus including: pathogens, opportunists, and saprophytes (organisms which obtain nutrients from dead organic matter)
-host preference |
|
|
Robert Koch
|
-1882 first isolation of mycobacterium tuberculosis
|
|
|
M. tuberculosis
|
-infects man and primates
|
|
|
M. bovis
|
-cattle, goats, deer, boar, badgers
-can infect humans but won't be sustained or transmitted |
|
|
M. avium subspecies paratuberculosis
|
-cattle, sheep, deer
|
|
|
M. avium complex
|
-most avians
|
|
|
M. lepraemurium
|
-rats, mice
|
|
|
Mycobacterium habitat
|
-lipid rich walls make them hydrophobic and resistant to adverse environmental influences
-environmental (atypical) mycobacteria are found in soil, on vegetation and in water...this includes Mycobacteria OTHER Than TB (MOTT) -obligate pathogens, shed by infected animals, can also survive in the environment for extended periods of time |
|
|
Mycobacteria-pathogen characteristics
|
-ZN staining method is used to differentiate mycobacteria from other bacteria
-pathogens grow slowly on solid media and colonies are not evident until cultures have been incubated for 3-6 weeks (37 degrees C) (m. avium 37-43 degrees C) -distinguished by their colonial appearance on egg-based media -disinfectant resistant and heat susceptible -pasteurisation kills pathogens |
|
|
Egg based media
|
-glycerol: M. tuberculosis
-sodium pyruvate: M. bovis -mycobactin: M. paratuberculosis |
|
|
Biochemical reactions for differentiation
|
-use nitrate reduction or niacin production
-move to genetic methods such as PCR: target genes that are present in one strain but not the others |
|
|
Bovine tuberculosis epidemiology (M. bovis)
|
-worldwide distribution
-eradication in some countries: Australia, France, Germany, Netherlands, etc. |
|
|
M. bovis transmission
|
-although it can survive for several months in the environment, transmission is mainly through aerosols generated by infected cattle (close contact)
|
|
|
M. bovis wildlife reservoirs
|
-badgers, deer, possums
-makes disease eradication difficult to achieve |
|
|
Virulence of M. bovis
|
-relates to its ability to survive and multiple in host macrophages
-specific toxins have not been identified, but rather virulence is a consequence of many pathogen factors working in concert to establish infection -cell wall lipids have immunomodulatory properties |
|
|
Host response to M. bovis
|
-cell mediated immune response
-delayed-type hypersensitivity reaction |
|
|
Clinical signs and lesions of M. bovis
|
-depend on immune response
-overactive immune response leads to the formation or lesions |
|
|
Pathogenesis of M.bovis
|
1. Following entry to the host via the respiratory tract, mycobacteria are engulfed by macrophages and dendritic cells
2. Mycobacterium engulfed by dendritic cells travel to the draining lymph nodes 3. Macrophages accumulate and secrete a range of cytokines which recruit lymphocytes to the lung thus aiding in granuloma formation 4. The gradual accumulation of macrophages around the developing lesion and the formation of a central necrotic core result in a tubercle or granuloma |
|
|
Tubercle: effective cell mediated immunity
|
-lesion is localized and arrested
-no shedding |
|
|
Tubercle: ineffective cell mediated immunity
|
-two outcomes:
1. active pulmonary tuberculosis: aerosol shedding and fecal shedding 2. generalized tuberculosis: shed in mucus, feces, urine and milk |
|
|
Tubercle structure
|
-fibroplasia produces early capsule formation and there is an area of central caseous necrosis
-appearance and consistency of soft cheese |
|
|
Anergy (immunologic tolerance)
|
-refers to the failure to mount a full immune response against a target
-immune cells get exhausted and won't respond to diagnostic test |
|
|
Clinical signs in M. bovis
|
-only evident in advance disease
-cattle with extensive lesions can appear to be in good health -loss of condition |
|
|
Tuberculin test
|
-based on a delayed-type hypersensitivity to mycobacterial tuberculin
-reactivity in cattle is usually detectable 30-50 days after infection -tuberculin is injected intradermally to detect sensitization |
|
|
Tuberculin
|
-prepared from mycobacteria
-called purified protein derivative (PPD) |
|
|
Two methods of tuberculin testing
|
1. single intradermal test
2. comparative intradermal test |
|
|
Single intradermal test
|
-bovine PPD is injected intradermally into the caudal fold of the tail
-injection site is examined 72 hours later -positive reaction is characterized by a hard or edematous swelling -sensitivity is high, but specificity is low -will detect every infected animal but will also pick up non infected animals |
|
|
Comparative intradermal test
|
-avian PPD and bovine PPD are injected intradermally into separate spots about 12 cm apart
-skin thickness is measured before injection and 72 hours later -an increase in skin thickness at the injection site of bovine PPD which exceeds that at the avian PPD injection site by 4mm or more is interpreted as evidence of infection and the animal is termed reactor |
|
|
Gamma interferon test (IFN-g)
|
-blood based test that is used in conjunction with tuberculin test
-identifies animals at a slightly earlier stage of identification than the TB test |
|
|
Direct microscopy diagnosis of M. bovis
|
-positive ZN staining of bacilli in smears from colonies
-histopathology for tubercle formation |
|
|
Isolation of M. bovis
|
-requires decontamination of specimens to eliminate fast growing bacteria
-slants of Lowenstein-Jensen medium, without glycerol and containing 0.4% sodium pyruvate, are inoculated and incubated aerobically at 37 degrees C for up to 8 weeks -culture is gold standard |
|
|
Molecular techniques for typing M. Bovis
|
-move away from biochemical tests (take too long)
-problem with PCR: doesn't tell you if pathogen is dead or alive, where a culture is obviously alive and growing -molecular epidemiology |
|
|
Bovine TB Control
|
-treatment not carried out
-vaccination not use: can't tell if animals is vaccinated for infected -test and slaughter -meat inspection: look for lesions -wildlife reservoirs: cull and vaccinate? (hard to do) |
|
|
Other members of M. tuberculosis complex in wild mammals
|
-M. microti: shrews, etc.
-M. pinnipedi: seals -M. mungi: mongoose -Dassie bacillus: causes TB in the dassie (type of rodent) |
|
|
Paratuberculosis (Johne's disease)
|
-chronic, contagious, invariably fatal enteritis (inflammation of SI) which can affect domestic and wild ruminants
-aetiological agent: M. avium subspecies paratuberculosis (MAP) -acid-fast short bacilli -particular growth requirements: medium containing mycobactin supports growth -may be associated with Crohn's disease in man |
|
|
Paratuberculosis epidemiology
|
-most cattle are infected as calves (<30 days old) by ingestion of MAP through fecal oral route
-adult animals can also become infected but it is rare (usually immuno-suppressed animals such as those with BVD) |
|
|
Incubation time for paratuberculosis
|
-variable
-typically 2-5 years -more prevalent in dairy because of production stress -early infection more likely to be followed by clinical disease |
|
|
Subclinical carriers of paratuberculosis
|
-signs of disease do not develop in all infected animals
-some becomes subclinical carriers and shed mycobacteria intermittently in their feces -organisms survives up to 1 year in environment |
|
|
Paratuberculosis pathogenesis
|
-intracellular pathogen
-cell mediated reactions are mainly responsible for the enteric lesions -the organisms are engulfed by macrophages in which they survive and replicate -T helper cell activity depressed -granulomatous lesions in wall of SI and LI -enteropathy with loss of protein and malabsorption |
|
|
Clinical signs of paratuberculosis in cattle
|
-persistant diarrhea
-emaciation |
|
|
Clinical signs of paratuberculosis in sheep
|
-weight loss
-may be no diarrhea |
|
|
Diagnosis of paratuberculosis
|
-cattle: mucosa of terminal SI and LI thickened and folded, lymph nodes enlarged
-sheep: less thickening, caseation of lymph nodes -scrapings and pinch biopsies from rectum-stain by ZN |
|
|
Diagnosis for paratuberculosis: poor sensitivity
|
-problem differentiating status
-infected, infectious, affected? -which animals to target? |
|
|
Culture of paratuberculosis
|
-difficult but sensitive
1. decontamination of specimen followed by centrifuge to concentrate the pathogen 2. inoculate the concentrated pathogen on Herrold's egg yolk medium with mycobactin 3. incubate at 37 degrees C for up to 16 weeks |
|
|
Serology of paratuberculosis
|
-ELISA: antigens specific for M. paratuberculosis
-low sensitivity (10-30%) *fecal culture maybe around 20-30% sensitive |
|
|
Johnin skin test
|
-cell mediated immune response
-counterpart of tuberculin PPD -reliability of test is questionable -may sensitize cattle to tuberculin so it's not used |
|
|
Gamma interferon assay
|
-cell mediated immune response
-widely used for early detection -sensitivity and specificity is variable |
|
|
PCR of paratuberculosis
|
-sensitive
-still technical difficulties (PCR from feces is difficult) |
|
|
Paratuberculosis control
|
-isolation, confirm diagnosis and slaughter
-disease control is currently voluntary not statutory -BUT control program is being introduce to IRE -detection and culling of subclinical excretors: fecal culture every 6 mo, PCR on feces, ELISA -separate calves from dams at birth -vaccination available for sheep: Weybridge live vaccine |
|
|
TB in dogs and cats
|
-M. tuberculosis: inhalation
-M. bovis: ingestion of milk/meat -diagnosis by ZN smear and culture -Do not treat: zoonotic risk of infection |
|
|
Feline leprosy
|
-M. lepraemurium
-bites from rodents -nodular lesions in the skin, frequently ulcerate -large numbers of ZN positive bacilli in smears -difficult to culture -opportunistic mycobacteria can also cause skin lesions |
|
|
M. avium complex
|
-disease in free range domestic poultry
-opportunistic infections in animals (pigs, cattle) -sensitize cattle to tuberculin |
|
|
Skin tuberculosis in cattle
|
-unspecified acid fast bacilli
-sensitize cattle to tuberculin |
