Week 6

• Mycobacterium key characteristics

  cytochemically gram-positive, rod shaped

  aerobic

  non-spore forming, non-motile

  acid-fast bacilli (lipid and mycolic acid - cell wall)
• Mycobacertium key facts

  lipid rich walls (hydrophobic and resistant to adverse environmental influences)

  susceptible to pasteurization

  environmental saprophytes, opportunistic invaders, obligate pathogen

  pathogenic species grow slowly, complex egg-enriched media

  disease in domestic animals are chronic and progressive
• Mycobacterium

  major diseases include tuberculosis, Johne's disease, and feline leprosy
• pathogenic Mycobacterium

  M. tuberculosis complex - M. tuberculosis (humans), M. bovis (cattle)

  M. avium complex (poultry)

  M. lepraemurium

  M. avium subsp. paratuberculosis (ruminants)
• M. avium subsp. paratuberculosis essential growth supplement - mycobactin
• pathogenic Mycobacterium diagnostic procedures

  biohazard cabinet

  negative staining rods on Giemsa, pink on acid-fast staining

  grow slowly on solid media (saprophytes grow fast)

  commercially available liquid culture (BACTECT) - improved isolation time

  Lowenstein-Jensen medium is one of enriched medium used

  PCR from culture and clinical samples, culture to confirm viable bacteria in clinical samples
• PCR pathogenic Mycobacterium

  M. tuberculosis complex - 16S-23S, IS6110, IS1081 genes

  M. bovis - oxaR, pncA, gyrB genes

  M. avium subsp. paratuberculosis - IS900 gene
• mammalian tuberculosis

  M. tuberculosis complex
• Johne's disease

  M. avium subsp. paratuberculosis
• avian tuberculosis

  M. avium subsp. avium serotypes 1-3
• leprosy

  M. leprae - humans

  M. lepraemurium - cat
• mammalian tuberculosis key factors

  reemerging, granulomatous disease in animals and people

  chronic and debilitating disease

  bovine TB - important zoonosis in non-industrial countries, endemic in some wildlife species
• mammalian tuberculosis etiology

  M. tuberculosis complex - M. bovis, M. caprae, M. pinnipedii, M. microti

  survive months in the environment - cold, dark, and moist conditions
• tuberculosis in humans

  main reservoirs of M. tuberculosis

  emerging zoonosis and antropozoonosis

  infect dogs, cats, pigs, nonhuman primate, psittacine birds and canaries

  elephant to human transmission

  endemic infection - banded mongoose in Botswana, suricates in South Africa
• tuberculosis symptoms in humans

  fever, night sweats, persistent cough, blood phlegm, chest pain or shortness of breath

  pulmonary disease - more common in reactivated infection

  cervical lymphadenopathy, tonsillar, and preauricular lymph nodes in children

  humans infected through skin - localized skin disease (benign and self-limiting)

  genitourinary disease - can result in kidney failure
• bovine tuberculosis (M. bovis)


  worldwide distribution , notifiable disease

  indistinguishable from M. tuberculosis in humans

  reservoirs in wildlife (eradication difficult to achieve)

  zoonotic implications and economic losses
• bovine tuberculosis (M. bovis) transmission

  cattle - aerosol, ingestion, cutaneous, genital, congenital, asymptomatic carriers

  humans - ingestion of unpasteurized dairy products or undercooked meat, aerosol, breaks in skin, person-to-person (immunosuppressed)

  cats - ingestion, aerosol, bites and scratches

  pigs, ferrets, deers - ingestion

  badgers - bites and scratches
• bovine tuberculosis pathogenesis 


  virulence - lipid composition, survive and multiple in macrophages

  cell protein antigens - tuberculin

  engulfed by macrophages and dendritic cells

  survival in macrophages - cell wall glycolipid blocks phagosome-lysosome fusion

  cell mediated immune response important in destruction of bacilli
• if M. bovis survive cell mediated immune response, chronic granulomatous inflammation and formation of tubercle (type IV hypersensitivity)
• bovine tuberculosis pathogenesis

  infected macrophages secrete cytokines to recruit lymphocytes

  lymphocytes assist granuloma formation and containment of organism

  T lymphocytes secrete cytokines recruiting more macrophages

  gradual accumulation of macrophages around lesion with central necrotic core (tubercle or granuloma)
• granuloma facilitate interactions between macrophages and T cells and containment or destruction of pathogen

  granuloma may be histologically visible as early as 3 weeks after experimental infection

  rupture of granuloma allows dissemination - migration of macrophages containing viable mycobacteria
• bovine tuberculosis clinical signs in cattle

  evident only in advanced disease

  loss of condition as disease progresses

  advanced pulmonary condition - cough and pyrexia

  is mammary tissue involved - marked induration of affect quarters

  tuberculous mastitis facilitates infection of calves and cats
• bovine tuberculosis lesions

  older lesions - capsule formation and central caseous necrosis, consistency of soft cheese
• tuberculin skin test

  cellular response

  tuberculin prepared from mycobacteria - called purified protein derivative

  injected intradermally to detect sensitization - caudal fold followed by comparative cervical

  screen cervids
• increased in skin thickness at injection site of bovine PPD that exceeds avian PPD injection site by 4 times = evidence for infection, animal is termed a reactor
• PPD false postives 


  sensitization to mycobacteria other than M. bovis

  retest comparative cervical
• PPD false negatives 


  cattle before 30 days infections

  unresponsive state (anergy) may accompany advanced tuberculosis

  transient desensitization - retest 60 days

  immunosuppression due to stress (early post partum)
• M. bovis detection

  clinical disease + histopathology

  samples - lymph nodes, tissue lesions, aspirates and milk

  direct acid-fast stain

  culture - long and need special methods (BACTEC faster)

  DNA methods (PCR) for detection and identification
• M. bovis serological tests

  gamma interferon - detects infection at an earlier stage than the tuberculin test

  ELISA - later stages of infection; countries at early stages of eradication programs
• bovine tuberculosis control: avoid foodborne, direct contact, or contaminated environment
• M. bovis control

  test and slaughter

  decreased interactions between wildlife and domesticated animals

  rodent control

  sanitation and disinfection may reduce spread - moist heat of 121C for a minimum of 15 minutes
• avian tuberculosis (M. avium complex, serotype 1-3)


  worldwide distribution

  disease in companion, captive exotic, wild and domestic birds and mammals

  excreted in feces of birds with advanced lesions (transmitted by fecal-oral)

  survive for long periods in soil

  nonspecific signs; granulomatous lesions in liver, spleen, bone marrow and intestines at post mortem
• avian PPD injected into the skin of a wattle
• avian tuberculosis diagnosis

  post mortem findings

  ZN-positive bacilli in smears from lesions and PCR
• M. avium complex

  infections in immunocompromized humans

  pigs infected through ingestion of uncooked swill - smal ltubercles in lymph nodes
• Johne's disease or Paratuberculosis

  M. avium subsp paratuberculosis

  chronic, contagious, fatal enteritis affect domestic and wild ruminants

  cattle - persistent diarrhea, progressive weight loss, debilitation, eventually death

  economic importance for goat industry in Spain & sheep in Australia
• Johne's disease transmission

  excreted in large numbers in feces and lower numbers in colostrum and milk

  fecal-oral route

  feeding pooled colostrum = risk factor
• Johne's disease development of disease

  infection early in life, but clinical signs rarely develop in cattle less than 2 years old

  resistance to infection increases with age
• Johne's disease pathogenesis

  ingestion and uptake in Peyer's patches of lower small intestine

  infects macrophages in GI tract and associated lymph nodes

  multiplies and provoke chronic granulomatous enteritis (interferes with nutrient uptake leading to cachexia in advanced infections)
• Johne's disease clinical signs

  cattle- weight loss and diarrhea

  as disease progresses - diarrhea, weight loss, coat color may fade, ventral and mandibular edema, terminates in emaciation and death

  dairy cattle and goats - milk production may drop

  infected herds - 50% may be subclinically infected with associated production losses