Emergent Paratuberculosis disease: current and prospective knowledge

1
Emergent Paratuberculosis disease current and
prospective knowledge

• Dr. Gaddo Vicenzoni
• Via S. Giacomo, 5 - 37135 Verona
• Tel. [phone] - Fax [phone]
• E-mail gaddovic.izsv_at_interbusiness.it

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Taxonomic position of M. paratuberculosis
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Johnes disease

• 106 years after the first report of the disease,
  no compulsory treatment plans have been put into
  effect in any part of the world this is largely
  due to the difficulty of diagnosis

Johnes disease
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Johnes disease

• The disease causes intestinal lesions, which
  normally occur in adult animals
• Generally, in rearing establishments, incidence
  does not exceed 30
• The clinical form generally occurs in up to 10
  of animals reared

Johnes disease
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Johnes disease

• In the USA, the cost of Paratuberculosis in cow
  herds has been estimated at
• 100 /cow in moderately infected rearing
  establishments
• 200 /cow in herds with a high incidence of
  infection
• Ott S.L. et al. Prev. Vet. Med. (1999)

Johnes disease
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Economic losses

• Shedding from animals with the clinical form
• Lower dietary efficacy
• Lowered milk production (7 - 25 drop)
• Predisposition to contracting other diseases
• Restrictions on sale of live animals
• Decrease in the economic value of infected animals

Johnes disease
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Clinical symptomatology

• Relentless diarrhoea
• and consequent loss of weight

Johnes disease
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Johnes disease

• In ruminants, the microorganism infects the
  macrophages of the intestinal mucosa and the
  mesenteric lymph nodes, inducing a chronic
  granulomatous enteritis

Johnes disease
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Herd control plans

• Epidemiological knowledge
• Application of health regulations
• Correct use of diagnostic tools
• Therapy ! ! ! !
• Vaccination ????

Johnes disease
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Epidemiology and prophylaxis

• Orally/fecally transmitted disease
• Microorganisms are shed with the feces
• Clinical cases shed large quantities of
  microorganisms
• Subclinical cases may shed or not shed
  microorganisms

Johnes disease
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Epidemiology and prophylaxis

• Calves under 30 days old are the most susceptible
  animals.
• Calves remain at risk until 1 year of age

Johnes disease
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Epidemiology and prophylaxis

• The microorganism is dependant on Fe, the
  alkaline pH of the adult intestine selects
  competing flora, the acid pH in the calf
  increases solubility and thus the availability of
  this ion
• Reduction of the intestinal barrier required for
  passage of the Ig-G of colostrum

Johnes disease
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Epidemiology and prophylaxis

• Health regulations
• Hygienic collection of the colostrum
• Remove the calf from its mother
• Disinfection of areas for calving
• Rearing in individual cages for 1 month
• Rearing in homogeneous groups for 1 year
• Non-contamination of feeds with feces

Johnes disease
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Epidemiology and prophylaxis

• Other routes of transmission
• Colostrum/milk
• Transplacental
• isolation from the foetus in 50 of clinical
  cases
• isolation from the foetus in 9 of subclinical
  cases
• Bull semen
• Embryos (donors/recipients)

Johnes disease
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Epidemiology and prophylaxis

• Two objectives
• To reduce exposure of susceptible animals to
  infected material
• To identify and isolate cows positive to M.
  paratuberculosis

Johnes disease
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Johnes disease

• Physiological/pathological concepts of
  diagnostic importance

Johnes disease
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Johnes disease

• During the initial subclinical stage, animals
• Have non-detectable specific Ab levels
• Have increased production of INF-?,
• Show little shedding (often below the threshold)
  of microorganisms with the feces

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Johnes disease

• During the late subclinical stage, animals
• Show presence of specific antibodies
• Have decreased production of INF- ?,
• Shed medium-large quantities of microorganisms
  with the feces

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Response to two diagnostic tests
Johnes disease
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Johnes disease

• The clinical stage is characterised by
• abundant presence of antibodies
• decrease in the INF-? response
• high shedding of bacteria with the feces

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Direct diagnostic methods
Johnes disease
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Traditional cultural examination

• Diagnostic sensitivity 50
• varies on the basis of
• type of decontamination
• age of the animal
• evolutionary stage of the disease
• analytical sensitivity 104 CFU/g

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Johnes disease

• Cultural examination is currently the most
  sensitive and specific test we have.
• Herrold's egg-yolk agar with mycobactin
• liquid media (Middlebrook 7H9 modified medium)

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Johnes disease

• Identification and typification of the strain
  using molecular biology methods

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IS 900 - PCR
M 1 2 3 4
453 bp
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Indirect diagnostic methods
Johnes disease
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Johnes disease

• The cell-mediated immune response keeps shedding
  of the microorganism under control
• the appearance of a humoral immune response is
  associated with a decrease in the cell-mediated
  response, with consequent progression of the
  clinical disease and a coincident increase in
  shedding of the bacteria

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Johnes disease

• INF ? is the most sensitive method in the initial
  stages of infection.
• Sensitivity decreases as the disease progresses.
• It is not very practical
• In any event, it is limited by low specificity.

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Johnes disease

• The low sensitivity of the ELISA tests for
  detection of antibodies in animals with
  subclinical infection, poses notable diagnostic
  limits in individual animals.

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Sensitivity of ELISA Whitlock RH et al. ICP99
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Hypothetical distribution of normalised tests
Cut-off
Non-infected
infected
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Sensitivity of Ptb serological tests
IZSVR(2001)
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Specificity of Ptb serological tests
IZSVR(2001)
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Predictive value of ELISA with a DSn of 62 and a
DSp of 96
IZSVR(November 2001)
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Estimate of seroprevalence in Belgium (1 of
rearing establishments - 0.5 of animals)
Boelaert F et al. ICP99,p.76
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Estimate of seroprevalence in Holland(378
rearing establishments - 15,822 cows gt3 years)
Muskens J. et al. ICP99,p.207 DSn (0,3-0,4) DSp
(0,98-0,99)
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• GUIDELINES

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Johnes disease

• Guidelines for diagnostic activity in the
  presence of clinical cases
• samples of feces and serum, even frozen

Johnes disease
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Johnes disease

• Guidelines for diagnostic activity in the absence
  of clinical cases
• serological examination (ELISA method) on all
  animals older than 24 months
• confirmation of the ELISA positives with the AGID
  method
• confirmation of the ELISA positive-AGID negatives
  with a cultural examination or DNA probe

Johnes disease
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Johnes disease

• On the basis of the axiom that the DSn of ELISA
  in animals of ? 2 years is 25 and the DSp of the
  cultural examination is 100
• The probability of finding positivity in infected
  animals in a rearing establishmentthe with an
  incidence of 2 is 95.

Bulaga Collins ICP 1999,p.39
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Johnes disease

• Guidelines for infected rearing establishments
• rigid application of health regulations
• cultural examination from feces and serological
  examination once a year in animals older than 24
  months

Johnes disease
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Johnes disease

• Guidelines for unaffected rearing establishments
• 3 ELISA controls and 1 cultural examination
• control of possible sources of introduction of
  the disease

Johnes disease
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Voluntary plans of certification in unaffected
rearing establishments

• Standard track

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Standard track
Unknown herds
Infected herd
A -
abandon
A -
ELISA
C-
Level 1
85
Confirmation test
C-
B -
B -
ELISA
C-
Level 2
95
D -
Fecal culture
D -
C -
ELISA
C-
98
Level 3
C -
99
C-
Level 4
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Johne's disease Unit cost of examinations (VAT
exempt)

• cultural examination 18.08
• serological examination ELISA 2.58