Johne's Disease Flashcards
Johnes first described when? found in NA when?
Described 1895
First found in North America in 1908
nature of Johnes disease and species affected? causative agent?
Paratuberculosis or Johne‘s Disease (JD) is a chronic bacterial enteric disease of ruminants
Causative Agent: Mycobacterium avium subspecies paratuberculosis (MAP)
geographic spread and prevalence of Johne’s in Ontario
Worldwide (Ontario: ~30% of dairy herds, 3-5% within-herd test- positive prevalence)
Johne’s bacterial strains? how well do they survive in environment? what is the organism susceptible to? what about pasteurization?
- Mycobacterium paratuberculosis
- 3 distinct groups of strains
- Persist in pasture (without replication) for prolong period (≈ year)
- Organism is susceptible to: sunlight, drying, high pH, soil calcium content, and contact with urine and feces
- Can survive pasteurization (i.e. 63°C x 30 minutes)
Johne’s pathogenesis
- Ingestion > organism localizes in: small intestine mucosa, associated lymph nodes, tonsils and supra-pharyngeal lymph nodes
- Replication in small and large intestine
- Three possible group of animals:
> Infected resistant - Develop resistance, control infection, do not shed
> Intermediate - Partly control the infection, shed the organism
> Clinical - Organism persist in the intestine and these animals develop clinical disease
what species are affected by Johne’s? what ages? incubation?
- Affects: cattle, sheep, goats, llamas
- Prenatal infections occur
> Up to 40% of fetuses from cows with clinical paratuberculosis
> 18% of asymptomatic but “heavy shedding” cows
> Rarely from “light shedders” - Infection more common after birth
- Long incubation period
what age group is most susceptible to Johne’s? how does the disease usually present and progress? at what age are clinical signs generally seen, if at all?
- Calves have highest susceptibility
- Infection progresses very slowly
- Most MAP infected cows are subclinical
- Clinical signs usually seen around 3-6 yrs of age
apparent prevalence of Johne’s and individual and herd level in canada
individual level ~1%
herd level ~5%
how often is MAP found in the environment?
- ~15% of chute systems down to ~4% of calving pens. Overall present in about ~10% of environmental samples
- also can be found in worms, ~22% of drone fly larvae, ~2% of other flies…
Johne’s transmission
- Subclinically infected cows can shed MAP in manure, colostrum and milk
- Transmission: fecal-oral & vertical transmission
risk factors for Johne’s
- Herd size
- Annual birth rate
- Annual herd replacement rate
- Number of infected cows at time zero
- Number of replacements purchased each year
- Risk of purchasing an infected heifer
- Number of infected cow-calf contacts per year
- Stages of the Johne’ s disease
- Silent infection (Stage 1)
- Subclinical (Stage 2)
- Clinical (Stage 3)
- Advanced clinical disease (Stage 4)
nature of Johne’s silent infection (stage 1) - what age group and signs, shedding, tests,etc.?
- Animals less than 2 years of age
- No clinical signs, or changes on body weight or body condition
- May be shedding the organism
- Clinico-pathologic tests do not detect infection
- Fecal or tissue culture may detect the organism
nature of Johne’s silent infection (stage 2) - what age group and signs, shedding, tests,etc.?
- Carrier adult animals
- No clinical signs but would be affected by other abnormalities such as mastitis or infertility
- Most of these animals are negative in fecal culture (only 15-25% would culture +)
- Also, negative to most serological tests
- Would move to stage 3 if not culled
nature of Johne’s clinical disease (stage 3) - what age group and signs, shedding, tests,etc.?
- “Tip of the iceberg”of the number of affected animals in a herd
- Clinical signs usually appear after 2 years of age, normally between 2-6 years of age
- Cases appear sporadically
- Gradual loss of body weight/normal appetite * Diarrhea
- Decreased milk production
