johnes Flashcards
explain aetiology of johne’s dx
caused by MAP resistant to disinfectants & abs survives >1y on pastures, survives well in slurry & water can infect other species: -sheep -deer -rabbits
what does MAP stand for?
mycobacterium avium subspecies paratuberculosis
epidemiology of johne’s?
transmission:
faeco-oral
transplacental
via milk/colostrum
w/i & btwn farms
btwn host species? potentially
when do 80% of johne’s infections occur?
within 1st month of life
=particularly susceptible
what are animals infected w MAP called?
supershedders
-can shed up to 100mil organisms/kg faeces
which animal group is most susceptible to MAP?
calves! (transplacental!)
less likely for older animals to pick up infection but still poss.
economical impacts of johne’s?
diff to estimate bcs:
-subclinical
-infected animals often culled for other reasons: lameness, infertility, reduced milk
can be high if valuable bull
becomes apparent @ age 3-5 so may impact greater in beef breeding animals due to reduced productive lifespan
where does MAP localise in the body?
GIT
-cell-mediated immune resp. may/may not eliminate MAP
what does MAP cause after localising in GIT?
chronic, granulomatous enteritis
thickening of intestinal wall, esp terminal ileum > results in PLE
CS of PLE?
decreased albumin (hypoabluminaemia)
prog. weight loss
D+
oedema
CS of johne’s (dairy)?
usually remain bright & appetent until terminal stages
reduced milk yield
increased ICSCC
reduced fertility
poor BCS
usually culled for poor perf: not v specific, can see increased culling rates
CS of johne’s (beef)?
poor fertility small calf born, does not do well poor BCS D+ peripheral oedema beef under less pdtn P
diagnosis of johne’s dx?
hx (herd & indiv lvl) CS detect ab: -serum ELISA -milk ELISA detect MAP organism: -faecal PCR -faecal smear -faecal culture -PM & histho
when do animals start producing Ab against MAP?
about 18mths of age gradual increase (can take up to 3y to hit detection threshold!)
if detect animal is infective but not showing CS = what stage?
preclin stage
how is serum ELISA testing carried out?
screening test
serology = plain tube ~50% se: false -ves poss.
99% spe
but beware after tb test! false +ves
how is milk ELISA testing carried out?
screened quarterly via milk recording
less se
false -ves & +ves
provides basis for many dairy herd control programmes
what to look out when doing faecal smear?
clumps of acid fasts
use Ziehl-Nielsen stain
false -ves v poss.
what diagnostic test is gold standard?
faecal culture
but can take several months
what is ELISA often used in conj w?
PCR testing - secondary test in some screening prog
more sensitive
what tests are used to establish herd status?
bulk tank ELISA: useful starting point but insensitive esp in low prev herds = false -ves
blood serology: 30 cow screen - select based on age/ICSCC
-all animals >2y
bioexlusion, test & cull strategies same as IBR (but no vax included! have vax but only avai. by import)
-
what entails the test & cull screening test?
ELISA-based -blood test all animals >2y annually -milk ELISA test quarterly cull +ves @ convenient time manage +ve cows as 'leper colony' johne's accredited free = 3x annual clear test
CHeCS dx status accred. lvl 1 =?
have been 3 clear annual herd tests
lowest lvl of risk
