Johnes

Question 1

what causes Johnes?

Answer 1

mycobacterium avium sub-sp paratuberculosis

Question 2

desc basic features of mycobacterium para-TB

Answer 2

slow growing
acid-fast
survives 2yrs in soil
lives in mphages –> granulomas in ilium + LNs

Question 3

what is the UK prevelance of johnes?

Answer 3

45% (4th year - 3-70% of UK herd are infected)

Question 4

desc the dz and signs?

Answer 4

>3yo, shows post-calving
d++ with bubbles
kg loss
bottle jaw (submand oedema)
seems 'happy' - BAR

Question 5

for every clinical case how many more are infected?

Answer 5

25, of which 30% are shedding!

Question 6

desc the transmission of johnes

Answer 6

face-poo
colostrum + milk (36% in heavy shedders)
20+% in clinical cases and 9% in asymptomatic cases via uterus
80% infected after birth, bw 0-4wo

Question 7

what is the economical importance?

Answer 7

4,000kg less milk prod in life
5x more lameness,
2x more mastitis, high SCC, more other dz (LDA)
1.8x more GI and resp disease

Question 8

disease progression, desc the immunological steps

Answer 8

CMI response fails to destroy (as live in mphages..)
the Th2 (ab) starts too late to get ahead and so the dz progresses

Question 9

what is the gold std to dx johnes

Answer 9

faecal culture

60% sensitivity

Question 10

control of johnes

Answer 10

vaccination - not pos as reacts with BCG test
reduce stress
prevent new calve infections
- do milk ELISA 4x yr
- green, yellow and red cows
- snatch calve
- very clean pens
- milk replacer/tested infection free frozen colostrum
-

Question 11

how can you ID a culture of mycobact. avian subspp para-tb

Answer 11

ZN staining - red

Question 12

what are the sub-clinical effects of Johnes

Answer 12

>50% losses (in total)
reduced yield
mastitis and high SCC 
infertility/reduced
lameness
LDA inc likelihood
inc cull rate

Question 13

shoud you trust the result of the ELISA

Answer 13

YES. if its +ve particularly - assume she is infectious

- as to have Ab suggests her CMI immunity failed at some point and so Th2 instead.

Question 14

what does ELISA -ve mean then - not infectious

Answer 14

it means that Th1 SI working if she is infected.. doesn’t mean she is either yet

Question 15

how many cfu does a super shedder shed

Answer 15

> 1 million cfu/g (poo)

Question 16

the culture is gold std, but how good is the ELISA in comparison

Answer 16

it will detect 40% of the culture +ve cows, as ELISA +ve

ELISA should be done 60d AFTER TB test

Question 17

what is sensitivity based on

Answer 17

the comparison to the gold standard

Question 18

what is specificity based on

Answer 18

the comparison against the general population

Question 19

why is the culture not v popular?

Answer 19

+ve result in 10d; -ve result in 3mths

Question 20

how can you reduce transmission of johnes

Answer 20

snatch calve
calve outside
clean/clip teats before calving
traffic light system
test and cull
ELISA 3xyr
test milk freq
avoid cohab with sheep and rabbits
no manure on pasture
no stagnant ponds