Johnes disease

What is the causative agent of Johnes disease?

Mycobacterium avium subspecies Paratuberculosis

What type of bacteria is Mycobacterium paratuberculosis?

• obligate intracellular pathogen

• Slow growing, fastidious acid fast bacillus

• member of Mycobacterium avium

• once infected —> infected for life

How long can Mycobacterium paratuberculosis live in the environment?

• 12 months in water

• 2 years in soil (low pH increases survival

What are the different types of MAP?

• Bovine or Type II (or C for Cattle) strains

• Sheep or Type I (S) strains

How does Johnes disease present pathologically?

• MAP in macrophages

• Granulomata in distal ileum & LN

  • infect macrophages & Lymph

• Cattle – diffuse thickening of distal ileum and colon

  • Lymph node involvement

  • Thick, corrugated intestine

What is the presentation of Johnes disease in clinical disease?

• older animals: >3yrs

• often seen after calving (stress)

• profuse diarrhoea (+/- bubbles) —> protein losing enteropathy

• weight loss

• bottle jaw

• BAR + DUDE

Why is this concerning?

• pooled milk so may infect many calves

• ok setup if milk replacer being used

• high risk of transmission if waste milk

What is the link of crohne's disease with johnes?

• mycobacterium avium ss. paratuberculosis has been found in some cronhes biopsies

• means crohne's may have many types some of which related to MAP

What is the effect of johnes disease on cattle + production?

• reduced milk yield

• increased risk of mastitis/ SCC/ digestive disease/ resp. disease

• Impaired mucosal barrier function

• malabsorption (& consequently diarrhoea)

• protein losing enteropathy (& consequently muscle wastage, hypoproteinaemia, oedema)

What is the difference between a clinical and sub-clinical case?

clinical is

• actively shedding

• ELISA +ve

  • lost immune control

List susceptible members of a herd to Johnes

most to least likely

• new born calf

• young heifer

• old cows and heifers

• before birth (in utero- dam is clinical)

What are the Johnes infection routes in young cows?

• faeco-oral transmission

• in utero (transplacental)

• dirty environment

• dam faeces

  • teat or environment

• colostrum- dam or pooled

What affects the likelihood of johnes infection?

Dam shedding status

How does the immune system respond to Johnes disease infection?

• infection as calf

• MAP in macrophages

• cell mediated immunity protective

  • halts disease progression

  • no shedding

• if cell mediated immunity fails —> disease progresses

  • antibody response

    • suppresses CMI

    • Shedding occurs

    • infectious

What are the different types of shedders?

Infectious

• low

• high

• super

infected but not shedding

How can Johnes disease be diagnosed?

• faecal culture +/- PCR (can also perform on blood + milk)

  • detects shedders (> threshold)

• ELISA (serology)

  • detects antibodies

  • probably a shedder

• Actiphage

  • releases DNA of MAP for PCR

• gamma interferon

  • detects cell mediated immunity

• PCR

• Stained faecal smears

• Tissue biopsy

• Postmortem examination

What are the pros and cons of:

• culture

• PCR

• ELISA?

What are the good standard diagnostic tool for Johnes disease?

Faecal culture

• detects shedders

  • affected by intermittent shedding

• lower sensitivity to PM biopsies

PCR

• use pooled samples

• higher sensitivity than culture for shedders

Outline sampling for Johnes detection

• milk/ blood antibodies

• to detect infection in herd

• select cows most likely to be +

  • thin,

  • mastitis

  • lame

  • poor yield

  • older

• can sample over period

How does ELISA work for Johnes Dx?

• detects antibodies

  • animal clinical

• sensitivity dependent on

  • age distribution of herd

  • stage of disease

  • sample: different cut-off values with milk or blood

What is the most sensitive testing programme for Johnes?

• repeated whole herd screens

What is phage testing?

• uses an antiphage (virus that targets bacteria) to lyse the MAP bacteria and increase the sensitivity of the PCR test

• try to increase sensitivity

Does a negative ELISA confirm the cow is free fromthe disease?

could be in cell mediated stage of disease + antibodies not yet being produced

What is a super shedder?

> 1 million cfu/g faeces

(colony forming units per gram)

List types of antibody testing strategies

• quarterly milk testing

  • allows creation of risk groups

• single test- pre dry off

  • segregate + animals away from low risk cattle

• double test- pre-dry off and pre- breeding

  • allows additional info for breeding decisions to be made

What is the most common route of transmission?

INGESTION > transplacental

Outline control of Johne's disease

• reduce transmission to young stock

  • reduce risk factors

  • cull animals likely to be shedding

  • possible faecal PCR testing of young stock

• improve husbandry

How can risk factors of Johne's be reduced?

• avoid faeces

• calving area: snatch calving at birth

• cleaning calving/ calf pens

• separate young stock from adults

• only dam's colostrum

• no pooled colostrum or waste milk feeding

What is the effect of colostrum use on Johne's transmission?

• frozen colostrum

  • from heifers

  • from test -ve cows

• Do not feed pooled colostrum or waste milk

• do not use on-farm pasteurised milk or milk replacer

  • potential contamination

What are some other transmission risk factors of Johne's?

• slurry / manure spread whilst grazing

• water courses esp. stagnant water

• contamination of feeds

• other hosts

  • sheep, deer, rabbits

How can the risk of purchasing animals into the herd be reduced?

• from low risk herds

  • no Hx

  • test negative on last 3 tests

    • CHeCS level 1

  • ELISA test result history of whole herd (or individual)

  • faecal culture indicidual

What breeds of beef sucklers is Johne's a problem?

Welsh blacks

Limousin

How can farm management be improved for Johne's control in beef sucklers?

• outdoor calving

  • or move outside immediately after calving

• cull daughters

• clip and clean teats prior to calving

• CHeCS level 1 clean bull

What is the affect of MAP and bTB on each others testing/ diagnosis?

• MAP may give false –ve to TB test

  • reacts +ve to avian ppd (“bigger top lump”)

    • TB test compares avian ppd and bovine ppd reactions

    • i.e. reduces TB test sensitivity

• TB test will give “false +ve” to MAP ELISA test

  • ensure 60-day time lag between TB test & ELI