What is Johne’s disease?

Johne’s disease is a bacterial infection of the intestine which primarily affects domesticated ruminant animals (cattle, deer, sheep, goats and alpaca). The infection causes the intestinal tissues to become thickened and inflamed resulting in reduced uptake of nutrients. The disease is chronic, infectious and progressive and results in decreased productivity, wasting and ultimately death. Johne’s disease is sometimes also referred to as paratuberculosis.
Johne’s disease is a straightforward bacterial infection caused by the bacterium Mycobacterium avium subspecies paratuberculosis, also known as MAP. Progression of the disease may be triggered by additional physiological stressors such as poor nutrition, parasitism, calving, weaning, lactation, transportation, social mixing or adverse environmental conditions.
Johne’s disease is primarily a condition of farmed ruminant species (cattle, deer, sheep, goats and alpaca). MAP infection (as distinct from Johne’s disease) has been observed in diverse species including rabbits, possums, hares, hedgehogs, stoats, cats and even ducks.
  • Overt signs of early stage clinical disease may be subtle, with mild weight loss and/or reduced milk yield.
  • Infected animals may lose weight or be unable to gain weight despite good appetite.
  • More severe disease will often, but not always, manifest with profuse and chronic, watery diarrhoea which does not respond to treatment and which may be intermittent. This is less common in sheep and goats. As the disease progresses, animals become progressively more emaciated and dehydrated.
  • Periods of remission may be seen in which affected animals appear to improve in condition.

How common is Johne’s disease in New Zealand?

Recent estimates suggest that as many as 60% of NZ dairy herds may now harbour some MAP infection, with 10% of herds experiencing clinical disease on farm. Similarly, 60% of deer herds, 31% of beef herds and 68% of sheep flocks are estimated to be exposed to MAP infection, although within herd incidence of clinical disease is much lower.

Is there a coordinated national approach for Johne’s disease control in New Zealand?

No. Unlike Australia, Canada, Denmark, France, Ireland, The Netherlands, the UK and the US, New Zealand has no coordinated surveillance or management schemes in place.

Why is Johne’s disease a problem?

In addition to animal health and welfare concerns, Johne’s disease is a production limiting disease which impacts upon growth, milk yield and fertility and imposes capital losses due to premature culling or death. On top of these production losses, the presence of Johne’s disease on an affected property causes significant indirect costs through constraints on management and restrictions on stock movements as well as causing tangible distress to herd owners. Of growing concern also is a reported association between MAP bacteria in dairy derived foodstuffs such as infant milk formula and Crohn’s disease in humans which has led many countries to establish national control programmes.

How do animals get infected?

Younger animals are most susceptible to MAP infection and the most common route of infection is faecal-oral. In calves the greatest risk of infection occurs before 30 days of age and usually occurs when young animals suckle teats contaminated by faecal material or graze MAP contaminated pasture. The feeding of colostrum from infected mothers is also considered a significant risk factor for MAP transmission to young animals. Intrauterine infection of the developing foetus has also been reported in the case of heavily-infected dams.

How do I know if Johne’s disease is in my cows/deer/sheep/goats/alpaca?

Although visible indicators of late stage disease typically include diarrhoea and progressive weight loss despite good appetite, these physical signs are also associated with a number of other conditions and should not be considered uniquely diagnostic for Johne’s. In addition, animals exhibiting physical symptoms arising from Johne’s disease will only be the tip of the iceberg and for every clinically affected animal, a minimum of 25 other animals are likely to be infected but asymptomatic. The only way to know for sure is through laboratory testing. Cull animals should have their Johne’s status confirmed.

How do I prevent Johne’s disease from entering my herd/flock?

Johne’s disease is usually ‘bought and paid for’ by introducing infected replacement animals into an otherwise clean, MAP-free environment. Avoid introducing MAP to your property by observing good biosecurity practices; operate a closed herd/flock or, failing that, only purchase from sellers with a verifiable, JD test negative history and test any replacements brought onto the property before they arrive. Quarantine new stock and ensure boundary fencing is secure. Avoid cograzing young and adult stock; a top priority should always be to reduce/eliminate calf and heifer exposure to adult faecal matter. Don’t allow replacement heifers to share grazing with adults or follow adult stock in a rotation.

Does Johne’s disease affect productivity?

Absolutely. In addition to animal health and welfare concerns, Johne’s disease is a production limiting disease which impacts upon growth, milk yield and fertility and imposes capital losses due to premature culling or death. On top of these production losses, the presence of Johne’s disease on an affected property causes significant indirect costs through constraints on management and restrictions on stock movements. Many studies have found MAP infection to be associated with a significant reduction in milk production in dairy cows. Our experience suggests that daily milk solids production is 4% less for infected cows, 6% less for moderately diseased cows and 12% heavily diseased cows shedding large numbers of bacteria, compared with uninfected cows.

How does Johne’s disease spread between different farms?

Most commonly through the purchase and introduction of infected stock. Johne’s disease is an infection of the intestine and the single greatest risk factor for disease transmission is contact with faecal material from infectious animals; anywhere that may be contaminated by faecal material from unknown animals such as stock trucks or shared water schemes should be considered potentially contaminated with MAP. Airborne transmission is not generally considered to be a risk factor for MAP although the bacteria maybe become aerosolised if effluent is sprayed onto nearby paddocks.

Can I control Johne’s disease?

Johne’s can be successfully controlled through careful planning and management, supported by test informed culling of high shedding animals and expert advice. Unlike tuberculosis (caused by the closely related Mycobacterium bovis) complete eradication of Johne’s disease at any level (on farm, regionally or nationally) is not considered feasible, achievable or likely and control efforts are instead focused upon cost-effectively managing clinical disease and associated production losses out of the herd.

How long can MAP bacteria last in the environment?

MAP bacteria can only multiply once inside the immune cells of a suitable host but following shedding may lie dormant outside of the animal host for long periods on pasture. Studies suggest that, in a temperate climate such as in NZ, viable MAP bacteria can persist under moist conditions in the environment in soil, dung and water for as long as 18 months. Conditions which promote killing of environmental MAP bacteria include desiccation and UV exposure through exposure to sunlight.

How should I collect/submit a sample to DRL for testing?

Serology (ETB/ParalisaTM)

  • Blood (serum or plasma tubes; min. 3ml).
  • While refrigeration is desirable it is not essential; please protect samples from extremes of heat or cold.
  • Do not freeze.

Faecal PCR

  • 5-10g of dung (about a tablespoon) from each individual, cleanly pottled and labelled, is all we require (while we can work with less, this is what we ask folks to aim for…).
  • The most important thing to remember when collecting and sending samples is to avoid any chance of cross-contaminating the samples. Tightly closed, plastic sample pottles work well (we can forward these on request; plastic ziplock bags or similar are not suitable have been known to fail quite catastrophically in the past…).
  • Dung samples freshly deposited on the ground are perfectly fine also – as long they can be unambiguously linked to their originator and land on an otherwise clean surface.
  • Always be sure to change gloves between each individual.
  • If sample pooling is requested, send individual samples as we will carry out the pooling here; that way we can easily retest individuals from positive pools as required. If a pool is positive, we will contact you concerning your preference for individual sample re-testing.
  • Send the samples in as soon as possible (but know also that they are quite all right for several days at ambient temperature).
  • Send the samples, preferably by overnight courier, to –
    Disease Research Ltd,
    Invermay Agricultural Centre,
    176 Puddle Alley,
    Mosgiel 9053.
  • A heads-up phonecall (03 4894832) or email (drl@otagoinnovation.com) to let us know they’re coming is always appreciated.

Can I treat an infected animal?

No. Animals with Johne’s disease don’t respond to any form of treatment. There is no cure and animals should be culled as soon as the diagnosis is confirmed.

Can Johne’s disease be cured?

No. Animals with Johne’s disease don’t respond to any form of treatment. There is no cure.

Can I vaccinate against Johne’s disease?

Vaccination may be an option for some species although currently available vaccines may cause false positive reactions with the TB skin test and are not commonly used in NZ cattle or deer herds. While vaccination does not prevent infection or disease, it may lessen or delay the onset of clinical disease and reduce overall shedding. We advise speaking with your veterinary practitioner.

What should I do if I have an animal that tests positive for Johne’s disease?

Generally speaking, test positive animals should be culled as soon as possible. Depending on herd prevalence, this may not be economically feasible or sensible. The advantage of fPCR test offered by DRL is that it measures the quantity of MAP bacteria within a faecal sample which in turn is a reliable measure of disease severity. Used singly or in conjunction with ELISA this test may be used to prioritise the elective culling of only those most seriously affected individuals which contribute the greatest infection risk for the remainder of the herd. This provides the farmer with assurance that they are making the best culling decisions as the most seriously affected animals are by far the biggest threat to the rest of the herd while less affected animals might be flagged for monitoring, rather than immediately culled.

What are common sources of MAP bacteria?

The single greatest source of infectious MAP bacteria is an actively shedding, Johne’s disease affected animal.

Is there a wildlife reservoir for MAP bacteria?

MAP infection has been found in all of the major farmed ruminant species and, while MAP has also been isolated from wildlife species such as rabbits, possums, hedgehogs, weasels and stoats, it is likely that wildlife species serve only as dead-end hosts. The vast majority of MAP transmission occurs between animal contact on farm due to affected animals shedding MAP bacteria directly into their environment.

Other than culling of test-positive animals, are there any other effective management practices which should be put in place in minimise the impact of Johne’s disease?

There are many useful, industry-relevant JD resources available to farmers prepared by the Johne’s Disease Research Consortium and their advisors. Links to some of these resources can be found in our Resources section.

Can humans get Johne’s disease?

The term Johne’s disease refers specifically to the manifestation of MAP infection in affected ruminant animals. The organism that causes Johne’s disease in animals, MAP, is not currently known to cause disease in humans, but has been detected occasionally in humans with Crohn’s disease, as have numerous other bacteria and viruses. This is not a consistent finding however and MAP or evidence of MAP is also reported in people not suffering from Crohn’s disease. There is currently no definitive or widely accepted evidence proving that MAP causes Crohn’s disease in humans. However, the spectre of any association between MAP bacteria in the food chain and inflammatory bowel disease in humans has led many countries to establish national surveillance or control programs aimed at reducing the amount of MAP bacteria entering the food chain in milk and value added dairy products in response to potential consumer pushback.