Johne's disease

Johne's disease is an infection of the small intestine by the bacteria Mycobacterium avium subspecies paratuberculosis (MAP for short). It is most common in farmed ruminants but can occasionally be found in other species too. Initial infection generally occurs when the animal is very young. Following this is a 'latent' period where the animal is infected but apparently healthy as the bacteria is essentially dormant within it. The latent period may be short or extend for years. Clinical signs of disease may emerge after times when the animal has been under stress.

The disease is caused by a bacterial infection (Mycobacterium avium subspecies paratuberculosis) in the gut. The infection starts in the small intestine and spreads to the related lymph nodes. As the disease advances the intestinal walls thicken, reducing digestion and absorption of nutrients and causing the characteristic diarrhoea.

Animals developing Johne's disease pass through a range of worsening clinical signs. The signs begin with a drop in productivity which may mean a failure to gain live weight, or weight loss, and a drop in milk production in dairy animals. This is followed by scouring and particularly foul smelling diarrhoea which leads to severe emaciation and eventually death.

They can go from healthy looking to severely ill in a couple of months.

In weaner and yearling deer outbreaks of Johne's disease are occasionally severe, affecting around 20 - 30% of a mob. In adult deer the disease usually only causes sporadic cases.

Why is Johne's Disease a problem?

It is a major cause of economic and productivity loss at the farm and industry level. Sporadic serious outbreaks on infected farms are a major animal health issue.

It is also difficult to control and it is present on many sheep, beef, and dairy farms in New Zealand. The complex nature of the infection cycle means a concerted effort is needed to control it.

It can cause false positive reactions to the test for bovine tuberculosis (Tb). Lesions caused by Johne's disease have an identical appearance to Tb lesions which complicates the control of this other important disease.

Johne’s Disease (JD) is caused by a bacteria (Mycobacterium avium subspecies paratuberculosis – or MAP for short). It was first isolated by german veterinarians Dr H A Johne and Dr L Frothingham in 1894. It is a very close relative of the bacteria that causes tuberculosis in cattle (Mycobacterium bovis). Today JD is a significant animal health issue worldwide in developed livestock industries, particularly dairy, but also sheep and deer. It can also be found in the environment and occasionally in some species of wildlife.

Johne’s disease typically enters an uninfected farm via the purchase of apparently healthy but infected stock. Diseased animals can shed millions of bacteria in every gram of their faeces, contaminating their environment.

Young deer are by far the most susceptible to infection, especially in the first few months of life. Infection occurs mainly when they consume feed, milk or water contaminated with faecal material from diseased animals. But once infected, they remain apparently healthy for an indefinite period until something triggers the disease phase, often stress related.

Sporadic cases also occur in mixed age deer. Severely diseased hinds can also pass the bacteria on to their fawns through the placenta, colostrum or milk.

Host range

Ruminant species are the main hosts for MAP.  From a farming perspective the most important hosts are cattle, deer, and sheep. The organism can also be found in a wide range of other ruminants and, occasionally, non-ruminant species.

JD affects farmed animals worldwide. It is probably more of a problem in farmed ruminants than in wild ruminants because of the higher density of animals on farms, which leads to higher contact rates between infected and susceptible animals and higher levels of contamination than would be found in the wild.

Disease process

JD affects the small intestine.  Typically, the bacteria enters the young deer by ingestion of infected faeces or milk and is then taken into the host’s own cells near the small intestine. The bacteria then sits dormant until triggered to multiply. The exact trigger(s) are not well understood and could range from various stresses like nutrition, climate, social stress, long distance transport and parasite burden. The trigger may also be influenced by the genotype of the animal.

Once triggered, the bacteria multiply and the host's immune system responds in an attempt to control the growing infection. The struggle between the bacteria and the host causes the wall of the intestine to thicken and this reduces the ability of the host to absorb nutrients from its food, resulting in diarrhoea and weight loss. The infection begins to spread from the small intestine into the nearby lymph nodes causing Tb-like lesions. On occasion, lesions caused by MAP can be found in lymph nodes elsewhere in the body but this is usually associated with severe infection.

The duration of the disease process, from when multiplication starts until death of the host, can be as short as four to six weeks, but it can also take many months or even years if the host gains better control of the infection. Even though the host may control the disease there are very, very few cases where it seems to eradicate the infection.  

How is Johne's Disease spread?

The main way that JD spreads between farms is through the trading of healthy looking but infected deer (subclinical JD).

The main way that JD is transmitted between individual animals is when young calves ingest infected faeces or milk. This is most likely when it is suckling from an infected hind (calves may suckle from hinds other than their mother) but can also happen when grazing contaminated pasture or eating contaminated supplementary feeds. The calf’s gut system matures in the months post birth and this process is likely to make it particularly susceptible to infection by MAP.

Calves may also be infected before birth through the placenta in the uterus.

Drinking water contaminated with MAP infected faeces is another potential source of infection.

There is no transmission risk through nose-to-nose contact through fences.

Wildlife are not considered a major source of transmission of JD. However the bacteria can be found in multiple wildlife species in New Zealand including rabbits, hedgehogs, ferrets, cats and gulls but the realistic chances of transmission from them to young calves is low compared to transmission from infected hinds or contaminated feed or water. 

The importance of transmission of JD between deer and other species of livestock is not yet well understood.

Johne's Disease in young deer and mature deer

JD manifests differently depending on the age of the deer. In weaner deer major outbreaks of disease can occur causing scouring, weight loss and death in up to 25% of the affected mob during the first winter of life. It is not clearly understood whether these outbreaks are due to infection passing between the weaners, or whether they were all infected at an earlier date then experience a common stress (like those associated with weaning, social mixing, overcrowding, nutritional and climatic stress in winter) causing disease.

In comparison, the disease in adult deer is usually seen as one-off cases in small herds or in the tail end of large mobs of animals, often after unusually stressful conditions.

If you notice well managed deer in your herd losing weight JD should be ruled out as a cause, given the many possible reasons for a loss of productivity. If those deer also have foul smelling diarrhoea you can be far more confident the cause is in fact JD. Get your veterinarian to confirm a diagnosis.

The first sign detected on-farm is usually a slowing and then reversal of growth rates in infected individuals. Muscle wasting, ill thrift, diarrhoea and eventually death follow.

A variety of compounding stressors can trigger the disease phase to begin (for example, a tough winter, a parasite burden, transport, social stress, drought, lactation, or the rut). Most infected deer show only early symptoms and are culled or processed before they become severely diseased and die. This means it can be hard to see the full scale of a Johne’s disease issue.

Clinical signs

Early signs

• Decreased weight gain relative to herd mates
• Diarrhoea – typically green sticky faecal pasting, often containing hundreds or even thousands of MAP/gram
• Weight loss and ill thrift
• Rough, light coloured coat with patchy hairloss
• Retention of winter coat
• Muscle loss, particularly over the loin

Late signs

• Diarrhoea containing millions or more MAP/gram
• MAP shed in the milk of hinds
• Emaciation
• Swelling under the jaw and brisket
• Death usually within weeks

Affected deer tend to remain alert and maintain their appetite.

Shedding of the bacteria is generally greater in more heavily diseased animals but this is not always the case. Sometimes apparently healthy animals can shed huge numbers of MAP in healthy looking faeces, while emaciated animals with severe diarrhoea may shed very few bacteria.

Health conditions that can look like Johne's Disease

Other animal health conditions that have similar clinical signs to JD are

• Yersiniosis
• Gastrointestinal parasitism/worms
• Avian tuberculosis
• Bovine tuberculosis
• Copper deficiency
• Inadequate nutrition
• Fading elk/Wapiti syndrome
• Chronic Malignant Catarrhal Fever
• Faulty teeth

Slow growth rates, a ‘tail-end’ and deaths in mobs of young deer being finished for processing are the main effects on production. In extreme cases up to 20% of weaner mobs have been affected.

Impact on the New Zealand deer industry

JD was first diagnosed in farmed deer in New Zealand in 1979. At that time deer had only been established in New Zealand farming systems for a couple of decades. Consequently, they had experienced far less exposure to MAP than the many generations of sheep and cattle. Their comparative naivity enabled the disease to sweep through the deer farming industry in an epidemic with much greater speed and more severe animal health consequences than were observed in other farmed species. 

Financial loss to the industry in 2008/09 due to JD was estimated at around $18 million per year. Key drivers of this loss were deaths and euthanasia of deer on farm, sub-optimal production in sub-clinically affected finishing stock, and slightly lower reproductive performance in infected breeding stock.

Several years later it was estimated again at around $8 million per year. While this reduction was a great relief, the latter loss was still substantial, equating to around $30 for every deer processed.

Any unusual drop in productivity, or emergence of signs of poor health should be diagnosed quickly and thoroughly by a veterinarian. The vast majority of testing for Johne’s disease is with the ‘Paralisa’ blood test offered by Disease Research Ltd (DRL) at the Invermay research centre near Dunedin. It is low cost (approximately $15), quick and effective but not absolutely perfect. A negative test result indicates a low chance of infection but does not guarantee freedom.

Johne's Disease diagnosis

If you see deer in your herd losing weight with diarrhoea JD needs to be ruled out as the cause, as these symptoms may be due to many things. To rule out JD, get your veterinarian to confirm a diagnosis. For Johne’s disease the diagnosis is based on a combination of the following tools:

• examination of the affected deer, possibly including post-mortem
• blood testing a group of animals
• reviewing the productivity trend of the farm with a DINZ Johne’s monitoring service Venison Production Report
• consulting with your veterinarian and discuss the history of the property and the source of deer on your farm

DINZ Johne’s monitoring service recommends veterinarians who are members of the New Zealand Veterinary Association Deer Special Interest Branch. For information on the member nearest you, please email deer@vets.org.nz

For high value animals or cases of particular interest a test measuring the number of bacteria in the faeces (qPCR test) is also offered by Disease Research Ltd and some other laboratories. It is approximately $50 per test. The faeces of up to 10 animals can be ‘pooled’ together to check in a single qPCR test. Contact DRL by phone (03) 489 4832 or email drl@drl.net.nz

DINZ Johne’s monitoring service checks every processed deer for signs typical of Johne’s disease (enlarged lymph node lesions in the gut). It reports back to farmers about these lesions, the subclinical effect of the disease and other venison productivity measures. It also has a range of resources and services to assist farmers and their veterinarians in controlling the disease.

Test submission forms

The Disease Research Laboratory at the Invermay Research Centre in Otago offers the Paralisa™ blood test for the detection of Johne’s disease in deer. They also offer faecal PCR tests. Follow these links for more information. The Paralisa™ test costs $15 (+GST) per sample and the faecal PCR is $40 (+GST per sample). Faecal samples can be pooled to test up to 10 deer for $50 (+GST) which is a cost-effective way of screening larger numbers of deer in a herd.

www.drl.net.nz/testing/paralisa-johnes-test

www.drl.net.nz/testing/faecal-pcr-johnes-test

Johne’s disease can be successfully and cost-effectively controlled and will:

• save you money and make your farming business more profitable
• improve the animal health status of your deer
• be a part in an industry wide effort to control this disease
• reduce stress on both the animals and the farmer!

Over a decade of experience has repeatedly shown control outcomes that farmers, veterinarians, and DINZ Johne’s monitoring service feel were successful.

Experience with the Deer Industry ‘Making a DIFFerence’ Focus Farms has demonstrated successful control and a cost-benefit analysis has shown it’s well worth the relatively low costs involved (see the Deer Industry News, issues 46 and 49).

Controlling JD is not as simple as giving an injection or a pill, so DINZ Johne’s monitoring service supports veterinarians to make on-farm control programmes.

Controlling JD will take a small but firm commitment on the farmer’s part to stick with the programme. But the programme will work. And the solution is achievable.

A control programme will involve the following steps:

• Determine the extent of Johne’s disease in your herd
• Culling test-positive deer
• Maintain a closed herd and good biosecurity (do not bring deer in, but if you must, ensure they are JD-test negative)
• Tweak management of young deer to minimise their chance of infection
• Incorporate health monitoring as part of general herd management

It will take a little work each year for several years to really minimise JD but after that, vigilance and some targeted monitoring are all that is required to ensure it stays minimised.

The bottom line is more animals, heavier sooner and better which is exactly the aim for the New Zealand Deer Industry.

Other control steps:

• Contact your veterinarian to establish an effective control plan, especially if you are euthanasing clinical cases of disease every year
• Immediately cull or euthanse and carefully dispose of deer with clinical signs of the disease – they are super-infectious!
• Ensure young stock do not graze areas contaminated in recent months by diseased deer
• As far as possible keep a ‘closed’ deer herd
• Ensure any purchased deer are blood test negative prior to arriving on your farm.
• Annually or bi-annually test a ‘tail-end’ or R2 hind mob to monitor infection rate
• Use the Deer Health Review booklet to document herd health including JD control.
• Vaccination is a possible option but interferes with the test for bovine tuberculosis. It may be an option for finishing animals destined for slaughter. A single dose at weaning is required and it reduces the incidence of clinical disease among the herd (it does not prevent infection altogether). All vaccinated animals must be ear-marked and the slaughter plant notified. It must not be given to breeding animals because it is very likely to interfere with TB testing and give false positives.

Veterinary Support

The DINZ Johne’s monitoring service assists the veterinary industry in helping deer farmers control Johne's disease, in particular the Deer Special Interest Branch of the New Zealand Veterinary Association who are located nation-wide and can be contacted via email at deer@vets.org.nz

We support veterinarians to offer a mix of local animal health expertise and the latest science-based control methods to create tailor-made on-farm JD Risk Management Plans as part of a wider herd health programme.

Expert advice

Contact your local veterinarian for expert advice.

DINZ Johne’s monitoring service
PO Box 10702
Wellington 6140

info@deernz.org

DINZ Johne’s monitoring service (formerly DeerPRO) is a national animal health and productivity programme with a primary focus on the control of Johne’s disease in farmed deer. 

DINZ Johne’s monitoring service has the following mission statement:

‘To provide services and assistance to the New Zealand deer industry for the control of Johne's disease based on monitoring and maintenance of a national database’

The national database

DINZ Johne’s monitoring service maintains a strictly confidential national database of all processed farm raised deer. The data includes the presence of lesions indicative of Johne's disease, termed JD-suspect lesions, identified in deer at processing during routine carcass inspection by AsureQuality meat inspectors. Over 99% of farmed deer processed since the start of 2007 are in this database and linked to their farm of origin.  Regular analyses monitor the disease in space and time. This data enters an algorithm that evaluates a series of health and productivity metrics to prioritise farms likely to have a high incidence or growing issue with this disease.

We notify and encourage the owners to complete a Deer Health Review with their veterinarians.

Guidelines for implementing control

A comprehensive Technical Manual for veterinarians has been created by the Johne's Research Group 2 to assist them in the Deer Health Review process for Johne's disease. This document as a key resource for veterinary understanding of the disease.

A Farmer Manual is also available which approaches the control of this disease from an on-farm perspective.

Copies of both manuals are available on request.

Programme activity on-farm

Every six months we contact two groups of farmers who have sent deer with JD-suspect lesions for processing during this period, via a notification letter. These groups are farmers that have had a high rate of JD-suspect lesions identified in their deer and farmers that have had the very first or second lesion detected in their deer. The letter describes the disease, the implications of the lesions and urges the farmer to seek veterinary support with a Deer Health Review to control the disease and review other aspects of herd health.

Research

The focus of DINZ Johne’s monitoring service is concentrated at farm level, rather than research into the disease. However we do undertake research in-house for monitoring and self-review. We support and assist research providers in Johne's disease including Crown Research Institutes, Universities. Strict protocols around data confidentiality regulate the contract conditions under which data is provided to these parties.

• Minimise the risk of importing JD by minimising the number of deer brought onto your farm.
• Ensure any deer purchased are of low risk, either by diagnostic testing or discussion with the vendor.
• Immediate euthanasia of clinically affected stock.
• Diagnostic testing where necessary to reduce infection rate (discuss this with your veterinarian).
• Good herd health and general management (see the Deer Health Review booklet as a guide).
• Miminise stress on deer where possible.
• Providing plenty of good quality feed.
• Monitor your status with a DINZ Johne’s monitoring service Venison Production Report.

DINZ Johne's monitoring service Johne's Disease and Venison productivity report (formerly DeerPRO Johne's disease and venison productivity report)

We have freely available Johne’s Disease and Venison Productivity Reports (see our example) that summarise key measures of your processed young deer over the last five seasons. They are an ideal way to see the impact of changes you've made to your deer system and for comparing your system against some broad industry benchmarks.

The reports include a five-season trend of:

• Tallies of both young and mature deer processed
• Total kilograms of carcass produced
• Average carcass weights for young deer
• Average kill dates for young deer
• Average growth rate for young deer
• A kill profile comparing your monthly tally of processed deer against the weekly Agrifax schedule
• The rate of Johne's disease suspect lesions
• NAIT RFID codes for your deer identified with Johne's disease suspect lesions

On request, we can also estimate the financial cost of Johne's disease in your deer.

This year-on-year information is a great help for working through a Deer Health Review with your veterinarian. It's also an excellent way of tracking the progress of your deer unit over time.

Your request is as easy as a call 04 475 4500 or email DINZ Johne’s monitoring service info@deernz.org

This information is completely confidential to you and not distributed to a third party without your prior consent.

Technical Manual

The Technical Manual is a cornerstone document for Johne's disease information. It collates all scientific information about Johne's disease, applicable to deer farming in New Zealand, into a single 130-page document. It is structured and written to make this information easily accessed and assimilated into practical on-farm control programmes for the disease in deer.

Farmer Manual

The Farmer Manual is based on the Technical Manual and provides farmers with an overview of managing Johne's disease in deer, based on science but without the lengthy scientific background of the Technical Manual. Copies are available on request info@deernz.org