Welcome to The Dairy Mail

by Liza Burger

Johne’s disease, also known as paratuberculosis, is a wasting disease mainly found in ruminants, which can have severe repercussions for infected dairy herds.

Although sheep and cattle are both affected by Johne’s disease, it is especially sheep that are at risk in South Africa. The threat to cattle and especially dairy cows does however remain.

According to Dr Mohammed Moola, veterinarian at Virbac in charge of the Gudair vaccine, aimed at preventing the disease in sheep and goats, dairy cattle are at great risk of contracting and spreading this gastrointestinal infection in countries such as Canada and the USA.

“Fortunately, we have seen very few cases in South Africa so far, but in the rest of the world it is a huge problem among dairy herds. The hope is that local cattle herds will remain free from Johne’s disease,” says Moola.

While the South African dairy industry has remained fairly free from the disease, it is interesting to note that it was first clearly described in a dairy cow in 1895.

Compared to other animal diseases, Johne’s disease is slow to show symptoms and animals infected by the bacterium, Mycobacterium ­avium (subspecies paratuberculosis), can remain healthy for a very long time after the actual ­infection. This Trojan horse approach means the disease can take its time to spread to the rest of the herd, without being detected.

Without testing your herd, it is impossible to be really sure that your herd is not affected by Johne’s disease. While some areas of the country show greater prevalence of the disease among different livestock, especially small stock, Johne’s disease is found worldwide. Even if your herd is clean today, it still takes strict biosecurity measures and protocols – especially when new animals are brought into the herd – to keep it clean.

The most important facts to note is that this disease is contagious, hardy, not effectively treatable and causes extreme weight loss and diarrhoea in ruminants. Despite a good appetite, the animal will eventually starve to death because of the malabsorption of nutrients.

Stopping the spread of this disease is not only in your own farm’s interest, but also in the interest of the national herd’s health.
Contracting Johne’s disease

Animals will mostly contract this disease in the first few months after birth. However, physical signs of the disease can remain latent for months or even years. It is a controlled disease in South Africa and a vaccine for sheep and goats does exist.

For cattle, there is no effective treatment or preventative medicine and the management of your herd and biosecurity controls are the most effective way to keep the disease at bay.

Usually, a clean herd will be infected by a new animal added to the herd. The animal may appear healthy, but be a carrier of the disease. The bacterium is typically spread in manure on pasture or contaminated water sources. As the pathogens are hardy and can survive outside the animal for months, pastures can remain contaminated for some time.

Since young animals can easily contract the disease, one should take care to keep calving pens free from contamination. Johne’s disease can also be spread to calves by contaminated milk from infected animals or through in-utero transmission.

Symptoms of Johne’s disease
To spot an animal with Johne’s disease is not easy, as the symptoms are not indicative of only Johne’s disease. Laboratory tests must be used to confirm any suspicion. The two prominent signs to look out for in dairy cows are rapid weight loss and diarrhoea. Although the cow’s apatite will remain good, she will quickly lose condition and become weak.

Scientists have yet to figure out exactly how and why Johne’s disease is like a ticking time bomb with a rather long fuse. However, what is known, is that the bacterial infection resides in the last part of the small intestine. At some point, the bacteria start to replicate and immune responses kick in. Granulomatous inflammation occurs, which causes the intestinal wall to thicken.

The result is that nutrients cannot be ­absorbed effectively and the increasing ­malabsorption eventually causes starvation. For a dairy cow, the effect of full-blown Johne’s ­disease is quickly visible in her sudden decline in body condition and drop in milk production. As there is no effective treatment against Johne’s disease, culling is the only viable option before natural death occurs.

Prevalence of paratuberculosis
Johne’s disease is found everywhere in the world, especially among contained animals, ranging from commercial llama and bison herds to goats, sheep and cattle. Herded animals, or where intensive livestock farming is practised, are more susceptible to contracting the disease than free-roaming animals. Ruminants are mainly affected, although the bacteria can spread to carnivores (without visible effect on their health).

A recent study in the United States has shown that an estimated 8% of beef herds and 68% of dairy herds tested positive for the Mycobacterium avium bacterium in at least one animal in the herd.

Australia is one of the countries where the prevalence of Johne’s disease has declined thanks to a significant national effort to cull infected animals, test herds and employ effective biosecurity measures in herds.

In South Africa, there have been substantial efforts to curb the occurrence of the disease, especially in sheep. Dr Jacoba Wessels at the Mpumalanga State Veterinarian in Nelspruit confirms that the disease is rarely noted in cattle, with sheep being mainly affected in South Africa. An outbreak in 2005 in Middelburg in the Eastern Cape saw 218 sheep killed.

Bovine cases are not unheard of and the most recent such cases reported since 2007 to the State Veterinarian occurred in Groblersdal, Mpumalanga (March 2007), Thaba Chweu, Mpumalanga (August 2007), Bronkhorstspruit and Pretoria (July 2008), Greater Zeerust, North West (May 2009) and Robertson in the Western Cape in May 2009.

Despite the disease being rarely diagnosed in cattle locally, this does not mean that Johne’s is not posing a threat, as the symptoms of this stealthy disease can be confused with a number of other diseases.

While most dairy farmers are vigilant regarding contagious diseases, not everyone believes in the relevance of even testing herds regularly for TB and brucellosis, let alone a disease such Johne’s disease. These unchecked herds could pose a threat to maintaining the integrity of the South African dairy industry, which currently enjoys a period of being relatively free from the disease.

Another threat is stray cattle, especially in rural areas, which may be infected and spread the disease to clean herds on neighbouring farms.

Lacking biosecurity protocols is another contributing factor to the possible spread of the disease.

The inclusion of new animals into a herd without the proper initial health certificates or employing standard quarantine and health check measures can cause a major breach of the biosecurity fence. This error is compounded by the buying and selling of untested animals at auctions or out of hand.

Threat to humans
Johne’s disease has not been confirmed as a zoonotic disease; however, the possible link between Johne’s disease in animals and Crohn’s disease in humans is still under scientific investigation. The cause of Crohn’s disease is still unknown and there is no cure for this chronic inflammatory bowel disease. Until now, no positive connection could be proven between contact with animals with Johne’s disease or dairy products.

Controlling Johne’s disease
The main source of Johne’s disease contamination is manure from an infected adult animal. To protect newborn animals, ensure a clean calving environment and feed milk and water free from the bacteria that cause Johne’s disease.

Adult animals infected with the disease must be identified, quarantined and managed to ensure no young animals are exposed to their milk or manure. Culling sick animals are usually the most cost-effective way to rid your herd of the disease.

Opsomming
Johne se siekte is ’n sluimerende gevaar wat plaaslik onder veral skaapkuddes vrektes veroorsaak. Vermaering en diarree is die hoofsimptome van Johne se siekte. Die siekte is ook bekend as paratuberkulose en melkbeeste is wel vatbaar vir die bakterie Mycobacterium avium, alhoewel dit nie algemeen in Suid-Afrika voorkom onder beeskuddes nie. Dit bly egter steeds belangrik dat melkboere bewus is van die siekte, hoe dit versprei en watter voorkomende stappe nodig is.