Contagious diseases are a large threat to the animal production industry, especially those that are deadly or incurable. One well-known bacterial infection found in ruminants such as goats, sheep and cattle is Johne’s disease.
Johne’s disease is caused by the mycobacterium Avium paratuberculosis, also known as MAP. MAP is found worldwide and is transmitted primarily through ingestion of either infected manure, water or milk. The disease was first recognized and reported in 1895, and has caused economic and health declines in livestock since.
The infection is more common in young animals, especially newborns with weak immune systems. Signs aren’t present until two or three years of age, making the disease hard to catch in its early stages. The only way to potentially notice Johne’s disease early is through a blood test. The disease progressively damages the intestines.
Due to its progression, Johne’s disease occurs in four main stages:
- Initial infection – The infected animal doesn’t display any signs. In this stage, the infected animal does not shed the bacteria, and therefore doesn’t infect other animals or the environment around them.
- Progression of the infection – Still a lack of presentation of clinical signs. In stage two, the infection can be spread to others as bacteria are secreted in fecal matter, infecting the environment.
- Beginning signs of disease may be present in the animal.
- Obvious signs of disease – The bacteria are detectable on diagnostic tests and the animal is close to death.
Some common signs in all infected species include chronic diarrhea and poor body condition. For dairy animals, there is a decrease in milk production, financially impacting the farm, as well as unresponsiveness. While cattle have diarrhea, they maintain a normal appetite. Cattle may also develop bottle jaw or intermandibular edema. The cows suffer protein loss from the bloodstream, causing a soft swelling under the jaw.
Clinical signs are harder to recognize in sheep and goats. Less than half of infected sheep end up having diarrhea, making their obvious signs very different from other ruminants. One of the main signs in sheep is they continue to eat normally but still progressively lose weight and body condition. In their case, the intestines become super thick, making it inefficient to absorb nutrients.
The main way to protect your farm from this deadly and contagious disease is through prevention and biosecurity. Cautiously choose who you purchase new animals from. The best option is to maintain a closed herd. However, this isn’t achievable for all farms. Only purchase from herds that do frequent testing for Johne’s disease and have no evidence of an infection.
Remember that MAP is very tough and persistent bacteria that can survive in the environment for over a year. It’s beneficial to wait at least three months after applying manure for young animals to graze on pasture.
Keep young animals in clean, well-bedded areas. Make sure babies are born in a clean area to prevent disease transmission from the mother due to manure in the bedding. When nursing, ensure mothers’ teats are clean to prevent ingestion of fecal matter.
There is not a known vaccination or treatment that will remove the infection from the herd. The best solution is to prevent the disease from entering your farm in the first place.
For testing, fecal matter can be cultured and analyzed to identify MAP bacteria, but it generally takes as much as six months for results to be completed. At this rate, bacteria have plenty of time to cause signs in infected hosts as well as spread to other animals. There is also the aforementioned blood test, but it’s common for antibodies to only show later in the infection, when the disease is already spreading.
When an infected animal is recognized, remove them from the herd as soon as possible to minimize exposure and spread. If the infected animal is a mother to a newborn animal, remove the offspring from the herd and avoid breeding them, as the chances of them also having the disease is high.
As with most diseases, infection increases the chance of a secondary disease, specifically since the immune system is preoccupied and the animal’s body condition is poor. A common secondary disease for animals to develop is mastitis, which is expensive to treat and increases cull rates on the farm.
With the lack of treatment, prevention and education is the main way to protect your herd from this deadly and contagious disease.
by Kelsi Devolve