Three diseases that have become frighteningly prevalent in the US sheep flock are little understood by the average shepherd. All three of these diseases are slow to show symptoms, are contagious before they are detected, and will significantly shorten the life of your ewes and otherwise lower their productivity.
CL is contagious to humans and there is some suspicions Johnes may be associated with Crohns disease (although there is more risk of Johnes from the cow’s milk in your refrigerator than your sheep). Given the prevalence of all three and the myriad myths surrounding them, taking some time to learn the facts can save you plenty of trouble.
The good news is that there are now excellent tests for all three diseases that are conclusive and not difficult to find a lab to do. Due to some incidents of false positives when a sheep shows positive for the disease on the OPP ELISA test, a different immunological test can be used to back up whether the sheep is really positive. There are a variety of tests for Johnes, depending on whether the feces, blood, or milk is being tested.
The Synergistic Hemolysin Inhibition (SHI) Test is used for CL and results are graded on intensity – pick an experienced lab for this one. The University of California, Davis lab has a high degree of proficiency in CL testing. Many state labs do both Johnes and OPP. Frequently, testing is subsidized by the state, so if you test in your own state your testing costs will be significantly less than if you use an out of state lab.
The bad news is that there are no cures and no really effective vaccines available for any of these diseases. Testing and removing positive animals as soon as they are identified is the only effective way to eliminate these diseases from a herd.
All three of these diseases have been found in the BFL herd in the US. It helps no-one to point fingers or keep the disease status of their animals secret. These diseases are too prevalent in the US to be sure that any herd that is not 100% closed has not acquired at least one of these infections.
All three diseases can be spread at shows. They come into your flock with perfectly healthy looking stock that did fine in quarantine. Your neighbors’ animals, their boots, and their equipment can be vectors if their flocks are infected. That dandy stud ram you borrowed can be carrying one of these diseases. What will make a difference is honest cooperation to minimize any potential risk of transfer and willingness to test our herds and the sheep that we sell.
Some sheep are more susceptible than others. Some can carry one of the diseases without ever being affected by it; some will be chronically afflicted by it very quickly. But, once exposed to the bacteria (including simply being with another sheep that has been exposed), a sheep must be considered infected unless testing proves they are not. All three diseases have been studied extensively and it is clear they all create a drag on the animals system, resulting in shorter lives and greater susceptibility to other problems and diseases in most infected individuals.
It is possible to continue to obtain clean lambs from valuable but infected breeding ewes if they are still reasonably healthy. In order to prevent infection of the lambs, the lambs need to be removed at birth, allowing as little contact with the mother as possible. She shouldn’t lick them. The lambs must be prevented from drinking any of the infected ewe’s milk or colostrums. In the case of Johnes, no feces contact is critical.
Ewes with CL should be examined carefully before they give birth and any CL cysts treated with antibiotic and cleaned out in order to minimize the possibility of a cyst contaminating the lamb. Any ewe with a chronic cough should be monitored very carefully to be sure she doesn’t contact her lamb.
Studies have shown that the likelihood of the disease agents crossing the placenta and infecting the lamb prior to birth are next to none, unless the ewe is very ill and her immune system has started to shut down. In any case, the lambs shouldn’t be introduced to the clean flock until they are tested at 6 months of age. By then any passive antibodies they have received from their mothers would be gone and a positive test would indicate active infection. While they still have antibodies from their mother, they may test positive, but not be infected.
The OPP society website has excellent directions and advice for anyone wanting to raise lambs that have been removed from their mother at birth. They have directions for pasteurizing colostrum and methods of feeding groups of lambs to get them off to a good start. Remember that cow colostrum often carries Johnes, so don’t use it without pasteurizing.
Caseous Lymphitis (CL or Cheesy Gland) is caused by a tuberculosis type bacteria that lives inside of cells, colonizes the sheep’s lymph system, and forms cysts in the lymph nodes that protect the bacteria from antibiotic. The disease is also common in goats. The bacteria is passed when cysts close to the skin, in the lungs, or in the mammary glands burst releasing thousands of bacteria into the environment and the bacteria is rubbed on skin, inhaled by other sheep, or passed through milk to the lambs.
The bacteria can live over a year in the environment and is quite good at entering through the skin of the sheep, even in the absence of a wound. Initial skin cysts may not be noticed and internal cysts cannot be seen. The animals system is weakened by the disease and production is seriously affected. Most animals are shipped before the CL becomes advanced, due to poor production.
The first cyst is typically confined to skin, but the bacteria move from the initial infection into the lymph system, where they encyst and hide from any antibiotic treatment and the animal’s immune system. CL will eventually take over the lymph system and the animal becomes emaciated and covered with oozing cysts. Many countries condemn the meat of animals when cysts are observed during slaughter. The US does not, but requires cysts in the meat to be cut out.
CL can infect humans and treatment is painful, expensive, and takes years. Sheep shearers are at risk because shearing commonly bursts any cysts present at the surface. The dipping bath post shearing has been identified as a major avenue of transmission for sheep in Australia and New Zealand. Injections cause a break in the skin that is another easy route of entry for the bacteria. Don’t use the same needle on different sheep and use an antiseptic to sterilize the skin at the site of the injection.
There is an inoculation called Colorado serum for CL, but it is generally considered only about 75% effective in preventing infection, it does not prevent cyst formation in already infected ewes, and it seems to cause some severe adverse effects in ewes that have already been infected. The biggest problem it poses for a purebred herd is that once an animal is inoculated it is impossible to tell if they have an active infection or if the antibodies in their blood are only due to the inoculation. The inoculation has been useful in reducing the economic impact of CL in commercial herds.
If you do decide to manage CL in an infected herd kept for meat production or in quarantined ewes being kept for breeding, there are some newer penicillins and tetracyclines in carriers that penetrate the puss in the cysts better. Cysts are best cleaned up by injecting them with one of these antibiotics well before they start to burst. Once the bacteria in them are dead, they dry up and are much less of a risk to other sheep. Talk to your vet about the best antibiotic to use.
Shearers , mostly in Australia and New Zealand are known to catch CL. They are probably exposed frequently through cysts that burst when they shear. There are other infrequent examples of people contracting the disease. Anyone cleaning and treating a cyst should be very careful not to expose their skin to the bacteria if they suspect CL. The disease is very expensive and takes a long time to eliminate in humans, frequently requiring surgery to eliminate infected lymph nodes.
The incident of CL in sheep is growing and has gone from a minor problem in the US to a major one in the last 10-15 years. Many commercial flocks are infected through new rams brought from purebred flocks. This is an unacceptable situation and it is paramount that purebred breeders behave responsibly to prevent the spread of the disease.
In Australia, neglect of the disease created such a problem that now vaccination of sheep is required by law and movement of animals from known infected flocks is restricted (they have a better vaccine in Australia). Unfortunately, many sheep farmers in the US feel that since CL is a slowly progressing disease, they do not need to remove a ewe until she becomes unthrifty and they have ‘gotten their money out of her.’
John Glenn, DVM at UC Davis has published some articles that clearly explain your options. A description of the tests can be found at this link for www.goatworld.
Johnes disease is found in sheep, goats, and cattle. It is another tuberculin type bacteria that infects the intestinal wall cells and becomes systemic as the disease advances into late stages. It slowly destroys the ability of the intestine to absorb nutrients. Poor doers, due to this disease, typically start to show low condition in spite of a good appetite during the second to third year and ewes commonly need culling at age 3-4.
As the disease progresses, the animal will starve to death while demonstrating a healthy appetite. The bacteria is present in the milk of an infected animal and infection of nursing young is almost 100% in calves. Little investigation has been done on sheep, but the organism has been found in sheep milk and is likely just as infection to lambs. Lambs will also contract the disease from cow colostrum.
The disease is endemic in US dairy cows and programs to address it in cattle have been started in states where dairy is an important part of the economy. Johnes bacteria have been linked to Crohn’s disease in humans, but there has been no conclusive evidence yet that it causes the disease.
In cattle and sheep, the bacteria is passed from one adult animal to the next through fecal contamination and ingesting the bacteria. The bacteria are shed from the intestinal wall during all stages of infection. Sometimes in early infection, a blood ELISA test will not be positive, but fecal testing will show the presence of the bacteria. Feeding off the ground and frequently moving pasture is recommended to minimize contamination.
Both blood ELISA testing and fecal testing are used for Johnes. If you want to find out if Johnes is an issue with your flock, collecting a representative sample of your flocks droppings and having the mixed group tested is a low cost approach to finding out if you need to investigate further. There is also a milk test used for dairy cattle, but most sheep producers will want to know if their animals are sick before they produce lambs.
There is a vaccine for Johnes for cattle, but it isn’t used in sheep. It has nasty side effects in both species and causes serious illness in humans if they are accidentally dosed with it. There is a new vaccine for sheep developed by Cornell University, but it has not been approved yet and is not on the market.
Johnes is less common in sheep than OPP and CL, but the problem is growing and if ignored will only get worse. It is a huge problem in the US dairy herd and major testing programs have begun in states where dairy is important. Check out the Wisconsin Johnes website for more resources at www.johnes.org
Ovine Progressive Pneumonia (OPP or Maedi Visna) is a retrovirus disease similar to AIDs in humans. It is does not infect humans. It causes a wasting disease in sheep, the common symptoms being hardened and unproductive mammary glands and chronic pneumonia that will not respond to antibiotics. The virus slowly destroys the immune system in the sheep, just like AIDs does in humans.
In advanced cases, neurological damage causing trembling and uncontrolled spasming of muscles may be seen. The disease is usually passed through breathing the virus in aerosol from a coughing sheep or to lambs through their mother’s milk. Studies shoe 30-50% of lambs born to an infected mother will test positive by 6 months of age. Other lambs in the herd frequently come up positive, also. Up to 17% of lambs from uninfected mothers have been found to have become infected in herds that include infected ewes.
Because lambs like to try and steal milk from other ewes, that may be a mode of transmission. OPP does not survive long in the environment and apparently needs to be transmitted via body fluids, similar to aids. Close winter housing seems to be a very high risk environment for transmission according to some studies. Needles are another route of transmission. One needle to one sheep is the rule for preventing transmission of all of these diseases. Extra needles are a minor cost compared to the economic damage these diseases do.
Research all three of these diseases and learn all you can so you’ll be prepared for the inevitable brush your herd will have with at least one of them. Quarantining and testing new sheep is one of the best preventions. Use the internet. There is a host of information available. New vaccines are being developed so it pays to keep up with the news.
The OPP Society website is a marvelous resource for breeders looking for solutions to managing infection in their herd. They recommend testing all animals and separating them into two herds. Routine testing at least once a year of the negative herd will pick up any animals missed or that contract the disease later. New positives are moved to the positive herd. The negative herd should not have nose or fecal contact with the positive herd, ideally separated by at least 200 feet.
The positive herd is slowly reduced by removing animals as they would normally be shipped. Ewes with valuable bloodlines are bred by AI and their lambs are removed at birth and not given any chance to nurse or be licked by their mothers. The OPP society page has some very good articles on successfully rearing orphan lambs. Colostrum can be saved from the negative herd or the lambs grafted to a negative ewe. Visit www.oppsociety.org
It’s recommended to continue testing all animals for two years after all known positives are off the property. Testing ewes after they give birth will give lots of false negatives because a majority of the ewes antibodies go into her milk and won’t be found in the blood. Testing lambs prior to 6 months, especially if they have nursed from a positive ewe, will give false positives because they have ingested their mother’s antibodies but may not have contracted disease themselves. Johnes antibodies frequently do not show up in the blood until an animal is 2 years old, even if it is present in the gut and shedding contagion in the feces.
One of the barriers to having more flocks test and eliminate these diseases is the cost of testing. This is not a huge problem if you have a small flock and collect your own samples (draw blood for all three diseases or collect feces for Johnes). Ideally, anyone starting up would test while their flock was still small and test any incoming animals. But there are many large flocks that cannot afford to test due to the number of sheep involved.
It would be a huge advantage to the whole industry if we could work with the USDA and the states to subsidize testing and start making progress eliminating these diseases. Many states are already trying to help with this and commonly, if the tests you need are available from you own state vet labs, the cost will be subsidized for you as a resident.
Our industry is small compared to the cattle industry and we need to make ourselves heard on this issue. Discuss your situation with your vet and call your state labs to find out what is possible.
It is much less expensive if you learn to draw the blood samples yourself. In most cases the serum is all that is required by the testing lab. You do not need to pay your vet to spin the blood to separate it.
Simply set the tubes of blood in a warm place over night and then use a clean hypodermic needle and syringe to carefully draw the clear serum off the coagulated blood cells and transfer it to a clean red top tube. Be careful not to cross contaminate your samples. Package them carefully, use an icepack in warm weather, and mail them overnight to the lab.
Purdue has an excellent web article demonstrating how to locate a sheep’s jugular vein and draw blood at www.ces.purdue.edu
Don’t bring a problem you don’t have into your herd. Don’t buy from herds that don’t test. Quarantine and test any animals you have any reason to be unsure of. Test your own herd regularly so you can catch any accidental introductions before they spread. Remember that shows, your neighbor’s flock, or other contact with the sheep community can bring infection into your flock unexpectedly. CL is also carried by goats. Johnes disease is spread by cow manure and cows milk.
Reputable breeders know that testing helps sell sheep. Good records allow you to market your sheep as disease free. Its good ethics, it’s good for our breed, and it’s good for your business.