Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

Proliferative enteropathy, caused by the bacterium Lawsonia intracellularis, is an important disease of older foals, particularly in certain regions and on specific farms. Infection by this bacterium results an abnormal small intestine, which ultimately causes severe loss of blood protein. One major problem with this disease is that it is not often spotted until it's very advanced. Like many diseases, the earlier you can diagnose it, the better you can treat it. Unfortunately, sometimes foals are so sick by the time anyone notices, it's very hard for them to recover, even with intensive care. There are a couple of different ways to diagnose Lawsonia infection, but I'm not going to get into specific testing (more information on that can be found in our archives and on the equIDblog Resources page). The point I want to emphasize is finding this disease early.

On farms that have had problems with Lawsonia in the past, specific testing may be part of a routine diagnosis and control program. However, that's not going to be the case for most farms. While specific testing for Lawsonia is hard to justify in those circumstances, close attention to early signs of diseases is critical.

This disease usually hits foals that are a few months of age (and is most commonly diagnosed in 5-6 month old foals). Foals this age are not always watched and handled closely, compared to younger foals and older animals. With Lawsonia, foals can look good from a distance, despite being quite sick. It's even more of a problem in the fall in cooler climates where a longer haircoat can more easily mask weight loss and poor body condition.

So, what can you do to help find the problem early?

• Get your hands on the foals. Handling them regularly will give you a better assessment of their strength, body condition and overall health. Actually touching them will let you feel muscle mass and tone, and detect foals that are not growing well or not in as good body condition as they should be. Such foals should be examined by a veterinarian promptly, with Lawsonia being one of the considerations for a cause.

Having good, regular contact with foals is a free and (relatively) easy way to help protect their health (and as a bonus, it also gets them used to people and used to being handled from an early age).

(click image for source)

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We've survived the summer, and with cool(er) weather soon on its way we are now into what I like to call "weanling season" (which follows naturally after "foal season").  One of the common things veterinarians get called about at this time of year is 5-6 month-old foals that just "aren't right."  They may not be growing well, they may be skinny, they may not have the same healthy haircoat as other foals in the same group, and they may generally just be "dragging their heels" a bit - not very energetic, and maybe sometimes a little depressed.  Of course this is particularly problematic in the fall when some farms are trying to get their foals ready for sale, and they want them looking their best!

Bloodwork on these scraggy foals often shows low - sometimes extremely low - protein levels in their blood.  Blood protein is very important for normal body function and controlling tissue fluid levels, and the body (especially the liver) works very hard to maintain normal levels.  Low blood protein (also called hypoproteinemia) in these animals usually indicates that the protein is being lost from the body, and the most common route for this to happen is through the intestine. (It can also be lost through the kidneys, but renal disease in young animals is generally uncommon.)  Some of these foals have diarrhea as well, or may go on to develop diarrhea if left untreated.

What is it that turns a foal's intestine into a protein sieve?  One possibility, and a hot research topic at the moment, is the bacterium Lawsonia intracellularis, which causes the condition known as proliferative enteropathy.  But any severe infection of the intestine has the potential to affect the barrier that normally keeps blood protein fluids in the bloodstream, so other causes of enteritis and colitis such as Salmonella and Clostridium also need to be considered.  Heavy burdens of intestinal parasites can cause similar problems - some of these may be difficult to test for because the larval stages do not produce eggs that can be found on a fecal test, and developing resistance issues mean that routine deworming cannot guarantee that parasites are not present.  There are no doubt other causes as well that haven't been identified - in half of all diarrhea cases in (adult) horses, a causative agent cannot be identified, even with a complete diagnostic work-up. 

In horses, if only the small intestine is affected (enteritis) - even in severe cases - the animal usually will not have diarrhea.  However, if the infection spreads to the colon, or if the bacterial populations in the colon are affected badly by the foal's poor health status and abnormal "flow" of feed material due to the infected intestine "upstream", then colitis will develop as well, resulting in diarrhea.  Anytime the normal intestinal bacteria of a horse are disrupted, the animal also becomes more susceptible to other bacterial pathogens such as Salmonella and Clostridium as well.

What should be done with these "scraggy" weanlings?

1. Have them examined by your veterinarian as soon as possible.  Don't wait for them to start looking really sick.  These weanlings can be frustrating to diagnose and treat at the best of times, but the farther they're allowed to slip, the harder it is (and the longer it takes) to bring them back.

2. Look for other foals that might be affected.  Especially in larger groups of foals, one particularly sick animal may stand out, but there could be several others flying just under the radar that you may not notice unless you really take the time to look at each foal individually.

3. Separate healthy weanlings from those that aren't 100%.  It may be difficult or impossible to individually isolate all the "scraggy" animals depending on numbers and the facilities available, particularly more severely hypoproteinemic foals that may take weeks to months to recover.  At a minimum, the foals that appear healthy should be separated from and always handled before the ones that may be affected by an intestinal infection.  Any animal with diarrhea should be isolated.  The duration of isolation required will depend on the specific diagnosis (if one can be made).

More information about Lawsonia is available on the equIDblog Resources page and in our archives.

Image source: www.virginiawildhorserescue.com

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Lawsonia intracellularis is an important cause of disease in weanling foals, causing a disease called proliferative enteropathy. Antibiotics, mainly erythromycin,are usually used as part of the treatment for this condition. However, little is known about the true antibiotic susceptibility of this bacterium. The problem is that Lawsonia does not grow in culture plates in a lab like most other bacteria with which we deal - it can only grow in cells, which makes it very difficult to test for  antibiotic resistance.  Antibiotic therapy for this disease is therefore chosen based on basic knowledge about the bacterium and anecdotal information about how animals respond to treatment.  Obviously, this is not the ideal situation.

A little more information is now available on this topic. In a recent edition of Veterinary Microbiology, researchers from the University of Minnesota published a study of the activity of different antibiotics on L. intracellularis. The study, by Suphot Wattanaphansak and colleagues, only involved 10 isolates of the bacterium, all of which were from pigs. (Lawsonia infection is an even bigger problem in pigs than it is in horses).  They only tested with a few drugs that are used in horses, and they used an unvalidated (but reasonable) test, so it's very important to be careful (and conservative) when extrapolating the results to Lawsonia in horses. However, they did have some potentially equine-relevant results. One important finding was that there was variation in susceptibility to some drugs between isolates, meaning some strains were susceptible and some were resistant to certain drugs. Although this isn't really surprising, it emphasizes the fact that the same treatment may not be suitable for all cases - antibiotic resistance can be present, and if it is it's critical to identify and address the issue.  This particular study showed that tetracycline, a drug sometimes used in horses, had "intermediate activity" against Lawsonia... not great, but not horrible. Unfortunately, they didn't test erythromcyin or chloramphenicol, which are two drugs more commonly used to treat Lawsonia in foals.

This study doesn't tell us much more about how to treat horses with this infection, but it does emphasize the need to test equine strains against drugs used in horses to see if we are doing things right, whether resistance to important equine drugs is present, and to determine if there are better and faster ways to detect resistance.

More information about Lawsonia intracellularis can be found on the equIDblog Resources page and in our archives.

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Lawsonia intracellularis is a bacterium that causes an intestinal disease called proliferative enteropathy in young horses. One of the reasons we still don't know a lot about this disease is that this bacterium can't be grown in a lab. One of the areas in which researchers are working to find more information is from where horses that become sick initially get Lawsonia...  Is it from healthy horses that are carriers? Does it circulate in the horse population, or is there an outside source? Does it come from pigs (pigs can also be affected by disease due to Lawsonia infection)?  Do other animal species such as wildlife carry it?

A recent study by researchers at the University of California (Davis), published in the Journal of Wildlife Diseases (2008 44:992-998), looked at the presence of Lawsonia in wildlife on horse farms. They found DNA from the bacterium in feces from jackrabbits, striped skunks, Virginian opossums, and coyotes, but not from feral cats, Brewer's Blackbirds, raccoons, or ground squirrels.

This study provides some interesting insights about Lawsonia in horses, and raises the possibility that wildlife could be a source of infection. However, it does not tell us how to prevent the disease or whether wildlife really are a relevant issue when it comes to infecting horses. We certainly do NOT recommend trying to eradicate wildlife in the vicinity of horse farms as a Lawsonia prevention tool. However, making horse barns (especially feed storage areas) less inviting to wildlife is a good idea - this is a sound standard infection control measure that everyone should consider, as it may reduce the risk of several infectious diseases (e.g. equine protozoal myeloencephalitis (EPM)).

More information on Lawsonia can be found on the equIDblog Resources page, and in our earlier post entitled "Lawsonia intracellularis - New Horizons".

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On December 9, the Infectious Diseases session was held at the 2008 AAEP Conference in San Diego, CA. Topics presented covered several conditions, including MRSA, Clostridium difficile, equine infectious anemia (EIA), parasite resistance and deworming protocols, and Lawsonia intracellularis.

Lawsonia intracellularis is a bacterium that causes a disease called (among other things) proliferative enteropathy in foals and weanlings. More information about this disease is also available on the equIDblog Resources page. This disease is relatively new in the horse world, being first identified in the 1990s. It has traditionally been considered a disease of pigs, where it causes several syndromes of clinical disease, including one similar to that seen in foals. In pigs that carry the bacteria in their intestine, clinical disease is brought on by stressful events, and the same may be true in foals. The infection causes severe thickening of parts of the small intestine, and the inflammation causes loss of large amounts of protein from the bloodstream. Affected foals are usually very “unthrifty” and quiet/depressed, and many often develop edema (non-painful, cool swelling) along their abdomens or under their jaws.

In pigs, prevention of disease due to Lawsonia infection involves decreasing stressful events and vaccination with an oral vaccine. Dr. Nicola Pusterla of the University of California (Davis) presented the results of a study that was done recently looking at the effects of vaccination of foals against Lawsonia in three different ways – giving the vaccine orally, giving the vaccine orally after treating the foals for three days with a gastroprotectant (omeprazole), and giving the vaccine rectally. The reason for the last two groups was to decrease the risk of the vaccine being destroyed by the acidic environment of the normal stomach. Indeed, they found the antibody response to the vaccine in the bloodstream was better in these groups than in the untreated foals that were given the vaccine orally. Of the 12 foals that received the vaccine, all of them stayed healthy throughout the study period (42 days).

Although seeing some work on developing a vaccine for this disease is great, we are still a long way from being able to use vaccination to prevent disease in foals. While the animals in the study produced antibodies in the bloodstream, Lawsonia actually lives inside cells, where antibodies usually cannot get to them. Immunity against intracellular pathogens like this requires cell-mediated immunity, which is much harder to measure. It’s also important to remember that even with a vaccine, control of this disease (as with any infectious disease) depends on a lot of other factors, like reducing stress on animals and preventing transmission and spread of the bacteria. Unfortunately, no one is even sure exactly what the source of the Lawsonia is in most foals (although there’s a good chance that they ingest it, possibly with fecal contamination from foals that are shedding Lawsonia).

As more and more cases of Lawsonia are seen, both in North America and now in Europe, researchers will continue to learn more about how this disease is spread, and hopefully one day develop a vaccine to help us prevent it.

Keep watching this site for more of the latest and greatest from the 2008 AAEP Conference!

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Click on any of the highlighted links below for more information about these horse-related infectious disease topics. Topics that are not highlighted are in development and coming soon. New information will be added as it becomes available, so be sure to check this page regularly for the latest updates.

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