Lawsonia intracellularis - New Horizons
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!
