Although trichinosis does not occur exclusively in pork, pork is the first thing that comes to mind and the reason Mom used to cook that pork to death until it had the taste and texture of shoe leather. Trichinosis is caused by microscopic live worms called trichinae. The parasites live and reproduce in the intestines and their larvae can make their way into the bloodstream and travel to the muscles causing pain, fever, muscle deterioration and even death. Nowadays, the threat of trichinosis is rare due to public awareness and strict government guidelines on the raising of pork.
Pork (deer and bear are also targets) used to get infected with Trichinae via their diet of uncooked meats, either foraged or scraps. Now the US requires that even garbage must be cooked before using as feed for commercial hog stock. Government standards now assure that cured ham produced by responsible meat processors is free of trichinae. Cooking to an internal temperature of 137 degrees F. kills the parasite. Minimum government standards require cooked pork to reach 140 degrees F. internal cooking temperature. Canned hams are always cooked to the minimum, and in fact, require very high temperatures during the canning process. As such, when proper cooking procedures are followed, they are inherently erradicated of trichinae and safe. Freezing at a temperature of minus 10 degrees F. for several weeks will also kill Trichinae in pork (but not wild game).
Interestingly enough, trichinae is not found worldwide. Southeast Asia and Europe have no problems with the parasite, allowing the consumption of raw pork without the risk of health problems. If you are purchasing your ham from a reputable retailer in the US, there is generally no need to worry about trichinosis, as long as you read the label and follow manufacturer's instructions for consumption.