In the Middle Ages, the range of types of diseases was similar to what we experience today, with some exceptions (HIV/AIDS). Viruses, of course, are no easier to combat now than then, but without vaccines and if the infected person was living in unclean or freezing conditions, or suffering from a poor diet, the disease was made that much worse. Antibiotics help with some diseases, but then again, more have sprung up in response to them (C-diff).
That said, these are some of the most common diseases people experienced in Europe in the Middle Ages (not including the Black Plague, see: http://www.sarahwoodbury.com/?p=1000; or leprosy, see: http://www.sarahwoodbury.com/?p=223)
Dysentary: Still common in poorer countries today, Dysentary is an infection caused either by bacteria or amoebas, spread through contamination of food and water by infected fecal matter. Typhoid is another such disease spread through bacteria and fecal matter which was not uncommon in the Middle Ages
“Symptoms: (Bacillary) After 1-6 days incubation, watery stools, fever, cramps, dehydration. In advanced stages, bloody stools, meningitis, conjunctivitis, and arthritis. (Amebic) Acute form: watery, bloody stools, cramps, fever, weakness. Chronic form: intermittent diarrhea, mild abdominal discomfort. Result: Generally weakened condition. Note: Endemic in medieval armies and pretty common in cities. Infantile diarrhea was a leading cause of death for infants. After the Black Death, many urban areas instituted public health reforms to improve sanitation and prevent these enteric fevers.” http://www.labelle.org/top_diseases.html
Symptoms: (Convulsive) Degeneration of the nervous system causes anxiety, vertigo, aural/visual hallucinations, and the sensation of being bitten or burned; stupor, convulsions, and psychosis. (Gangrenous) Constriction of the blood vessels causes reddening and blistering of skin, then blackening, with itching and burning, and finally necrosis. Result: 40% mortality. Lingering symptoms, including mental impairment, among survivors.
Note: Ergotism was known as a rural disease, particularly of marshy areas, and one that followed crop damage or famine; especially after a severe winter and a rainy spring. Children are more susceptible because of their smaller body weight. Because England did not rely on rye as much as populations on the continent, it suffered fewer cases of the convulsive type.” http://www.labelle.org/top_diseases.html
Sexually Transmitted Diseases (Gonorrhea, Syphilis):
“In the early part of the 14th century there were outbreaks of typhoid fever, dysentery and diphtheria. It has been estimated that in 1316 about 10% of the population died from these three diseases.” http://www.spartacus.schoolnet.co.uk/YALDdisease.htm