Pellagra is a disease resulting from a nutritional deficiency, the lack of niacin, one of the B vitamins. Since pellagra is caused by lack of niacin, which is present in many foods and can be synthesized in the body from the tryptophan in others, only a few types of diet lead to it. The disease was almost unknown to the world before the 1500s, because the most common cause of pellagra is a diet made up almost exclusively of corn (that is, maize or Indian corn -- the plant of the scientific name zea mays). Since this plant is native to the Western Hemisphere, pellagra was not found in the Eastern Hemisphere until this plant had been imported and become a major food crop.
However, pellagra seems to have been quite rare in the Western Hemisphere before the arrival of Europeans, even though corn was one of the major food crops. This seems to be because the other major plant foods, beans and squashes, provided sufficient niacin and also because the methods used to make corn tortillas involved soaking the kernels of corn in alkali or lime and water, processes which release what little niacin is present in corn from the chemical bonds that usually make it unavailable for the body's nutritional needs. The disease remained rare in areas where these foods continued to be the standard diet after European colonization.
However, in places where cornbread, corn mush/polenta, and other corn products became the major food for poor people who could not afford additional foods, pellagra became widespread among the poor. Doctors first recorded the disease in Europe in the early 1700s in northwestern Spain; it was then called "mal de la rosa," or the illness of redness. Certainly the red scaly sores were the first noticeable symptom of the three major ones (later called the three Ds: dermatitis, diarrhea, and dementia). Similar symptoms got different names in other areas, such as "mal del higado" in other parts of Spain and "mal de la teste" in parts of France. "Pellagra" is a regional Italian name for the disease which means "rough skin."
These different names made it difficult for doctors to realize that it really was the same disease. Probably that was a handicap in figuring out what caused the condition. French physicians in the 19th century often thought it was something caught from sheep that for which certain types of people had a hereditary susceptibility. Others realized that it only affected those who ate mostly corn, but thought the disease was a result of mold on the corn, in the same way that ergotism is caused by rye infected with the ergot fungus. Additional theories included bad water, excessive use of sea salt, sunstroke (since the skin lesions of the disease tend to recur in spring and summer) and that it was just a hereditary condition. Also, many cases of pellagra went unrecognized, mistaken for some other condition.
Pellagra was not much recorded in North America until the late 1800s, though examining of old records makes it seem to have been around for at least half a century before. It became widely known as a health problem in the early 1900s, particularly in the South. At the 1909 First National Conference on Pellagra, the fact that the disease seemed to occur mostly in people who subsisted on corn was emphasized, but the speakers seemed to support the idea that moldy corn or some problem with imported corn was the cause -- no one seemed to want to think that ordinary, locally grown corn could cause any problems.
Treatment ideas varied widely. Arsenic was popular for a while, as was Paul Ehrlich's arsenic-related anti-syphilis drug Salvarsan; other drugs administered included strychnine and quinine. And that's just the things that doctors prescribed -- the number of quack remedies was enormous.
Dr. Joseph Goldberger's observations and experiments in 1914-6 with children in orphanages and volunteer prison inmates showed that pellagra could be cured and prevented by adding other kinds of foods to the diet, that it could not be transmitted from one person to another, and finally that it could be induced in previously healthy people by giving them the limited diet that had been observed in areas where pellagra was prevalent. (His conclusions took a while to be accepted widely, but are now recognized to be the first proof.) At this time, though, it was still not known exactly what component was lacking in the diet.
A disease called blacktongue found in dogs was discovered to be the canine equivalent of pellagra, and this allowed Goldberger and others to experiment with exactly what foods and what chemicals caused and prevented the disease. Brewer's yeast was discovered to prevent and cure pellagra, but this only worked for pellagrins who could still eat -- those far into the course of the disease had loss of appetite, burning in the throat, nausea, and often delusions, and any of those could interfere with administering a curative by mouth. An extract of liver was found to work if injected in large doses, but this was very expensive and the poor people who got the disease could not usually afford it.
In 1935, Conrad A. Elvehjem and Carl J. Koehm, employees of the Department of Agricultural Chemistry at the University of Wisconsin, isolated two chemicals, nicotinic acid and nicotinamide, which both would cure blacktongue in dogs in a very short time. Nicotinic acid was eventually discovered to be the real factor needed to prevent the disease, but in 1941 the chemical was renamed "niacin" to avoid confusion with nicotine.
The discovery of the vitamin lacking in the pellagrin diet did not automatically make the disease disappear. However, in the early 1940s, U.S. bakeries and mills started enriching the flour they ground with some of the nutrients the wheat lost in the milling process. Some Southern states started to require the same be done with cornmeal. In 1943 during World War II, enrichment was made mandatory by the U.S. government. After the war, it was no longer mandatory but most bread producers continued to enrich their bread, and this essentially eliminated pellagra in the U.S. except as a side effect of other diseases (alcoholism, anorexia) in which little niacin is eaten or something prevents the proper absorption of niacin.
The same reduction of pellagra has happened in most other industrialized countries. The place it is most often seen now is portions of the Deccan Plateau of India, where the main food source is a type of millet/sorghum which, although it technically contains sufficient niacin, also contains a substance called leucine which prevents the proper absorption of the niacin. Parts of Egypt and South Africa also had a lot of pellagra among the poor in the later 20th century.
The first visible symptom of pellagra is usually the lesions on the skin and mucous membranes. It also causes weakness, weight loss, irritability, depression, and eventually mental confusion and memory loss. Pellagra victims often ended up in insane asylums. Without treatment, pellagra leads to death, sometimes by malnutrition, since the patient often loses the strength to eat, has mouth lesions making it painful to eat, suffers enough intestinal damage that anything they do eat cannot be absorbed, and loses nutrients from extreme diarrhea. Other causes of death can be blood loss from intestinal bleeding or the encephalopathic syndrome resulting from the effects on the brain.
There's no chemical test for pellagra; it is diagnosed from the symptoms and from the patient's improvement when given niacin.
Roe, Daphne A. A Plague of Corn: A Social History of Pellagra. Ithaca: Cornell University Press, 1973.