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I found this excerpt about Celiac & Sprue here -
http://www.rehydrate.org/dd/html/dd10.htm  -

thought it was interesting.  Along with the problems in 3rd world
countries this panel of International Doctors were the first I've heard
mention Celiac Sprue being provocked by Tropical exposure (which really
helps put the pieces together for me (as far as probabilities go).

Major causes of chronic diarrhoea

Dietary causes
A component of food grains (particularly wheat) known as gluten can
cause small bowel disease (gluten enteropathy or coeliac disease). The
mucosal lining of the gut is more severely affected than in tropical
malabsorption and the condition can, on rare occasions, be provoked by
tropical exposure. The only effective treatment is to completely remove
gluten from the diet; there is no response to antibiotics and folic
acid.

Hypolactasia is a deficiency of the digestive enzyme which splits
lactose, the sugar found in milk. Any condition which damages the
mucosal lining of the small intestine can produce hypolactasia. It also
occurs any time after three or four years of age as an inherited
characteristic among a significant range of populations. Chronic
diarrhoea results if large amounts of milk are consumed but the
absorption of other foods is not affected.