Tropical sprue

Tropical sprue is a gastrointestinal disease that results in malabsorption of nutrients and water.

Just like the other “sprue” diseases, like celiac sprue which is more often known as celiac disease, in tropical sprue the villi of the small intestine become flattened, but the exact cause isn’t known.

The biggest clue is that tropical sprue seems to mostly affect individuals living in the the tropical regions of the world, like the Caribbean, India, and Southeast Asia.

The most widely accepted theory is that an acute intestinal infection, which could be bacterial, viral, or protozoal, initially damages the intestinal lining, and this causes the first bit of inflammation.

In response, the intestinal cells secrete enteroglucagon, which is a hormone that decreases intestinal motility.

Decreased motility means that food’s allowed to linger in the intestines for longer than usual.

More food means more resources, so this sets the stage for a change in the normal bacterial flora, which leads to bacterial overgrowth.

Bacterial overgrowth refers to the idea that some organisms begin to overpopulate and therefore dominate the bacterial ecosystem of the intestines.

In tropical sprue, Klebsiella, E. coli, and Enterobacter end up becoming those dominant bacteria. These guys release toxic byproducts as they ferment the food that lingers in the gut, and these toxins can damage the intestinal lining, leading to more inflammation.

Over time, all of this chronic inflammation leads to villous atrophy, which is flattening of the villi that line the small intestine.

Villi are important because they provide the surface area and digestive enzymes necessary for nutrient absorption.

Flattening of the villi reduces this surface area, which means less nutrients and water can be absorbed across the intestinal wall, which leads to malabsorption.

This (1) means more food is left behind for the bacteria, which leads to more intestinal wall injury and inflammation, and (2) the malabsorption also causes depletion of vitamin B12 and folate over time.