Secondary lactase deficiency is distinct from genetically determined loss of lactase with age. Secondary lactase deficiency is frequently associated with diseases of the small intestine. Enteric viruses, such as rotavirus and Norwalk agent, can induce lactase deficiency by penetration of the enterocyte in the small intestine Rotaviruses are a principal cause of diarrhea and lactose intolerance in infancy. Denudation of the brush border of the jejunal mucosa associated with diarrhea can lead to the loss of the other two disaccharides, maltase and sucrose. Continued diarrhea may also lead to severe complications such as monosaccharide intolerance. Giardiasis have also been implicated as contributing to lactose maldigestion. An additional infection resulting in an interference with lactose digestion is Ascaris lumbricoides. Severe protein malnutrition is frequently associated with lactose maldigestion. Other disease conditions that give rise to secondary lactose maldigestion are celiac disease, gluten-induced enteropathy, and tropical and nontropical sprue. The mucosal brush border of the small intestine is severely damaged in each case.
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