Tropical Diarrhea and Malabsorption

Infectious Diarrhea In The Tropics

Acute and chronic infectious diarrhea in the tropics are caused by a variety of bacterial, viral, and parasitic agents ( Box 108.1 ). Although these pathogens affect the indigenous population of the tropics, many infected adults remain asymptomatic, probably because of immunity acquired by earlier exposures to the same or related infectious agents. Short-term visitors to the tropics, however, are at significant risk for diarrhea with nearly 50% developing a diarrheal illness during their stay. In the past decade, incidence rates of diarrhea during travel to countries with improving economies dropped significantly, although rates remained high with travel to South Asia, Western Asia, northern and tropical Africa, and Central America.

Cholera is the most dramatic form of acute diarrhea, and results in death from dehydration and electrolyte imbalance if untreated. Cholera continues to be endemic in the Indian subcontinent, particularly in the southern and eastern parts; the Indonesian islands; the Philippines; and Latin America; it may also afflict travelers to these countries. Epidemics of cholera occur intermittently in tropical developing countries, related to breakdown in sanitation and hygiene during or shortly after the rainy season, during large gatherings of people such as occurs at places of religious significance, and also during war or civil strife. In the past decade, cholera has become endemic in major parts of sub-Saharan Africa, affecting nearly 150,000 persons per year. Among 10,032 patients in the US with illness related to foreign travel, acute diarrhea was most common, accounting for 22% of cases. The etiology of acute diarrheal illness in travelers is often geographically determined. Thus, enterotoxin-producing Escherichia coli was associated with travel to South America or to Mexico; Giardia lamblia and Cryptosporidium spp.with travel to South Central Asia; and Campylobacter spp. with travel in South and Southeast Asia and less commonly to West or East Africa, and not with travel to or in South America or the Caribbean. Campylobacter exhibited a high degree of resistance to fluoroquinolones. When molecular methods are used to diagnose which infection is causing diarrhea, multiple pathogens are detected in nearly a half of samples. Enteropathogenic E. coli and enteroaggregative E. coli were more common than enterotoxigenic E. col i or Campylobacter. Arcobacter species and enterotoxin-producing Bacteroides fragilis have been identified as important causes of diarrhea in some areas. Infection with the coccidian parasites, Cyclospora, Cryptosporidium and Cystoisospora, and with the fungus, microsporidia, causes transient or no illness in immunocompetent residents of the tropics, but may cause persistent diarrhea in travelers who have returned from the tropics. The opportunistic heterokont Blastocystis and the protozoan Dientamoeba fragilis may often be identified in the stools of symptomatic returned travelers, but their frequent carriage in stool even prior to travel means these must be viewed with caution when assigning causation for diarrhea. Noroviruses are another emerging cause of diarrhea associated with travel to tropical countries.

Tropical Sprue

TS remains the major cause of malabsorption in tropical countries. Despite much investigation, the etiology of this disease has never been satisfactorily elucidated. In recent times, TS has been overshadowed by the emergence of celiac disease as a major cause of malabsorption in some parts of the world (e.g., in some states of northern India). TS continues to be reported in individuals who return to temperate climates after prolonged stays in tropical developing countries. TS needs to be differentiated from a variety of other conditions that also cause malabsorption in residents of the tropics ( Box 108.2 ).