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Tropical Sprue

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September 04, 2019

April 21, 2021

Tropical Sprue
Tropical Sprue

Tropical sprue is a digestive disease endemic to India and Pakistan, though cases have also been reported from Burma, Malaysia, Indonesia, Singapore and Vietnam. Scottish physician Sir Patrick Manson coined the term in 1880, while he was studying tropical diseases in China. 

The “tropical” in the name refers to countries between the Tropic of Cancer and the Tropic of Capricorn, and “sprue” is a modification of the Dutch word “Indische sprouw” - a term that was used to indicate the presence of mouth ulcers and glossitis, or inflammation of the tongue.

In India, tropical sprue is among the major causes of malabsorption syndrome - which affects the small intestine. Patients with tropical sprue can’t absorb sufficient quantities of essential nutrients, usually folate (the natural form of vitamin B9) and vitamin B12, from their food. 

Though we don’t yet know the exact cause of tropical sprue, researchers argue that it could be environmental or nutritional. Researchers also say that tropical sprue may be the result of a bacterial infection. The treatment for tropical sprue depends on the patient's nutritional deficiencies and infection, if it is present.

Symptoms of Tropical Sprue

The onset of symptoms can be sudden. The underlying malabsorption of essential nutrients gives rise to symptoms like:

  • Diarrhoea - the most common symptom of tropical sprue
  • Megaloblastic anaemia, a characteristic symptom of the disease, occurs because of folate and vitamin B12 deficiency. The bone marrow of patients produces abnormally large red blood cells and fewer red blood cells in the body - resulting in anaemia
  • Steatorrhoea - or fatty stool which is difficult to flush, foul-smelling, bulky with pale and oily appearance - indicates malabsorption of fats
  • Abdominal cramps
  • Fatigue
  • Loss of appetite
  • Weight loss
  • Sore tongue
  • Night blindness
  • Asthenia (lack of energy and strength)
  • Fever

Causes of Tropical Sprue

The exact cause of tropical sprue is not known yet. However, there are several clues for scientists: first, tropical sprue is usually seen in people who are from the tropics or have had a prolonged stay in a tropical country.

Second, patients often see rapid improvement after taking folic acid and vitamin B12 supplements.

Third, bacterial colonies isolated from the small intestines of travellers to the tropics suggest overgrowth of coliforms - a class of bacteria - like Klebsiella, E.coli and Enterobacter. However, as a counterpoint, several studies also point out that bacterial population is present in the small intestine of patients with tropical sprue as well as in healthy people.

Prevalence of Tropical Sprue

Tropical sprue is a disease endemic to the tropical countries - India and Pakistan especially, but also Burma, Indonesia, Borneo, Malaysia, Singapore, Vietnam, Haiti, the Dominican Republic, Puerto Rico, and Cuba. 

Foreigners who stay in the tropics for prolonged periods (more than one month) can also get the disease. Though, tourists who spend less than two weeks in the tropics rarely get the infection.

Diagnosis of Tropical Sprue

A doctor may suspect tropical sprue in a patient who has the characteristic symptoms (like megaloblastic anaemia) and nutritional deficiencies (example, folate and vitamin B12 deficiencies), and is a resident of a tropical country.

Tropical sprue affects the absorption of essential nutrients through the small intestine - a diagnostic procedure called enteroscopy can help to examine the state of villi and microvilli in the small intestine. (Villi and microvilli are tiny finger-like protrusions on the surface of the small intestine - their function is to increase surface area so the small intestine can absorb maximum nutrients. In patients with malabsorption syndrome, these villi and microvilli are somewhat flattened. An enteroscopy can help to ascertain this.)

Enteroscopy is a minimally invasive outpatient procedure in which the doctor inserts an illuminated tube called an endoscope into the small intestine. The endoscope has a microscope attached to it which helps the doctor check for any structural changes. Sometimes, the doctor may take a small tissue sample from the small intestine for further histological examination

A blood test helps to examine your nutritional level. Your doctor could ask for the following tests:

stool examination to assess the amount of fat excreted through stool.

Tropical Sprue Treatment

The course of treatment depends on the severity of the disease. To control the infection, your doctor may prescribe a course of antibiotics along with nutritional supplements.

Antibiotics: The patient is usually given tetracycline (250 mg, four times a day) for one to two months - your doctor may then change the dosage to twice a day for six months. Doxycycline (100 mg, twice a day) may be prescribed alternatively. Both tetracycline and doxycycline are strong antibiotics with side-effects like nausea and vomiting, diarrhoea and loss of appetite. Patients may break out into rashes and hives. It is crucial to check with your doctor, and only take these medicines if they are prescribed by a certified physician.

Nutritional supplements: Folate supplements (5 mg to 10 mg/day) are given to patients for one month along with vitamin B12 supplements (1 mg/week) for several weeks.

Your doctor will be able detect severe deficiencies of any other essential nutrient by physical examination and through tests, and recommend supplements to manage the deficit in the body.

Patients usually respond well to antibiotic treatment and supplements. If, however, doctors don’t see an improvement after four weeks of treatment, they may suspect another intestinal disorder such as:

  • Gluten-sensitive enteropathy or non-tropical sprue or celiac sprue
  • Giardiasis: An infectious disease of the small intestine caused by a unicellular organism known as Giardia lamblia
  • Crohn's disease: An inflammatory bowel disease in which there is severe inflammation of the intestinal wall or gut
  • Ulcerative colitis: An acute inflammatory bowel disease with multiple ulcerations in the gut, diarrhea and blood in the stools because of multiple, irregular ulcerations of the bowel

The relapse rate of tropical sprue is also higher in tropical countries - up to 20%. Practising good hygiene helps to reduce the risk of infection among the general population.

Prognosis of tropical sprue

Changes are seen in the small intestine at the microscopic level. 

The small intestine comprises folds - tiny projections with crests (villi) and depressions (crypts) - to increase the surface area. These villi, in turn, have microvilli to further increase the surface area for absorbing nutrients. In a healthy person, the small intestine is usually 20 feet long but it has a surface area of over 300 square feet.

In tropical sprue patients, the villi and crypts start to degenerate progressively. As a result, the absorptive surface area of the small intestine decreases. Tropical sprue also damages the epithelial cells of the microvilli, which results in inadequate absorption of xylose (plant-based glucose), fats and fat-soluble vitamins.

Structural changes in different parts of the small intestine represent malabsorption of different nutrients. If parts of the first section of the small intestine (duodenum) are damaged, folate and iron deficiency can be seen. If the third and last section of the small intestine (ileum) is damaged, vitamin B12 and bile acid absorption are hampered. Unabsorbed bile acid along with water and electrolytes from the large intestine cause diarrhoea.



References

  1. National Organization for Rare Disorders [Internet], Tropical Sprue
  2. MSDmannual Professional version [internet].Tropical Sprue. Merck Sharp & Dohme Corp. Merck & Co., Inc., Kenilworth, NJ, USA
  3. Prashant Singh et al. Tropical sprue. UpToDate, Jan 16, 2019. [internet]
  4. BMJ Best Practice. Tropical sprue. BMJ Publishing Group [Internet]
  5. Health Harvard Publishing. Harvard Medical School [Internet]. Tropical Sprue. Harvard University, Cambridge, Massachusetts.
  6. Christine Wanke. Tropical Sprue. Infectious Disease Advisor. [internet]
  7. Westergaard H. Tropical Sprue. Curr Treat Options Gastroenterol. 2004 Feb;7(1):7-11. PMID: 14723833
  8. B S Ramakrishna, S Venkataraman, A Mukhopadhya. Tropical malabsorption. Postgrad Med J. 2006 Dec; 82(974): 779–787. PMID: 17148698
  9. Uday C. Ghoshal, Sunil Kumar, Asha Misra, Gourdas Choudhuri. Pathogenesis of tropical sprue: A pilot study of antroduodenal manometry, duodenocaecal transit time & fat-induced ileal brake . Indian J Med Res. 2013 Jan; 137(1): 63–72. PMID: 23481053

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