A 31-year-old man visits relatives in Barcelona at the beginning of an extended vacation. He asks for ideas on how to spend his time, and his relatives suggest a leisurely tour of the northern Mediterranean coast. This sounds great, so the man spends the next six weeks enjoying the beaches and other coastal features between Gibraltar and Monaco.

About 10 months after returning to the U.S. from his vacation, the man starts to experience malaise and fatigue that slowly becomes more noticeable over a period of two months. He then starts to experience occasional diarrhea and low-grade fever. The fever, malaise, and fatigue persist over the next few weeks, and the man begins to lose weight. He then begins to experience abdominal discomfort, which worsens over the next month or so, and he continues to lose weight. At this point, he seeks medical advice.

Vital signs are T = 38.3ºC, P = 85, R = 17, BP = 135/85 mm Hg. On physical examination, the man appears somewhat malnourished. He has pronounced splenomegaly and the liver span is increased, but neither organ is tender. There is also evidence of lymphadenopathy. There are no abdominal masses and no abdominal tenderness. Bowel sounds are present. A stool sample for occult blood is negative. There are no other remarkable findings.

Question 3.1: What is your preliminary diagnosis?

The symptoms are too general to be overly suggestive. This appears to be another case of "fever of unknown origin" that can only be diagnosed accurately with more information.

Question 3.2: What tests should you perform?

Serum chemistries and a CBC with differential may shed some light on the situation. You might also want to order blood and lymph or marrow cultures in hopes of identifying a causative agent.

Test Results:

Blood cultures for typical pathogenic bacteria are negative. CBC results are as follows: WBC count = 3350/microliter, Hgb = 11.8 g/dL, Hct = 34.9%, MCV = 90 fL, and platelet count = 89,000/microliter. The differential shows 29 segs, 5 bands, 48 lymphs, and 18 monos. The serum chemistries are: sodium = 140 mmol/L, potassium = 4.4 mmol/L, CO2 = 25 mmol/L, creatinine = 0.9 mg/dL, glucose = 69 mg/dL, total protein = 7.6 g/dL, albumin = 3.2 g/dL, AST = 67 U/L, ALT = 51 U/L, alkaline phosphatase = 190 U/L, and total bilirubin = 1.3 mg/dL.

Question 3.3: How can you confirm a diagnosis?

Some of the test results (e.g., eosinophilia) suggest a parasitic disease, which would be consistent with the negative blood bacterial cultures. The pancytopenia implies bone marrow involvement, possibly enhanced by the enlarged spleen. The results suggest liver involvement. If this is a parasitic disease, the best fit to this combination of symptoms would be visceral leishmaniasis (sometimes known as kala azar). The diagnosis can be confirmed by examination of tissue biopsy, bone marrow aspiration, lymph node aspiration, or liver biopsy, and by thorough examination of properly stained smears.

Test Results:

The bone marrow biopsy shows a maturing hematopoiesis that is reduced. The marrow is infiltrated by macrophages. Protozoan amastigotes with a nucleus and rod-shaped kinetoplast are visible in a Giemsa-stained smear.

NOTE: The causative agent can also be cultured in vitro, using Novy-MacNeal-Nicolle medium. The possible use of molecular methods, such as PCR, in place of marrow or lymph node aspirations is now under investigation.

Question 3.4: What is the causative agent?

Visceral leishmaniasis is caused by protozoa in the Leishmania donovani complex, including L. donovani, L. donovani infantum, and L. donovani chagasi. Of these, only L. donovani infantum is endemic to southern Europe and the Mediterranean area, and this makes it the most likely specific causative agent. (This strain is also endemic to China, central and southwestern Asia, the Middle East, North Africa, Ethiopia, and sub-Saharan Africa.)

Question 3.5: How does this agent cause disease?

Members of the L. donovani complex enter the human body in the promastigote stage (which is a long, slender form with a free flagellum). The promastigotes lose their flagella, enter the amastigote stage, and invade reticuloendothelial cells. Reproduction occurs in the amastigote stage, in leukocytes. As the infected leukocytes rupture, destruction of specific tissues (e.g., liver, spleen, bone marrow) develops.

Question 3.6: How is this disease transmitted?

Visceral leishmaniasis is transmitted to humans by the sandfly (Phlebotomus), which serves as a biological vector. (The promastigote stage of the protozoan is present in the sandfly's saliva and, as a result, is automatically injected when an infected fly bites a human.) The reservoir hosts for L. donovani infantum include dogs, foxes, jackals, and porcupines.

Question 3.7: How is this disease prevented?

Transmission typical is focal, with local "hot spots," in part because of the limited flight range of the sandflies. (These insects a short, hopping flight style and generally remain within a few hundred meters of their breeding site. They nest in dark, moist places in habitats ranging from rain forests to deserts, or in debris or rubble near buildings. Personal protective measures include the avoidance of outdoor activities when sandflies are most active (dusk to dawn), the use of barriers such as screens and bed-nets that keep out sandflies, the wearing of protective clothing, and the use of insect repellent on exposed skin. Vaccine strategies are being investigated.

Question 3.8: How is this disease treated?

Visceral leishmaniasis is treated with pentavalent antimonial compounds. The drug of choice is stibogluconate. Therapy is not universally successful, and relapse rates of 2-8% are seen. Alternative approaches include addition of allopurinol and the use of pentamidine or amphotericin B. If not treated, visceral leishmaniasis can develop into a fulminating, debilitating, lethal disease in a few weeks, or it may persist as a chronic debilitating disease that leads to death in 1-2 years.