Visceral Leishmaniasis: diagnosis

Leishmaniasis should be suspected in case of persistent fever, emaciation, hepatosplenomegaly and signs of pancytopaenia. Differential diagnosis includes tuberculosis, brucellosis, Hodgkin’s or non-Hodgkin’s lymphoma, leukaemia, myelofibrosis, chronic malaria (HMS), liver cirrhosis, schistosomiasis with liver fibrosis and, more rarely, metabolic diseases such as Gaucher type 1 disease (glucocerebrosidase deficiency) or Nieman Pick type B disease (sphingomyelinase deficiency).

Direct diagnosis is made by demonstrating the presence of the parasite. This is usually done on bone marrow obtained by sternum aspiration. The parasite is egg-shaped and measures 2-3 x 5 m. There is a pale blue cytoplasm, a well defined nucleus and a smaller kinetoplast (Giemsa staining). In very rare instances, when there is a considerable delay between the aspiration itself and the preparation of the microscopic slide in the laboratory, promastigotes can be seen. In these cases the amastigotes had the time to change their morphology. The technique of spleen aspiration is more sensitive (in some studies very nearly 100%, though in reality slightly lower) than bone marrow aspiration, but can be risky (spleen rupture, haemorrhage). If one wants to use a splenic aspirate, it is better to use the intercostal rather than the transabdominal route (safer, can be carried out more often). The 10th intercostal space between the anterior and the mid-axillary line is generally used. The procedure is safe when performed by an experienced physician, and when the prothrombin time is normal. The platelet count should be above 40 x 10⁹/liter. One can use a 21-gauge needle and a 5 ml syringe. After penetration of the skin, the plunger is withdrawn, the needle is quickly inserted into the spleen while maintaining suction and withdrawn immediately. Lymph node aspiration and liver biopsy are sometimes necessary. The parasites can rarely be detected in peripheral blood monocytes. Serology is positive in visceral leishmaniasis. The DAT (direct agglutination test) is often used, as this test has a high sensitivity and specificity. The best possibility in a small regional clinic is to absorb a drop of blood from a patient suspected to have kala azar on a small filter paper and then to punch out a standard size disk from the blood spot. In this way one obtains a well-defined, accurate aliquot of absorbed blood. This can be transported and used for DAT in a well equipped laboratory. Serology will remain positive after cure. If Leishmania-HIV co-infection is suspected, blood smears, buffy coat or blood cultures can be used to detect the parasites. The parasites can be cultured, both in vitro (NNN-medium, Schneider’s medium, Tobie rabbit blood agar (only Old World) or Nogushi soft agar with rabbit blood (Old and New World), as well as in test animals (golden hamsters), though this is usually not feasible in clinical practice in developing countries. A Leishmania parasite can survive for 3 days at a temperature of 4 C, but for only 1 day at room temperature, in Locke transport medium (a buffered glucose-salt solution with antibiotics).

Category: Medicine Notes