LIVING THE LAB LIFE
A BLOG FOR ASCLS REGION V
Last month, the microbiology department at the lab that I work in got a unique request from one of our Infectious Disease attending physicians. The doctor informed us that she had a patient who she suspected had been infected with Leishmania. She had been in contact with experts at the Centers for Disease Control and Prevention about how to diagnose this patient, and therefore, we should expect to receive a special kit from them with materials to properly process a culture for Leishmania.
Since I live and work in Minnesota, a disease like Leishmaniasis is not routinely seen. But as we live in an increasingly diverse world where our hospitals may be treating patients from all over the world, we laboratorians need to be ready to handle the unexpected. Here, I will do a brief review of Leishmaniasis.
Leishmania is intracellular, flagellate parasite transmitted through the adult female sand fly. Over twenty species of Leishmania have been identified. It is endemic throughout the tropical and sub-tropical regions of the world. For this reason, most patients in the United States who present with the disease will either be immigrants or travelers. The disease manifests in three forms: cutaneous, muco-cutaneous, and visceral leishmaniasis.
In cutaneous leishmaniasis, a self-limiting, red, cutaneous papule appears at the site of the sand fly bite. It takes two to eight weeks for the lesion to form after the initial bite. With time, the lesion will pruritic, enlarged and eventually ulcerates. The ulcer will then crust over and exude a serous fluid. At this point, the lesion is prone to secondary infections. Best case scenario, the lesion will heal over but leave a pronounce scar. Depending on the species of Leishmania, the infection may spread to other cutaneous sites, causing more lesions. Another route for spread of Leishmania infection is through direct contact with skin lesions.
In muco-cutaneous leishmaniasis, or espundia, the infection starts as a cutaneous lesion that spreads to oral and nasal mucosal membrane. The lesions that form on muco-cutaneous membranes are persistant and destructive to the tissue. Secondary infections are very common with muco-cutaneous lesions and can be fatal.
Visceral leishmaniasis (dumdum fever, kala-azar) manifests as a widespread, systemic disease causing hepatosplenomegaly and bone marrow infection. The severity of the disease varies from asymptomatic, subclinical presentations to fulminate, rapid onset presentation that is often fatal. First symptoms to appear are fever, anemia, and diarrhea. As the Leishmania parasites proliferate, they invade more tissues, causing hepatosplenomegaly, anemia, kidney damage, and weight loss.
Treatment of Leishmania has typically involved use of sodium stibogluconate (Pentostam), but emerging resistance to the drug has complicated treatment. The drug is also quite toxic, expensive, and it has variable effectiveness in patients. In cases of cutaneous leishmaniasis, the disease is treated by directly injecting the chemotherapeutic agent (fluconazole, miltefosine, amphotericin B), or by surgical excising the lesion.
Multiple methods are available for diagnosing Leishmaniasis. Many tissues or fluids can be used, depending on the exact manifestations of the disease. Culturing of Leishmania sp. can be achieved through use of a special culture media: Novy-MacNeal-Nicolle (NNN) media. After the organism is grown in culture, the isolate can that be speciated with PCR or isoenzyme techniques. PCR methods can also be used for direct detection of Leishmania. Serological testing is also available, but these methods are not useful in all clinical presentations.
On biopsy, Leishmania can be diagnosed in any infected tissue. Using a Giemsa or H&E stain, small amastigotes can be visualized within the histiocytes, forming Leishman-Donovan bodies. The amastigotes appear as small (2-5 µM), ovoid structures with a small nucleus that lies adjacent to a rod-shaped kinetoplast. Diagnosis via biopsy must be done with cautious, as other intracellular organisms such as trypanosomes, Toxoplasma, and Histoplasma can have similar appearance to Leishmania.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, Missouri: W.B. Saunders Company.
Mais, D. D. (2014). Practical Clinical Pathology. Hong Kong: ASCP Press.
Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2009). Medical Microbiology (6th ed.). Philadelphia: Mosby Elsevier.