CASE DISCUSSION
1. The lesion and the organism detected by culture are both consistent with the protozoan Leishmania sp. There are three major disease syndromes caused by this parasite: cutaneous, mucocutaneous, and visceral leishmaniasis. Conventional wisdom concerning Leishmania contends that the different forms of the disease are caused by different species of the parasite. These species specificities are believed to be related to the temperature range of the individual parasites, with species unable to grow at the core human body temperature causing cutaneous disease, while those capable of growing at higher temperature cause visceral disease. Recent cases of atypical visceral disease caused by species which typically cause cutaneous disease have led to the reexamination of that idea.
This patient had Old Word cutaneous leishmaniasis. This form of leishmaniasis is found in Mediterranean, Middle Eastern, and African countries and is caused by two species, L. tropica and L. major. The chief difference between these species is the character of the cutaneous lesion produced. The patient's lesion which was described as "draining" is consistent with L. tropica. L. major tend to produce "dry" ulcers which crust over.
The question of how the patient did not have systemic symptoms may appear confusing since the patient had severe diarrhea with a 20-lb. weight loss at the time his first skin lesion appeared. He in fact had systemic symptoms at that time. However, it is more likely that his symptoms were due to "traveler's diarrhea" contracted while visiting Egypt. The concurrent diarrhea and lesion appearance were a coincidence. Since his diarrhea had resolved 5 months previously, it clearly was not part of his current illness. This type of coincidence, which occurs frequently in medicine, can cloud the diagnostic picture.
Since this patient had cutaneous leishmaniasis, in which the disease process is limited to the skin, the absence of systemic symptoms is expected.
2. The natural history of this disease is consistent with the patient's clinical presentation. After infection, it takes approximately 1 week to 6 months for lesions to appear. In L. tropica infection the ulcers have raised borders and are often moist appearing. They usually spontaneously heal within several months, although they may results in disfiguring scars on the face.
When multiple lesions are observed with this disease, they usually are the result of multiple bites by the disease vector. Metastatic lesions from a single lesions can also occur.
3. Old World leishmaniasis is speared by the bite of the sand fly belonging to the genus Phlebotomus. It is believed that rodents act as a reservoir for this parasite and that the life cycle is competed in the insect vector. The infective phase, the promastigote, develops in the gut of the insect and is injected into the skin during the insect's blood meal on a mammal.
The sand fly's habitat is in rodent burrows and stone, concrete, or earthen cracks or crevices. The insect is typically found in shaded areas. It is a nocturnal feeder, so preventive measures are most important in the evening and at night. They include the use of insect repellents, wearing long-sleeved shirts and pants. and using insecticides in sleeping areas. The insect's small size (3 mm) makes screens and mosquito netting of limited protective value.
4. The sand fly cannot bite through clothes. Therefore, it can feed on exposed areas of the skin. This typically is the head and neck in individuals who wear clothing that covers the trunk and extremities or sleep under bed clothing. The patient discussed here reported that he frequently or only shorts and received multiple insect bites, explaining why he had lesion on his back and legs.
Reference
1. Evans, T.G. 1993 Leishmaniasis. Infect. Dis. Clin. North Am. 7:527-546.
2. Neva, F.A. and H. W. Brown. 1994. Basic and Clinical Parasitology, . 71-81, 286-287. Appleton and Lange, Norwalk. Conn.
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