As it does in southern Mexico and central America, a focus of cutaneous leishmaniasis also exists in central and southern Texas. All of the 27 patients in this series of cutaneous leishmaniasis, 20 of whom were identified between 1980 and 1989, and some of whom have been previously reported as individual cases, were Texas residents with no history of travel to other endemic areas. Isoenzyme analysis of organisms isolated from eight cases was consistent with L. mexicana. The distribution of cases followed the natural habitat of the southern plains woodrat, Neotoma micropus (a resident of San Antonio recently described these animals to me as very common local denizens and not very rat-like, but more like a "cute" little ground squirrel).
Twenty of 27 patients presented with a single lesion that began as a papule and which subsequently ulcerated; three patients had strictly papular or nodular lesions, and the lesions in two were described as plaques. Two cases involved the nasal mucosa. Of the lesions, 20 were located on the head, six on the upper extremities, three on the lower extremities, and one on the buttock. All but one lesion was painless.
Two of the patients presented with evidence of disseminated disease and diffuse cutaneous involvement, one of whom had a 60-year history of extensive lesions that had eluded diagnosis. The remaining patient had extensive large lesions but a good lymphoproliferative response atypical of classical Disseminated cutaneous leishmaniasis (DCL). One-fifth of the lesions healed spontaneously; the remainder were successfully treated with a variety of local measures (e.g., excision, electrodessication, cryotherapy, topical antimony cream) or systemic treatments (e.g., ketoconazole, itraconazole, stibogluconate, g interferon). Only one patient (with DCL) failed therapy (with cycloguanil).
COMMENT BY CAROL A. KEMPER, MD
While this report suggests that leishmaniasis is, at least thus far, primarily limited to the southernmost border of Texas (2 of the 27 cases were identified in central Texas), it is worth noting that, similar to malaria, both the potential vector and the host (e.g., woodrats, cotton rats, opossums, and armadillos) exist throughout a sizable area of the United States. In fact, leishmaniasis has been documented in domestic dogs and cats, as well as wild canids throughout Texas, and autochothonous visceral leishmaniasis has been reported in at least 14 dogs from Oklahoma and Kansas.
While the identity of the vector for leishmaniasis in Texas remains controversial, one of several sandflies is a likely candidate. One such candidate, Lutzomyia diabolica, is endemic throughout the southwest, has been found in association with woodrats, and is avidly anthropophilic (it enjoys human blood). In this regard, the ecology of leishmaniasis in Texas may more closely resemble that of L. major in the Old World where the organism circulates among burrowing rodents and the sandflies that inhabit their burrows.
The authors, however, point out that all of these 27 cases had prolonged or repeated exposure to the natural habitat, and none of the 13 household or family members tested showed a positive lymphoproliferative response to preparations of L. mexicana antigen. These data suggest that infection in humans remains infrequent and is limited to those with a significant risk of exposure.
The diagnosis of leishmaniasis was significantly delayed in several of the patients described, ranging from several days to 64 years (median, 3 months). Many had been treated with topical ointments and antibacterials for weeks to months before the correct diagnosis was made, and one had been treated for leprosy for four years. Serological diagnosis was only positive in three cases and negative in one. The recognition of infection, therefore, requires a high index of suspicion and the identification of the amastigotes, by either light microscopy, electron microscopy, or in vitro culture, within the lesion.
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