Descriptive and molecular epidemiology of leishmaniasis diagnosed from clinical samples in the United States, 2021-2022

Abstract

ABSTRACT Leishmaniasis is a rare disease in the United States, with an estimated annual incidence of dozens of cases occurring primarily in travelers, migrants, and military personnel. True disease incidence is unknown, since leishmaniasis is not a nationally notifiable condition. Here, we describe the results of molecular leishmaniasis over a 1-year interval (September 2021 to August 2022) when our laboratory served as the primary national reference laboratory for molecular diagnosis of civilian leishmaniasis. We tested 218 specimens submitted from 36 states yielding 94 of the 186 (50.5%) positive cases with species or species complex-level identification and 18 novel mini-exon alleles. Most species belonged to subgenus Viannia (75.6%) and associated with cutaneous or mucocutaneous disease. Cases were associated with recent travel (18.1%), travel timing unspecified (7.4%), migration (7.4%), remote travel (2.1%), military (1.1%), or unknown history (63.8%). These data illustrate the clinical utility of molecular testing for leishmaniasis and provide unique insight into disease epidemiology. IMPORTANCE Leishmaniasis is a disfiguring, neglected parasitic infection endemic to the Southern United States and the Americas. Despite significant populations at risk—travelers, military and foreign service members, and migrating persons—the epidemiology of the disease in the United States is poorly understood. Moreover, few clinical laboratories in the United States can test for the disease. Here, we present results from 1 year of testing for this disease at a major reference laboratory. These findings are particularly relevant because they coincide with a temporary “pause” on all clinical testing at the CDC. Our findings suggest at least several hundred cases occur each year in the United States. In particular, mucosal leishmaniasis may be more common than previously reported. We also highlight greater genetic diversity in Leishmania species endemic to the Americas than has been previously sampled, with implications for diagnostic specificity.