Reevaluating leishmanin skin test as a marker for immunity against cutaneous leishmaniasis

The leishmanin skin test (LST) has been used for clinical diagnosis of leishmaniasis and epidemiological studies of the disease. Thus far, evidence has suggested that LST conversion indicates a degree of protection against leishmaniasis. In this study, we have put this assumption to test.

A total of 273 participants with positive LST living in a hyperendemic area for leishmaniasis were followed for three years for any occurrence of cutaneous leishmaniasis.

Twenty-two of the 273 participants contracted leishmaniasis during the 3-year follow-up. These new cases included participants who had a previous history of active disease, those who had a history of leishmanization, or those who were suspected of having a history of subclinical infection.

In this study, the incidence of leishmaniasis in individuals with positive LST was close to the general incidence of the disease in the same hyperendemic area. These results suggest that although LST conversion may be a marker for partial immunity towards leishmaniasis, it may not, however, indicate complete protection against the disease, and consequently there is a need for revision of current vaccine development approaches which are based on rendering vaccinated individuals LST positive.