Reappraisal of Leishmanin Skin Test (LST) in the management of American Cutaneous Leishmaniasis: A retrospective analysis from a reference center in Argentina

Abstract

Leishmania (Viannia) braziliensis is the species most frequently implicated with cutaneous and mucosal leishmaniasis in the Americas; its diagnosis is based on the identification of amastigotes in lesions, which is limited by low parasite burden. Leishmanin Skin Test (LST) is a support tool for diagnosis, based on delayed type hypersensitivity responses to Leishmania antigens injected intradermally, used in endemic areas as a complement to diagnosis. A retrospective analysis of individuals evaluated for their first episode of tegumentary leishmaniasis at a reference center in Argentina during the period 2006-2015 was performed, with the goal of assessing its usefulness as a support tool in the diagnosis of leishmaniasis. Demographic, clinical and diagnostic work-up were analyzed in individuals with clinically compatible lesions, lesion's smear and LST. A total of 733 cases that met the case definition were included in the analysis; 678 (93%) localized cutaneous cases, 50 (7%) with mucosal involvement and 5 (<1%) disseminated. Diagnostic confirmation was reached in 474 (65%) cases through positive smears from skin or mucosal lesions, with only 6 cases among this group having negative LST. Among smear negative cases, 190 were negative also by LST, but in 69 instances LST was positive. Across age groups, similar ratios of sensitivity between smear and LST were calculated. Lesions older than 21 days-old were found to correlate with positive results both for smear and LST significantly more than younger lesions. These findings support the clinical use of LST as a diagnostic complement for American Cutaneous Leishmaniasis across all age groups even in endemic areas. In this analysis, the correlation with smear was high. Standardization of this technique and further research into its most adequate preparation and utilization protocols across different sites will help in the management of suspicious clinical cases. Funding: The author(s) received no specific funding for this work. Competing interests:The authors have declared that no competing interests exist. Author summaryAmerican Cutaneous Leishmaniasis (ACL) is a vector borne Neglected Tropical Disease with skin ulcers as the main clinical manifestation. Diagnosis is suspected when characteristic lesions occur in patients in areas known to be endemic and confirmed with microscopic identification of amastigotes in samples obtained from lesions. The Leishmanin Skin Test (LST) is an aid in the diagnosis based on the elicitation of delayed type hypersensitivity responses upon exposure to Leishmania antigens injected intradermally into the patient´s forearm and measured as the induration size after 48 hours. This analysis of 733 cases, which is the largest series of cases evaluating the role of LST in ACL highlights and establishes the usefulness of this complementary diagnostic tool with a strong correlation with lesion smear and a demonstration that false positive responses due to previous exposure to the parasite are not of concern. The results support the use...

Molecular Identification of Leishmania spp. DNA from Archived Giemsa-Stained Slides of Patients from Salta, Argentina

“…As in our study PCR assays have been carried out from smears' DNA, the molecular results were highly dependent on the samples collected and prepared for microscopy; and because P1+ smears had the lowest proportion of positive PCR (Figure 3), the importance of considering LST as a complementary diagnostic tool is highlighted. In a previous study, our group has shown that the ratio of positive LST to positive smear was ³ 1 and maintained across age groups, 19 supporting its diagnostic ability and suggesting that within an adequate epidemiologic frame, cases with positive LST but negative smear, can be related to the limited sensitivity of direct diagnostic methods rather than to LST sensitization due to exposure to parasite but with no clinical symptoms.…”

“…The results do not agree with recent research in the same study area in a larger group of patients. 19 No significant correlation was found for microscopic diagnosis and diameter of the lesion. The results agree with a previous work, where parasite burden was quantified by qPCR.…”

“…Localized cutaneous form is frequently observed there, and it can be simple or multiple depending on the number of lesions [25][26][27] ; also, mucocutaneous disease is found in the region. 7,8,19,24 Entomological surveys carried out there, have determined that the predominant species is Nyssomyia neivai, 28,29 which has been linked to outbreaks and human cases in our country. [29][30][31] In addition, this sand fly species is a proved vector of L. (V.) braziliensis.…”

“…34 Induration size has been observed to be larger among cases with mucosal involvement in some reports but not in other larger case series. 19 Hence, for those patients (LST < 19), a milder cellular response might be responsible for a higher parasite burden, which would explain their higher PCR positivity and an increased amastigote density on microscopy, being all P2+ and P3+ smears positive for PCR ( Figure 4). In agreement with this, treatment response has been reported to be higher among patients with larger LST induration, 35 which might be indicating an effective cellular response.…”

“…Leishmanin was locally prepared with a soluble extract of promastigotes of L. (V.) braziliensis, obtained in culture from a patient of our region (strain MHOM/AR/03/OLO1) as described elsewhere. 19 Indurations were considered positive if diameter was ³ 5 mm. For comparison with other variables, the values of the LST induration diameter were categorized into two classes with 19 mm (< 19 and ³ 19 mm) as the class mark.…”