Abstract
BackgroundLeishmanin Skin Test (LST) is considered as a useful indicator of past infection by Leishmania parasites. However, the temporal dynamics of a positive LST under different epidemiologic scenarios and whether it relates to the protection against the recurrence of an overt disease are not fully documented.Methodology/Principal findingsWe report here on a population based prospective study conducted on 2686 individuals living in two foci located in Central Tunisia, to assess over a one-year epidemiologic season, the incidence of Leishmania (L.) major infection and disease and changes in LST reactivity. The two foci were both endemic for Cutaneous Leishmaniasis (CL) due to L. major, but contrasted in their history for this disease (ie: an old focus versus a recent focus).We found that most infections occurred in the new focus (290/1000; 95% CI: 265–315 person-years) with an incidence rate of CL lesions 2.4 times higher than in the old focus. Likewise, the rates of LST reactivity reversion and loss, in the new focus, were 99/1000[38–116] person-years and 14/1000[8–21] person-years, respectively. Loss of LST reactivity was not noticed in the old focus. Interestingly, the incidence rates of symptomatic infection did not differ significantly according to the LST status at enrolment (negative versus positive) between the combined foci and the new one.Conclusions/SignificanceOur findings confirm LST as a good tool for assessing L. major cryptic infection. However, the instability of the LST positivity in new foci should be considered as an important confounder of the outcome of this infection when developing a research protocol for vaccine trial.
Highlights
Leishmaniasis is a group of vector-borne diseases transmitted by the bite of phlebotomine sand-flies that generate a heavy disease burden at the global level
We report here on a population based prospective study conducted on 2686 individuals living in two foci located in Central Tunisia, to assess over a one-year epidemiologic season, the incidence of Leishmania (L.) major infection and disease and changes in Leishmanin Skin Test (LST) reactivity
The instability of the LST positivity in new foci should be considered as an important confounder of the outcome of this infection when developing a research protocol for vaccine trial. This population-based cohort study is the first one conducted in the Old World which compares the incidence of Zoonotic Cutaneous Leishmaniasis (ZCL) to the temporal dynamics of LST in two foci contrasting in their past history for L major transmission
Summary
Leishmaniasis is a group of vector-borne diseases transmitted by the bite of phlebotomine sand-flies that generate a heavy disease burden at the global level. The most frequent form, known as Zoonotic Cutaneous Leishmaniasis (ZCL), is caused by Leishmania (L.) major with rodents as animal reservoir and occurs in Central and Southern Tunisia [1]. In epidemiological surveys, LST positivity in individuals without active cutaneous lesions or typical scars or any history of patent cutaneous sore (s), is considered as indicative of prior asymptomatic infection [4]. It is well known that patients developing overt ZCL are to some degree, protected against disease recurrence when exposed in subsequent years to infected sand fly bites; LST positivity is inferred to correlate with this protection [4, 5] and LST negative individuals are considered as constituting the pool of susceptible in the exposed population. The temporal dynamics of a positive LST under different epidemiologic scenarios and whether it relates to the protection against the recurrence of an overt disease are not fully documented
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