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. 2012;6(5):e1633.
doi: 10.1371/journal.pntd.0001633. Epub 2012 May 1.

Temporal dynamics and impact of climate factors on the incidence of zoonotic cutaneous leishmaniasis in central Tunisia

Amine Toumi  1 , Sadok Chlif, Jihene Bettaieb, Nissaf Ben Alaya, Aicha Boukthir, Zaher E Ahmadi, Afif Ben Salah
Affiliations

Temporal dynamics and impact of climate factors on the incidence of zoonotic cutaneous leishmaniasis in central Tunisia

Amine Toumi et al. PLoS Negl Trop Dis. 2012.

Abstract

Background: Old world Zoonotic Cutaneous Leishmaniasis (ZCL) is a vector-borne human disease caused by Leishmania major, a unicellular eukaryotic parasite transmitted by pool blood-feeding sand flies mainly to wild rodents, such as Psammomys obesus. The human beings who share the rodent and sand fly habitats can be subverted as both sand fly blood resource. ZCL is endemic in the Middle East, Central Asia, Subsaharan and North Africa. Like other vector-borne diseases, the incidence of ZCL displayed by humans varies with environmental and climate factors. However, so far no study has addressed the temporal dynamics or the impact of climate factors on the ZCL risk.

Principal findings: Seasonality during the same epidemiologic year and interval between ZCL epidemics ranging from 4 to 7 years were demonstrated. Models showed that ZCL incidence is raising i) by 1.8% (95% confidence intervals CI:0.0-3.6%) when there is 1 mm increase in the rainfall lagged by 12 to 14 months ii) by 5.0% (95% CI: 0.8-9.4%) when there is a 1% increase in humidity from July to September in the same epidemiologic year.

Conclusion/significance: Higher rainfall is expected to result in increased density of chenopods, a halophytic plant that constitutes the exclusive food of Psammomys obesus. Consequently, following a high density of Psammomys obesus, the pool of Leishmania major transmissible from the rodents to blood-feeding female sand flies could lead to a higher probability of transmission to humans over the next season. These findings provide the evidence that ZCL is highly influenced by climate factors that could affect both Psammomys obesus and the sand fly population densities.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Location of study area.
(a) Tunisia Location Within Mediterranean Basin. (b) Location of Sidi Bouzid Governorate Within Tunisia.
Figure 2
Figure 2. Box plot with monthly ZCL incidence.
Data was aggregated from January 1991 to December 2007. The box represents the 25th and 75th percentiles. The median is represented by a solid horizontal line. The whiskers of the graph show the 1st percentile to the 99th percentile. Values lower than the first and greater than the 99th percentile are represented by a point.
Figure 3
Figure 3. Autocorrelation Function (ACF) of monthly ZCL incidence.
Figure 4
Figure 4. Monthly ZCL incidence adjusted vs not adjusted for monthly seasonality (1991–2007).
Figure 5
Figure 5. Adjusted relationship between ZCL incidence and humidity, temperature and rainfall.
There were no turning points in the relation between temperature/humidity and ZCL incidence. Therefore, we assume these relationships as linear. For rainfall lagged by 12 to 14 months, a turning point equal to 37.34 exists. The range, from each plot, that the climate variables have a positive effect on ZCL incidence is over the zero axis.
See this image and copyright information in PMC

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