Irrigation in the arid regions of Tunisia impacts the abundance and apparent density of sand fly vectors of Leishmania infantum

Abstract

The distribution expansion of important human visceral leishmaniasis (HVL) and sporadic cutaneous leishmaniasis (SCL) vector species, Phlebotomus perfiliewi and P. perniciosus, throughout central Tunisia is a major public health concern. This study was designed to investigate if the expansion of irrigation influences the abundance of sand fly species potentially involved in the transmission of HVL and SCL located in arid bioclimatic regions. Geographic and remote sensing approaches were used to predict the density of visceral leishmaniasis vectors in Tunisia. Entomological investigations were performed in the governorate of Sidi Bouzid, located in the arid bioclimatic region of Tunisia. In 2012, sand flies were collected by CDC light traps located at nine irrigated and nine non-irrigated sites to determine species abundance. Eight species in two genera were collected. Among sand flies of the subgenus Larroussius, P. perfiliewi was the only species collected significantly more in irrigated areas. Trap data were then used to develop Poisson regression models to map the apparent density of important sand fly species as a function of different environmental covariates including climate and vegetation density. The density of P. perfiliewi is predicted to be moderately high in the arid regions. These results highlight that the abundance of P. perfiliewi is associated with the development of irrigated areas and suggests that the expansion of this species will continue to more arid areas of the country as irrigation sites continue to be developed in the region. The continued increase in irrigated areas in the Middle East and North Africa region deserves attention, as it is associated with the spread of L. infantum vector P. perfiliewi. Integrated vector management strategies targeting irrigation structures to reduce sand fly vector populations should be evaluated in light of these findings.

Keywords: Human visceral leishmaniasis; Integrated vector management; Phlebotomus perfiliewi; Remote sensing approaches.

Figure 1

Bioclimatic map of Tunisia. Tunisia has a wide climatic range from a Mediterranean climate with its rainy winter in the north to a Saharan climate in the south.

Figure 2

The 16 sand fly sampling sites in the governorate of Sidi Bouzid, Tunisia.

Figure 3

Poisson regression predicated density of two important Leishmania vectors: A) P. perfiliewi and B) P. perniciosus. Models used three independent covariates: minimum EVI (2011), minimum EVI (2012), and SD EVI (2011) and sand fly vector distributions reported in the present report and Zhioua et al. 2007.