Effects of land use type, spatial patterns and host presence on Leishmania tropica vectors activity

Abstract

Background Leishmaniasis is a vector-borne disease, caused by the infection of Leishmania parasites which are transmitted by the bite of infected female phlebotomine sand flies. Leishmania tropica is transmitted by Phlebotomus sergenti and Phlebotomus arabicus while the main reservoir host is the rock hyrax. A marked increase in the incidence of cutaneous leishmaniasis (CL) caused by L. tropica has been detected in recent years in Israel; it is associated with infections which have emerged in new urban and rural foci. The objective of this study is to contribute to a better understanding of the preferred habitat, spatial activities and host-sand fly relationships of both species of vectors within various types of land use. Methods Using CDC-type traps, we investigated the activity levels of sand flies. A field survey was conducted in 2016 at Elifelet, an agricultural village characterized by various types of land use. Movement patterns of P. sergenti between rock-piles were investigated by using colour-marked sugar baits and analyses of recapture patterns. In 2017, a survey was conducted in the hilly Jordan River area, by comparing sand flies and rock hyrax activities in relation to the size of rock-piles and vegetation cover. Results Both sexes of both species were found to have a clear preference for rocky habitats over other land use types in rural landscapes. Movement patterns of P. sergenti were characterized by their high presence close to the rocks and an exponential decrease in their recapture, commensurate with the distance from the rocks. Host-sand fly relationships were found to have a higher correlation between rock hyrax activity levels for females than for males of both species of sand flies. Males exhibited the strongest association with the size of rock-piles. Conclusions The results suggest a strong affinity of both phlebotomine vector species to the rocky habitats of the Mediterranean areas. We suggest that rock-piles are associated with populations of rock hyraxes attracting female sand flies seeking blood sources. Rapid human population growth, coupled with intensive land-use changes and the creation of artificial rock-piles, which created potential habitats for both vectors and hosts in the proximity of many settlements, have increased the prevalence of L. tropica among the human population in the region. Electronic supplementary material The online version of this article (10.1186/s13071-019-3562-0) contains supplementary material, which is available to authorized users.

Expanded genome-wide comparisons give novel insights into population structure and genetic heterogeneity of Leishmania tropica complex

“…These issues demonstrate the importance of additional strategic sampling of WGS data to identify genetic traits associated with potential distinct insect-mammalian infection cycles, under consistent in vitro conditions and a passage-controlled manner [ 19 ]. The distribution of the rock hyrax across Africa and the Middle East [ 68 ] could explain the broad distribution of the African/Galilee population of L . tropica , with the rock hyrax considered by some as the main reservoir for L .…”

“…tropica , with the rock hyrax considered by some as the main reservoir for L . tropica across Africa and the Middle East [ 68 ]. The distinct MLMT defined Asian/India lineage, that has isolates derived from regions beyond the distribution of the rock hyrax, might represent genetic variants associated with a distinct set of mammalian hosts.…”

“…Such genes represent attractive targets to gain new insights into the molecular basis of host-parasite interactions in either insect or mammalian, or both, hosts. These could also be exploited to design more accurate typing schemes for more detailed epidemiological analyses to, for instance, differentiate potential zoonotic from anthroponotic infection cycles [ 68 ]. Our analyses also further highlight the importance of future strategic sampling of genome sequences across the broad genetic diversity and broad host and geographic range for L .…”

“…These issues demonstrate the importance of additional strategic sampling of WGS data to identify genetic traits associated with potential distinct insect-mammalian infection cycles, under consistent in vitro conditions and a passage-controlled manner [19]. The distribution of the rock hyrax across Africa and the Middle East [68] could explain the broad distribution of the African/Galilee population of L. tropica, with the rock hyrax considered by some as the main reservoir for L. tropica across Africa and the Middle East [68]. The distinct MLMT defined Asian/India lineage, that has isolates derived from regions beyond the distribution of the rock hyrax, might represent genetic variants associated with a distinct set of mammalian hosts.…”

Strengthening the global response to climate change and infectious disease threats

“…Increasingly widespread disruption of landscapes and biodiversity, through deforestation and agricultural development, changes socio-ecological systems and forces humans, vectors, livestock, and pathogens into increasingly closer contact 21. For example, land use and land cover changes, in parallel with temperature increase, may contribute to the spread of leishmaniasis by moderating vector activity 2223. This, combined with unplanned and precarious urbanization, increasing global connectivity via international travel and trade, and climate variability, can allow invasive vectors and novel pathogens to spread widely, with the potential for transcontinental pandemics with devastating public health, social, and economic consequences 24…”