Human-made and environmental changes
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Human-made and natural changes to the environment may lead to changes in the range and densities of leishmania vectors and reservoirs, hereby increasing human exposure to infected sand flies.
For instance, in several southern Mediterranean countries, new villages are developed with inadequate abattoirs. These are attractive hangout areas for semi-domestic or stray dogs. This creates a situation likely to favour the increase of the population of these animals and, consequently, the sources of L. infantum for human infection. In parallel, a high density of susceptible human hosts is also the consequence of human made changes, like fast urbanization and widespread migration from rural to urban areas. In the city of Kabul for example, an estimated 67 500 cases of cutaneous leishmaniasis occurred in 2001 among the less than 2 million inhabitants of the city.
Other contributors to increased density of susceptible human hosts are population movements for economic reasons, such as the development of agro-industrial projects or seeking safe heaven from civil unrest. The latter is best illustrated by the recent epidemics of VL in Sudan, where 100.000 persons (out of 300.000 infected) died of VL in the Western Upper Nile State.
Concerning environmental changes, projections of potential geographic distributions across scenarios of global climate change have suggested that some Lutzomyia species are likely to be experiencing dramatic changes in conditions in areas where cutaneous leishmaniasis appears to be re-emerging, as it has been observed in south-eastern Brazil.
Last but not least, the disruption of public health systems will lead to both increased sand fly densities when vector control is compromised, and to an expansion of the disease incidence.