Leishmaniaareprotozoabelongingtothefamilytrypanosomatidae.Theparasitesexistintwoforms:thepromastigotesinthemidgutofthevectorinsect,and
theamastigoteswithinthephagolysosomesofmacrophagesintheirmammalianhosts.Inthemacrophagestheyliveasround,non-motileamastigotes(3-7mm
indiameter).Themacrophagesareingestedbythesandflyduringblood-mealandtheamastigotesarereleasedintotheirstomach.Almostimmediatelythe
amastigotestransformintothemotile,elongated(10-20µm),flagellatepromastigoteform,whichmigratetothealimentarytractoftheflyandafter
multiplicationmoveforwardtothesalivaryglandsoftheinsect.Leishmaniasesareagloballywidespreadgroupofparasiticdiseases;the“type”isdetermined
bytheprimarylocationofthemacrophagesthatareinfected.InhumansfourdifferentformsofLeishmaniasiswithabroadrangeofclinicalmanifestationsare
present;allcanhavedevastingconsequences.Leishmaniasiscurrentlyaffectssome12millionpeoplein88countries,allbut16ofwhichareinthedeveloping
world.Itisestimatedthat350millionpeopleareexposedtotheriskofinfectionbythedifferentspeciesofLeishmaniaparasite;theannualincidenceofnew
casesisabout2million(1-1.5millioncasesofCL,500,000casesofVL).Visceralleishmaniasis(VL)isthemostsevereformofthedisease,which,if
untreated,hasamortalityrateofalmost100%.Likemanyothertropicaldiseases,theleishmaniasesarerelatedtoeconomicdevelopmentandman-made
environmentalchanges,whichincreaseexposuretothesandflyvector.Thegeographicaldistributionislimitedbythedistributionofthesandfly.AIDSand
otherimmunosuppressiveconditionsincreasetheriskofLeishmaniainfectedpeopledevelopingvisceralillness(VL).Leishmania/HIVco-infectionsare
consideredtobeareal“emergingdisease”,especiallyinsouth-westernEurope,where25-70%ofadultVLcasesarerelatedtoHIVinfection,and1.5-9.5%of
AIDScasessufferfromnewlyacquiredorreactivatedVL.Intravenousdrugusershavebeenidentifiedasthemainpopulationatrisk.