Combining epidemiology with basic biology of sand flies, parasites, and hosts to inform leishmaniasis transmission dynamics and control
Fig 2
Two modes of sand fly transmission under the influence of dose and the biological inputs that influence them.
Flies feeding on mammalian hosts with a high parasite load are infected with a high dose of parasites, generating infections with a high frequency of metacyclic promastigotes that are transmitted to a second mammalian host with high efficiency and in larger numbers, resulting in more severe disease [54]. Higher dose infections in the mammalian host result in more severe acute disease but with more complete resolution and lower parasite loads in the chronic phase. Lower dose infections result in mild acute disease but chronic moderate disease [58, 59]. High acute parasite loads act as highly efficient reservoirs for disease, while low chronic parasite loads are very poor reservoirs for disease, and chronic moderate parasite loads are moderate reservoirs for disease [58–60]. Individuals with high parasite loads are mammalian “super-spreaders” by virtue of their high reservoir potential, while sand flies with high parasite loads are sand fly “super-spreaders” by virtue of their highly efficient transmission of parasites.