Fig 1.
Reported cases of visceral leishmaniasis in India from 1977 to 2014.
Data 1977–1985 are from Bihar only; data from 1986 onward include all reported cases in India. Source of data: Ministry of Health and Family Welfare, Government of India, as published in [17, 18].
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.