There are 20 named species of the genus Leishmania at present recognized in
the New World, of which 14 are known to infect man. The present paper
discusses the biological, biochemical and ecological features, where known,
of six species which have not till now been found to cause human
leishmaniasis; namely, Leishmania (Leishmania) enriettii, L. (L.) hertigi,
L. (L.) deanei, L. (L.) aristidesi, L. (L.) forattinii and L. (Viannia)
equatorensis. A protocol is suggested for attempts to discover the natural
mammalian host(s) and sandfly vector of L. (L.) enriettii. Doubt is cast on
the validity of the species L. herreri, described in Costa Rican sloths.
Following the concensus of opinion that modern trypanosomatids derive from
monogenetic intestinal flagellates of arthropods, phlebotomine sandflies
are best regarded as the primary hosts of Leishmania species, with mammals
acting as secondary hosts providing a source of parasites for these
insects. There are probably natural barriers limiting the life-cycle of
most leishmanial parasites to specific sandfly vectors.
