Lutzomyia

Lutzomyia is a genus of phlebotomine sand flies consisting of nearly 400 species, at least 33 of which have medical importance as vectors of human disease. Species of the genus Lutzomyia are found only in the New World, distributed in southern areas of the Nearctic and throughout the Neotropic zone. Lutzomyia is one of the two genera of the subfamily Phlebotominae to transmit the Leishmania parasite, with the other being Phlebotomus, found only in the Old World. Lutzomyia sand flies also serve as vectors for the bacterial Carrion’s disease and a number of arboviruses. The genus, named after Adolfo Lutz, is known from the extinct Burdigalian (20-15 mya) species Lutzomyia adiketis found as a fossil in Dominican amber on the island of Hispaniola. It is thought that species in the genus Lutzomyia all originated in the lowland forests to the east of the Andes mountain range, and that their radiation throughout the Neotropics was sparked by dry periods of the Pleistocene, driving colonisation further north and west to areas of higher humidity and leading to reproductive isolation. The classification of species within the genus Lutzomyia is largely unresolved, and relies on often controversial divisions based on morphological taxonomic characters. Such analyses can suffer from polymorphisms within a species, the existence of cryptic species and the frequent lack of distinct morphological characters amongst females. Research has begun in an attempt to resolve evolutionary relationships between species in the genus, using molecular methods to create phylogenies based on ribosomal DNA sequences. The Lutzomyia sand flies are small, biting insects with a body length of up to only 3mm. They are hairy insects with their colour ranging from a near-white to near-black. Only the female Lutzomyia sand flies are blood-feeding, requiring the bloodmeal to provide the nutrients for the maturation of eggs. Therefore, it is only the females who have medical importance as vectors of disease. Both males and females require carbohydrate food as adults, the source of which remains unclear. The most medically important species for human disease transmission are those which predominantly favour humans as a source of bloodmeal. These species are known as anthropophillic and tend to feed at around dusk. However, there are examples of anthropophillic species that will attack in the daytime. The majority of anthropohillic Lutzomyia species in the Americas are exophillic, which means that they favour biting outside of homes. The resting behaviour of Lutzomyia sand flies, like many other aspects of their biology, is important to understand for targeted, vector-based control methods to reduce transmission of Leishmaniasis. For example, residual spraying of insecticides can be targeted at known resting sites to increase effectiveness. Lutzomyia sand flies generally rest outdoors, with the type of resting site varying between species and in response to the seasons and the availability of particular microhabitats. The largest resting microhabitat is the forest floor, but sand flies will also rest in a variety of other areas, such as in the nests and burrows of mammals, within the trunks of hollow trees and inside bat caves. The resting position adopted by Lutzomyia sand flies is characteristic to the genus, with wings angling above the abdomen. The sand fly genus Lutzomyia includes all species responsible for transmission, in the New World, of the Leishmania parasite; the causative agent of leishmaniasis. Of the more than 350 Lutzomyia species identified, less than 10% are known or suspected to transmit leishmaniasis to humans. The disease is in endemic in 22 countries of tropical and subtropical America, where it is generally considered a zoonosis. That is, the parasite cycles between mammalian reservoir hosts and the sand flies, with humans serving as incidental, dead-end hosts. Common reservoirs in the Americas include a number of rodent species, as well as dogs, sloths and armadillos. The Lutzomyia sand flies maintain transmission amongst reservoir species and allow the disease to ‘jump’ to humans, causing the visceral, cutaneous or mucocutaneous forms of the disease depending on the Leishmania species. The human-sand fly-human cycle of transmission, known as anthroponotic, is limited to two Leishmania species endemic in the Old World and so does not involve Lutzomyia sand flies.