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 Neotropical realm. 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.

Systematics

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.

Medical importance

Leishmaniasis

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 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. These genetically distinct parasites show markedly different patterns of development within the New World sand flies when compared to those seen in the Old World Phlebotomus sand flies. The first stages of development are similar between all Leishmania species, with the sandfly taking up the amastigote form of the parasite following a bite of an infected host. However, unlike in the Old World, the replicated parasites then migrate to the hindgut of the Lutzomyia sand fly, a feature which is thought to be essential in allowing the parasite to become established. The parasite then undergoes further development into the infective, promastigote stage as it migrates to anterior end of the insect, ready for inoculation into a new, susceptible host.

The high level of species diversity in the genus Lutzomyia, coupled with its high adaptability is leading to increasing risk of Leishmania transmission in the New World in response to global change. Lutzomyia sand flies transmit the disease in the tropics and subtropics, regions which are subject to high levels of deforestation associated with continual development. Deforestation, with the establishment of settlements at the periphery of primary or secondary forest, increases the risk of Leishmania transmission by creating a selection pressure for the adaptation of sand flies to these new peridomestic environments. In southern Brazil, for example, levels of cutaneous leishmaniasis are increasing as a result of the adaptation of three, formerly forest-inhabiting species (Lutzomyia intermedia, Lutzomyia whitmani and Lutzomyi migonei) following deforestation. Now, a disease which previously only affected forest workers is becoming more prevalent in urbanisations. Similar increases in risk factors are also driving higher rates of visceral leishmaniasis in north-eastern Brazil. Increased urbanisation, driven by climate change and socio-economic factors, is bringing the adapting sand flies into closer contact with both humans and the domestic canine reservoirs of the disease. The lifecycle of the bacteria within Lutzomyia sand flies remain largely unknown, with speculation that the bacteria are spread between sandflies sharing the same breeding grounds and water supplies. The existence of bartonellosis transmission in areas not inhabited by Lutzomyia verracarum suggests that secondary vectors, and potentially other Lutzomyia species, are important in the spread of the disease.

Viruses

A number of arthropod-borne viruses (arboviruses) are transmitted by Lutzomyia sand flies. One such virus of medical importance is the vesicular stomatitis virus (VSV) of the genus Vesiculovirus. Viruses of this genus are typically associated with flu-like symptoms, but have also been known to cause encephalitis.

See also

Maria Cristina Ferro

References

  • CIPA Computer-aided Identification of Phlebotomine sandflies of America
  • Lutzomyia shannoni, a sand fly on the UF / IFAS Featured Creatures Web site
  • General information on Leishmaniasis from the CDC