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There are about 700 species of phlebotomine sand flies of which about 70 are considered to transmit diseases to people. The term sand flies is also sometimes confusingly used for other small biting flies, especially ceratopogonid flies (biting midges) of the genus Culicoides. It is used below exclusively for the Phlebotominae. Sand flies are found mainly in the tropics with a few species also found in the temperate regions. They occur in a wide range of habitats and species often have very specific habitat requirements. In the Old World, leishmaniasis is found mainly in dry, semi-arid areas whereas in the New World, this disease occurs mainly in tropical forests and savannas.
Sand flies (Phlebotominae) are blood suckers and their larvae inhabit places where there is high organic matter such as in animal burrows, termite hills and tree holes. Sand flies are best known as vectors of trypanosome species in the genus Leishmania, causing diseases collectively known as leishmaniasis.
New World sand flies
Old World sand flies
Disease organisms transmitted
It is difficult studying the life cycle of sand flies because the larvae are tiny and don't live in well defined places, like mosquito larvae. The entire life cycle takes 20-40 days except in diapausing species (i.e. those that stop developing when conditions become too cold).
Eggs. The female lays 30-70 eggs by scattering them around a potential breeding site. They hatch within 1-2 weeks.
Larvae. Larvae feed on dead organic matter and are found in damp places containing organic matter such as cracks in walls or rock, animal burrows and shelters, caves, or in leaf litter. In regions with cool winters, larvae diapause in the fourth (final) instar.
Pupae. Pupal development takes 5-10 days.
Adults. Emerge from the pupae in darkness, often just before dawn. Only the female sucks blood, the food being used for egg production. Both males and females feed on sugary secretions from plants or from honeydew produced by homopteran bugs. Mating takes place at or near hosts: the males congregate in leks on or near the host and produce sex pheromones. Females home in on hosts using both host odor and the odor produced by the males. Vibration of the wings by males can be important in encouraging females to mate.
Adults are mainly active in the early morning, evening and at night although they can bite during the day if disturbed. When inactive, adult sand flies have habitat-specific resting sites that are characteristic of particular species. One of the main ways in which entomologists study sand flies is by locating and studying them at their resting sites. Resting sites are often similar or near to the larval breeding sites and are usually places that are cool, humid and dark. Sand flies are able to survive in dry environments by withdrawing to cool, humid resting sites during the day and then becoming active at night when ambient temperatures drop and humidity increases.
Seasonal activity of adults is affected mainly by temperature and rainfall.
The diseases of the 'Leishmaniasis' group are caused by intracellular protozoan parasites of the genus Leishmania. There is a large number of species and subspecies of Leishmania, grouped according to their development within the sand fly vector. Among the 30 known species, 21 infect humans. All are spread by bites of infected sand flies. Leishmania is named after Dr Leishman, who first described it in London in May 1903. Leishmania are intracellular parasites that infect the mononuclear phagocytes. The spectrum of human disease ranges from self-healing localized ulcers to widely disseminated progressive lesions of the skin, mucus membranes, even the entire reticuloendothelial system. There are two major forms of leishmaniases: cutaneous and visceral leishmaniases. Cutaneous leishmaniases afflict 1.5 millions of people all over the World. They cause sores on the skin, which can be disfiguring. They can spread to mucus linings of the nose and throat to cause a less common disease known as mucosal leishmaniasis. In contrast, visceral leishmaniases cause a disruption of the immune system, resulting in fever, enlargement of the liver, enlargement of the spleen, anemia, and loss of weight. There are half a million new cases of visceral leishmaniases around World each year. If untreated, visceral leishmaniases are fatal.
Some sand flies are also vectors of several animal trypanosomes (Wallace & Hertig 1968) and probably of an Endotrypanum of sloth's (Shaw 1964). A reptilian malaria parasite has been found to develop to the sporozoite stage in two species of Lutzomyia (Ayala & Lee 1970).
Bartonella bacilliformis is bacterium causing the disease bartonellosis, which takes the form of the dermal Verruga Peruana or the Severe Oroya Fever or Carrion's Disease, in Northwestern part of South America (Peru, Colombia and Ecuador) (Lewis 1973).
Vesicular Stomatitis is an acute viral vesicular disease that primarily affects cattle, horses, and swine's. The virus that causes Vesicular Stomatitis has a wide host range. This disease also occasionally affects sheep and goats. Many species of wild animals, including cattle, deer, bobcats, pigs, goats, raccoons, and monkeys, have been found to be susceptible hosts. Humans can also become infected with Vesicular Stomatitis when handling affected animals. The etiologic agent, Vesicular Stomatitis Virus (VSV), is a rhabdovirus. One type of VSV is spread by phlebotomine sand flies. Once introduced into a herd, the disease apparently moves from animal to animal by contact or exposure to saliva or fluid from ruptured lesions.
The genus Phlebovirus comprises over 50 viruses which are transmitted by mosquitoes or phlebotomine flies. Rift Valley Fever Virus and Sand Fly Fever Virus are the most medically important agents which have been the greatest focus of study. Toscana Virus occurs in the Northern and Western Mediterranean area. Chagres and Punta Toro Viruses occur in the New World.