Biology

The eggs (around 50) are laid separately in various types of habitats, such as cracks in the ground, burrows of small mammals, caves, slits of walls and the

Figure 1.9 Female Phlebotomus papatasi sandfly (Photo courtesy of CDC/Frank Collins/James Gathany).

grounds of dwellings or cattle sheds. Habitats are generally quiet, dark, cool and damp places with the presence of organic detritus. The egg incubation lasts 4 to 17 days according to temperature and season. Larvae are sedentary, saprophagous and phytophagous. There are four larval stages and the last moult produces the pupa which remains fixed by its abdominal end in the larval habitat and does not feed. The immature development lasts 20 to 75 days.1 The adults encounter each other in habitats that are calm, in the proximity of vertebrate hosts (blood meals), and near favourable larval habitats. Females are hematophagous (pool feeding lasting 10-30 min). They can be found in both domestic and natural (e.g. associated with reptiles and rodents) environments. The majority of the species are rather zoophilic (e.g. bat, rodents, carnivorous, marsupials, birds, reptiles, etc.), but the main vectors of leish-maniasis, Lutzomyia intermedia and L. longipalpis in America and P. papatasi in the Mediterranean basin, are anthropophilic and endophilic. Sandflies are generally active at sundown or at night, but they can be diurnal in the canopy (e.g. L. trapidoi in Panama). They have a short flight (< 1 km), but considerable dispersion with the wind is possible.

Transmission of Leishmania

Sandflies are the only vectors of Leishmania, a protozoan parasite.29 More than 50 species of sandflies are involved in the transmission of several Leishmania species to man, such as species of the Lutzomyia donovani complex (e.g. Le. donovani, Le. infantum and Le. chagasi); the Le. mexicana complex (e.g. Le. mexicana, Le. amazonensis and Le. venezuelensis); Le. tropica; Le. major; Le. aethiopica; species of the sub-genus Viannia (e.g. Le. braziliensis, Le.

guyanensis, Le. panamensis and Le. peruviana). Morphologically indistinguishable, species within a complex require molecular techniques for reliable identification.

The human parasites at the amastigote stage are ingested during the bite, and they transform into promastigotes with flagellum and multiply within the sandfly gut. The promastigotes are highly motile and they migrate forward to the oesophagus and the pharynx, and gain the oral parts about 9-10 days after the blood-meal. Leishmania parasites are deposited passively on the wound of the bite. The entire development lasts up to two weeks, depending on the Leishmania species and temperature, and it stays infective throughout the life of the infected sandfly. Phlebotomus ariasi of southern France (see Table 1.3) infected by Le. infantum can normally survive 30 days carrying out three to four gonotrophic cycles (3-4 changes to transmit).

Visceral leishmaniasis or kala-azar: More than 90% of the world's incidences of visceral leishmaniasis occur in India, Bangladesh, Nepal, Sudan and Brazil, but cases are also found along the Mediterranean basin, the Middle East, Central Asia and northern China (see Table 1.3). The parasites are Leishmania of the Donovani complex, especially Le. infantum (Mediterranean basin), Le. donovani (India and Bangladesh), Le. archibaldi (East Africa) and Le. chagasi (Latin America). The hosts are man (children), dog, fox, jackal and rodent. The vectors are Phlebotomus major (Israel), P. perniciosus (Northern Africa), P. longicuspis, P. ariasi (Southern France), P. chinensis (Northern and Eastern China, Central Asia) and P. sergenti (Afghanistan).

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