Phlebotomine Sand-flies PDF

5 Phlebotomine sand-flies (Phlebotominae) 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0 ...

5 Phlebotomine sand-flies (Phlebotominae) 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  94 Phlebotomine sand-flies (Phlebotominae) There are approaching 1000 species of sand-flies in six genera, within the subfamily Phlebotominae of the family Psychodidae. Species in three genera – Phlebotomus, Lutzomyia and Sergentomyia – suck blood from vertebrates; the former two are the more important as they contain dis- ease vectors. The genus Phlebotomus occurs only in the Old World, from southern parts of the northern temperate areas, mainly the Mediterranean region, to central Asia, and in tropical areas, but there are not many species in sub-Saharan Africa or South-east Asia and none in the Pacific area. Most Phlebotomus species inhabit semiarid and savannah areas in preference to forests. Lutzomyia species are found only in the New World, and, by con- trast, occur mainly in forested areas of Central and South America. Sergentomyia species are also confined to the Old World, being found mainly in the Indian subregion, sub-Saharan Africa and Asia. Although a few species bite people they are not vectors. Adult flies are often called sand-flies because of their colour. However, this can be confusing because in some parts of the world the small biting midges of the family Ceratopogonidae (Chapter 6) and black-flies (Simuli- idae, Chapter 4) are called sand-flies. The medically most important species include Phlebotomus papatasi, P. sergenti, P. argentipes, P. ariasi, P. perniciosus and species in the Lutzomyia longipalpis and L. flaviscutellata complexes. In both the Old and New Worlds sand-flies are vectors of leishmaniasis and viruses responsible for sandfly fever, and in the Andes the bacterium Bartonella bacilliformis, causing bartonellosis (Carrión’s disease). 5.1 External morphology Adults of Phlebotomus and Lutzomyia are difficult to distinguish, but as the former genus is found only in the Old World and the latter in the New World this is not a problem. Adult phlebotomine sand-flies are readily recognized by their minute size (1.5–3.5 mm in length), hairy appearance, relatively large black eyes and their long and stilt-like legs (Plate 6). The only other blood-sucking flies which are as small as this are some species of biting midges (Cer- atopogonidae), but these have non-hairy wings and differ in many other details (Chapter 6). Phlebotomine sand-flies have the head, thorax, wings and abdomen densely covered with long hairs. The 16-segmented anten- nae are long and composed of small bead-like segments having short hairs; antennae are similar in both sexes. The mouthparts are short and inconspic- uous and adapted for blood-sucking, but only females bite. At their base is a pair of five-segmented maxillary palps which are relatively conspicuous and droop downwards. Wings are lanceolate in outline and quite distinct from the wings of other biting flies. The Phlebotominae can be distinguished from other subfami- lies of the family Psychodidae, which they may superficially resemble, by their wings. In sand-flies the wings are held at an angle of about 40! over 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  Life cycle 95 Figure 5.1 Adult male phlebotomine sand-fly showing genital claspers at end of abdomen, and a diagrammatic representation of the double branching of wing vein 2. the body when the fly is at rest or blood-feeding, whereas in non-biting psy- chodid flies they are folded, roof-like, over the body or flat. Wing venation also differs. In phlebotomine sand-flies, but not in the other subfamilies of Psychodidae, vein 2 branches twice, although this may not be apparent unless most of the hairs are rubbed from the wing veins (Fig. 5.1). The abdomen is moderately long and in the female more or less rounded at the tip. In males it terminates in a prominent pair of genital claspers (Fig. 5.1) which give the end of the abdomen an upturned appearance. Identification of adult phlebotomine sand-flies to species is difficult and usually necessitates the examination of internal structures, such as the arrangement of the teeth on the cibarial armature, the shape of the sper- matheca in females, and in males the structure of the external genitalia (terminalia). 5.2 Life cycle The minute eggs (0.3–0.4 mm) are more or less ovoid in shape and usually brown or black, and careful examination under a microscope reveals that they are patterned, as shown in Figure 5.2. Some 30–70 eggs are laid singly at each oviposition. They are thought to be deposited in small cracks and holes in the ground, at the base of termite mounds, in cracks in masonry, on stable floors, in poultry houses, amongst leaf litter and in between buttress- roots of forest trees, etc. The type of oviposition site presumably varies greatly according to species. Although eggs are not laid in water they require a microhabitat with high humidity. They are unable to withstand desiccation and hatch after 4–20 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  96 Phlebotomine sand-flies (Phlebotominae) Figure 5.2 Egg of a phlebotomine sand-fly showing mosaic-type pat- tern, and a larva with matchstick hairs and caudal setae. days, although hatching may likely be delayed in cooler weather. Larvae are mainly scavengers, feeding on organic matter such as fungi, decaying forest leaves, semi-rotting vegetation, animal faeces and decomposing bodies of arthropods. Although some species, especially of the genus Phlebotomus, occur in semiarid areas, the actual larval habitats must have a high degree of humidity. Larvae may be able to survive by migrating to drier areas if their breeding places are temporarily flooded. There are four larval instars. The mature larva is 3–6 mm long and has a well-defined black head which is provided with a pair of small mandibles; the body is white or greyish and 12-segmented (Fig. 5.2). Ventrally the abdominal segments have small pseudopods, but the most striking feature is the presence on the head and all body segments of conspicuous thick bristles with feathered stems, which in many species have slightly enlarged tips. They are called matchstick hairs and identify larvae as those of phle- botomine sand-flies. In most species the last abdominal segment bears two pairs of conspicuous long hairs called the caudal setae. First-instar larvae have two single bristles, not two pairs. Larval development is usually complete after 20–30 days’ duration depending on species, temperature and availability of food. In temperate areas and arid regions species may overwinter as diapausing fully grown larvae. Prior to pupation the larva assumes an almost erect position in the habitat, the skin then splits open and the pupa wriggles out. The larval skin is not completely cast off but remains attached to the end of the pupa. The presence of this skin, with its characteristic two pairs of caudal bristles, aids in the recognition of the phlebotomine pupa. The pupal shape is as shown in Figure 5.3. Adults emerge from the pupae after about 6–13 days. The life cycle, from oviposition to adult emergence, is 30–60 days, but extends to several months in some species with diapausing larvae. In temperate areas adults die off in late summer or autumn and species overwinter as lar- vae, with the adults emerging the following spring. It is usually extremely 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  Life cycle 97 Figure 5.3 Pupa of a phlebotomine sand-fly with larval skin still attached. difficult to find larvae or pupae of sand-flies, and relatively little is known about their biology and ecology. 5.2.1 Adult behaviour Both sexes feed on plant juices and sugary secretions but females in addi- tion suck blood from a variety of vertebrates, including livestock, dogs, urban and wild rodents, snakes, lizards and amphibians; a few species feed on birds. Females of many Phlebotomus species in the Old World and Lutzomyia species in the New World bite mammals, including humans. Bit- ing is usually restricted to crepuscular and nocturnal periods but people may be bitten during the day in darkened rooms, or in forests during over- cast days. Most species feed out of doors (exophagic) but some species also feed indoors (endophagic). A few species are autogenous, that is they can lay eggs without blood-feeding. Adults are weak fliers and usually disperse 100 metres or less from their breeding places. Consequently biting is often very localized. However, adults of at least some species have been known to fly up to 2.2 km over a few days. When close to a host sand-flies may have a characteristic hopping type of flight, so that there may be several short flights and landings before females settle on a host. Even a light wind inhibits flight activities and biting. Because of their very short mouthparts sand-flies are unable to bite through clothing. During the day adult sand-flies rest in sheltered, dark and humid sites, but on dry surfaces, such as on tree trunks, on ground litter and foliage of forests, in animal burrows, termite mounds, tree-holes, rock fissures, caves, cracks in the ground and inside human and animal habitations. Species that commonly rest in houses (endophilic) before or after feeding on humans are often referred to as domestic or peridomestic species. Examples are 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  98 Phlebotomine sand-flies (Phlebotominae) Phlebotomus papatasi in the Mediterranean area, P. argentipes in India and the Lutzomyia longipalpis complex in South America. In temperate areas of the Old World sand-flies are seasonal and adults occur only in the summer months. In tropical areas some species are com- mon more or less throughout the year, but in other species there may be well-marked changes in abundance of adults related to the dry and wet seasons. 5.3 Medical importance 5.3.1 Annoyance About 70 species are vectors of disease to humans, but apart from their importance as vectors, sand-flies may constitute a serious, but usually localized, biting nuisance. In previously sensitized people their bites may result in severe and almost intolerable irritations, a condition known in the Middle East as harara. 5.3.2 Leishmaniasis Leishmaniasis is a term used to describe a number of closely related dis- eases caused by about 20 distinct species, subspecies and strains of Leishma- nia parasites in approximately 90 countries. The three main clinical forms are cutaneous, mucocutaneous and visceral leishmaniasis. A fourth, less common form is diffuse cutaneous leishmaniasis, while post-kala-azar der- mal leishmaniasis is caused by Leishmania donovani donovani following cure of the initial visceral form. The epidemiology of leishmaniasis is complex, involving not only different parasite species but different strains of para- sites and different reservoir hosts. Basically amastigote parasites ingested by female sand-flies with a blood-meal multiply in the gut and develop into promastigotes, which are elongate, have a flagellum and attach to the mid-gut or hind-gut wall and multiply rapidly. Many, however, are voided when the fly defecates. After further development the survivors migrate to the anterior part of the mid-gut and then to the fore-gut. Here some parasites become meta- cyclic forms. Four to twelve days after the sand-fly has taken an infec- tive blood-meal the metacyclic forms are found in the mouthparts, and are introduced into a new host during feeding. Infective flies often probe more often than uninfected flies, thus maximizing transmission of para- sites during blood-feeding. Previous feeding by females on sugary sub- stances, mostly obtained from plants, is essential not only for the survival of the sand-fly but also for the development of the parasites to the infective form. Most types of leishmaniasis are zoonoses. The degree of involvement of humans varies greatly from area to area. The epidemiology is largely determined by the species of sand-flies, their ecology and behaviour, the 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  Medical importance 99 availability of a wide range of non-human hosts, and also by the species and strains of Leishmania parasites. In some areas, for example, sand-flies will transmit infections almost entirely among wild or domesticated animals, with little or no human involvement, whereas elsewhere animals may be important reservoir hosts of infection for humans. In India the disease may be transmitted between people by sand-flies, with animals taking no identifiable part in its transmission. The epidemiology of the leishmaniases is complex, and only simplified accounts are given below. Cutaneous leishmaniasis (CL) In the Old World, CL is known also as oriental sore. It occurs mainly in arid areas of the Middle East to north-western India and central Asia, in North Africa and various areas in East, West and southern Africa. The principal parasites are Leishmania major, transmitted mainly by Phlebotomus papatasi, and Le. tropica, transmitted by P. sergenti. Leishmania major is usually zoonotic and in most of its range gerbils (e.g. Rhombomys opimus) are the reservoir hosts; Le. tropica occurs in densely populated areas and humans appear to be the main reservoir hosts. In the New World, CL is found mainly in forests from Mexico to northern Argentina, and is caused by Leishmania braziliensis, Le. amazonensis and Le. mexicana. Rodents and dogs appear to be reservoir hosts. Vectors include Lutzomyia wellcomei and L. flaviscutellata. Mucocutaneous leishmaniasis (ML) (espundia) A severely disfiguring disease found from Mexico to Argentina. It is mainly caused by Leishmania braziliensis. Dogs may be reservoir hosts. Lutzomyia wellcomei is an important vector. Diffuse cutaneous leishmaniasis (DCL) A form that causes widespread cutaneous nodules or macules over the body. It is confined to Venezuela and the Dominican Republic and the highlands of Ethiopia and Kenya. In South America the parasite is Le. ama- zonensis transmitted by Lutzomyia flaviscutellata and spiny rats (Proechimys species) are reservoir hosts. In Ethiopia and Kenya the parasite is Le. aethiopica, transmitted by Phlebotomus pedifer and P. longipes, with rock hyraxes (Procavia capensis) as reservoir hosts. Visceral leishmaniasis (VL) Often referred to as kala-azar. It is caused by Leishmania donovani donovani in most areas of its distribution, such as India, Bangladesh, Sudan, East Africa and Ethiopia. Among the vectors are P. argentipes and P. orientalis. Rodents, wild cats and genets (Genetta genetta) may be reservoir hosts. In the Mediterranean basin, Iran and central Asia, including northern and central China, Leishmania donovani infantum is the parasite, and the vec- tors include P. ariasi and P. perniciosus. Dogs and foxes (Vulpes vulpes) are 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  100 Phlebotomine sand-flies (Phlebotominae) reservoir hosts. Visceral leishmaniasis also occurs sporadically in Central and South America, where the parasite is Leishmania donovani infantum (Le. chagasi of some authors), transmitted by species in the Lutzomyia longipalpis complex. 5.3.3 Bartonellosis Bartonellosis, sometimes called Oroya fever or Carrión’s disease, is encoun- tered in arid mountainous areas of the Andes, mainly in Peru, but also in Ecuador and Colombia. It is caused by the bacterium Bartonella bacilliformis and is transmitted by Lutzomyia verrucarum and probably by other Lut- zomyia species, such as L. colombiana in Colombia. Transmission is possibly only by contamination of the mouthparts. 5.3.4 Sandfly fevers Sand-flies transmit the seven viral serotypes responsible for sandfly fevers, also called papataci fever (sometimes spelt papatasi or pappataci fever), three-day fever or Phlebotomus fevers. The classical form of the disease is found in the Mediterranean region, but also extends up the Nile into Egypt, and from the Middle East to northern India, Pakistan, Afghanistan and probably China. The most important vector is P. papatasi. Other forms of the virus in Central and South America are transmitted by Lutzomyia species such as L. trapidoi. Female sand-flies become infective 7–10 days after taking a blood-meal. Infected females lay eggs containing the virus and these eventually give rise to infected adults. This is an example of transovarial transmission, a phe- nomenon that is more common in the transmission of various tick-borne diseases (Chapters 16 and 17). There are probably mammalian reservoir hosts. 5.4 Control Although phlebotomine sand-flies are very susceptible to insecticides, until recently there have been few organized attempts to control them. However, in most areas where house-spraying has been used to control Anopheles vectors there have been large reductions in sand-fly populations followed by interruption of leishmaniasis transmission. When houses in Kabul, Afghanistan, and in the Peruvian Andes were sprayed with the pyrethroid lambda-cyhalothrin cutaneous leishmaniasis was reduced by 60% and 54% respectively. In Venezuela spraying houses with lambda- cyhalothrin substantially reduced the vector (Lutzomyia ovallesi) of cuta- neous leishmaniasis. Obviously where sand-flies bite and rest out of doors house-spraying will have little effect. However, if the outdoor resting sites are known (e.g. animal shelters, stone walls, tree trunks, termite hills) they can be sprayed 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0  Further reading 101 with residual insecticides. Insecticidal fogging of outdoor resting sites may also give some, but temporary, control of vectors. Personal protection can be achieved by applying efficient insect repel- lents such as DEET, piperidene-based ones and 2–5% neem oil. Mesh screens or nets with very small holes can give protection, but they reduce ventilation and cause it to be unpleasantly hot in screened houses or under sand-fly bed-nets. However, such nets, or even mosquito nets with larger holes, can be impregnated with pyrethroids (e.g. permethrin and deltamethrin) to give protection against biting for up to 6–12 months. In Afghanistan and Syria insecticide-treated polyester bed-nets gave good protection against cutaneous leishmaniasis (Le. tropica transmitted by Phle- botomus sergenti). In some countries there is a combined campaign of insecticidal spraying of houses and the distribution of insecticide-treated bed-nets, a strategy which targets both Anopheles mosquitoes and sand-flies (see control mea- sures, Chapter 2). Control of sand-fly larvae remains impossible because the breeding sites of most species are unknown. Because most leishmaniasis transmission involves reservoir hosts, such as rodents and dogs, attempts have been made to destroy them. In China leishmaniasis was effectively eliminated in the 1950s by killing dogs, but although similar culls have been made in parts of Brazil and the Mediter- ranean region results have been disappointing. Dogs have sometimes been dipped or sprayed with pyrethroids such as deltamethrin, but repeated treatments, typically every 2–3 months, are needed. Deltamethrin-treated collars on dogs, which can remain effective for 8 months, have also given good, albeit local, control of Le. donovani infantum in Italy and Iran. Trials in the Mediterranean with a new vaccine against visceral leishmaniasis have proved promising in protecting dogs, thus reducing the numbers of reservoir hosts. In Russia and Jordan zoonotic cutaneous leishmaniasis has been controlled by destroying rodent colonies, but elsewhere results have not been encouraging. Insecticide resistance to DDT has been found in P. papatasi and P. argen- tipes in India, and greater tolerance or resistance to several insecticides, such as pyrethroids, has been reported in other sand-flies. In 2005 India, Bangladesh and Nepal signed an agreement to eliminate visceral leishmaniasis from the Indian subcontinent, mainly by integrated vector control. Further reading Alexander, B. and Maroli, M. (2003) Control of phlebotomine sandflies. Medical and Veterinary Entomology, 17, 1–18. 7 8B :DD C 5 4B 97 B9 5 B7 2 7BC D 8 1 CC7 / 4B B. D C 4 75D D D:7 , 4B 97 , B7 D7B C 8 C7 4 7 D :DD C 5 4B 97 B9 5 B7 D7B C :DD C B9 , 0