Medical entomology for students pdf

 

    PDF | 5+ minutes read | On Aug 1, , Michael L. Levin and others published Medical Entomology for Students, 5th Edition. PDF | On Jun 1, , Randy Gaugler and others published Medical Entomology for Students: Fifth Edition. Cambridge Core - Infectious Disease - Medical Entomology for Students - by Mike Service. Frontmatter. pp i-vi. Access. PDF; Export citation. Contents. pp vii -x.

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    Medical Entomology For Students Pdf

    Medical Entomology for Students Fifth Edition Mike Service Emeritus Geneva: WHO. whqlibdoc. dersdolcemana.ml Medical Entomology for Students (5th).pdf - Ebook download as PDF File .pdf), Text File .txt) or read book online. Your use of this PDF, the BioOne Complete website, and all posted and research. Medical Entomology for Students. medical students be aware of the basic.

    Review This twelve year-old publication was first in the book stores two years after I took up my own Chair of Medical Entomology at Keele University. It is one of those "first call" volumes off the shelf when you are struggling to remember if endemic or epidemic typhus is transmitted by the tropical rat flea. In his preface Mike Service points out that the approach has not changed consisting of morphology — lifecycle — medical importance and control and that the main areas where changes have been made relate to vector control. Striking new features of the book include a colourful front cover bearing a female Anopheles farauti looking replete following lunch and a central block of 24 colour plates depicting a range of vectors of medical importance. Unlike Lady Thatcher, Mike is not afraid of the odd U-turn and has decided to unadopt the Culicine genus Ochlerotatus which is again included as a subspecies of Aedes. Many a late night pre-exam revision student will thank him for this kindness. Two useful epidemiological cartoons dealing with the mosquito borne transmission of West Nile Virus and Japanese Encephalitis are added to those on Yellow Fever.

    Some Culex species also transmit Wuchereria bancrofti as well as several arboviruses. Aedes species are important vectors of yellow fever, dengue, West Nile virus and many other arboviruses, and in a few restricted areas they also transmit Wuchereria bancrofti and Brugia malayi.

    Mansonia species transmit Brugia malayi and sometimes Wuchereria bancrofti and a few arboviruses. Haemagogus and Sabethes mosquitoes are vectors of yellow fever and a few other arboviruses in Central and South America, while the genus Psorophora contains a few species that transmit arboviruses and others that are troublesome biters in North and South America.

    Many mosquitoes which are not vectors can nevertheless be troublesome because of the serious biting nuisances they cause. The hind-wings are represented by a pair of small, knob-like halteres.

    Mosquitoes are distinguished from other ies of a somewhat similar shape and size by: 1 the possession of a conspicuous forward-projecting proboscis; 2 the presence of numerous appressed scales on the thorax, legs, abdomen and wing veins; and 3 a fringe of scales along the posterior margin of the wings. Mosquitoes are slender and relatively small insects, usually measuring about 36 mm in length.

    Some species, however, can be as small as 2 mm while others may be as long as 19 mm. The body is distinctly divided into a head, thorax and abdomen.

    The head has a conspicuous pair of kidney-shaped compound eyes. Between the eyes arises a pair of lamentous and segmented antennae. In females the antennae have whorls of short hairs i. Mosquitoes can thus be conveniently sexed by examination of their antennae: individuals with feathery antennae are males, while those with only short and rather inconspicuous antennal hairs are females Figs.

    Just below the antennae is a pair of palps, which in female anophelines are pointed apically while in males they are dilated. In female culicines the palps are very short while in males they are long Fig. Arising between the palps is the single long proboscis, which in females contains the piercing mouthparts. In mos- quitoes the proboscis characteristically projects forwards Fig.

    The thorax is covered, dorsally and laterally, with scales, which may be dull or shiny, white, brown, black or almost any colour. It is the arrange- ment of black and white, or coloured, scales on the dorsal surface of the thorax that gives many species, especially Aedes mosquitoes, their distinc- tive patterns Fig.

    The wings are long and relatively narrow, and the number and arrange- ment of the wing veins is virtually the same for all mosquito species Fig. The veins are covered with scales which are usually brown, black, white or yellowish, but more brightly coloured scales may occasion- ally be present. The shape of the scales and the pattern they create differs considerably between both genera and species of mosquitoes.

    Scales also project as a fringe along the posterior border of the wings. In life the wings of resting mosquitoes are placed across each other over the abdomen in the fashion of a closed pair of scissors.

    The legs are long and slender and are covered with scales which are usually brown, black or white and may be arranged in patterns, often in the form of rings Fig.

    The tarsus usually terminates in a pair of toothed or simple claws. Some genera, such as Culex, have a pair of small eshy pulvilli Fig. The abdomen is composed of 10 segments, but only the rst seven or eight are visible. Mosquitoes in the subfamily Culicinae usually have the abdomen covered dorsally and ventrally with mostly brown, blackish or whitish scales.

    In the Anophelinae, however, the abdomen is almost, or entirely, devoid of scales. The last abdominal segment of a female mosquito terminates in a pair of small nger-like cerci, whereas in males there is a pair of prominent claspers, comprising part of the male external genitalia.

    In unfed mosquitoes the abdomen is thin and slender, but after females have bitten a host and taken a blood-meal only females bite the abdomen becomes greatly distended and resembles an oval red balloon. When the abdomen is full of developing eggs it is also dilated, but whitish and not red in appearance.

    In mosquitoes the proboscis is long and projects conspicuously forwards in both sexes although males do not bite. The largest component of the mouthparts is the long and exible gutter-shaped labium, which terminates in a pair of small ap-like structures called labella. In cross-section the labium is seen to almost encircle all other components of the mouthparts Fig.

    The individual components are held close External morphology 5 Figure 1. Figure 1. The uppermost structure, the labrum, is slender, pointed and grooved along its ventral surface. In between this upper roof labrum and lower gutter labium are ve needle-like structures, namely a lower pair of toothed maxillae, an upper pair of mandibles, which usually lack teeth although in Anopheles they are very nely toothed , and nally a single untoothed hollow stylet called the hypopharynx.

    When a female mosquito bites a host the labella, at the tip of the eshy labium, are placed on the skin and the labium, which cannot pierce the skin, curves backwards.

    This allows the paired mandibles, paired maxillae, labrum and hypopharynx to penetrate the hosts skin. Saliva from a pair of trilobed salivary glands Fig. Saliva contains antihaemostatic enzymes that produce haematomas in the skin and facilitate the uptake of blood. Saliva also contains anticoagulants to prevent blood from clotting and obstructing the mouthparts as it is sucked up, and anaesthetic substances that help reduce the pain inicted by the mosquitos bite, so reducing the hosts defensive reactions.

    Although male mosquitoes have a proboscis, the maxillae and mandi- bles are usually reduced in size or the mandibles are absent, and conse- quently males cannot bite. Sperm from a male enter the spermotheca of a female, and this usually serves to fertilize all eggs laid during her lifetime; thus only one mating and insemination per female is required.

    With a few exceptions, a female mosquito must bite a host and take a blood-meal to obtain the necessary nutrients for the devel- opment of her eggs. This is the normal procedure and is referred to as anautogenous development. A few species, however, can develop the rst Life cycle 7 Figure 1. Each cycle begins with an unfed adult, which passes through a blood-fed, half-gravid and gravid condition. After oviposi- tion the female is again unfed and seeks another blood-meal.

    This process is called autogenous development. The speed of digestion of the blood-meal depends on temperature.

    In most tropical species it takes only 23 days, but in colder, temperate countries blood digestion often takes as long as days. After a blood-meal the mosquitos abdomen is dilated and bright red, but some hours later the abdomen becomes a much darker red. As the blood is digested and the white eggs in the ovaries enlarge, the abdomen becomes whitish posteriorly and dark reddish anteriorly.

    This condition represents a mid-point in blood digestion and ovarian development, and the mosquito is referred to as being half-gravid Fig. Eventually all blood is digested and the abdomen becomes dilated and whitish due to the formation of fully developed eggs Fig. The female is now said to be gravid, and she searches for suitable larval habitats in which to lay her eggs. After oviposition the female mosquito takes another blood-meal, and after 23 days in the tropics a further batch of eggs is matured and laid.

    This process of blood-feeding and egg-laying is repeated several times through- out the females life and is referred to as the gonotrophic cycle. Male mosquitoes cannot bite but feed on the nectar of owers and other naturally occurring sugary secretions.

    Males are consequently unable to transmit any diseases. Sugar-feeding is not, however, restricted to males: females may also feed on sugary substances to obtain energy for ight and dispersal, but only in a few species the autogenous ones is this type of food sufcient for egg development.

    Eggs are brown or blackish and 1 mm or less in length. In many Culicinae they are elongate or approximately ovoid in shape, but eggs of 8 Introduction to mosquitoes Culicidae Mansonia are drawn out into a terminal lament Fig. In the Anophelinae eggs are usually boat-shaped Fig. Many mosquitoes, such as species of Anopheles and Culex, lay their eggs directly on the water surface. In Anopheles the eggs are laid singly and oat on the water, whereas Culex eggs are laid vertically in several rows held together by surface tension to form an egg raft which oats on the water Fig.

    Mansonia species lay their eggs in a sticky mass that is glued to the underside of oating plants. None of the eggs of these mosquitoes can survive desicca- tion, and consequently they die if they become dry. In the tropics eggs hatch within 23 days, but in cooler temperate countries they may not hatch until after days, or longer. Other mosquitoes, such as those belonging to the genera Aedes, Psorophora and Haemagogus, do not lay eggs on the water surface. Instead they deposit them just above the water line on damp surfaces, such as mud and leaf litter, or on the inside walls of tree-holes and clay water-storage pots.

    Eggs of these genera can withstand desiccation, especially those of Aedes and Psorophora, which can remain dry for months or even years but still remain viable and hatch when covered with water. Because their eggs are laid above the water line of larval habitats it may be many weeks or months before they become ooded with water and can hatch.

    However, even when ooded, hatching may extend over relatively long periods because the eggs hatch in instalments. The authors, editors and publishers therefore disclaim all liability for direct or consequential damages resulting from the use of material contained in this book.

    Readers are strongly advised to pay careful attention to information provided by the manufacturer of any drugs or equipment that they plan to use. To Wendy, for all her help over many years with this and previous publications.

    Contents ix The only areas from which they are absent are Antarctica and a few islands. This results in Aedes albopictus and Aedes aegypti becoming Ochlerotatus albopictus and Stegomyia aegypti. The most important pest and vector species belong to the genera Anopheles. Mosquitoes are divided into three subfamilies: Brugia malayi and Brugia timori and a few arbovi- ruses. The hind-wings are represented by a pair of small.

    Mansonia species transmit Brugia malayi and sometimes Wuchereria bancrofti and a few arboviruses. The body is distinctly divided into a head. West Nile virus and many other arboviruses. They have been found at elevations of m and down mines to depths of m below sea level.

    For example. Haemagogus and Sabethes. Some species. Some Culex species also transmit Wuchereria bancrofti as well as several arboviruses. Mosquitoes are slender and relatively small insects. Anopheles species. Aedes species are important vectors of yellow fever. Mosquitoes have a worldwide distribution.

    Anophelinae anophelines and Culicinae culicines. Many mosquitoes which are not vectors can nevertheless be troublesome because of the serious biting nuisances they cause. Haemagogus and Sabethes mosquitoes are vectors of yellow fever and a few other arboviruses in Central and South America.

    It is the arrange- ment of black and white. The veins are covered with scales which are usually brown. When the abdomen is full of developing eggs it is also dilated. Just below the antennae is a pair of palps. In female culicines the palps are very short while in males they are long Fig. The thorax is covered. The abdomen is composed of 10 segments. In mos- quitoes the proboscis characteristically projects forwards Fig.

    In the Anophelinae. Arising between the palps is the single long proboscis. Some genera. The tarsus usually terminates in a pair of toothed or simple claws. In unfed mosquitoes the abdomen is thin and slender. The legs are long and slender and are covered with scales which are usually brown. Mosquitoes can thus be conveniently sexed by examination of their antennae: In females the antennae have whorls of short hairs i.

    The wings are long and relatively narrow. External morphology 3 The head has a conspicuous pair of kidney-shaped compound eyes. Mosquitoes in the subfamily Culicinae usually have the abdomen covered dorsally and ventrally with mostly brown. In life the wings of resting mosquitoes are placed across each other over the abdomen in the fashion of a closed pair of scissors. Scales also project as a fringe along the posterior border of the wings.

    The shape of the scales and the pattern they create differs considerably between both genera and species of mosquitoes. In mosquitoes the proboscis is long and projects conspicuously forwards in both sexes — although males do not bite. In cross-section the labium is seen to almost encircle all other components of the mouthparts Fig. The individual components are held close.

    Figure 1. The uppermost structure, the labrum, is slender, pointed and grooved along its ventral surface. Saliva from a pair of trilobed salivary glands Fig. Saliva contains antihaemostatic enzymes that produce haematomas in the skin and facilitate the uptake of blood. Although male mosquitoes have a proboscis, the maxillae and mandi- bles are usually reduced in size or the mandibles are absent, and conse- quently males cannot bite.

    Sperm from a male enter the spermotheca of a female, and this usually serves to fertilize all eggs laid during her lifetime; thus only one mating and insemination per female is required. With a few exceptions, a female mosquito must bite a host and take a blood-meal to obtain the necessary nutrients for the devel- opment of her eggs.

    This is the normal procedure and is referred to as anautogenous development. Each cycle begins with an unfed adult, which passes through a blood-fed, half-gravid and gravid condition. After oviposi- tion the female is again unfed and seeks another blood-meal. This process is called autogenous development.

    The speed of digestion of the blood-meal depends on temperature. In most tropical species it takes only 2—3 days, but in colder, temperate countries blood digestion often takes as long as 7—14 days.

    As the blood is digested and the white eggs in the ovaries enlarge, the abdomen becomes whitish posteriorly and dark reddish anteriorly. This condition represents a mid-point in blood digestion and ovarian development, and the mosquito is referred to as being half-gravid Fig. Eventually all blood is digested and the abdomen becomes dilated and whitish due to the formation of fully developed eggs Fig. The female is now said to be gravid, and she searches for suitable larval habitats in which to lay her eggs.

    After oviposition the female mosquito takes another blood-meal, and after 2—3 days in the tropics a further batch of eggs is matured and laid. Males are consequently unable to transmit any diseases. Sugar-feeding is not, however, restricted to males: Eggs are brown or blackish and 1 mm or less in length.

    In many Culicinae they are elongate or approximately ovoid in shape, but eggs of. In the Anophelinae eggs are usually boat-shaped Fig. Many mosquitoes, such as species of Anopheles and Culex, lay their eggs directly on the water surface. None of the eggs of these mosquitoes can survive desicca- tion, and consequently they die if they become dry.

    In the tropics eggs hatch within 2—3 days, but in cooler temperate countries they may not hatch until after 7—14 days, or longer. Other mosquitoes, such as those belonging to the genera Aedes, Psorophora and Haemagogus, do not lay eggs on the water surface.

    Instead they deposit them just above the water line on damp surfaces, such as mud and leaf litter, or on the inside walls of tree-holes and clay water-storage pots. Eggs of these genera can withstand desiccation, especially those of Aedes and Psorophora, which can remain dry for months or even years but still remain viable and hatch when covered with water.

    Moreover, eggs of Aedes and Psorophora may require repeated immersions in water followed by short periods of desiccation before they will hatch. In temperate regions many Aedes and Psorophora species overwinter as diapausing eggs. There are four active larval instars.

    All mosquito larvae require water in which to develop; no mosquito has larvae that can with- stand desiccation, although they may be able to survive short periods, for example, in wet mud. Larvae have a well-developed head bearing a pair of antennae and a pair of compound eyes. Prominent mouthbrushes are present in most species and serve to sweep water containing minute food particles into the mouth.

    The thorax is roundish and has unbranched and branched hairs, which are usually long and conspicuous. The segmented abdomen has nine visible segments, most of which have unbranched or branched hairs Figs. The last segment, which differs in shape from the preceding eight. This last segment ends in two pairs of transparent sausage-shaped anal papillae, which although often called gills are concerned not with respira- tion but with osmoregulation.

    Mosquito larvae, with the exception of Mansonia and Coquillettidia spe- cies and a few other species , must come to the water surface to breathe. Atmospheric air is taken in through a pair of spiracles situated dorsally on the ninth abdominal segment. In the subfamilies Toxorhynchitinae and Culicinae these spiracles are situated at the end of a single dark-coloured and heavily sclerotized tube termed the siphon Fig. Mansonia and Coquillettidia larvae possess a specialized siphon that is more or less conical, pointed at the tip and supplied with prehensile hairs and serrated cutting structures Fig.

    These enable the siphon to be inserted into the roots or stems of aquatic plants, from which oxygen for larval respiration is obtained. In contrast, larvae of the Anophelinae do not have a siphon Figs.

    Mosquito larvae feed on yeasts, bacteria, protozoans and numerous other microorganisms, as well as on decaying plant and animal material found in the water. Some, such as Anopheles species, are surface-feeders, whereas many others species browse over the bottoms of habitats. A few mosquitoes are carnivorous or cannibalistic. There are four larval instars, and in tropical countries larval development, that is the time from egg hatching to pupation, can be as short as 5—7 days, but many species require about 7—14 days.

    In temperate areas the larval period may last several weeks or months, and several species overwinter as larvae. Some species prefer shaded larval habitats whereas others like sunlit habitats.

    Many species cannot survive in water polluted with organic debris, whereas others occur in water contami- nated with excreta or rotting vegetation.

    A few mosquitoes are found almost exclusively in brackish or salt waters, such as saltwater marshes and man- grove swamps, and are consequently restricted to mostly coastal areas. Each segment has numerous short hairs. Pupae do not feed but spend most of their time at the water surface taking in air through the respiratory trumpets. The head and thorax are combined to form the cephalothorax. The abdomen is segmented. If disturbed they swim up and down in the water in a jerky fashion.

    Some of the developing structures of the adult mosquito can be seen through the integument of the cephalothorax. Almost any collection of permanent or temporary water can be a mos- quito larval habitat.

    Species that usually feed on humans are said to be anthropophagic in their feeding habits. Females are attracted to hosts by various stimuli emanating from their breath or sweat. Life cycle 11 Pupae of Mansonia and Coquillettidia differ in that they have relatively long breathing trumpets. Mosquitoes that feed on birds are sometimes called ornithophagic instead of zoophagic. Female adults of Aedes aegypti a vector of yellow fever and dengue. In the tropics the pupal period lasts only 2—3 days.

    Many species bite humans to obtain their blood- meals. At the end of pupal life the skin on the dorsal surface of the cephalothorax splits. A few species of mosquitoes frequently enter houses to feed and are said to be endophagic in their feeding habits.

    As a consequence their pupae remain submerged and rarely come to the water surface. Some species feed more or less indiscriminately at any time of the day or night. Vision usually plays only a minor role in host orientation.

    In contrast. Some species rest inside houses during blood digestion and development of the eggs and are called endophilic. The feeding behaviour of a species may also change. After having bitten humans. Adults are large 19 mm long.

    Many species are less adaptable in their feeding behaviour and will never rest in houses or enter them to feed on the occupants. There are records of mosquitoes being found km or more from their larval habitats.

    In several malaria control campaigns the interior sur- faces of houses. Many mosquitoes probably disperse only a few hundred metres from their emergence sites. Adults are easily. The resting behaviour of adult mosquitoes may be important in planning control measures.

    The biting behaviour of female mosquitoes may be very important in the epidemiology of disease transmission. This approach will. Mosquitoes feeding on people pre- dominantly out of doors and late at night will not bite many young children.

    Clearly the behaviour of both people and mosquitoes may be relevant in disease transmission. Consequently young children will be less likely to be infected with diseases that these mosquitoes might transmit. During hot and dry seasons sub- stantial numbers of people may sleep out of doors and as a consequence be bitten more frequently by exophagic mosquitoes.

    Mosquitoes may get transported long distances in aeroplanes. In tropical countries adult female mosquitoes probably live on average 1—2 weeks. Some mosquitoes bite predominantly within forests or wooded areas. Adult males usually have a shorter life span than females. Species that hibernate or aestivate live much longer: Larvae are found mainly in container-habitats. In addition. The following characters serve to separate anopheline from culicine mosquitoes.

    Anopheline eggs are unable to withstand desiccation. Their larvae are also large 12—18 mm long. Anopheline eggs Eggs are laid singly on the water surface. Anopheline larvae Larvae lack a siphon and lie parallel to the water surface. They are surface-feeders and so spend most of their time at the water surface. They have occasionally been introduced into areas in the hope that their voracious larvae will help reduce the numbers of pest mosquitoes. In most species they are typically boat-shaped.

    Examination under a microscope shows that the abdomen has small. They are predaceous on larvae of other mosquitoes and on their own kind. These abdominal palmate hairs and a single pair. All these structures identify larvae as belonging to the genus Anopheles. Plate 1. The most reliable character for identifying anopheline pupae is the presence of short. Laterally on each side of segment 8 8 and 9 are combined there is a sclerotized comb-like structure with teeth called the pecten.

    This is a very useful char- acter. Anopheline adults Adult Anopheles usually rest with their bodies at an angle to the surface. In some species they rest at almost right angles to the surface. A few species. Anopheline pupae The respiratory trumpets of anopheline pupae are short and broad distally. If the adults are females and also Anopheles then the palps will be about as long as the proboscis and usually lie closely alongside it Fig.

    European Anopheles claviger. The palps are usually blackish with broad or narrow rings of pale scales. The most reliable way to distinguish between adult Anopheles and Culicinae is by examination of their heads.

    Mansonia Fig. Culicine larvae All culicine larvae possess a siphon Fig. They are laid either as a number of single eggs e. Principal characters for separating the various stages in the life cycles of anopheline and culicine mosquitoes are given in Table 1. Sabethes and Psorophora. In male Anopheles the palps are also about as long as the proboscis but are distinctly swollen at their ends and are said to be clubbed Fig.

    They hang upside down at an angle from the water surface when they are getting air Fig. Culex and Coquillettidia. There are no abdominal palmate hairs or tergal plates on culicine larvae. Other differences are that in Anopheles there is only a single spermotheca in females. The most important medically are the genera Aedes. Methods for distinguishing the more important genera within the Culicinae are given in Chapter 3.

    The following characters separate the Culicinae from Anopheles mosquitoes. Subtend an Have abdominal palmate angle from the water hairs and tergal plates surface. Rest with body more or sexes In most species dark and pale less parallel to the scales on wing veins arranged surface. No palmate hairs or tergal plates Pupae Breathing trumpets short and Breathing trumpets short or broad apically.

    Courtesy of Miss M. Gordon and M. Short peg-like long. Lie All larvae have a short or parallel to water surface. Culex Mansonia Aedes Figure 1. In females which have non-plumose antennae the palps are shorter than the proboscis. Note absence of lateral spines as found on anopheline pupae. The most reliable method for identifying the Culicinae is to exam- ine their heads. Culicine pupae The length of the respiratory trumpets in culicine pupae is variable.

    Culicine adults Culicine adults rest with the thorax and abdomen more or less parallel to the surface Fig. Sometimes there are contrasting dark and pale scales. Abdominal segments 2—7 lack peg-like spines. The scales covering the wing veins are commonly uniformly brown or black.

    In males which have plumose antennae the palps are about as long as the proboscis but are not. Their role in the transmission of these diseases is discussed in Chapters 2 and 3. Because of their elongated mouthparts female mosquitoes can easily bite through clothing such as socks. Either the numbers of predators. The greatest numbers of mosquitoes are found in the northern areas of the temperate regions.

    Mosquitoes are important as vectors of malaria. Control measures can be directed at either the immature aquatic stages or the adults. Also in culicines the middle lobe of the salivary glands is about as long as the other two. Other differences separating the Culicinae from Anopheles are that in culicines there are two or three spermathecae in females.

    They are. It takes some days. Biological control of mosquitoes was very popular during the early twentieth century. Southeast Asia and Africa. Fish are unsuitable for controlling mosquitoes in small water containers and in pools and puddles that rapidly dry out. Mosquito control 23 worthwhile control. There are also several parasitic nematodes that kill mosquito larvae.

    Pathogens and parasites There are numerous pathogens. Bacillus thuringiensis var. When Bti is ingested. Sometimes Bti is formulated as a powder that is mixed with water and sprayed on larval habitats. Lagenidium and Culicinomyces that cause larval mortality. Resistance to both Bti and B. Other predators of mosquito larvae include tadpoles of frogs and toads and various aquatic insect larvae.

    A few mosquitoes. Bacillus sphaericus can be formulated much as for Bti and kills mosquito larvae in a similar fashion.

    This species is also more effective in organ- ically polluted waters and is especially effective against Culex species. Both these Bacillus species are more like a microbial insecticide than a true biological living agent that recycles and maintains itself in the environment. There has been interest in predaceous copepods such as Mesocyclops species to control larvae in water containers such as tyres.

    None of these biological agents has given satisfactory control of mosquitoes. Eggs layed by such females are sterile and fail to hatch.

    Medical Entomology for Students (5th).pdf

    In a transgenic Anopheles stephensi was created that had both a reduced life span and complete resistance to infection with Plasmodium falciparum. Mosquito control 25 25 years. India and Thailand. Genetic control Although genetic control methods are directed against the adults. Neither of these genetic approaches is simple. In El Salvador Anopheles albimanus. More recently this approach has been used against the vector of dengue see Chapter 3. Field populations of B.

    There are basically two approaches to genetic control. Recently genetic engineering techniques. It is impossible. This suffocates larvae and pupae and also prevents mosquitoes laying their eggs on the water surface. Larger and more permanent habitats such as swamps may prove too costly to drain.

    Larval habitats such as ponds. Various container-habitats such as abandoned tin cans. Mosquito breeding in water-storage pots that are in use can be reduced by covering up their openings. Some mosquitoes. This mosquito also commonly breeds in pit latrines.

    In the Indian subcontinent water tanks are commonly sited on rooftops. In Zanzibar and India such beads substantially reduced Cx. The feasibility of eradicating breed- ing places must be assessed individually in each area. Fitting these with mosquito screening would prevent breeding. The addition of detergents or vegetable oils increases the spreading power of oils. Chemical control Most control directed against mosquitoes.

    It makes the habitat unsuitable for many mosqui- toes.

    Dosage rates are commonly 9—27 litres per hectare or less. Both small and large freshwater and saltwater marshy areas can be converted into impounded waters. There is the danger. Instead of draining marshy areas. Mosquito control 27 Environmental manipulation If it is not feasible to eliminate mosquito larval habitats it may be possible to alter them to make them unsuitable for mosquitoes.

    Although such oils may sometimes still be used. This proc- ess is called impoundment. Pyrethroids such as permethrin and delta- methrin can also be used as larvicides. In organ- ically polluted waters insecticides are less effective.

    This attitude is likely to spread. Chlorpyrifos is more toxic to mosquito larvae than many other insecticides. DDT and other organo- chlorine insecticides should not now be used as larvicides. Less persistent and biodegradable insecticides should be used. Larvicides are usually delivered from knapsack-type sprayers car- ried on the backs of operators. Insecticides formulated as slow-release granules or pellets can be scattered over marshy areas when they are relatively dry. All the above insecticides usually have to be sprayed on larval habitats in tropical areas every 10—14 days.

    Mansonia larvae can be killed by spraying herbicides to destroy the aquatic vegetation on which they rely to obtain their oxygen. Insecticides With the availability of insecticides such as DDT in the mid s. Because temephos has a very low mammalian toxicity.

    Less frequent applications are made in cooler temperate areas because the aquatic life cycle is much longer. Larvicides are usually applied as emulsions or oil solutions. This gives a concentration of 1 mg active ingredient per litre of water. Recommended chemicals for larviciding include malathion. Nets should be tucked in under mattresses or bedding. Nets should be placed over beds before sunset. Insect growth regulators IGRs These are compounds.

    Many IGRs can be formulated as liquids. Small spray-guns e. Although mosquitoes have not been reported as developing resistance to IGRs.

    Screens of 6—8 mesh i. If houses are unscreened. It is essential that screening is kept in good repair. Integrated control It has become fashionable to advocate integrated control. The main disadvantage of nets is that they can reduce ventilation. Mosquito control 29 vehicle-mounted spraying machines. Torn nets are useless unless they have been impregnated with pyrethroid insecticides see Chapter 2.

    Several insecticides can be used. Indoor-resting endophilic adults are also occasionally killed by mist- blowers or thermal foggers.

    Picaridin and Icaridin. In brief. Although such applications can be. Citronella oil and lemon eucalyptus oil can give protection against mosquitoes. Mosquito coils impregnated with pyrethroid insecticides. A more sophisticated.

    Under optimal conditions these repellents can provide protection for 6—10 hours. Although it has periodically been suggested that it may cause side effects. Sweating and rubbing usually reduce the period of effectiveness of repellents. An effective repellent is DEET. If treated clothing is kept in plastic bags when not in use it should remain effective for many months before re-impregnation is needed. These piperidine-based repellents are about as effective as DEET. A new botanical repellent known as PMD para-menthane Repellents are applied to the hands.

    Medical Entomology for Students (5th ed.) by Mike Service (ebook)

    Cutter Advanced. In emergency situations aerial spraying gives fast and effective vector control. Further reading 31 spectacular. Repeated applica- tions are needed to sustain control. Applications of aerosols and mists are best made in calm weather. ULV spraying is used in potential or actual epidemic situations to prevent or control disease outbreaks. Indoor residual spraying IRS Some mosquitoes.

    Insecticides commonly used include organophosphates and pyreth- roids. Further reading Becker. In addition to rapidly reducing outdoor resting and biting mosquitoes.

    It should be emphasized that most countries have legislation regulating what insecticides can be used against pests and vectors. Annual Review of Entomology. Journal of the American Mosquito Control Association. Their populations can be reduced by insecticidal spraying of houses. Ultra-low-volume applications Ultra-low-volume ULV techniques apply the minimum of concentrated insecticides.

    Japanese encephalitis. Volume 2: Biocontrol and Other Innovative Components. Academic Press. Faber and Faber. American Journal of Tropical Medicine and Hygiene. Volume 1: Experience and Components from Conventional Chemical Control. Crosskey eds. A symposium. Their Bionomics and Relation to Disease.

    Lane and R. New York. World Health Organization Vector resistance to pesticides. Field Sampling Methods. Durden eds. Parasitology Today. Sensory Reception and Behaviour. Nutrition and Reproduction. Medical Insects and Arachnids. Medical and Veterinary Entomology. Proceedings of a sympo- sium on vector control. Volume 3: Viral and Bacterial Pathogens and Bacterial Symbionts.

    Walter Reed Biosystematics Unit Mullen and L. World Health Organization Vector Control: Methods for Use by Individuals and Communities. World Health Organization. See also references at the ends of Chapters 2 and 3. When feeding. In both sexes the palps are about as long as the proboscis. Anopheles eggs cannot withstand desiccation and in tropical countries hatch within 2—3 days. The most important disease transmitted by Anopheles mosquitoes is malaria.

    Life cycle 35 The subfamily Anophelinae contains three genera. Pupal abdominal segments have numerous short setae. There are about species. A few species transmit arboviruses that are mainly of minor medical importance. Larvae do not have a siphon and consequently lie parallel to the water surface Fig.

    Unlike culicines. As in all mosquitoes there are four larval instars. A tergal plate and paired palmate hairs are present dorsally on most abdominal segments Fig. Anopheles mosquitoes have an almost worldwide distribution. See Chapter 1 page 14 for minor differences distinguishing anophelines from culicines. The number. Some Anopheles prefer habitats with aquatic vegetation while others favour waters without vegetation. Unlike culicine larvae. In general Anopheles are found in clean and unpolluted waters.

    In tropical countries the larval period frequently lasts only about 7 days. Anopheles larvae occur in many different types of more or less permanent habitats. Most Anopheles species are not exclusively exophagic or. As already discussed in Chapter 1.

    The pupal period lasts 2—3 days in tropical countries but sometimes as long as 1—2 weeks in cooler climates. Both before and after blood-feeding some species rest in houses endophilic. Thus blood- feeding and oviposition normally occur in the evenings. In the Neotropical region Central and South America and the West Indies a few Anopheles breed in water that collects in the leaf axils of epiphytic plants such as bromeliads.

    They resurface some seconds or minutes later. In temperate areas some Anopheles overwinter as larvae and consequently may live many months. Larvae are also found in small and often temporary habitats such as puddles. The most important malarial parasites are Plasmodium falci- parum. The microgametes break free and fertilize the female gametes macrogametes which have formed from the macrogametocytes. This is one of the reasons why An.

    The nucleus of the oocyst divides repeatedly to produce numerous spindle-shaped sporozoites. Medical importance 37 endophagic. Because the sexual cycle of the malaria parasite occurs in the vector. As a result of fertilization a zygote is formed. However, the time required for this cyclical development extrinsic cycle depends on both temperature and Plasmodium species. With Plasmodium vivax sporogony develops faster: The mosquito is now infective, and sporozoites are inoculated into people the next time the mosquito bites.

    However, the number may be much smaller than this, and very few sometimes just 5—10 are actually injected into a person during feeding. The sporozoite rate, that is the percentage of female vectors with sporo- zoites in their salivary glands, varies considerably from species to species of mosquito but also according to locality and season.

    For practical purposes it can be said that once a vector becomes infective it remains so throughout its life. Malaria vectors are often divided into primary and secondary vectors, but this can be misleading because a species may be considered a primary vector in some areas but only a secondary vector in others.

    Although presenting a list of important malaria vectors is somewhat subjective I have nevertheless attempted to do this, and I provide notes on their principal larval habitats and biting behaviour. Several species occur as species complexes, which comprise virtually identical-looking species that can be separated only by their chromosomal banding patterns, by biochemical procedures or by molecular methods.

    However, species within a complex may differ in their behaviour, distribution and vector status. The best known complex is probably the An. To give an example of the differences in biology and vector status that can occur in a species complex, mosquitoes of the An.

    Adults bite humans both indoors and outdoors, and also feed on domesticated animals. They rest mainly indoors, but sometimes outdoors. Other malaria vectors in the An. Anopheles arabiensis Another important malaria vector.

    Larvae in the same habitats as An. Adults bite humans indoors and outdoors but also cattle; after feeding they rest either indoors or outdoors. This species tends to occur in drier areas than An. Anopheles melas and An. Adults of both species bite humans and rest both indoors and outdoors; they are both regarded as secondary malaria vectors.

    Medical Entomology for Students (5th ed.)

    Anopheles bwambae A rare species restricted to breeding in the warm mineral springs in Semuliki National Park, Uganda. Not considered an important vector, although locally it can transmit malaria. Anopheles quadriannulatus and An. Prefers shaded habitats. Adults bite humans predominantly, but also domesticated animals. Feeds indoors and also outdoors; after feeding adults rest mainly indoors.

    Adults bite humans and domesticated animals and usually rest in stables, cowsheds and piggeries. Adults hibernate in these. Anopheles labranchiae Another species in the An. Bites humans and domesticated animals indoors and outdoors; rests mainly in houses or animal shelters after feeding.

    Overwinters as hibernating adults. Adults bite humans and animals indoors or outdoors, and rest outdoors after feeding. Anopheles sacharovi Fresh or brackish waters of coastal or inland marshes, pools and ponds, especially those with vegetation. Prefers sunlit habitats. Bites humans and animals indoors or outdoors; usually rests in houses or animal shelters after feeding.

    Adults bite humans or animals indoors or outdoors, resting in houses and caves after feeding. Anopheles stephensi Probably a species within a complex.

    Can be an important vector locally, especially in towns. Apart from being found in Egypt, Iraq, Iran and Saudi Arabia it is common in the Indian subcontinent, where it is commonly the main vector of urban malaria. Larvae breed in fresh, brackish or even polluted waters in man-made habitats such as water tanks, cisterns, wells, gutters, water-storage jars and containers. Adults bite humans indoors or outdoors, and rest mainly indoors afterwards.

    Anopheles stephensi has a very wide distribution extending from the Middle East across Pakistan and India, to Myanmar, Thailand and China. Anopheles superpictus Flowing waters such as torrents of shallow water over rocky streams, pools in rivers, muddy hill streams.

    Vegetation may be present; prefers sunlight. Bites humans and animals indoors and out- doors, and after feeding rests mainly in houses and animal shelters, but also in caves. Can be an important vector in India. Adults bite humans and cattle outdoors and indoors, and rest mainly outdoors after feeding. Anopheles baimai Pools, small streams, ditches, animal footprints, in partial sunlight or in forests.

    Bites humans both indoors and outdoors, and also domesticated animals; often enters houses to feed, but rests outdoors. Anopheles culicifacies A species in the An. Most important vector in the Indian subcontinent. Adults prefer domesticated animals but commonly bite humans indoors or outdoors; rests mainly indoors after feeding.

    The main malaria vector in much of the region. Flowing waters such as hill streams, pools in riverbeds, irrigation ditches, seepages; prefers sunlight. Bites humans and domesticated animals; feeds and rests either indoors or outdoors. Anopheles minimus A species in the An. Feeds mainly on humans, but will bite domesticated animals; feeds and rests mainly indoors. Anopheles sundaicus A species in the An.

    Salt or brackish waters including lagoons, marshes, pools and seepages, espe- cially with putrefying algae and aquatic weeds. Mainly a coastal species, but found in freshwater inland pools in Java and Sumatra. Bites humans and domesticated animals indoors and outdoors; rests mainly indoors after feeding. Adults feed indoors or outdoors on humans but also commonly on cattle; rests indoors or outdoors after feeding. Adults bite humans indoors and rest mainly indoors after feeding.

    Anopheles balabacensis Muddy and shaded forest pools, animal hoof- prints and vehicle ruts, occasionally in deep wells. Adults bite humans and cattle and feed and rest outdoors. Morphologically and biologically very similar to An. Anopheles campestris A species in the An. Bites humans and animals indoors and outdoors, and rests indoors or outdoors after feeding. Anopheles dirus A species in the An.

    Shaded pools, hoofprints in or at the edges of forests. Adults bite humans and domesticated animals, mainly outdoors, and stay outdoors after feeding. Bites domesticated animals but also feeds on humans inside or outside houses; rests mainly outdoors.

    Prefers shaded areas of sunlit habitats. Feeds mainly on humans, but also on domesticated animals; feeds indoors or outdoors but rests mainly outdoors after feeding.

    Basically a forest species, biting people in forests or near forests in rubber plantations and orchards. Anopheles letifer Often in acidic and stagnant pools, swamps and ponds, especially on coastal plains; prefers shade. Adults bite domesticated animals and humans mainly outdoors, and rest afterwards outdoors. Anopheles leucosphyrus A species in the An. Clear seepage pools in forests. Adults bite humans inside and outside houses, but afterwards rest outdoors.

    This species is morphologically and biologically similar to An. Anopheles maculatus A species in the An.

    Seepage waters, pools formed in streams, rock-pools, edges of ponds, ditches and swamps with much vegetation; prefers sunlight. Bites humans and animals mainly outdoors and rests outdoors after feeding. Adults bite humans and animals mainly outdoors, and rest mainly outdoors. Anopheles sinensis Has been often confused with An. Common in China, where in some localities it may be a more important vector than An. Adults bite cattle and humans, indoors or outdoors; rests indoors or outdoors.

    Anopheles subpictus A species in the An. Muddy pools near houses, borrow pits, gutters, also brackish waters. Bites mainly animals, but also humans both indoors and outdoors; rests indoors or outdoors after feeding. Adults feed on humans and domesticated animals both indoors and outdoors; after feeding adults rest mainly indoors. Anopheles albitarsis A species in the An. Bites humans and domesticated animals almost indiscrimin- ately.

    Feeds outdoors and also indoors, and usually rests outdoors after feeding. Anopheles nuneztovari A species in the An. Anopheles darlingi Freshwater marshes. Guyana and Brazil. Anopheles pseudopunctipennis A species in the An. Feeds almost indiscriminately indoors or outdoors on humans and domesticated ani- mals. Anopheles darlingi See entry under Mexico and Central America.

    Adults rest mainly outdoors. Anopheles cruzii Another malaria vector that breeds in bromeliad axils. Anopheles bellator Larvae found only in water collected in the leaf axils of bromeliads. Adults bite humans indoors and outdoors. Feeds mainly on animals. Adults bite humans and domesticated animals indoors or outdoors. Muddy waters of pools. Mainly shaded larval habitats. Bites humans and domesticated animals both indoors and outdoors. Adults bite humans during the day in shaded forests. Feeds mainly on humans indoors.

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