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BEDBUGS: PUBLIC HEALTH IMPORTANCE
CHAPTER 4
Bedbugs, fleas, lice, ticks and mites
Ectoparasites that live on the body, in clothing and in beds There are many different species of bloodsucking fleas, lice, ticks and mites. Licelive on humans or in their clothing, while fleas are frequently found taking blood-meals on people and domestic animals. Bedbugs, which can be found in beds orfurniture, feed on humans to obtain blood-meals. Some mites live in people's skin,e.g. the mites that cause scabies. Other mite species and ticks may take blood-meals on humans. Fleas, bedbugs and lice are insects, whereas ticks and mitesbelong to another group of arthropods, the Acarina. Unlike adult insects they haveonly two main sections to their body, and the adults have four pairs of legs (asopposed to three pairs in insects).
Bedbugs, head lice and crab lice do not carry disease, but their biting can be a serious nuisance. However, important diseases of humans and animals are trans-mitted by other arthropods dealt with here, among them the following: — epidemic typhus and epidemic relapsing fever (body lice);— plague and murine typhus (certain fleas);— Lyme disease, relapsing fever and many viral diseases (ticks);— scrub typhus (biting mites).
Two species of bedbug feed on humans: the common bedbug (Cimex lectularius),which occurs in most parts of the world, and the tropical bedbug (Cimexhemipterus), which occurs mainly in tropical countries. They are a severe nuisancewhen they occur in large densities, being commonest in places with poor housingconditions. They are not important in the transmission of diseases, although theypossibly play a role as vectors of hepatitis B virus.
Bedbugs have a flat, oval-shaped body with no wings, and are 4–7 mm long. Theircolour is shiny reddish-brown but after a blood-meal they become swollen anddark brown in colour. There are three stages in the bedbug's life cycle: egg, nymphand adult (Fig. 4.1). The eggs are white and about 1 mm long. The nymphs looklike adults but are smaller. Complete development from egg to adult takes from sixweeks to several months, depending on temperature and the availability of food.
Both male and female bedbugs feed on the blood of sleeping persons at night. Inthe absence of humans they feed on mice, rats, chickens and other animals.
Feeding takes about 10–15 minutes for adults, less for nymphs, and is repeatedabout every three days. By day they hide in dark, dry places in beds, mattresses,cracks in walls and floors, and furniture; they are also found behind pictures andwallpaper; hiding places are also used for breeding. The bugs are frequently CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.1
Life cycle of the bedbug (by courtesy of the Natural History Museum, London).
Fig. 4.2
Bedbugs are almost always found in bedrooms.
abundant in bedrooms in warm climates. Heated bedrooms in cooler climates arealso favourable for the bugs, which cannot develop below 13 °C (Fig. 4.2). Adultscan survive for several years without food.
Because they have no wings, bedbugs travel only short distances. In poorly builthouses with many suitable hiding places they crawl from one bedroom to another;they spread from one house to another mainly in second-hand furniture, beddingand, sometimes, clothes.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
Public health importance
Bedbugs are not considered vectors of disease. It has been suggested that they playa role as vectors of the hepatitis B virus (1, 2) but this was denied in a recent studyin the Gambia (3). They are mainly important as a biting nuisance. Some people,especially those exposed for a long time, show little or no reaction to the bites,which appear as small red spots that may not even itch. People never bitten beforemay suffer from local inflammation, intense itching and sleepless nights. The biteproduces a hard whitish swelling that often continues to bleed. Scratching maycause secondary infections.
In heavily infested houses where people may receive one hundred or more bites a night it is possible that the blood loss causes mild anaemia in infants.
Bedbugs can move rapidly when disturbed and are not easily detected while biting.
Some people may not even be aware that they are bitten each night by largenumbers of bedbugs. Control measures are therefore carried out only if there isevidence of the presence of the insects.
Infestations can be detected by the examination of possible hiding places for thepresence of live bugs, cast-off nymphal skins, eggs and excreta. The excreta mayalso be visible as small dark brown or black marks on bed sheets, walls andwallpaper (4). Houses with large numbers of bedbugs may have a characteristicunpleasant smell. Live bugs can be detected by spraying an aerosol of pyrethruminto cracks and crevices, thus irritating them and driving them out of their hidingplaces.
Deet and other insect repellents are effective against bedbugs. They can be used bytravellers who have to sleep in houses infested with the insects. However, repel-lents applied to the skin are unlikely to last the whole night. It is likely that burningmosquito coils offer some protection (see Chapter 1).
Simple household measures Small numbers of bedbugs can occur in any household, especially when second-hand furniture or bedding is used. Light infestations can be treated by thoroughlycleaning infested articles, pouring boiling water over them and exposing themto sunlight. Aerosol spray cans can be used to spray household insecticideson to mattresses, in crevices in walls, and in other possible hiding places.
Among the effective insecticides are the pyrethroids, propoxur, bendiocarb anddichlorvos. The procedure should be repeated if bugs are still found after a fewweeks.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Total release fogger
This device is similar to the aerosol spray can but is designed to release the totalcontents of the can in a single shot through a special valve. The fog contains ratherlarge droplets that do not penetrate well into crevices. Cans containing an insec-ticide–kerosene mixture should not be used for fogging because of the risk ofexplosion.
Impregnated mosquito nets Mosquito nets impregnated with a long-lasting pyrethroid insecticide are effectivein repelling and killing bedbugs (Fig. 4.3) (5, 6). Such nets are increasinglypopular for the control of malaria mosquitos. A commonly reported incidentalbenefit of the use of these nets is the complete disappearance of bedbug and headlouse infestations, which makes the nets highly popular among people in bedbug-infested areas.
Smoke generators, which are commercially available and usually contain pyre-throid insecticides, can be used to fumigate the interior of houses. They burn for3–15 minutes and can be used only once. A smoke of very small droplets ofinsecticide is produced which can penetrate into cracks and crevices to kill bed-bugs, fleas, flies, mosquitos and tropical rat mites. Smoke generators do not alwayswork well, as the insecticide may settle on horizontal surfaces without penetratinginto deep crevices. They have a brief effect and do not prevent reinvasion fromneighbouring, untreated dwellings. They are mainly used where quick action isneeded. A fumigant canister developed in South America against the triatominebugs is described in Chapter 3, together with general instructions on how to Fig. 4.3
The use of mosquito nets
impregnated with a pyrethroid
insecticide may result in the
reduction or even eradication
of bedbug and head louse
infestations.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
BEDBUGS: CONTROL MEASURES
Fig. 4.4
The fumigant canister releases insecticide vapour for up to 15 minutes.
fumigate a house (Fig. 4.4). It contains an irritant insecticide that drives the bugsout of hiding.
Residual insecticides Houses with heavy infestations need to be treated with long-lasting residualinsecticide. One treatment is normally sufficient to eliminate bedbugs but, if aninfestation persists, re-treatments should be carried out at intervals of not less thantwo weeks. In many countries, resistance of bedbugs to DDT, lindane and dieldrinis common. The insecticide selected should thus be one known to be effectiveagainst the target population (see Table 4.1). The addition of an irritant insecti-cide, e.g. 0.1–0.2% pyrethrin, helps to drive the bugs out of their hiding places,thus increasing exposure to the residual insecticide. Most pyrethroids are effectiveflushing and killing agents.
A residual spray is applied with a hand-operated compression sprayer (see Chapter 9). Special attention should be given to mattresses, furniture, and cracksand crevices in walls and floors (Fig. 4.5). In severe infestations, walls and floorsshould be sprayed until they are visibly wet (point of run-off). Usually thiscorresponds to 1 litre per 50 m2 on non-absorbent surfaces and to 5 litres or moreper 50 m2 on absorbent surfaces such as those of mud-brick walls. Rooms in humidtropical countries must be treated in the morning so that they are dry and suitablefor re-entry in the evening. Mattresses and bedding should be treated carefully toavoid staining and soaking, and should be thoroughly aired and dried before use.
Hand dusters containing insecticide powder may be used to dust mattresses andbedding, to avoid wetting them. Bedding used for infants should not be treatedwith residual insecticide, but with a short-lasting insecticide such as may be foundin most aerosol spray cans.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Table 4.1
Residual insecticides for use against bedbugs
Concentration in spray (%)
pirimiphos methyl Fig. 4.5
Spray residual insecticide on to mattresses, cracks in walls, floors and other hiding places with a
compression sprayer.
Bedbugs and malaria control
House spraying against malaria was very popular in many tropical countries, partly because itkilled bedbugs. Unfortunately, the bugs quickly developed resistance to the insecticides, resultingin numerous complaints that spraying no longer controlled bedbugs, even though it still killedmosquitos.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
BEDBUGS: CONTROL MEASURES
Another possible explanation for the increase in the numbers of bedbugs observed is that theinsecticide spray irritated the bugs, causing them to leave their hiding places. Seeing many morebedbugs than before, people believed that spraying caused an increase in the bug population(7, 8).
As a result, many householders refused malaria spraying teams access to their homes. It ispossible that in some areas the occurrence of bedbugs contributed indirectly to the ineffective-ness of malaria control programmes.
Fleas are small, wingless bloodsucking insects (order Siphonaptera) with a charac-teristic jumping movement. They feed mainly on mammals but also on birds. Ofthe 3000 species only a dozen commonly attack humans. The most importantspecies are the rat flea, the human flea and the cat flea (Fig. 4.6). Their bites cancause irritation, serious discomfort and loss of blood. The rat flea is important asa vector of bubonic plague and flea-borne typhus. Cat fleas incidentally transmittapeworms. The sand flea or jigger burrows into the skin of humans and may causeinfections. Fleas that bite people occur in most parts of the world.
The life cycle of fleas has four stages: egg, larva, pupa and adult (Fig. 4.7). Adultfleas are 1–4 mm long and have a flat narrow body. They are wingless with welldeveloped legs adapted for jumping. They vary in colour from light to dark brown.
The larvae are 4–10 mm long and white; they have no legs but are very mobile.
The cocoon (pupal stage) is well camouflaged because it is sticky and soonbecomes covered with dust, sand and other fine particles.
Both female and male fleas take blood-meals. Fleas breed close to the resting and sleeping places of the host, in dust, dirt, rubbish, cracks in floors or walls,carpets, animal burrows and birds' nests. High humidity is required for develop-ment. The larvae feed on organic matter such as the faeces of the host, small dead Fig. 4.6
A cat flea (Ctenocephalides felis felis) (by
courtesy of the Natural History Museum,
London).
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.7
The life cycle of the flea (by courtesy of the Natural
Natural History Museum, London).
Fig. 4.8
A scratching cat is an indication
of a flea infestation.
insects and undigested blood expelled by adult fleas. At the end of the larval periodthe larva spins a loose whitish cocoon within which it develops into a pupa.
The adult fleas are fully developed within 1–2 weeks but only emerge from the cocoons after receiving a stimulus, such as the vibrations caused by movement ofthe host. In vacant houses they may survive in the cocoons for up to a year. Peoplemoving into a vacant house can cause many fleas to emerge simultaneously fromthe cocoons and attack people or animals in large numbers. Under optimalconditions the development from egg to adult takes 2–3 weeks.
Fleas avoid light and are mostly found among the hairs (Fig. 4.8) or feathersof animals or in beds and in people's clothing. If possible, a flea will feed severaltimes during the day or night. Heavy infestations with fleas are recognized by BEDBUGS: PUBLIC HEALTH IMPORTANCE
marks on clothing and bedding of undigested blood ejected by the fleas. Most fleaspecies feed on one or two host species, but in the absence of their normal hostthey feed on humans or other animals. Adult fleas can survive several monthswithout food. Fleas move around by jumping; some species can jump as high as30 cm.
Public health importance
Humans are most commonly bitten by the cat flea, Ctenocephalides felis and, lesscommonly, the dog flea, C. canis. The so-called human flea (Pulex irritans) is, inspite of its name, less important. Fleas jump up from the ground and mostfrequently attack people on the ankles and legs, the easiest parts to reach, althoughsleeping people can be attacked anywhere on the body. Flea bites cause irritationand sometimes extreme discomfort. Heavy infestations may cause allergic reac-tions and dermatitis.
Plague is a disease caused by the bacterium Yersinia pestis. It occurs primarily inwild animals, such as rats and other rodents. Plague bacteria are transmitted byfleas, and humans may be infected by fleas that have fed on infected animals. Inthe past, plague was called the black death and caused disastrous epidemics.
Plague is still dangerous because it occurs widely in rodent populations. Rural or sylvatic plague may be contracted in the western USA, South America, Africa,the former USSR, parts of the eastern Mediterranean area, and central and south-east Asia. Human plague frequently occurs in several countries in Africa, Bolivia/north-eastern Brazil, Ecuador, Myanmar, Peru and Viet Nam (9).
Rural plague is acquired by people entering rural areas and handling wild animals. Most at risk are hunters who may be bitten by infected fleas whilehandling recently killed animals.
Urban plague may occur when rats living in and around human dwellings are infected. Rat fleas (Xenopsylla species) that normally feed on rats may occasionallyfeed on humans and thus spread the disease to them. When rodents infected withplague die the fleas leave their hosts and are then likely to attack and infect people.
Other fleas, such as the human flea, may subsequently transmit the disease fromperson to person.
There are three clinical types of plague: • Bubonic plague. Swellings (buboes) filled with bacteria develop in the lymph nodes, especially in the armpits and groin. This form is normally transmittedto humans by infected fleas. If left untreated, it causes death in about 50%of cases.
• Pneumonic plague. This is a secondary form in which the lungs become affected. It is highly contagious, the plague bacillus easily spreading fromperson to person in sputum or droplets coughed up or sneezed by sickpeople. Pneumonic plague occurred in epidemics in past centuries, killingmillions of people. If left untreated it very often results in death.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
• Septicaemic plague. The bloodstream is invaded by the plague bacillus, result- ing in death before one of the above two forms can develop.
Prevention and control
Partial immunity is acquired after an infection. A vaccine is available whichprovides protection for a period of only a few months. Treatment with streptomy-cin, tetracycline or its derivatives or chloramphenicol is highly effective if usedwithin a day after the onset of symptoms.
Urban plague is controlled by rapidly applying insecticide dusts in rodent burrows and on to rodent runways where it will be taken up by the animals on theirfur, thus killing the vector fleas. Dusting against fleas should be followed bymeasures to control rodents.
People working in the field may protect themselves by dusting their clothing with insecticidal powder, using impregnated clothing, and using repellents on adaily basis.
Flea-borne typhus Flea-borne typhus, also called murine typhus fever, is caused by Rickettsia typhiand occurs sporadically in populations of rats and mice. It is transmitted mainlyby rat fleas and cat fleas, and humans can become infected as a result of con-tamination from the dried faeces and crushed bodies of the fleas. The diseaseoccurs worldwide and is found in areas where people and rats live in the samebuilding. Its symptoms are similar to those of louse-borne typhus (see p. 257) butmilder.
Prevention and control
Immunity is acquired after the first infection. The treatment of sick people issimilar to that for louse-borne typhus (see p. 257). Control is carried out byapplying residual insecticides to the runs, burrows and hiding places of rats. Ifthese measures are successful in killing fleas, rodent control measures can be taken(see p. 250, box).
Fleas occasionally transmit other diseases and parasites from animals to humans,for instance tularaemia caused by the bacillus Francisella tularensis, and the para-sitic tapeworms that occur in dogs and cats. Children playing with domestic petsmay become infected by swallowing fleas that carry the infective stage of theworms.
The recommended control methods depend on whether the intention is to dealwith fleas as a biting nuisance or as vectors of disease.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
FLEAS: CONTROL MEASURES
Fleas as a nuisance An effective repellent, such as deet, applied to skin and clothing, prevents fleasfrom attacking. A disadvantage is that repellents applied to the skin last only afew hours (see Chapter 1). Longer-lasting protection is obtained by dustingclothing with insecticide powder (see p. 262) or by using insecticide-impregnatedclothing (see Chapter 1).
Simple hygienic measures
Fleas and their eggs, larvae and cocoons can be effectively removed by keepinghouses well swept and floors washed. Removal with a vacuum cleaner is alsoeffective. When people enter an infested house that has been vacant for some time,large numbers of newly emerged fleas may attack. The treatment of floors withdetergents, insecticides or a solution of naphthalene in benzene is recommended;care should be taken to avoid inhaling benzene fumes.
Application of insecticides
Heavy infestations can be controlled by spraying or dusting insecticides into cracksand crevices, corners of rooms and areas where fleas and their larvae are likely tooccur. Insecticides can also be applied to clothing and the fur of animals. Fumi-gant canisters that produce aerosols of quick-acting insecticides (e.g. the pyre-throids, propoxur and bendiocarb) kill fleas directly and are convenient to use (seep. 240 and Chapter 3). However, the insecticidal effect is brief and reinfestationsmay appear quickly.
Cat and dog fleas
Fleas can be detected in the hair around the neck or on the belly of cats and dogs.
Treatment involves applying insecticidal dusts, sprays, dips or shampoos to thefur. Dusts are safer to use than sprays because the insecticides are less likely to beabsorbed through the skin in the dry form. Dusts also produce less odour and donot affect the skin as much as sprays. Carbaryl and malathion should not be usedon kittens and puppies under four weeks of age. Pets can be provided with plasticflea collars impregnated with an insecticide. Flea collars are effective for 3–5months, whereas other treatments give only short-term control.
Recently, lufenuron tablets have been used to control fleas in cats and dogs.
The tablets are administered once monthly at a dose of 30 mg per kg of bodyweight to cats and 10 mg per kg of body weight to dogs and are safe for use inpregnant and nursing animals. Lufenuron is taken up by the female flea duringfeeding and acts by inhibiting egg development (10).
Dusts must be rubbed thoroughly into the hair and can be applied by means of a shaker (Fig. 4.9). They must not be allowed to get into the eyes, nostrils andmouths of animals. Heavy applications should not be made to the abdomen as thematerial will be licked off. Application should begin above the eyes and all theareas backward to the tail and haunches should be covered, ensuring thoroughtreatment around the ears and underneath the forelegs. A small animal can be CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.9
Dusting a dog with insecticide
powder to control fleas.
treated with one tablespoonful of dust, while 30 g may be required for a large dog.
Sprays must wet the hair completely and can be applied with a hand-compressionsprayer. It is also possible to spray with an insecticide aerosol from a pressurizedspray can.
Re-treatment may be necessary if reinfestation occurs. Important sources of reinfestation are the places where animals or humans sleep or spend much time,such as beds, bedding and kennels. Where possible, animal bedding should beburned or laundered in hot soapy water. A vacuum cleaner may be used to removeaccumulations of dust that contain flea larvae and pupae, and infested premisescan then be treated with a residual insecticide. Treatment with insecticidal pow-ders or solutions is possible (11). Because flea cocoons are much less susceptibleto insecticides than the larvae and adults, treatments should be repeated every twoweeks over a period of six weeks to ensure that all emerging fleas are killed (12).
Human flea
This flea species does not usually remain on the person after feeding and by day itrests in cracks, crevices, carpets and bedding. Regular cleaning of houses, and ofbedrooms in particular, should prevent large infestations.
More effective control is achieved by dusting or spraying insecticides on to mattresses and cracks and crevices in floors and beds. Bedding left untreatedshould be washed and cleaned during insecticide application. Fleas in many partsof the world have developed resistance to DDT, lindane and dieldrin (13–15).
Suitable insecticides for spraying or dusting are indicated in Table 4.2.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
FLEAS: CONTROL MEASURES
Table 4.2
Insecticides and application methods effective against fleas
Type of application
Pesticide and formulation
malathion (2%), diazinon (0.5%), propoxur (1.0%),dichlorvos (0.5–1.0%), fenchlorvos (2%), bendiocarb(0.24%), natural pyrethrins (0.2%), permethrin (0.125%),deltamethrin (0.025%), cyfluthrin (0.04%), pirimiphos methyl(1%) Pesticide power (dust) malathion (2–5%), carbaryl (2–5%), propoxur (1%),bendiocarb (1%), permethrin (0.5–1.0%), cyfluthrin (0.1%),deltamethrin (0.05%), temephos (2%), pirimiphos methyl(2%), diazinon (2%), fenthion (2%), fenitrothion (2%),jodfenphos (5%), (+)-phenothrin (0.3–0.4%) propoxur (0.1%), (+)-phenothrin (0.4%) Fumigant canister propoxur, dichlorvos, cyfluthrin, permethrin, deltamethrin,(+)-phenothrin Flea collar for dog or cat dichlorvos (20%), propoxur (10%), propetamphos, diazinon diethyl-toluamide (deet), dimethyl phthalate, benzylbenzoate Retreatment is probably not needed if all infested places in a house are treated orcleaned. Infants' bedding should not be treated but should be thoroughly washed.
Fleas that transmit diseases Control measures during epidemics of plague or typhus must be effected in twostages: (1) insecticidal dusting of rat habitats to kill rat fleas;(2) rat control.
A control campaign with the sole aim of killing rodents could result in increaseddisease transmission to humans: the deaths of many rodents could cause largenumbers of fleas to leave the dead hosts and seek alternative sources of blood.
The most common and effective method of controlling rodent fleas has been to useDDT in a 10% dust formulation. Alternative insecticides in dust formulation areincreasingly used (see Table 4.2) because of the resistance of fleas in many areasto DDT and also because of environmental concerns.
Dust is applied to burrows, runways and other sites where rodents are likely to pick it up. When the rodents groom themselves they spread the dust on their fur,thus killing the fleas.
Before control is begun, it is important to know where rodent burrows and runways are. To save insecticide, the burrows should first be closed off; only those CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.10
Equipment for applying anti-flea dusts ( WHO).
that are subsequently reopened should be treated. Insecticidal dust should beblown into each burrow with a duster. A patch of dusting powder, 1 cm in depth,should be left around the opening. Patches of dust 15–30 cm wide should beplaced along runways. Dust should be applied only where it will remain undis-turbed by humans and the wind. Care must be taken not to apply insecticides toareas where they can contaminate food. Many insecticidal dusts remain effectivefor 2–4 months if used indoors in undisturbed places.
A plunger-type duster is suitable for fast applications of dust to rodent burrows and runways, in attics and spaces under buildings. It consists of an air pump likea bicycle pump to which a container for the dust is attached. The air from thepump is led into this container, agitating the contents and expelling them from anorifice (Fig. 4.10).
Alternatively, a hand shaker can easily be made from a can by fitting a 16-mesh screen at one end. A can with nail-holes punched in the top can also be used.
Insecticidal dust of low toxicity can be applied to human clothing or the fur ofanimals with such equipment.
Integrated rat and flea control
To control urban outbreaks of plague or typhus, insecticides to kill rat fleas are applied at thesame time as or a few days earlier than rat poisons. Suitable rat poisons are warfarin, coumafuryl,difenacoum, brodifacoum, coumatetralyl, bromadialone, chlorophacinone and zinc phosphide(16, 17).
In places where food for human consumption is stored and in crowded areas, such as markets,it is safer to use bait boxes (Fig. 4.11) in which the rodents contaminate themselves with the anti-flea dust before they die from eating the toxic bait. Bait boxes can be placed along rodent runsat intervals of 60 metres. A suitable bait consists of 100 g of rolled oats mixed with rat poison.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
FLEAS: CONTROL MEASURES
Fig. 4.11
Models of bait boxes. (a) Boxes made of bamboo. (b) A bait box made of floorboard (30 × 20 cm) covered by
a metal roof ( WHO).
Sand fleas or jigger fleas
The sand flea, chigoe or jigger flea (Tunga penetrans) is not known to transmitdisease to humans but, unique among the fleas, it is a nuisance because the femalesburrow into the skin. Sand fleas occur in the tropics and subtropics in Central andSouth America, the West Indies and Africa.
The larvae of sand fleas are free-living and develop in dusty or sandy soil. Theadults are initially also free-living but, after copulation, the fertilized females attachthemselves under the skin of humans, pigs, dogs, poultry and other animals,penetrating soft areas of skin, for instance cracks in the soles of the feet, betweenthe toes, and under the toenails. Other parts of the body may also be affected.
Public health importance Usually a person is infested by only one or two jiggers at a time but infestation withhundreds is possible. People who do not wear shoes, such as children, are mostcommonly affected. The flea burrows entirely into the skin with the exception ofthe tip of the abdomen. It feeds on body fluids and swells up to the size and shapeof a small pea in 8–12 days (Fig. 4.12). The body of the female flea is completelyfilled with thousands of eggs which are expelled in the next weeks (Fig. 4.13).
Most of the eggs fall to the ground where they hatch after a few days.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.12
The female sand flea attacks bare-footed persons by burrowing into soft skin on the feet (18).
Fig. 4.13
Detail of foot with jigger infections. Eggs are expelled through the dark opening in the centre (by
courtesy of the Natural History Museum, London).
An infestation begins to irritate and itch when the female is almost fully developed.
Sometimes it causes severe inflammation and ulceration. If the female flea dies inthe skin it may cause a secondary infection which, if ignored, could lead to tetanus,gangrene and even the loss of a toe.
Natural extrusion of the egg sac or removal of the jigger with a dirty pin or needle leaves a tiny pit in the skin which may develop into a sore. The sore mayextend and develop into a septic ulcer. An infection under a toenail may cause pusto form.
Prevention, control and treatment
Jigger populations often maintain themselves in the domestic environment bybreeding on livestock and domestic animals. Efforts should be made to remove thejiggers from these animals. Infections in dogs can be controlled by the administra-tion of ivermectin (0.2 mg/kg of body weight) or by bathing the feet with dichlorvos BEDBUGS: PUBLIC HEALTH IMPORTANCE
SAND FLEAS OR JIGGER FLEAS
(0.2%) (19). The former treatment may kill other parasites, such as Dermatobialarvae, which causè skin infections. In infested areas, people should inspect theirfeet daily for freshly burrowing jiggers, which are visible as minute black spots andcause an itchy sensation.
Wearing shoes prevents attacks. The fleas may also be deterred by a repellent applied to the skin, although walking bare-footed in dirt quickly removes it. If it ispossible to locate the area of soil where the jiggers originate it could be burnt offor sprayed with a suitable insecticide in an effort to kill the fleas.
With some skill it is possible to remove the jigger with forceps or with a sharpobject, such as a needle, a thorn or the tip of a knife (Fig. 4.14). The object andthe site of infection should be cleaned, if possible with alcohol, to reduce the riskof infection. Removal can be done in a painless way but care should be taken notto rupture the egg sac. Infection may result if eggs or parts of the flea's body areleft in the wound. After removal, the wound should be dressed antiseptically (withalcohol or iodine) and protected until healed.
Lice are small bloodsucking insects that live on the skin of mammals and birds.
Three species of lice have adapted themselves to humans: the head louse (Pediculushumanus capitis), the body louse (Pediculus humanus) and the crab or pubic louse(Pthirus pubis) (Fig. 4.15). All three species occur worldwide. Lice infestations cancause severe irritation and itching. In addition the body louse can transmit typhus Fig. 4.14
The egg sac of the sand flea can be removed with a sharp object.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.15
Human sucking lice are
flat wingless insects with
legs adapted for grasping
hairs (infested man L.
Robertson; Lice WHO).
fever, relapsing fever and trench fever. Outbreaks of louse-borne typhus fever,sometimes claiming thousands of lives, have occurred in colder areas where peoplelive in poor, crowded conditions, especially in some highland areas of Africa, Asiaand Latin America.
The three species live only on humans (not normally on animals) and feed onhuman blood; the life cycle has three stages: egg, nymph and adult (Fig. 4.16).
Development from egg to adult takes about two weeks. The white eggs (callednits) are glued to a hair or, in the case of the body louse, to fine threads on clothes.
The nymphs are similar to the adults but much smaller. Fully grown lice are up to4.5 mm long and feed by sucking blood. Feeding occurs several times a day. Licecan only develop in a warm environment close to human skin, and die within afew days if they lose contact with the human body. They are normally spreadby contact, e.g. in overcrowded sleeping quarters and other crowded livingconditions.
The three species of human lice are found on different parts of the body: • the head louse occurs on the scalp and is most common in children on the back of the head and behind the ears; • the pubic louse or crab louse is mainly found on hair in the pubic region but it may spread to other hairy areas of the body and, rarely, the head; • the body louse occurs in clothing where it makes direct contact with the body; it is similar to the head louse but slightly bigger.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
Fig. 4.16
Life cycle of the louse ( WHO).
Body lice are most commonly found in clothing, especially where it is in directcontact with the body, as in underwear, the crotch or fork of trousers, armpits,waistline, collar and shoulders. They attach themselves to body hair only whenfeeding. The eggs are attached to thin threads of clothing. Body lice are mostcommon in colder areas where people do not frequently wash or change clothes.
Body lice are spread by close contact between people. They are most com- monly found, therefore, on people living in overcrowded, unhygienic conditions,as in poorly maintained jails, refugee camps and in trenches during war. They alsospread by direct contact between people in crowded transport vehicles and mar-kets. Body louse infestations may also be acquired through sharing bedding, towelsand clothing or by sitting on infested seats, chair covers or cushions.
The head louse is the most common louse species in humans. It lives only in thehair on the head and is most often found on children. The eggs (or nits) are firmlyglued to the base of hairs of the head, especially on the back of the head and behindthe ears (Figs. 4.17 and 4.18). Because the hairs grow about a centimetre a monthit is possible to estimate the duration of an infestation by taking the distancebetween the scalp and the furthest egg on a hair. Infested persons usually harbour10–20 adult head lice. The females lay 6–8 eggs per day. Head lice are spread byclose contact between people, such as children at play or sleeping in the same bed.
Head lice are also spread by the use of other people's combs that carry hairs witheggs or lice attached.
Crab or pubic lice Crab lice, also called pubic lice, are greyish-white and crab-like in appearance.
They are most often found on hair in the pubic region, and eggs are laid at the base CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.17
Inspection of the hair for head lice. Girls tend to have
heavier infestations than boys.
Fig. 4.18
Close-up of hair infested with
lice and eggs (by courtesy of
the Natural History Museum,
London).
BEDBUGS: PUBLIC HEALTH IMPORTANCE
of the pubic hair. Heavy infestations may spread to other hairy areas of the body,such as the chest, thighs, armpits, eyelashes, eyebrows and beard. Crab lice aremainly spread through sexual or other close personal contact, and are mostcommon in young, sexually active adults.
Public health importance
Only the body louse is a vector of human diseases. It transmits typhus fever,relapsing fever and trench fever.
Lice feed several times a day and heavy infestations can cause intense irritation andsevere itching. Toxic reactions to the saliva injected into the skin may lead toweariness and a general feeling of illness.
Louse-borne typhus fever This disease is caused by a microorganism, Rickettsia prowazekii, and is an acute,highly infectious disease with headache, chills, fever and general pains as symp-toms. It may be fatal in 10–40% of untreated cases.
The disease has occurred on all continents except Australia. It is prevalent in cool areas where heavy clothing is worn and where the vector is most common. Inthe past the disease was most common during war and famine. Today, foci oftransmission are found in mountainous regions of South America, in Central andEast Africa and in the Himalayas.
Body lice take the disease organisms up with the blood of an infected personand then expel it with their faeces. Since louse faeces dry to form a fine blackpowder they are easily blown about. The powder can infect small wounds, such asthose caused by scratching, or the mucous membranes of the nose and mouth.
Because the disease organism can remain alive for at least two months in driedlouse faeces, it is dangerous to handle the clothing or bedding of patients withtyphus.
Effective treatment is possible with tetracycline, doxycycline or chloramphenicol.
Prevention and control
A vaccine has been prepared but is not yet commercially available. Infection canbe prevented by controlling the body lice. Epidemic outbreaks are controlled bythe application of a residual insecticide to the clothing of all persons in affectedareas.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Louse-borne relapsing fever This disease is caused by a microorganism, Borrelia recurrentis. Infected peoplesuffer periods of fever lasting 2–9 days which alternate with periods of 2–4 dayswithout fever. Usually, about 2–10% of untreated persons die but the mortalityrate may be as high as 50% during epidemics. The disease occurs in limited areasof Africa, Asia and South America.
Louse-borne relapsing fever occurs under similar conditions to those of typhusfever and the two diseases may appear together. Humans become infected bycrushing infected body lice between the fingernails or the teeth. The diseaseorganisms are thus released and can enter the body through abrasions, wounds orthe mucous membranes of the mouth.
Treatment is possible with tetracycline.
Prevention and control
Prevention and control are as described for typhus fever; no vaccine is available.
This bacterial disease, caused by Rochalimaea quintana, involves intermittent fever,aches and pains all over the body, and many relapses. Infection rarely results indeath.
The disease can probably be found wherever the human body louse exists.
Cases have been detected in Bolivia, Burundi, Ethiopia, Mexico, Poland, theformer USSR and North Africa. Epidemics occurred during the First and SecondWorld Wars among troops and prisoners living in crowded and dirty conditions,hence the name "trench fever".
Transmission occurs through contact with infected louse faeces, as for typhusfever.
Tetracycline, chloramphenicol and doxycycline are probably effective but, as thedisease is rather mild, they have not been adequately tested.
Prevention and control
Prevention and control are as for typhus fever; no vaccine is available.
BEDBUGS: PUBLIC HEALTH IMPORTANCE
LICE: CONTROL MEASURES
The control methods used depend on the importance of the health problem.
Individual or group treatment may be carried out where lice are merely a nuisance.
Large-scale campaigns are recommended for the control of epidemic outbreaks ofdisease.
Regular washing with soap and warm water and regular combing may reduce thenumbers of nymphs and adults. However, washing will not remove the eggs, whichare firmly attached to the hair. A special louse comb with very closely set fine teethis effective in removing both adults and eggs (Fig. 4.19). Shaving the head iseffective and this measure is sometimes adopted with young boys; however, it isoften objected to and should not be insisted on.
Insecticide applications to the hair give the most effective control (20–26). Theycan be in the form of shampoos, lotions, emulsions or powders (Fig. 4.20;see also Table 4.3). Some pyrethroids are the most recommended products, sincethey do not cause the burning sensation of the scalp or other side-effects some-times associated with other insecticides, such as lindane (27, 28). Powder or dustformulations are usually less effective and less acceptable for use than lotions oremulsions. A soap formulation containing 1% permethrin can be applied as ashampoo (see box, p. 261).
How to make insecticidal dusts, shampoos and lotions
An insecticidal dust can be made by adding insecticide powder (wettable powder)to talcum powder to obtain the recommended dosage of active ingredient (ingrams). An insecticidal shampoo is made similarly by adding insecticide powder oremulsifiable concentrate to hair shampoo with a neutral pH. An insecticidal lotionis made by mixing an emulsifiable concentrate with water or alcohol.
Fig. 4.19
A louse comb has very closely set fine teeth and is effective in
removing head lice and their eggs.
CHAPTER 4 • BEDBUGS, FLEAS, LICE, TICKS AND MITES
Fig. 4.20
Hair can be treated with an anti-louse shampoo or
lotion.
Table 4.3
Insecticides and formulations commonly used to control lice
Formulation and concentration (%)
BEDBUGS: PUBLIC HEALTH IMPORTANCE
LICE: CONTROL MEASURES
The insecticidal soap bar is a recently developed inexpensive formulation of permethrin(1%) which is effective in killing head lice. It can also be used against the scabies mite (seep. 282).
The bar can be used as a shampoo. Apply to wet hair, work it into a lather and thoroughlymassage into the scalp. Allow to remain on the head for 10 minutes, then rinse and dry the hair.
Dead lice can be combed out over a towel. Repeat the procedure after three days. The hair willremain free of reinfestation for at least several weeks.
The bar, which is commercially available, can be produced locally for non-commercial purposes.
Crude raw coconut oil Caustic soda solution Premix the permethrin with the mineral oil at room temperature and add the mixture to thecoconut oil in which the antioxidant has been dissolved. To this blend, add the caustic sodasolution at ambient temperature, with rapid stirring. When all the caustic soda has beenadded, sprinkle the clay in and pour the emulsion into moulds, where the reaction continues for12 hours.
The following day, cut the blocks into 40-g bars. If the bars are wrapped in polypropylene film andplaced in an airtight box, the product will retain its effectiveness for more than two years. If theyare packaged in a small plastic sandwich bag, or placed unwrapped in an airtight box, the shelflife is one year. If the product will be used up within a few weeks of manufacture, the lower-costpackaging is sufficient.
Impregnated mosquito nets
Head louse infestations disappear from people sleeping under mosquito netsimpregnated with a long-lasting pyrethroid insecticide (5) (see Chapter 1 andp. 240).
Crab or pubic lice Shaving the infested pubic hairs from the body has been replaced by the applica-tion of insecticidal formulations, as described for head louse control. In heavyinfestations all hairy areas of the body below the neck should be treated.

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