Bedbugs, Lice and Ticks (Who)

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  • Topic: Head louse, Pediculosis, Body louse
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BEDBUGS: PUBLIC HEALTH IMPORTANCE

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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. Lice live on humans or in their clothing, while fleas are frequently found taking bloodmeals on people and domestic animals. Bedbugs, which can be found in beds or furniture, 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 bloodmeals on humans. Fleas, bedbugs and lice are insects, whereas ticks and mites belong to another group of arthropods, the Acarina. Unlike adult insects they have only two main sections to their body, and the adults have four pairs of legs (as opposed 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 transmitted 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).

BEDBUGS
Two species of bedbug feed on humans: the common bedbug (Cimex lectularius), which occurs in most parts of the world, and the tropical bedbug (Cimex hemipterus), which occurs mainly in tropical countries. They are a severe nuisance when they occur in large densities, being commonest in places with poor housing conditions. They are not important in the transmission of diseases, although they possibly play a role as vectors of hepatitis B virus.

Biology
Bedbugs have a flat, oval-shaped body with no wings, and are 4–7 mm long. Their colour is shiny reddish-brown but after a blood-meal they become swollen and dark brown in colour. There are three stages in the bedbug’s life cycle: egg, nymph and adult (Fig. 4.1). The eggs are white and about 1 mm long. The nymphs look like adults but are smaller. Complete development from egg to adult takes from six weeks 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. In the 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 repeated about 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 and wallpaper; hiding places are also used for breeding. The bugs are frequently

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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 are also favourable for the bugs, which cannot develop below 13 °C (Fig. 4.2). Adults can survive for several years without food.

Dispersal
Because they have no wings, bedbugs travel only short distances. In poorly built houses with many suitable hiding places they crawl from one bedroom to another; they spread from one house to another mainly in second-hand furniture, bedding and, sometimes, clothes.

BEDBUGS: PUBLIC HEALTH IMPORTANCE

239

Public health importance
Bedbugs are not considered vectors of disease. It has been suggested that they play a role as vectors of the hepatitis B virus (1, 2) but this was denied in a recent study in 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 before may suffer from local inflammation, intense itching and sleepless nights. The bite produces a hard whitish swelling...
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