University:
American Career College
Course:
NURS115 | Intermediate Medical
Academic year:

2021
Views:

215

Pages:

52
Author:

Neulri

Medical Entomology 1 • Entomology = Entomo (insect) + logy • a highly successful group of animals • everywhere • and have adapted to nearly every imaginable source of food, including vertebrate blood. • Ectoparasites Phylum: Arthropoda = Arthros ( joint) + Podos (foot) Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Phthiraptera Family: Pediculidae Genus: Pediculus Species: P. humanus • • • • • • • a segmental body plan chitinous exoskeletal plates a ventral chain of segmental ganglia, an open dorsal circulatory system, a body cavity that is a hemocoel. ventilate by means of a tracheal system have well-developed appendicular mouthparts. THE INSECTS (HEXAPODA) • • • • • • About 1 million species. small size, short generation time, rather sophisticated nervous system ability to fly, different development strategies. THE INSECTS (HEXAPODA)     three main body regions (head, thorax, abdomen), three pairs of legs (restricted to the thorax), one pair of antennae have wings, but there are groups of primitively wingless insects and many groups that have secondarily lost wings. An insect’s life-cycle: Hemimetabolous, or incomplete metamorphosis. Insect young are usually similar to the adult. Wings appear as buds on the nymphs or early instars. Holometabolus, or complete metamorphosis. These insects have a different form in their immature and adult stages, have different behaviours and live in different habitats. The immature form is called larvae and remains similar in form but increases in size. They usually have chewing mouthparts even if the adult form mouth parts suck. At the last larval instar phase the insect forms into a pupa, it doesn’t feed and is inactive, and here wing development is initiated, and the adult emerges Sucking lice (Anoplura) Three types of blood-sucking lice occur on humans: 1. the body louse (Pediculus humanus) 13 2. the head louse (Pediculus capitis) 3. the pubic or crab louse (Pthirus pubis). • • • • • • flattened dorsoventrally Males measure about 2–3mm and females about 3–4mm. The head has a pair of small black eyes a pair of short five-segmented antennae. In males the tip of the abdomen is rounded, whereas in females it is bifurcated and used to grip fibres of clothing during egg-laying. Pediculus humanus male 18 • The egg, commonly called a nit is oval, white, about 1mm long, • has a distinct operculum (cap) containing numerous small perforations which give the egg the appearance of a minuscule pepper pot. • Intake of air through these holes not only supplies the tissues of the developing embryo with oxygen but aids hatching. Lice have a hemimetabolous life cycle. The louse hatching from the egg is termed a nymph and resembles a small adult. Body lice are spread by close contact Life cycle • Both sexes take blood-meals, and feeding occurs at any time during the day or night. • Both adults and immature stages live permanently on humans, clinging mainly to fibres of their clothing and usually only to body hairs during feeding. • Lice are very sensitive to changes in temperature. Medical importance for body louse (Pediculus humanus) • Pediculosis: Presence of body, head or pubic lice on a person • The skin of people may become pigmented and tough, a condition known as vagabond’s disease • Louse-borne epidemic typhus: Rickettsia prowazekii, are passed out in the faeces of the louse, and people become infected when these are rubbed or scratched, or come into contact with delicate mucous membranes such as the conjunctiva. • Infection can also be caused by inhalation of the very fine powdered dry faeces. Humans, therefore, become infected with typhus either by the faeces of the louse or by crushing it, not by its bite. • recrudescence of typhus is termed Brill–Zinsser disease. Medical importance for body louse (Pediculus humanus) • Louse-borne epidemic relapsing fever: Borrelia recurrentis is ingested with the louse’s blood-meal. the louse being crushed and faeces of infected lice can contain live B. recurrentis. • Trench fever: is caused by Bartonella Quintana. conveyed to humans either by crushing the louse or by its faeces coming into contact with skin abrasions or mucous membranes or arise from inhalation of the dust-like faeces. Control • • • • • Lice are killed with insecticidal dusts, such as carbaryl, propoxur, malathion Permethrin (the best pyrethroid for control) The head louse (Pediculus capitis) • Medical importance: • head lice are a serious public health problem • the USA and the UK almost 50% of pupils have head lice • • • • Control: A plastic louse comb the head can be shaved!pyrethroids such as phenothrin or permethrin, or organophosphates such as malathion. The pubic louse (Pthirus pubis) is smaller (1.3–2mm) than Pediculus species, it almost round. the middle and hind-legs are much thicker than the front legs have massive & very large claws, more sluggish movements, has resulted in the pubic louse being aptly called the crab louse. Medical importance • Infestation with crab lice is usually through sexual intercourse • Severe allergic reactions (pruritus) can develop in response to their bites, due to the injection of saliva and the deposition of faeces around the feeding sites. • Control: • shaving pubic hairs from the body, • application of insecticidal lotions. Fleas (Siphonaptera) • • • • • oval in shape and relatively small (1–6 mm); compressed laterally vary from light to dark brown Wings are absent, there are three pairs of powerful legs, with the hind legs specialized for 31 jumping. • The head is approximately triangular, bears a pair of conspicuous eyes (a few species are eyeless) Comb: a row of coarse, well-developed toothlike spines 1. combless fleas. 2. In some genera fleas have both combs, 3. in other species the pronotal comb is present and the genal comb absent the mesopleuron is located above the middle pair of legs. In several genera, including Xenopsylla, this sternite is clearly divided into two parts by a thick vertical rod-like structure called the meral rod, pleural rod, mesopleural suture or just rod. In female fleas the tip of the abdomen is more rounded than in males. Internally in about the sixth to eighth abdominal segments are one or two distinct brownish spermathecae male fleas both take blood-meals and can be vectors feed on humans or animals A minute legless larva emerges from the egg, Larvae feed on almost any organic debris, At the end of the larval period the larva spins a whitish cocoon from silk produced by its salivary glands. • cat and dog fleas (Ctenocephalides felis and C. canis) will readily feed on humans • Human fleas (Pulex irritans) often feed on dogs and pigs • rat fleas (Xenopsylla species) will attack people in the absence of rats Medical importance • Flea nuisance: • their troublesome bites, by cat flea on the ankles and legs • hypersensitive to flea bites can suffer from dermatitis, and inhalation of flea faeces can cause allergies Medical importance • • • • • Plague There are three main types of plague: bubonic, septicemic and pneumonic, all caused by the bacterium Yersinia pestis. The transmission cycle of plague between wild rodents, is termed sylvatic, campestral, rural or enzootic plague. • An important form of plague is urban plague. It is maintained in the rat population by fleas such as Xenopsylla cheopis. On their death infected fleas leave the rats and feed on humans. • Murine typhus or endemic typhus or Mexican typhus • is caused by the bacterium Rickettsia typhi • Rickettsiae of murine typhus can pass to the flea’s ovaries and subsequently to the eggs, larvae and adults, that is transovarial transmission. • Cestodes • Dipylidium caninum is the commonest tapeworm of dogs and cats, and it occasionally occurs in children. It can be transmitted by fleas (C. felis, C. canis and P. irritans) to both pets and humans • Hymenolepis diminuta and H. nana Control of fleas • Repellents such as DEET Bedbugs (Cimicidae) • • • • oval, wingless insects flattened dorsoventrally, They are about 5–7mm long The prothorax is much larger than the meso- and metathorax • has distinct wing-like expansions. 44 males the tip of the abdomen is slightly more pointed than in females, while closer examination shows a small well-developed curved penis In females there is a small incision ventrally on the left side of the apparent fourth abdominal segment, organ of Berlese or organ of Ribaga, which collects and stores sperm female Life cycle • Unlike lice, bedbugs do not remain on people but stay only to take blood-meals • Bedbugs are usually spread to new houses by being introduced with furniture and bedding, or more rarely with clothing and hand baggage. • Buying secondhand furniture can result in the introduction of bedbugs into houses. Newly hatched bedbugs (nymphs) are very pale yellow and resemble adults, but are much smaller The life cycle is hemimetabolous 49 Both sexes of bedbug take blood-meals Medical importance • not considered as vectors. • Some people show little or no reaction to their bites, but others may suffer severe reactions and have sleepless nights. • Repeated feedings of large numbers of bedbugs can cause iron deficiency in infants and some elderly people. Control • Insect repellents and insecticide-impregnated bednets can give considerable personal protection against bedbugs. • Floors and walls of infested houses, together with as much furniture as possible, should be sprayed with the carbamate bendiocarb, organophosphates such as malathion, a range of pyrethroids including cypermethrin and also insect growth regulators (IGRs)

Medical Entomology Part 1

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