Medical And Veterinary Entomology

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

Order: Phthiraptera (Sucking and chewing lice) 1- Sucking lice Family: Pediculidae E.g. 1 Pediculus humanus humanus (body louse)

External morphology Adults are small, wingless, dorso-ventrally flattened insects. Body lice are pale beige or grayish in color, whereas head lice have dark beige abdominal margins. Head louse is distinguished from body louse by having festoonlike structures laterally on its body. Head with a pair of inconspicuous simple eyes and a pair of short five-segmented antennae. Mouthparts are different from those of other blood-sucking insects. They consist of a flexible, sucking, almost tube-like mouth called haustellum, which is armed with teeth to grip the host skin during feeding. Needle-like stylets penetrate into the skin and saliva is injected into the wound made by the bite Thoracic segments are fused; each leg has one tarsal segment and a large claw constituting the "clinging leg". Abdomen without cerci. Metamorphosis incomplete metamorphosis (egg, nymph and adult).

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E.g. 2 Pediculus humanus capitis (head louse)

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

Natural History Museum, London); b) a body louse (CSIRO).

Biology Both adult and immature stages live permanently on humans, clinging mainly to hairs of their clothing and usually only to body hairs during feeding. Both sexes, as well as immatures, take blood-meals. Feeding occurs at any time during the day or night (permanent parasite). Female head louse deposits its eggs (nits) at the base of hairs on the head. Eggs are deposited, as well, behind and above the ears, and at the back of the neck. The body louse deposits its eggs on cloth fibers. Unfed lice die within 2-4 days if kept away from humans and without a blood meal, but blood-fed individuals may survive for 510 days. Lice are very sensitive to changes in temperature. They quickly abandon a dead host, owing to cooling down of the body, and seek out a new host. They also leave a person with a high temperature. They are unable to feed at temperatures above 40º C.

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Fig.1. An image taken through a microscope shows a) a head louse (Vincent S. Smith,

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

Medical importance 1) Pediculosis: Pediculosis is an infestation of lice -- which are parasitic insects -- on the bodies of humans. The condition is more commonin case of head lice, body lice. These are appellations of lice and not a pathological condition). 2) Lice as diseases vectors: 1- Louse-borne epidemic typhus: Causative organism: rickettsiae, Rickettsia prowazeki Vector: The human body louse Pediculus humanus humanus Host: Human

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Fig.2. Life cycle of the head louse has three stages: egg, nymph, and adult (from CDC).

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) - The infection is transmitted to a healthy human who scratches the louse bite (which itches) and rubs the feces into the wound. 2. Trench fever: Causative organism: Bacterium , Bartonella quintana Vector: Host: Human

- Transmission of the infection to people may occur by rubbing the feces of an infected louse into abraded skin or into the eyes. Scratching and accidentally crushing the louse also expresses large amounts of bacteria that is then rubbed into the skin. 3- Louse-borne epidemic relapsing fever Causative organism: Spirochetes, Borrrelia recurrentis. Vector:

Pediculus humanus, is the specific vector. -

The only way by which a human being may become infected with louse-borne epidemic relapsing fever is through louse crushing that releases the spirochetes which then enter the host body through abrasions or mucous membranes.

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The human body louse Pediculus humanus humanus

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) Family2: Haematopinidae E.g. Haematopinus tuberculatus (Cattle louse) General characters: The cattle louse is primarily a parasite of the water buffalo; it also infests domestic cattle when in association with water buffaloes. It causes irritation to the infested animal.

but without eyes (Copyright to MCP, 1998).

2- Chewing lice Family1: Philopteridae E.g. Lipeurus caponis

Fig.4. Lipeurus caponis (copyright to University of São Paulo).

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Fig.3. Species of Haematopinus are large lice measuring about 4 mm with prominent ocular points

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

Habits and Medical importance 1) These are permanent ectoparasites on birds, where they feed on sloughed epidermal tissues, feathers and sebaceous secretions of the host. 2) Parts of feathers, particularly the barbs and barbules constitute a major part of the food of this louse. therefore affecting its feeding, habits and digestion. Egg production is greatly reduced and development retarded. 4) Lice tend to be abundant where uncleanliness and overcrowded conditions exists. 5) Generally chewing lice act as intermediate hosts to the tapeworm

Dipylidium caninum, as it is easy for lice to become infected by swallowing worm egg capsules.

Family2: Menoponidae E.g. Menopon gallina

Fig.5. Menopon gallina.

1) Small insects; occurring mainly on the shafts of feathers. 2) Has the same character as sucking lice but differentiated from them by having chewing mouthparts. Body is oval.

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3) The irritation louse feeding causes the host to become restless,

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) 3) It may infest turkeys, ducks, and guinea fowls, when they are housed with chickens, It sometimes infests horses that are stabled.

Medical importance Biting and annoyance domestic animals, especially poultry; they feed on feathers or hairs of the host, may cause considerable losses in the wool, meat, and diary production.

Order: Siphonaptera (Fleas) External morphology and biology of fleas ♦ Adult fleas are small insects (1-4mm), more or less oval, laterally

compressed, highly scletorized. Head is triangular in shape and bears a pair of conspicuous black eyes (few species are eyeless) and short three-segmented antennae. Some flea species, it may have an oral/genal ctenidium, which is a conspicuous comb of heavy spines located just about the mouthparts. Mouthparts are of the piercing-sucking type. - Thorax, is compact, the pronotum immediately behind the head with a comb of spine-like processes known as: pronotal comb (ctenidium) in many species. They are wingless insects; this can be considered a secondly adaptation to obligate parasitism. The hind legs are adapted for jumping.

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Chewing lice don't attack man but several species are important pests of

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) - A flat or convex plate called the sensilium is characteristic of fleas , which is present dorsaly on the 8th abdominal segment. ♦

Adult females often oviposit their eggs in debris, which accumulate in dwelling places such as rodent burrows or nests. Hatched larvae have chewing mouthparts and feed on variety of organic material found in the places where they live.

Fig.6.

The mouth parts of the flea appear to be of the dipterous type in structure, but they are more generalized than those of any adult fly. None of the usual pieces are lacking. The labrum is long and slender but is blunt at the apex; its lateral edges are rolled downward between the mandibles, forming the anterior wall of the food canal. The hypopharynx is short and projects into the proximal end

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Fleas' mouthparts:

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) of the food canal between the bases of the mandibles; upon it opens the duct of the salivary glands, the secretion of which is conveyed to the wound through a channel between the posterior edges of the mandibles. The mandibles are long, sharp-pointed blades armed distally

The maxillae are short, rather wide plates, bearing each a long segmented palpus. The labium consists of a short median body, hollowed anteriorly, bearing distally a pair of segmented palpi.

Family: Pulicidae e.g1 Pulex irritans (Human flea)

Fig.7. Pulex irritans (copyright to CSIRO) They feed preferentially on human. However, surprisingly, they can feed on domesticated animals.

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with minute teeth.

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) They are characterized by the absence of oral/genal and pronotal ctenidium ctenidia.

e.g2 Ctenocephalides canis (Dog flea) e.g3 Ctenocephalides felis (Cat flea) a)

b)

- Both species attack dogs and cats as well as men. - They have pronotal and genal ctenidia consisting of 7 or 8 sharp black teeth. - To distinguish between Ctenocephalides canis and Ctenocephalides felis:

The first spine in the genal comb is nearly half the length of the second spine.

C. canis

The first spine in the genal comb is nearly equal to the length of the second spine.

C. felis

e.g4 Xenopsylla cheopis (Oriental rat flea)

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Fig. 8. a) Ctenocephalides canis , b) Ctenocephalides felis.

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

Fig. 9. Xenopsylla cheopis (SMC Images/Getty Images)

rodents are found. - They are characterized by the absence of oral/genal and pronotal ctenidia, and the presence of a mesopleural suture. - It habitually occurs in buildings and bites man freely. In this flea species, both oral and pronotal ctenidia are absent.

Medical importance A) Both

male

and

female

fleas

are

temporary

ectoparasites. B) Fleas act as a vector for a number of diseases: 1- Plague - Pathogen: Yersinia pestis - Vector: Xenopsylla cheopis

Pulex irritans - Host: human - Transmission (see figure 9):

obligate

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- They are present wherever Rattus rattus and other

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) Both male and female fleas transmit the bacilli of plague. The fleas leave a rat as it cools after death, taking the pathogen directly to man. The pathogen is introduced directly with the bite. This mode of transmission is due to regurgitation of the infected blood meal caused by temporary obstruction at the entrance of the stomach. Te bacilli cause a gelatinous mass to develop among the spines backpressure caused by the oesophagus wall causes some of infectious blood to be driven back into the feeding wound. The pathogenesis of plague infection follows from lymphatics and lymph nodes, to blood stream.

Fig.10. Plague transmission cycle.

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of proventriculus, and when the flea tries repeatly to refeed,

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE)

2- Murine typhus (endemic typhus fever) - Pathogen: Rickettsia typhi - Vector: Xenopyslla cheopis - Host: human - Transmission (see figure 10): The pathogen multiplies in great abundance within the epithelial release free rickettsia into the lumen. Rodent is the main host, although man may act as an accidental host.

Fig.11. Transmission cycle of Rickettsia typhi inside both hosts and flea (copyright to Azad et al., 1998).

3- Helminth infestations Fleas, especially, Ctenocephalides canis, and C. felis play a significant role as an intermediate host of double-pored dog tapeworm, Dipylidium caninum Transmission (see figure 11): - This tapeworm normally develops in the digestive tract of dogs, cats, and occasionally occurs in man especially young children.

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cells of the flea mid-gut, and when packed these cells burst to

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) - The eggs of tapeworms are discharged in the feces of vertebrate host and are ingested by chewing mouthparts of larval fleas. - Larval worms hatching from the ingested eggs penetrate the gut wall of the larval flea and pass across into the body cavity. They remain trapped within this space and pass on the pupa and finally to the adult flea where they encapsulate and become cysticercoids. - When infected fleas are ingested by a cat or a dog while licking their into tapeworms in the digestive tract. - Similarly, young children fondling and kissing dogs and cats become infected with the tapeworms: by swallowing cat and dog fleas or by being licked by dogs which have crushed infected fleas in their mouths, thus, liberating the infective cysticercoids.

Fig.12. Dipylidium caninum transmission cycle (Copyright for CDC).

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coats during grooming, the cysticercoids are liberated and develop

March. 16, 2009 (Lab.3.)

Medical and Veterinary Entomology (MVE) References: 1. 2. 3.

4.

Mike W. Service (2000). Medical Entomology for Students. Second Edition. Ewing, H. E. and I. Fox (1943). The fleas of North America. Miscellaneous Publications, United States Department of Agriculture 500:1–142. Pratt, H. D. and J. S. Wiseman(1962). Fleas of public health importance and their control. U. S. Department of Health, Education, and Welfare. Publication No. 772. 36 p. Azad A.F. and Beard C.B (1998). Rickettsial Pathogens and Their Arthropod Vectors. Emerg Infect Dis. 4(2):179-86. Review

Lab. 3. available online on Saturday March 14, 2009 (www.pdfcoke.com)