Entomology 4

Question 1

Ectoparasites Definition

Answer 1

A parasite that live son the outside of its host. Many parasitic arthropods (insects and acarines) are ecto (outside) parasites in a sense, but the four taxonomic groups: fleas, lice, mites and ticks are more intimately associated with their human hosts, especially lice.

Question 2

Ectoparasites Human lice

Answer 2

Pediculus humanus (clothing), Pediculus capitis (head lice). Pthirus (crab lice). Engorged lice are dark red/brown (due to blood meal). Nymphs, adult males and females blood-feed frequently (~2 days). Comb with conditioner - will remove nymphal stages (but not the empty egg ‘nits’) - need to do it repeatedly over 2 weeks to cover the full life cycle

Question 3

Ectoparasites Pediculus spp

Answer 3

Do not need to speciate. Translucent (beige/grey, unless blood-fed). Well developed claws. Wingless (need close contact for transmission), dorsoventrally flattened, narrow head. Antennae have 5 segments. Male has enlarged tibial thumb and tarsal claw. Look at base of abdomen - male = rounded, female = bilobed. Head, thorax (3 legs), abdomen. Disperse 4.2m/d. P humanus search clothing (particularly seams and hems). P capitis search hair on head (eg wet combing with conditioner)

Question 4

Ectoparasites Pthirus spp

Answer 4

Translucent (beige/grey, unless blood-fed). Well developed claws. Wingless (need close contact for transmission), dorsoventrally flattened, narrow head. Antennae have 5 segments. Look at base of abdomen - male = rounded, female = bilobed. Division of thorax and abdomen is not well defined. Smaller and rounder than Pediculus ‘Crab like’. 1st pair of legs is slender (2nd and 3rd pairs are large with large claws). Disperse 10cm/d - go to tip of hair to swing to the next hair. Search coarse hair (pubic, beards and eyelashes/eyebrows)

Question 5

Ectoparasites Lice life cycle

Answer 5

1 Eggs - dark (empty egg ‘nit’ white) 2 Nymphs three instars 3 Adults: longevity ~9 days. Pe humanus (body lice) - uncommon in developed countries. Pe capitis (head lice) worldwide, mostly children. Pt pubis (crab lice) mainly in sexually active groups, can occur on beards and eyelashes

Question 6

Ectoparasites Pediculus spp egg

Answer 6

Operculum flattened, egg attached to hair

Question 7

Ectoparasites Pthirus spp egg

Answer 7

Operculum raised, egg attached to hair

Question 8

Ectoparasites P humanus importance

Answer 8

Typhus (R prowazekii - multiples in midgut, passed in faeces - infected for 3 months) anthroponosis. Symptoms: headache, chills, fever, general pains (fatal 10-40% if not treated). Trench fever (Bartonella quintana). Louse-borne relapsing fever (Spirochete Borrelia recurrentis. 20-10% die untreated). Fever 2-9d every 2-4d)

Question 9

Ectoparasites Pediculosis

Answer 9

Infestation with louse. ‘Pediculosis capitis’ (In UK 1 in 10 primary school children infected. Causes social distress. Heavy infestations: irritation, itching, and saliva toxic reaction (weariness)). ‘Pediculosis pubis’ Pthirus pubis (characteristic bluish spots at bite site, associated with sexually transmitted infections)

Question 10

Ectoparasites Pediculus humanus control

Answer 10

Environmental (replace clothes/isolate clothes for 17+ days, boil wash clothes, hot tumble dry (60oC for 15min)). Chemical (insecticidal treatment of clothes) Burundi prison (cleanse prison, shave and dust prisoners with 0.5% permethrin powder, changed beds and clothes)

Question 11

Ectoparasites Pediculus capitis

Answer 11

Chemical control (insecticide resistance to all over-the-counter treatments containing either malathion, permethrin or phenothrin is widespread and ovidal activity is poor). Physical removal (using wet combing with condition is more effective), Dimeticone 4% gel/lotion (prevents respiration - no resistance - expensive and need to treat multiple times to cover life cycle). Treat all individuals in household with an active infestation. No need to treat clothing/bedding.

Question 12

Ectoparasites Pthirus pubis control

Answer 12

Eyelashes (Petroleum jelly 2x/day for 10d), Pubic hair and beards (water-based insecticide lotions - alcohol based lotions sting delicate areas).

Question 13

Ectoparasites Fleas

Answer 13

Small (1-8mm long), oval, wingless, laterally flattened, colour varies (brown to reddish black), cuticle has spines and bristles, one pair of eyes, club antenna tucked behind eyes, some species have combs (ctenidium). Head, thorax (3 legs), abdomen. Jump from host to host. Need to identify four different types of comb. Genal comb near mouth. Pronotal comb on back. Beneath pronotal comb there is a mesopleural rod - these are used for identification. Look behind eye - club-like structure is an antenna. Differentiate gender male: terminal segments upturned with curled intromittent organ, female = rounded abdomen with hilla and bursa. Blood feeding behaviour - males and females are obligate blood feeders. Not host specific (but nest/habitat specific). Primary host required to achieve sexual maturity and reproduction. Saliva (anticoagulant) injected when mouthparts penetrate.

Question 14

Ectoparasites Xenopsylla

Answer 14

No combs, Mesopleural rod located in second thoracic segment. Transmits plague. Yersinia pestis. Primary host rodents. Transmission bite of infected flea. Presentation: bubonic, septicaemic or pneumonic. Africa (90%), Asia, USA and South America 2-3000 cases/year. Development of plague in flea - plague replicate and block the proventriculus opening to the oesophagus and are regurgitated out during blood meal. Transmits murine typhus (R typhi) Primary host rodents. Transmission dried flea faeces (open sores, mucus membranes). Milder than louse-borne typhus 1-2% mortality. Distribution: USA, Mexico, South America, India, SE Asia, Australia

Question 15

Ectoparasites Pulex irritans

Answer 15

No combs. Has sclerotised antennal fossae (looks like it’s wearing headphones). Human flea

Question 16

Ectoparasites Ctenocephalides

Answer 16

Genal and pronotal comb present. Mesopleural rod (second pair of legs) Transmits Dipylidium caninum, Hymenolepis diminuta (dog and cat tapeworm). Transmission: flea is ingested by animal. Worldwide. Treatment: Endogard for dogs (Praziquantel, Pyrantel, Emonate, Febantel) every 2 weeks until 12 weeks, then every 3 months

Question 17

Ectoparasites Tunga penetrans

Answer 17

No comb, head has upturned point, mouth parts are long and serrated. Round body shape with compressed thoracic segments - can see the three legs, but at the ‘neck’ the thoracic segments are very compressed. Much bigger than other flea. Tunga penetrans (primary host pigs and human). Pits and ulcers in the foot by female flea. Tropical Africa, Central and South America. Females seek host and bury head-first in skin. Tip of abdomen (spiracles) exposed. Pain, secondary infection, tetanus, gangrene, loss of toes.

Question 18

Ectoparasites Flea life cycle

Answer 18

Complete metamorphosis (immatures differ from adults), adult longevity 6-12 months (up to 2 years), female produce 3-25eggs/day (300-1000/lifetime), eggs hatch in 2-14d. Caterpillar-like larvae undergo two moults (three instars) in 2-3 weeks. Pupae housed in silk cocoon (2-3 weeks). Adults sheds pupal skin and remains dormant within cocoon (up to one year) until stimulated by a host (vibration). Can copulate immediately after emergence. Eggs laid 1-2d after bloodmeal.

Question 19

Ectoparasites Flea egg

Answer 19

Small and oval, white or yellowish, lack any pattern, thinly coated with a sticky substance

Question 20

Ectoparasites Flea larva

Answer 20

4-10mm long, white with a small head, 2 antennae. 13 body segments each with a circclet of setae. Anal struts on last segment. Feed on organic debris (chewing mouthparts) and dried blood (faeces from adults). Third instar spins cocoon. Can be found on host (or in nest/burrow/carpets - prefer dark areas. (differentiate from sandfly as they have long caudal setae)

Question 21

Ectoparasites Flea pupa

Answer 21

Look like a small adult flea. Inactive, developmental phase, protected by cocoon - can remain in cocoon for over a year in adverse conditions. Emerge when given host stimuli - CO2, heat and movement

Question 22

Ectoparasites Flea cocoon

Answer 22

Spun from silk by mature larva. Camouflaged by debris that adheres to the sticky silk. Protects the pupa and the adult prior to emergence

Question 23

Ectoparasites Flea where to find

Answer 23

Direct search of host (can find adults on pets [but quickly jump off], hosts [small] and/or bedding can be placed in clear plastic bag and anaesthetised with ether - fleas are recovered from bottom of bag. Hosts can be put in a cage with a wire mesh floor over soapy water - fleas collected as they leave host. Jigger fleas: female burrows into skin, mostly on soles of feet. Examine feet daily for small, black itchy spots). Domestic fleas (pupae are inactive, found around carpet edges and in pet bedding. Can place sticky traps around carpets for detection, adults emerge when sense vibration from a potential host)

Question 24

Ectoparasites Flea importance

Answer 24

Biting nuisance (especially cat fleas). All are zoonoses: plague, flea-borne typhus, tapeworms

Question 25

Ectoparasites Flea control

Answer 25

1 Chemical (domestic fleas - insecticide treatment of houses with residual sprays, pets treatment, other hosts malathion, carbaryl, permethrin - reapplication necessary - reinfestations may appear quickly [insecticide bombs - Permethrin]). 2 Environmental control (vacuuming, around edges of carpets in particular and washing floors). 3 Personal protection (wearing shoes (jiggers), repellents (DEET-efficacy prolonged by treating clothes rather than skin). 4. Rodent control and rodent proofing of buildings.

Question 26

Ectoparasites Bed bugs egg

Answer 26

Bed bug eggs 1mm, pearly white with a fine pattern and are curved anteriorly with an eye spot.

Question 27

Ectoparasites Bed bugs

Answer 27

Bed bugs of all stages are oval, dorso-ventrally flattened insects (shape and colour of apple pip). The cuticle colouration increases with each stage, from the yellow cuticle of the first instar nymph to the brown cuticle of the adult. Adults are 5.5-7mm long and 2.5-3mm wide. Females are generally larger with a rounded abdomen, males have pointed tip that can be seen microscopically. Both sexes and all stages are without functional wings and are obligate blood feeders, needing a blood meal for development and reproduction. Bed bugs use a combination of heat and semiochemicals (like pheromones) to locate a suitable host at night. During the day they aggregate (huddle) within refuges in conspicuous cracks and crevices, consisting of all developmental stages. When arriving at a hotel - inspect the room for bed bugs - look at the sheets - seams of the mattress, within the bed frame, bedside cabinet - look for faecal spots (brown/black spots which are defaecated blood)

Question 28

Ectoparasites Bed bug lifecycle

Answer 28

First instar nymph hatches from an egg and the goes through four further nymphal instars, before moulting to become an adult. Without restrictions due to temperature or host availability, the bed bug lifecycle can be completed in 3 weeks. Peak infestation occurs in around September followed by a decline during the winter and a steady increase throughout the spring and summer months.

Question 29

Ectoparasites Bed bug importance

Answer 29

Biting nuisance, allergic reactions, secondary infections, anxiety, evidence of vectoral status is unclear except for Trench fever (Bartonella quintana), pest on poultry farms.

Question 30

Ectoparasites Bed bug control

Answer 30

Important public health problem. Infestations are increasing. Pesticide resistance is developing. No passive monitoring device. New approaches are needed (control, monitoring), semiochemicals (pheromones) for odour-baited traps

Question 31

Ectoparasites Mites

Answer 31

Acarines - mites - have eight legs. Small (microscopic or just visible by eye). Like ticks: body divided into capitulum (head) and idiosoma (unsegmented thorax/abdomen). Wingless. Adults have four pairs of legs. 0.5-1 million species

Question 32

Ectoparasites Distinguish mite from tick

Answer 32

Tick has toothed hypostome, first leg has sensory pit ‘Haller’s organ’ to detect semio chemicals (mites do not have either of these)

Question 33

Ectoparasites Mite Lifecycle

Answer 33

1. Eggs (few, large), hexopod larva, 3 two or three octopod nymphal stages: protonymph, deutonymph, tritonymph. 4 Adults

Question 34

Ectoparasites Mite Dermatophagoides

Answer 34

House dust mite - trigger asthma. Dermatophagoides translates to skin-eating. Everyone has a few million in their bed, worldwide distribution. Optimal 25oC 80% humidity (soft furnishing, especially beds, also sofa etc). Life-span 3 months, life-cycle 25d. 3-4 egg batches. 20-40 eggs/batch. Slow <15 or >35oC. Death <-18 or >55oC. Mite allergen is released as faecal pellets (10-20um in diameter, 20-30 faecal pellets/day, 2-3000/lifetime). Mite allergen triggers: asthma (12.9 million DALYs, 186,000 deaths), eczema, perennial rhinitis - prevalence of atopic diseases increasing. Survey buy sampling dust - use vacuum cleaner with special nozzle 2min/m2 and express densities per unit weight. Repeated measurements may artificially deplete the amount of dust and confound estimates. Thus, express densities per unit area. Simple mite extraction methods exist, Rapid lateral flow (dust sample from bedding or carpet and apply the sample to the test. Indicator line shows whether the sample contains low, medium, or high allergen levels. ELISA also possible by inbio).

Question 35

Ectoparasites Flour mite

Answer 35

Store flower in airtight container - avoid damp and mite infestation. Can cause oral mite anaphylaxis (Pancake syndrome) Route of infection - ingestion of flour ingested with mites (eg Dermatophagoides farinae)

Question 36

Ectoparasites Mite control

Answer 36

1 Physical (semi-permeable mattress encasing, removal of domestic habitats/dust (HEPA vacuum cleaners, ionisers), Making habitats less favourable for HDM (dehumidifiers, removing soft furnishing). 2 Chemical (allergen sprays, fungicides, acaricides - most of these do not work)

Question 37

Ectoparasites Sarcoptes scabiei

Answer 37

Obligate parasite. Fertilised female lives in epidermal burrow, Female lays 50 eggs/burrow. Feed on oozing liquid from gnawed cells. Nomadic male moves between burrows to mate. Larva excavates new, short burrow. Lifespan 4-5 weeks. WHO NTD: transmitted through skin to skin contact (sometimes bedding), host specific, itchy red rash, typically found where skin is thinning (finger webs, wrists, genitals), diagnosis: skin scrapes (low sens, high spec), burrows show as raised lines, immunocompromised hosts may developed crusted lesions). Sample: skin scraping (smear on slide, examine under microscope, place scraping in NaOH-sugar flotate).

Question 38

Ectoparasites Scabies lifecycle

Answer 38

Females lay 1-3 eggs/day, eggs hatch in 3-5 days, larvae crawl to the surface along burrows, they make a small moulting pocket in skin or hair follicles, after 3-4 days the larva moults to a protonymph and after another 2-3 days to a tritonymph. The tritonymph moults to either a male or female, females stay put and only start to burrow after fertilisation. Adult lifespan 1-2 months.

Question 39

Ectoparasites Scabies treatment

Answer 39

Scabicides: Permethrin 5% cream (best for children) - Malathion solution (not <6y) and Benzyl benzoate emulsion (not ovicidal. Treatment should be applied on cool, dry skin (apply to entire body below neck, apply before bedtime, repeat after 7-10days). MDA if prevalence is >2% 2 doses of oral ivermectin (200ug/kg) given 7-14 days apart.

Question 40

Ectoparasites Trombiculid mites

Answer 40

Larvae climb up grass and drop onto host. Scramble to secluded/sweaty areas. ** Sampling techniques: catch rodent host. Remove mites from host with fine forceps. Suspend host in mesh cage over soapy water (engorged mites will drop off and can be collected in water)

Question 41

Ectoparasites Trombiculid mites lifecycle

Answer 41

Nymphal stages are below ground - nymphs and adults live in soil (feed on arthropods and eggs). Eggs laid in damp soil. Larvae ‘chiggers’ fall on host and feed on cell tissue fluids through a stylosome

Question 42

Ectoparasites Trombiculid mites importance

Answer 42

1 Trombidiosis (Scrub itch) intense, itchy dermatitis. Larvae feed for up to 10d on host (saliva produces itchy, red lumps found, typically in armpits, leg calves and pelvic region). 2 Scrub Typhus (Chigger-borne rickettsiosis) Orientia tsutsugamushi. Typically confined to rodents/insectivores. Humans typically get infected when they invade ‘mite islands’. Endemic in SE Asia and Australia. Symptoms: mild fever, to fatal multiple-organ failure (1 million cases/year, up to 40% mortality).

Question 43

Ectoparasites Trombiculid mites prevention

Answer 43

Avoid Chigger habitats/mite islands (patchy distribution: need environment with abundant prey, for adults, and with mammals, for larvae). Spray vegetation with an acaricide (eg benzylbenzoate). Impregnate socks/trousers with repellent DEET. Treatment for scrub typhus: doxycycline

Question 44

Ectoparasites Ticks

Answer 44

All ticks are parasitic, toothed hypostome present. Haller’s organ present. Tough leathery cuticle. Incomplete life cycle. Not host specific

Question 45

Ectoparasites Hard tick

Answer 45

Hypostome (mouthparts) visible from dorsal surface (soft ticks are not). Scutum present. Six legged larvae, eight legged lymph and adults. Sexual dimorphism well marked. Eyes are mid-thoracic behind second legs.

Question 46

Ectoparasites Hard tick lifecycle

Answer 46

Females feed for 6-12 days. Then engorged female drops off the host and matures her eggs. The female lays 1000-10000 eggs then dies. Eggs hatch in 10-20 days, or may over winter. 6-legged larva feeds for 2-6 days. 8 legged nymph feeds for 3-8 days. Nymph moult into males or female. Males feed only briefly. Lifecycle takes on average 2-3 years for most temperate species.

Question 47

Ectoparasites Hard tick medical importance

Answer 47

Arboviruses (Tick-borne encephalitis, CCHF, Colorado tick fever). Rickettsiae (Rocky mountain spotted fever [Dermacentor andersoni], Boutonneuse fever (tick typhus), Queensland tick typhus). Spirochetes (Lyme disease)

Question 48

Ectoparasites Hard tick - Ixodes

Answer 48

Differentiated from other genera by the anal groove which runs anteriorly around the anus. In all other genera the anal groove is posterior to the anus. Vector of Lyme disease.

Question 49

Ectoparasites Soft tick

Answer 49

Mouthparts are not visible from dorsal surface. Scutum absent. Coxal glands. Sexual dimorphism slight. Six legged larvae, eight legged lymph and adults. Collecting: drag white cloth through vegetation, lures (animal baits and CO2), direct examination of hosts.

Question 50

Ectoparasites Soft tick lifecycle

Answer 50

There is little sexual dimorphism. Females lay several small egg batches, of 15-100 eggs, after each blood meal. Eggs hatch after 1-3 weeks. 1 larval stage. Argasid/soft ticks take short feeds of 20-30 minutes. Lifecycle takes 6-12 months to complete. Multiple nymphal stages (4-5) each requires a bloodmeal. Adult lifespan of up to 15-20 years. Adults can survive for 12 years without a bloodmeal.

Question 51

Ectoparasites Soft tick medical importance

Answer 51

Tick-borne relapsing fever. Several Borrelia species Ornithodoros species. Man is the sole reservoir of disease (B. duttonii). Endemic in Africa and southern Asia. Foci in North America and Europe.

Question 52

Ectoparasites Tick control

Answer 52

Avoidance. Repellents (20%+ DEET). Clothing (and permethrin impregnated clothing). Check yourself and pets for ticks. Safe removal of attached ticks. Tumble dry clothing on high heat to kill ticks. Insecticidal treatment of animals. Insecticidal treatment of breeding sites.

Question 53

Ectoparasites Tick removal

Answer 53

Using fine forceps gently (but firmly) grasp the tick as close to the skin as possible. Pull the tick gently but firmly away from the skin without twisting the body or mouthparts. Thoroughly clean the bite area and your hands with rubbing alcohol, iodine scrub or soap and water.

Question 54

Ectoparasites Summary

Answer 54

Ectoparasites (lice, fleas, bed bugs, mites and ticks) have close associations with humans - because of this, they are good vectors of diseases. They have morphological adaptations for their mode of life. Life-cycles vary: all stages may be on the host, or some stages may be free-living, This influences control options. Generally, lice are usually more host-specific and transmit anthroponotic diseases, whereas diseases vectored by the other ectoparasites are zoonotic. Routes of transmission vary - either through blood-feeding or through faeces and trans-stadial or trans-ovarial transmission can occur. Bodies of some ectoparasites cause allergic reactions. Treatment of diseases varies (eg antibiotics, ivermectin).