Lice, mites and fleas Flashcards
What are the order and suborder of lice?
Order - pthiroptera
Suborder - anoplura
What are the species and subspecies of lice?
Pediculus humanus
- humanus
- capitis
Pediculus pubis
What is subspecies known as the the body louse?
Pediculus humanus humanus
Describe the general external morphology of pediculus humanus humanus
Small (2-4mm), pale, beige
Wingless
Dorsoventrally flattened
Eyes = simple ocelli
Mouthparts adapted for piercing and sucking (tube-like haustellum with tiny teeth for gripping during feeding)
Describe the female external morphology of pediculus humanus humanus
Short, thick tibia with small thumb-like pike on inner apex side and curved claw on tarsus
Spine and claw used to grip host hair/clothing
Bifurcated abdomen for gripping fibers of cloth during egg laying
Describe the male external morphology of pediculus humanus humanus
Smaller
Camouflaged
Longer foreleg claws
Rounded abdomens
Describe the life cycle of pediculus humanus humanus
Hemimetabolous life cycle 17-19d
Egg -> 3 nymphal stages -> adult
Discuss the behaviour of pediculus humanus humanus
Both sexes take blood meals
Live in host clothing and feed off body
Slow feeders
Defecate during feeding
Discuss the eggs/nits of pediculus humanus humanus
6-9 eggs per day in seams of clothes
Occasionally lay eggs on body hairs (pubic, perineal, axillary)
Oval, white, 1mm long eggs
Hatch after 7-10d
Do not survive >4/52
When do nymph instars of pediculus humanus humanus occur?
After blood meal
How soon do pediculus humanus humanus adults die without a blood meal?
Within 4-2d
What is the medical importance of pediculus humanus humanus?
Most cases have itchiness only (intermittent, at night)
Small, red papules w/ red punctum from scratching
7d post bite small weal/papules develop
Longstanding infection
- rough, thickened skin appearance with fine furfuraceous scaling (“Vagabond disease”)
- secondary infection with impetigo
What are pediculus humanus humanus a vector for?
Typhus
Trench
Relapsing fever
Which organism causes typhus?
Rickettsia prowazekii
Which organism causes trench?
Bartonella quintana
What was bartonella quintana previously known as?
Rochalimoea quintana
Which organism causes relapsing fever?
Borrelia recurrentis
How is pediculus humanus humanus transmitted?
Female cannot transmit transovarially
Transmission via rubbing infected material (faeces, body fluids, louse hemolymph) into skin wound
How is bartonella quintana transmitted to lice?
Transmitted via faeces and body fluids and ingested and multiplies in the midgut
How is rickettsia prowazekii transmitted to lice?
Ingested with blood meal into the gut where it multiplies in the epithelial cells, causing them to rupture and release the rickettsiae into gut content
Is rickettsia prowazekii pathogenic to lice?
Yes, die within 7-20d
Is bartonella quintana pathogenic to lice?
No
How is borrelia recurrentis transmitted to lice?
After ingestion, spirochetes develop in the lice hemolymph
Transmission to humans via the crushed louse’s hemolymph
Is borrelia recurrentis pathogenic to lice?
No
Discuss control of pediculus humanus humanus
Ironing of clothes
Washing of clothes >60 degrees
Malathion and carbaryl to treat as a 0.5% alcohol lotion (kills all louse stages)
10% DDT dust with talcum powder of body and underclothes
What can you offer if pediculus humanus humanus is resistant to insecticides?
2% temephos
5% carbaryl
1% propoxur
2% pyrethrum
Discuss the external morphology of pediculus humanus capitis
Very similar to humanus humanus
Live on scalp
Can interbreed with humanus humanus
Discuss the life cycle of pediculus humanus capitis
Takes 17-25d
Similar to humanus humanus
Egg at first is cemented in the angle between hair and scalp
3 nymphal stages
Live and feed on scalp
10-20 lice per individual
How are pediculus humanus capitis spread?
Close contact
Sharing of clothes, hairbrushes, headgear
What is the medical importance of pediculus humanus capitis?
Itchiness in the early stages that causes restlessness, irritability in children due to scratching
Scratching -> secondary infections eg impetigo
Can transmit rickettsia and spirochetes in lab conditions
Discuss the control of pediculus humanus capitis
Head lice campaign
- education
- regular inspection of school children
- regular home inspection
Treatment
Discuss treatment of pediculus humanus capitis
Malathion and carbaryl as 0.5% alcohol lotion, apply a few drops and massage into entire scalp esp per-auricular and suboccipital region
Louse comb
Discuss the external morphology of pthirus pubis
Narrow head with 6 segmented antennae
Lateral eyes
Slightly longer body than broad
Dorsoventrally flattened
3 pairs of legs
- 1st are slender
- each ends with a powerful claw
Lateral protrusions that end in cluster of setae on many of the abdominal segments
Discuss the lice cycle of pthirus pubis
Similar to humanus
Egg -> 3 nymphal stages -> adult
22-27d
Egg incubation 7-8d
Several eggs laid on the same hair
What is the medical importance of pthirus pubis?
Mostly affects pubic and axilla regions
Can affect eyebrows and eyelashes in children (only in adults if heavily infested)
How does eyelid infestation of pthirus pubis appear?
Yellowish encrustation with nits attached to eyelashes and skin
Eye edema if severe
How is pthirus pubis spread and does it transmit disease?
Spread by close contact (sex, bed sharing)
Does not transmit disease
Discuss the control of pthirus pubis
- HCH (must be repeated as not ovicidal)
- 1% malathion and carbaryl lotion for 12 hours then washed off
- Golden eye ointment
What is HCH?
Hexachlorocyclohexane
What is the issue with 1% malathion and carbaryl lotion for pthirus pubis?
Cannot use on the eyelids
Discuss the external morphology of mites
Small arachnids
Head, thorax and abdomen fused in unsegmented body
Part of head region including mouthparts is attached to anterior of body by a moveable hinge
Integument may be membraneous OR thickened into plates on dorsal and ventral surfaces
How did habit of mites feeding develop?
Developed from free-living forms inhabiting nests of small animals and feeding on decayed organic matter
What is the habitat of mites?
Terrestrial and aquatic
Certain species are endo/ectoparasities
Ectoparasites of skin, mucous membranes and feathers
Discuss the life cycle of mites
Egg -> larvae -> nymph -> adult
Relatively large eggs deposited on soil/host skin
1-2 eggs laid at each oviposition
What is the difference between mite larvae and adults?
Larvae - 3 pairs of legs
Adults - 4 pairs of legs
What are the significant mites?
Sarcoptes scabiei
Sarcoptes mites
Describe the external morphology of sarcoptes scabiei
Hemispherical
Short walking legs
1st 2 pairs of legs have ambulacral process used in burrowing
3rd and 4th leg pairs bear long setae
Females larger than males
How is sarcoptes mites transmitted?
Direct physical contact
Clothing
Linen
Can survive up to 48h outside of host
Discuss the burrowing of sarcoptes mites
Burrow into host skin within 2.5 minutes
Extend burrow up to 4mm per day
Fertilized female lays eggs in burrows
Small vesicles and papules form at entry site (intensely itchy especially at night)
What is the most common infection site of sarcoptes mites?
Between fingers
Knee flexors
Elbow flexors
Groin
Breasts
Shoulder blades
Waist
Genitals
What are the histological changes seen in scabies?
Epidermis
- acute eczematous tissue reaction
- acanthosis
- spongiotic edema
- exocytosis
- formation of intraepidermal vesicles
Dermis
- prominent perivascular inflammatory cell infiltrate
- extravasation of erythrocytes
Stratum corneum - mite burrows
Old lesions
- excoriation
- parakeratosis
Discuss diagnosis of scabies
Mite/egg in skin scrapings
Skin scraping site important as mite usually burrows a few mm away from lesion
3-20 mites per patient
What is norwegian scabies?
Infestation of thousands of mites
Characterised by extensive, heavily crusted skin lesions
Usually in immunocompromised or disabled individuals
Discuss treatment of scabies
Tetmosol soap
Benzyl benzoate 2 applications
Alpha BHC/sulphur in ointment
Discuss the external morphology of demodex
Minute
Obligate parasite
Stub-like legs
Elongated opisthosoma
What are the 2 common species of demodex?
D. folliculorum
D. brevis
Where do the 2 common demodex species occur?
D. folliculorum - hair follicles
D. brevis - sebaceous glands
What are demodex associated with?
Acne rosacea
Discuss the treatment of demodex infection
Tetmosol
Ascabiol
Beta-naphtol
Sulphur in ointment
What are dermatophagoides ubiquitous in?
House dust
Bedding
Furniture
Feed on human scales
What can dermatophagoides cause due to the allergen they produce?
Asthma
Severe dermatosis
Discuss control of dermatophagoides
Frequent dust removal
Avoidance of down pilows
Household insecticide
What is the latin for fleas?
Siphonaptera
Discuss the external morphology of fleas
Head, mouthparts, thorax, legs, abdomen and external genitalia
Laterally compressed
Wingless
Blood sucking ectoparasites
Discuss the head of fleas
Compressed like the body
Divided by deep groove containing the antennae into frons and occiput
Frontal portion of head carries mouthparts
Discuss the mouthparts of fleas
Consist of sucking tube which is enclosed in a sheath formed by pair of labial palpi at rest
Broad maxillary serrated stilettos near base
Discuss the ocelli of fleas
Ocelli and NOT facetted eyes
Some have enlarged
Some have reduced/absent
Discuss antenna of fleas
Sense organ
Used by males to capture and hold female during copulation
Discuss the thorax of fleas
Compact thorax
- prothorax
- mesothorax
- metathorax (highly developed to sustain jumping mechanism)
Discuss the pronotum of fleas
Pronotum lies immediately behind head
At posterior margin is comb of spine-like processes called pronotal ctenidium
Discuss the mesonotum of fleas
Simple arched palate
Discuss the abdomen of fleas
10 segments made up of plates/sclerites
Apical edge of tergite 7 are antepygidial bristles
Tergite 9 has pygidium (pincushion structure)
Tergite 8/9 sacculated spermatheca on females that have shape unique to species
Discuss male genitalia of fleas
Claspers
Moveable portions
Non-moveable portions
Manubrium
Discuss legs of fleas
Number and length of bristles important for taxonomy
Variation indicates lines of evolution
Discuss the life cycle of fleas
Egg ->larvae -> pupae -> adult
30-75 days
Oviposition occurs in host nest (larval food)
3-18 large, glistening white, rounded eggs deposited in 1 laying
Eggs are not attached to host
Take 2-14 days to hatch
Larvae are active, slender, segmented with segmentally arranged bristles and biting mouthparts
Larvae enter quiscent stage after active feeding period and spin cocoon of silk and sand grains
Pupa can remain in cocoon until vibrations indicate presence of possible host
Adult fleas only feed on blood
How can female fleas lay fertilised eggs 2 months after copulation?
Store sperm in the spermatheca and release them as eggs ripen
What is the primary reaction to flea bites?
Allergic (flea saliva)
What do immune person’s have with flea bites?
Evanescent erythema with central hemorrhagic punctum, non-itchy
Which diseases do fleas transmit?
Plague
Tularemia
Murine typhus
Salmonella
Myxomatosis
Trypanosomiasis
Nematodes
Cestodes
What is the sandflea?
Tunga penetrans (smallest known flea)
Cause tungiasis
What is the external morphology of tunga penetrans?
Reddish maroon with pointed head to penetrate host skin
Which part of the female tunga penetrans is visible on the skin surface after burrowing?
Posterior segments of abdomen
What is the common site for tunga penetrans lesion?
Feet
Mild itch, slight pain which worsens as flea enlarges
Discuss treatment of tungiasis
Remove flea with needle/excision
Antibiotics if secondary infection
What advice would you give to prevent tungiasis?
Wear boots
Never sit on infested ground
What is the name of the stick tight flea?
Echidnophaga gallinacean
Dogs, cats, rats, birds, humans
Feeds continuously on host blood
Which flea is suspected in the spread of plague in earlier times?
Pulex irritant
Which flea is the most abundant flea in tropical and subtropical regions?
Xenopsylla cheopis
Common parasite of synanthropic rats
Associated with plague
What is the principle plague carrier in South Africa?
Xenopsylla brasiliensis
Which fleas transmit sylvatic plague?
X. philoxera
X. piriei
What are the common cat and dog fleas?
Ctenocephalides canis
Ctenocephalis felis
Names are illogical as in SA they infest the opposite animal more
Can common cat and dog fleas transmit plague?
Not efficient
Can transmit intestinal worms
Discuss flea control
Vioform and hydrocortison topical application
Repellants
Disinfect animals
Regular vacuuming
