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Parasitology and entomology > Ectoparasites > Flashcards

Ectoparasites Flashcards

1
Q

What are the two genera of medically important lice?

A

Pediculus and phthirus.

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2
Q

How are lice flattened compared to fleas?

A

Lice- dorsoventrally flattened
Fleas- laterally flattened
Each flattening allows them to get through hair.

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3
Q

Describe the Terminalia of phthirus lice.

A

Females- bilobed

Males- rounded

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4
Q

How many segments do the antenna of lice have?

A

5

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5
Q

How many nymphal stages do lice have and what does this mean about their lifecycle? What do the nymphal stages feed on?

A

3 nymphal stages, no larval stages which means there is no complete metamorphosis.
All nymphal stages blood feed. Feed frequently and need multiple blood meals to survive.

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6
Q

Which is the only louse that transmits disease to humans?

A

Pediculus humanus

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7
Q

Why are lice dependent on being close to skin?

A

They require temperatures of about 24 degrees for the eggs to hatch.

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8
Q

How long do adult lice live (in lab conditions)?

A

About 9 days.

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9
Q

What is the diff in eggs between pediculus and phthirus?

A

Pediculus- flat, one cell thick operculum

Phthirus- raised, multiple cell thick operculum.

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10
Q

What are the clinical effects of heavy lice infestations and why?

A
  • Anaemia and feeling suboptimal

- Because of frequent blood-feeding by many individuals

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11
Q

How far do phthirus and pediculus move per day?

A

Phthirus- 10cm a day

Pediculus- 4.20m a day

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12
Q

How are lice best removed?

A

Wet comb with conditioner.

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13
Q

P humanus is the vector of which diseases?

A
  • Typhus (headache, chill, fever… non-specific symptoms and is fatal in 40% of cases).
  • Louse borne relapsing fever (Borrelia recurrentis)
  • Trench fever (Bartonella quintana)
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14
Q

How do we control for pediculus humanus?

A
  • Wash clothes and bedding at high temps
  • Chemical control (e.g. permethrin)

-All to interrupt lifecycle which lasts about 2 weeks.

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15
Q

How do we control for pediculus capitis?

A
  • Chemical control e.g. dimeticone gel- most resistant to available chemicals
  • Physical removal (however does not get rid of smaller nymphs).
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16
Q

How do we control for/ treat phthirus?

A
  • Coat eyelashes in petroleum jelly

- Water based insecticides.

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17
Q

What is the name for flea combs?

A

Ctenidium(/a)

18
Q

Where is the mesopleural rod?

A

On the second thoracic segment.

19
Q

See revision cards/ notes to differentiate fleas based on combs, mesopleural rod, antennal fossae etc.

A

-

20
Q

Describe the lifeycle of a flea. Does it undergo complete metamorphosis?

A

Egg takes about 2-14 days to hatch. Pupation is in a silk cocoon. Respond to vibration and co2 signals from host.. Emerge from the cocoon and immediately blood feed. Lay eggs after 1-2 days following blood meal.

21
Q

How do we identify flea larvae? What do they feed on?

A
  • Anal struts
  • White head (not pigmented like sandfly larvae).

Feed on dried blood in faeces and organic material.

22
Q

Describe flea pupa.

A

-Sticky so lots of debris attach and help camouflage it

23
Q

Describe a unique feature of flea digestive systems.

A

Has a proventriculus which is similar to a stomodeal valve and keeps the blood in the gut and is also involved in parasite transmission (parasites multiply and cause a plug in the proventriculus and subsequent feeding causes regurgitation of the plug and the parasites into the feeding wound.

24
Q

What are the features of -capitulum and -idiosoma and which insect are these a part of?

A

-Capitulum- like head
-Idiosoma - rest of body
Mites!

25
Q

How many nymphal stages do bedbugs have?

A

5

26
Q

How do we differentiate between adult and larval mites?

A

Adults have 8 legs, larvae have 6

27
Q

What do ticks have that mites dont?

A
  • Haller’s organ (sensory organ on leg).

- Toothed hypostome.

28
Q

How long does the lifecycle of dermatophagoides take?

A

About a month but can survive up to 3 months.

29
Q

How do dermatophagoides digest skin?

A

Using secreted protease enzymes

30
Q

Why are dermatophagoides allergenic?

A

The protease enzymes that are used to digest skin are shed in faecal pellets, the ingestion/ inhalation of which causes allergic reactions.

31
Q

How do we sample for dust mites?

A
  • Multiple hoover sampling over time. Express density per unit weight.
  • Can also do semi quantitative rapid tests using a drop of dust.
  • Quantitative using ELISA
32
Q

How do we control for dust mites?

A
  • Semi permeable mattress casings
  • Dehumidifiers
  • HEPA filters for vacuums
  • Chemical spraying
33
Q

How do Sarcoptes scabei feed?

A

From oozing liquid from gnawed cells. The enzymes used to do this cause itchiness.

34
Q

Where do male and female Sarcoptes live?

A

Fertilised females in burrows laying eggs. Males are nomadic and wander around going into burrows fertilising females. Moulting pockets are made for nymphs (three stages).

35
Q

How do we diagnose scabies?

A

Scalpel dipped in oil to do a skin scrape.

36
Q

How do we treat scabies?

A

Cove whole body (ex head) in permethrin for at least 8 hours. (Ivermectin can be used in immunocompromised people).
Repeat for 7-8 days to account for the lifecycle.

37
Q

Where do trombiculid mites have their lifecycle, location wise?

A

Below ground.

38
Q

What do trombiculids eat?

A

Detritus, adults may predate.

39
Q

What do trombiculids transmit?

A

Scrub typhus - orientia tsutsugamushi

40
Q

How do we control for trombiculids?

A

Avoid scrub islands.
Spray areas with acarides
Repellent e.g. 40% deet
Treat with doxycycline.

41
Q

Do more on this topic! Look at lifecycles, which have transovarial transmission and which ticks transmit which diseases.

A

-

Parasitology and entomology (26 decks)

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