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Parasitology and entomology > Blackflies and filariasis vectors > Flashcards

Blackflies and filariasis vectors Flashcards

1
Q

What is onchocerca transmitted by and where is it found?

A

Blackflies. Neo and Afrotropical regions, as well as the Arabian peninsula and Yemen.

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2
Q

What is the vector for loa loa?

A

Chrypsops, of the family Tabanidae. (Deerflies).

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3
Q

Where is the geographical distribution of loa loa?

A

Mainly in West and Central Africa.

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4
Q

How do we identify the family tabanidae (horseflies)?

A

Look for the characteristic split vein which divides at the point of their wings.

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5
Q

What are the three important genera of the family tabanidae?

A

Chrysops, haematopota and tabanus.

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6
Q

Describe the differences in antenna between the three genera of the tabanidae family.

A

Chrysops: long simple antennae

Tabanus: short antennae with dorsal protrusions

Haematopota: short antennae without dorsal protrusions.

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7
Q

Describe the most commonly seen wing colourations of the three genera of the tabanidae family.

A

Chrysops: large dark patches/ lines

Tabanus: clear wings

Haematopota: mottled wings.

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8
Q

How are the males and female tabanus distinguished?

A

Females have a gap between their eyes whereas males meet along the middle of the forehead.

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9
Q

Where are tabanus and chrysops eggs laid? Why are they laid here?

A

Mostly damp soil. Because the larvae are carnivorous for soil invertebrates.
Chrysops larvae, as well as being carnivorous, eat decaying organic matter too.

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10
Q

What do tabanidae males and females feed on?

A

Both take sugar meals, only females take blood.

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11
Q

How do tabanidae find prey?

A

Visually detect prey. Are attracted to large, dark objects.

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12
Q

When and where do Tabanidae horseflies usually bite?

A

Day biters, bite outdoors.

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13
Q

Which species of chrysops does sometimes bite indoors and what is it attracted to? Why is this important?

A

Chrysops silacea. It is attracted to wood smoke. Important because it is the most important vector of loa loa- the presence of wood fire increases the number of flies coming inside to bite by 7 times.

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14
Q

Describe how chrysops uses its mouthparts to feed.

A

Use long mouthparts to CUT into skin. Labellum and labarum (“lips”). Daggar like mandible cuts the capillaries which bleed into the wound which the fly can then suck up.

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15
Q

What are three notable features that may make chrysops more effective vectors?

A
  1. Easily disturbed but persistent when trying to feed. This means that if they take a partial meal, they may be mechanical vectors when they go on to take their second meal.
  2. They are BIG so take a large volume of blood so there is an increased chance of picking up a parasite even at low parasitemia.
  3. The labella is spongey (soaks up blood) so this may be a mode of mechanical transmission.
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16
Q

What is the non medical as well as medical importance of chrysops?

A

Non-medical:

  • Nuisance biters
  • Economic implications (farming and livestock- animals gain less weight as they are moving around a lot to avoid the flies).

Medical:

  • Vectors for loa loa
  • Mechanical vectors for anthrax and tularemia
  • Trypanosoma vivax vector of cattle in S America.
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17
Q

What are the two vectors for loa loa?

A

Chrysops silacea and C. dimidiata.

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18
Q

How are tabanids controlled? What are the limitations of these control methods?

A

Hard!

  • Repellents (small effect)
  • Breeding site modification e.g. through vegetation clearance (may not be sustainable to chop down large areas of vegetation)
  • Insecticides (ineffective as they chelate quickly in soil, and large amounts needed to spray the soil).
  • Manitoba traps- pretty effective for some tabanus species.
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19
Q

How do manitoba traps work?

A

No chemicals used! Large black object inside trap which the flies are attracted to. They fly upwards when they reach it and realise their mistake and get into the trap where they can be bottled up and removed.

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20
Q

What is the scientific name for biting midges?

A

Ceratopogonidae

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21
Q

What is the main food source for biting midges?

A

Most bite other insects and feed on their haemolymph. Some steal blood by piercing the abdomen of mosquitos.

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22
Q

Which genera of biting midges regularly bite humans?

A

Culicoides and leptoconops.

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23
Q

Describe the wings of culicoides and leptoconops.

A

C: mottled wings, presence of crossvein
L: milky white wings, absence of crossvein

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24
Q

Describe the wing venation of culicoides and leptoconops.

A

Culicoides has M1 and M2 veins that split.
Leptoconops has an intercal vein.

Both have heavy veins that split.

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25
Q

In which medical area is culicoides very important in? Why is this important (with relation to humans)?

A

Vet med. They carry lots of filariases (e.g. 3 species of mansonella) and viruses. They impact humans through their veterinary importance.

26
Q

How are biting midges important vectorially, despite their size?

A

Enormous numbers of them mean that even at low parasitemias, picking up a parasite is likely. However, they do have a low rate of infectivity.

27
Q

What is the rate of infectivity of biting midges with mansonella?

A

1/1000

28
Q

What is the biting pattern of culicoides?

A

Diurnal, NOT crepuscular. Meaning they bite in the early morning and afternoon.
Diurnal = activity in the daytime, not at dusk like other vectors.

29
Q

How do culicoides feed?

A

Cutting mouthparts allow FEMALES to blood feed.

30
Q

Where do culocoides larvae reside?

A

Damp, organic matter rich soil as they feed on dead organic matter.

31
Q

Where do leptoconops larvae reside?

A

Prefer damp but sandy soil.

32
Q

How is culicoides controlled?

A

Difficult!

  • Topical repellents
  • Insecticide spraying (not effective as larvae are spread out in soil and insecticides chelate in soil)
  • Avoidance- don’t go out to locations/ at times when they are active.
33
Q

What is the lifecycle of culicoides ?

A

Eggs laid and hatched larvae go have 4 instars before pupating and then the adult emerges.

34
Q

What is the latin name for blackflies?

A

Simuliidae (family).

35
Q

Where do blackflies lay eggs?

A

Eggs laid in flowing water on a surface (e.g. hanging vegetation, a rock etc). The eggs are dropped as females fly over.

36
Q

How long does hatching of blackfly eggs take?

A

Around 7 days in tropical climates.

37
Q

What is the lifecycle of a blackfly?

A

Eggs laid, hatch after approx 7 days, 7 larval instars, pupate under water for about ten days, adults hatch.

38
Q

How do blackfly larvae feed?

A

Filter feeders.

39
Q

How long does black fly pupation take?

A

Around 10 days. Pupae are brown/ black and get darker as the pupa matures.

40
Q

How are the eggs, larvae and pupa and adult blackflies identified/ what are their characteristics?

A

Eggs: asymmetrical/ triangular shape.
Larvae: hourglass shape, head with fans
Pupa: in a silk cocoon, may be slipper shaped (with or without a collar).
Adults: antennae are banana shaped, with multiple segments. Can’t see any obvious wing venation (other than the front vein). Females eyes don’t met (dichoptic).

41
Q

What are the blood hosts for blackflies?

A

Warm-blooded vertebrates (mammals and birds)

42
Q

What attracts blackflies to hosts?

A

Smell and vision. Like the smell of CO2 at a distance and are also attracted to the smell of the lower body (feet and legs).

43
Q

how many bites per hour is common for Simuliium damnosi?

A

Around 60 bites per hour- biting nuisance!

44
Q

What do blackflies transmit?

A

Leucocytozoan, filaria, onchocerca, mansonella.

45
Q

How do blackflies bite?

A

The mandible is serrated with harpoon-like hooks. They push their mouth down, the lacinia (harpoons) go in and pull the face down so the mandibles can cut in and cause the blood to pool which is then sucked up.

46
Q

What is the lifecycle of filarial worms in blackflies?

A

Microfilariae picked up in blood meal –> travel to the midgut where they burst out–> travel to the flight muscles –> undergo 2 moults to produce L3 larvae –> larvae work their way into the labarum and burst out and wiggle into the wound.

47
Q

What is the function of the blackfly peritrophic matrix and how do filarial worms overcome this?

A

Thought to be specifically secreted to protect the blackfly against becoming infected.
Worms overcome this by breaking through it or exiting before it forms.

48
Q

When is the blackfly potentially infective for filarial worms?

A

On the third blood meal

49
Q

What is classified as the neotropics?

A

Central and South America.

50
Q

Where does filaria infection occur?

A

Mainly in Africa, only 1% of infection occurs outside of Africa and is confined to isolated foci (e.g. foci in Amazonia).

51
Q

What drug is used for filariasis and how long is the course?

A

Ivermectin. 12 years.

52
Q

Describe the Amazonia foci of filariasis and how this was thought to come about.

A

Small mobile communities in the Amazon have the same genetic type of filariasis as found in Africa, thought to have disseminated through slaves being brought to S America.

53
Q

What is the only active focus in S America of filariasis?

A

The one in Southern Venezuela/ Brazil.

54
Q

What are the vectors for filariasis in S America? Where do they bite?

A

(Simulium): Yarzabali (secondary)
Guianense, roramense, oyapokense (primary)

Legs and head, causing nodules on head and hips. (Mainly bite legs rather than head).

55
Q

Why are a lot of blackflies not effective vectors of filariasis?

A

Cibarial armature (head) cut and damage microfilaria as they pass which kills them.

56
Q

How is the level of transmission of filariasis self-controlled?

A

Despite being able to reach heavy levels of infection in humans, this is NOT the case within the vector! Limited by the vector which reduces transmission.

57
Q

How is onchocerca limited in S America?

A

Limited by the distribution of the parasite but NOT by the distribution of competent vectors as there is a plethora of species which are anthropophilic/ competent.

58
Q

What are the three groups of vectors for Onchocerca in Africa?

A

Simuliium damnoni and naevei (naevei ss, woodi, ethiopiense).

59
Q

Which species of blackfly are the only species that sit on crabs? Why do they do this?

A

Naevi larvae and pupa. May be as a defence against being eaten or may be because they eat the same food as crabs and the crabs are messy eaters.

60
Q

Where are simuliium damnosi larvae/ eggs found?

A

Like medium to large streams and rivers. Like rapids/ white water.

61
Q

What are the morphological characteristics of the damnosi vector?

A
  • Swollen foretarsus
  • Legs all black except a white band on the back leg
  • Gills of pupa look like a bunch of bananas
  • Some larvae have dorsal tubules (NO other spp have this).
  • Lots of scales, one species has scales on the proleg.

Parasitology and entomology (26 decks)

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